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Accumulation and partitioning of nitrogen, phosphorus and potassium in different varieties of sweet sorghum
Field Crops Research 120 (2011) 230–240
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Accumulation and partitioning of nitrogen, phosphorus and potassium in different varieties of sweet sorghum Li Pu Han a , Yosef Steinberger c , Ya Li Zhao a,d , Guang Hui Xie a,b,∗ a
College of Agronomy and Biotechnology, China Agricultural University, 100193 Beijing, PR China Biomass Engineering Center, China Agricultural University, 100193 Beijing, PR China The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, 52900 Ramat-Gan, Israel d Agronomy College, Henan Agricultural University, 450002 Zhengzhou, PR China b c
a r t i c l e
i n f o
Article history: Received 22 June 2010 Received in revised form 21 October 2010 Accepted 21 October 2010 Keywords: Energy crop Nutrient uptake Harvest time Bio-fuel
a b s t r a c t This study investigated changes in accumulation and partitioning of nitrogen (N), phosphorus (P), and potassium (K) with harvest dates of early, middle, and late maturity sweet sorghum varieties in 2006 and 2007 in North China. All the varieties exhibited an obvious trend of decrease in concentrations of N, P and K in aboveground plants from elongation to 60 days after anthesis (DAA). The reduction in nutrient concentrations was found in the order of K (14.5 − 4.5 g kg−1 ) > N (13.3 − 7.4 g kg−1 ) > P (2.40 − 0.96 g kg−1 ). Conversely, N, P, and K accumulation significantly increased from elongation to anthesis, and continued to increase until 40 DAA. The accumulation of N, P, and K at maturity (40 DAA) was 128–339 kg ha−1 , 30–75 kg ha−1 and 109–300 kg ha−1 , respectively. Between elongation and anthesis, the middle and late maturity varieties had a higher ratio of N (50–82%), P (55–83%), and K (62–88%) accumulation than the early varieties (51–64% for N, 40–62% for P, and 55–75% for K). Sweet sorghum exhibited only one important K uptake stage from elongation to thesis according to the accumulation ratio (percentage of the nutrient accumulated at a given stage relative to that at physiological maturity) and rate (kilogram of nutrient accumulated per day per hectare). The stage from anthesis to grain maturity was the second important N and P uptake period. During the delay harvest period between 40 and 60 DAA, the early varieties exhibited significant increases in N accumulation; and the late varieties exhibited the reverse. P accumulation did not decrease significantly, whereas K accumulation decreased for all varieties in both years. Although of the N and P concentrations in straw were significantly lower than in grains, the N, P and K accumulation in straw was 2.2–9.3, 1.7–7.7, and 8.1–30.5 times higher than in grains, respectively. The concentrations of N and P in leaves were higher than in stems after anthesis. We found significantly higher accumulation of P and K in stems than in leaves, with a comparable N accumulation. The findings are helpful to make a fertilization regime recommendation for sweet sorghum production as a bioethanol crop in North China. It also suggests a further genetic improvement for optimizing nutrient use. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Sweet sorghum (Sorghum biocolor (L.) Moench) is a C4 plant characterized by high biomass and sugar yield (Amaducci et al., 2004; Antonopoulou et al., 2008; Gnansounou et al., 2005; Zhao et al., 2009). The high carbohydrate content of its stalk is similar to sugarcane, but its water requirement is much lower (Almodares and Hadi, 2009). Its wide adaptability (Gnansounou et al., 2005; Kangama and Rumei, 2005) and resistance to salinity and drought
∗ Corresponding author at: College of Agronomy and Biotechnology, China Agricultural University, No. 2 Yuanmingyuan West Road, Haidian, 100193 Beijing, PR China. Tel.: +86 10 62734888; fax: +86 10 62731298. E-mail address: [email protected] (G.H. Xie). 0378-4290/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2010.10.007
(Tsuchihashi and Goto, 2004; Rajagopal, 2008; Wortmann et al., 2010) indicate less competition with food security for human beings, as a result of the possibility to exploit less resources such as productive land and irrigation water for food crops. Sweet sorghum therefore has been widely considered a feedstock for producing fuel ethanol (Buxton et al., 1999; Liu et al., 2008; Almodares and Hadi, 2009; Yu et al., 2008; Liu and Lin, 2009) and biodiesel (Gao et al., 2010). China is not only currently facing an energy shortage, but is also pressured to reduce CO2 emission from the international community. Sweet sorghum plantations are among the most promising solutions (FAO, 2002; Cheng et al., 2009; Li and Chan-Halbrendt, 2009; Tian et al., 2009). Although the dry matter and chemical composition, particularly soluble and insoluble carbohydrates, have been well documented in sweet sorghum, little is known about its mineral nutrient accu-
L.P. Han et al. / Field Crops Research 120 (2011) 230–240
mulation. Sorghum has been recognized as a “nutrient depletion crop” by farmers, compared with cereals in China. The dynamics of mineral element uptake and partitioning are essential for forming a high biomass yield, and are closely related to nutrient cycling in the soil–plant-processing system (Epstein and Bloom, 2005). For the most field crops, some organs (e.g. grains, tuber, etc.) are harvested and the field residues are possibly incorporated into soils and compensate partially the nutrient losses. It is different that the entire aboveground part of sweet sorghum, as a bio-fuel feedstock, are considered to be harvested for ethanol production from sugar, starch, and cellulosic materials. The understanding of nutrient dynamics of the energy crop will be helpful to maintain soil nutrient balance via genetic improvement or/and fertilization. Of the essential mineral nutrients, nitrogen (N), phosphorus (P), and potassium (K) are the most important macro-nutrients affecting crop yields on one hand, fertilization for the three elements constitutes a considerable proportion of production cost on the other. It is essentially important for bio-ethanol production to reduce its feedstock cost. Information of N, P, and K uptakes and partitioning of sweet sorghum could serve for optimizing fertilization application for a high biomass yield. In our previous study we investigated the dynamics of biomass and chemical composition of sweet sorghum varieties differing in physiological maturity in North China during in growth (Zhao et al., 2009). In the present study we tested the N, P, and K contents in five sweet sorghum cultivars with a crop cycle length that varied between 111 and 165 days (the same field experiment as our previous study) in North China. The objectives of this study were: (1) to investigate the changes in accumulation and partitioning of N, P, and K with the harvest date of sweet sorghum varieties; and (2) to determine the differences in accumulation and partitioning of N, P, and K in sweet sorghum between early, middle, and late maturity varieties. 2. Materials and methods 2.1. Study site A field study was conducted in 2006 and 2007 at the Shangzhuang Experimental Station (39◦ 56 N, 116◦ 20 E) of China Agricultural University in Beijing, China. The site has a continental monsoon type climate, with an average multi-annual solar radiation of 2423 h and average multi-annual temperature of 11.5 ◦ C. Annual mean precipitation is 554.2 mm, falling mostly in July and August. Monthly precipitation and air temperature data during the study period and main physical and chemical properties of the soils in the two years are presented in Zhao et al. (2009).
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2.3. Sampling and measurements Ten aboveground sweet sorghum plants were taken on the date of elongation and 0, 20, 40, and 60 DAA from each plot. In 2006, each plant was divided into stems, leaves and a panicle for biomass estimation. One internode was taken after every two internodes from the base of each plant and was cut into 10–15 cm long pieces. The grains were threshed and the panicle axis and rachis branches were cut and mixed with stem pieces proportionately on a basis of oven-dried weight. In 2007, apart from grains, the tissues were not separated and a mixed plant sample of the whole plant was made. After being placed in an individual paper bag, it was oven dried at 70 ◦ C to constant weight in order to gravimetrically estimate plant biomass. The changes in biomass with harvest time are presented in Zhao et al. (2009). The dried samples were ground with a Wiley mill to pass through 0.5 mm mesh for nutrient determination. The ground samples were stored at 4 ◦ C for qualitative analyses. 2.4. Chemical analysis Grains, leaves and stems were separated, oven-dried to constant weight at 70 ◦ C and ground for N, P, and K analyses following Kjeldahl digestion with H2 SO4 –H2 O2 (Wolf, 1982). N concentration was determined by semimicro-Kjeldahl digestion and distillation (Nelson and Sommers, 1980). P concentration was determined by the vanadomolybdate yellow method (Jackson, 1958). K concentration was measured using a flame spectrophotometer. All analyses were performed in duplicate. The chemical composition of the plant parts is presented as nutrient concentration (g kg−1 ). 2.5. Calculation and statistical analysis The nutrient accumulation in grains, leaves and stems was computed as the product of the concentration multiplied by the dry weight of biomass. The nutrient accumulation ratio (%) at different growth stages was the percentage of the nutrient accumulation at a given stage relative to that at physiological maturity (40 DAA). The nutrient accumulation rate (kg ha−1 day−1 ) at each growth stage was obtained from the nutrient accumulation divided by the number of days of the growth stage. Means and standard errors were calculated for the four replicates from each treatment. ANOVA was conducted using SAS (SAS Institute, 1999). The statistical significance of the differences between means was determined by the least significant difference. All significant results are reported at the P < 0.05 level. 3. Results
2.2. Experiment design and crop cultivation
3.1. N, P, and K concentrations
Sweet sorghum hybrid Zaoshu-1 (ZS1), Chuntian-2 (CT2), and inbreed Italy (ITY), Lvneng-3 (LN3), M-81E were tested using a randomized block design with four replications. It was sown on April 26 in 2006 and 2007. The ITY and ZS1 varieties exhibited early maturity (111–116 days), CT2 exhibited middle maturity (138–143 days), and LN3 and M-81E exhibited late maturity (160–165 days). Basal fertilizer of 48 kg N ha−1 as urea, 90 kg P2 O5 ha−1 as diammonium phosphate and 50 kg K2 O ha−1 as potassium sulfate were applied just before sowing. 48 kg N ha−1 as urea and 50 kg K2 O ha−1 as potassium sulfate were applied at elongation, and 24 kg N ha−1 as urea were applied at anthesis. Sweet sorghum grains matured around 30 days after anthesis (DAA) for the early varieties and 36–44 DAA for the middle and late varieties. Further details of the crop management and the main morphological phases of sweet sorghum were described by Zhao et al. (2009).
Sweet sorghum exhibited an obvious trend of decrease in N, P and K concentrations in aboveground plants from elongation to 60 DAA across all the early, middle, and late maturity varieties we used in 2006 and 2007 (Fig. 1). N and K concentrations ranged between 23.7–32.4 g kg−1 and 19.6–29.7 g kg−1 at elongation and were significantly (2.3–3.2 times and 1.6–3.5 times) higher (P < 0.001) than at anthesis (0 DAA) on the whole plant basis. The variations in P concentrations between elongation (2.1–3.3 g kg−1 ) and anthesis (1.5–2.4 g kg−1 ) were smaller than the N or K concentration (Fig. 1). The N, P, and K concentration in aboveground plants at grain maturity (40 DAA) was 7.5–10.2 g kg−1 , 1.4–2.5 g kg−1 and 5.0–9.6 g kg−1 , respectively. The reduction in nutrient concentrations from anthesis to 60 DAA was in the order of K (14.5 − 4.5 g kg−1 ) > N (13.3 − 7.4 g kg−1 ) > P (2.40 − 0.96 g kg−1 ) for all the varieties in both years. Although the K concentration in
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Fig. 1. Changes in concentration of nitrogen (N), phosphorus (P) and potassium (K) of the sweet sorghum cultivars Italy (ITY), Zaoshu-1 (ZS1), Chuntian-2 (CT2), Lvneng-3 (LN3) and M-81E on elongation stage () and 0 ( ), 20 ( ), 40 ( ) and 60 ( ) days after anthesis (DAA). The vertical bars indicate standard errors. The different small letters indicate significant differences within each cultivar and each year at a P < 0.05 level.
plants of the late maturity varieties LN3 and M-81E was significantly (P < 0.05, statistical analysis not shown) lower than each of the early or middle varieties on the same harvest date, there was generally no significant difference (P < 0.05) in N and P concentrations on the whole plant basis between varieties. 3.2. N, P, and K accumulation Although the nutrient concentrations at elongation were much higher than at anthesis (Fig. 1), it was obvious that the nutrient accumulation significantly (P < 0.001) increased from elongation to anthesis for all varieties in both years (Fig. 2) due to the highest fraction of biomass accumulation from elongation (0.6–1.5 t ha−1 , data not presented) to anthesis (5.5–27.1 t ha−1 , see Zhao et al., 2009). Afterwards, all the varieties with different maturity continuously exhibited increases in nutrient accumulation from 0 DAA (anthesis) to 40 DAA (maturity). The accumulation of N, P, and K in aboveground plants at maturity (40 DAA) was 128–339 kg ha−1 , 30–75 kg ha−1 and 109–300 kg ha−1 , respectively. The early varieties ITL, ZS1 and middle variety CT2 exhibited significant increases (P < 0.05) in N accumulation from 40 DAA to 60 DAA, with the exception of CT2 in 2006; whereas the late varieties LN3 and M-81E showed significant decreases (P < 0.05) in N accumulation during the delay harvest period. P accumulation did not decrease significantly (P < 0.05) from 40 DAA to 60 DAA for all varieties with the only exception of M-81E in 2006. How-
ever, K accumulation mostly decreased for the varieties in both years. Generally, similar to the pattern of the nutrient concentrations, N had similar accumulation ranges with K, whereas P accumulation was significantly lower (P < 0.001) for the same harvest date (Fig. 2). Accumulation of N and K ranged between 105–339 kg ha−1 and 85–300 kg ha−1 , respectively. P accumulation ranged between 19 and 75 kg ha−1 from 0 DAA to 40 DAA in both years. In the early variety group, hybrid ZS1 exhibited a significantly higher N, P, and K accumulation (P < 0.05) than the inbred ITL. The middle hybrid variety CT2 exhibited similar N and K accumulation levels with the late inbred LN3, and significantly higher levels (P < 0.05) than inbred M81E for the same harvest date. CT2 also had a significantly higher K accumulation (P < 0.05) than either LN3 or M-81E. The findings indicated that sweet sorghum hybrid varieties had a higher N, P, and K accumulation than the inbred varieties. 3.3. N, P, and K accumulation ratio All the sweet sorghum varieties exhibited significantly larger fractions (P < 0.05) of N, P, and K that accumulated from elongation to anthesis in the two years (Fig. 3). In the period between elongation and anthesis, the middle and late maturity varieties had a higher ratio of N (50–82%), P (55–83%), and K (62–88%) accumulation than the early varieties (51–61% for N, 40–62% for P, and 55–75% for K). The second largest fraction of N was accumulated in
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Fig. 2. Changes in accumulation of nitrogen (N), phosphorus (P) and potassium (K) of the sweet sorghum cultivars Italy (ITY), Zaoshu-1 (ZS1), Chuntian-2 (CT2), Lvneng-3 (LN3) and M-81E on elongation stage () and 0 ( ), 20 ( ), 40 ( ) and 60 ( ) days after anthesis (DAA). The vertical bars indicate standard errors. The different small letters indicate significant differences within each cultivar and each year at a P < 0.05 level.
the period from sowing to elongation or in the period between 0 and 20 DAA, depending on different varieties and years, with the exception of CT2 in 2006. The P accumulation ratio in the period from sowing to elongation was significantly lower than in the period between 0 and 20 DAA, and K accumulation ratio exhibited the reverse. There was a trend that the varieties had the lowest N, P and K accumulation ratio between 20 and 40 DAA. In the period of delay harvest between 40 and 60 DAA, N accumulation increased by 8–19% for the early maturity varieties ITL and ZS1; whereas it decreased by −11 to −0.21% for the late varieties LN3 and M-81E in the delay harvest period (Fig. 3). The minus values indicate percentage of the nutrient lost from the aboveground sweet sorghum plants after grain maturity. All the varieties exhibited loss of K, ranging from −26% to −0.8% after grain maturity in both years. P either accumulated or was lost, depending on varieties and years. A generalization of the above results had illustrated the importance of maturity and nutrient relation—the later the variety maturity, the higher the nutrient loss when delaying the harvest beyond grain maturity.
3.4. N, P, and K accumulation rate Accumulation rates of N (1.3–4.3 kg ha−1 day−1 ) and K (1.1–4.6 kg ha−1 day−1 ) were significantly higher (P < 0.05) in the period from elongation to anthesis in the two years for all five
varieties with the exception of M-81E in 2006 (Fig. 4). P accumulation rates were significantly lower (P < 0.01) than those of N or K for the same harvest dates. The highest P accumulation rate was between elongation and anthesis (0.27–0.94 kg ha−1 day−1 ) or between 0 and 20 DAA (0.16–1.08 kg ha−1 day−1 ). It should be noted that N and K were lost at rates comparable to the highest accumulation rates in the delay harvest period between 40 and 60 DAA for the middle and late maturity varieties.
3.5. N partitioning The concentration of N in grains was 1.7–3.2 times higher (P < 0.01) than in straw on 20 and 40 DAA for all sweet sorghum varieties in both years (Table 1). However, because most of the biomass was found in straw (Zhao et al., 2009), N accumulation in grains was 2.2–9.3 times lower (P < 0.01). Although there was a slight reduction in the N concentration in straw from 20 DAA (7.9–13.3 g kg−1 ) to 40 DAA (6.2–9.2 g kg−1 ), the differences were not significant (P < 0.05) between 20 DAA (105–274 kg ha−1 ) and 40 DAA (95–256 kg ha−1 ) for all varieties. The N concentration in grains decreased from 20 DAA to 40 DAA (P < 0.05) for each of the varieties, whereas N accumulated in grains increased significantly (P < 0.05) during the same period resulted from a considerable increase in grain biomass. There was also a trend that N accumulated in straw on 60 DAA was higher than on 40 DAA for each early maturity
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Fig. 3. Changes in accumulation ratio of nitrogen (N), phosphorus (P) and potassium (K) of the sweet sorghum cultivars Italy (ITY), Zaoshu-1 (ZS1), Chuntian-2 (CT2), Lvneng-3 (LN3) and M-81E between sowing and elongation ( ), elongation and anthesis ( ), anthesis and 20 days after anthesis (DAA) ( ), 20 and 40 DAA ( ), and 40 and 60 DAA (). The vertical bars indicate standard errors. The different small letters indicate significant differences within each cultivar and each year at a P < 0.05 level.
Table 1 Changes in concentration and accumulation of nitrogen (N) in straw and grains of the sweet sorghum cultivars Italy (ITY), Zaoshu-1 (ZS1), Chuntian-2 (CT2), Lvneng-3 (LN3) and M-81E on 20, 40, and 60 days after anthesis (DAA). The different small letters indicate significant differences within each cultivar and each year at a P < 0.05 level. Variety
Harvest date
2006
2007 −1
N concentration (g kg
)
−1
N accumulation (kg ha
Straw
Grain
Straw
)
Grain
N concentration (g kg−1 )
N accumulation (kg ha−1 )
Straw
Grain
Straw
Grain
ITL
20 DAA 40 DAA 60 DAA
9.4 ± 0.3a 8.4 ± 0.3b 7.5 ± 0.1c
20.2 ± 0.8a 17.3 ± 0.7b –
103.3 ± 5.4ab 94.9 ± 2.9b 111.6 ± 4.4a
16.3 ± 1.2b 32.8 ± 2.7a –
9.1 ± 0.3a 8.4 ± 0.2a 8.9 ± 0.3a
20.6 ± 0.3a 17.8 ± 0.3b –
119.4 ± 5.3b 106.6 ± 1.6c 134.7 ± 1.7a
21.0 ± 2.1b 34.7 ± 0.7a –
ZS1
20 DAA 40 DAA 60 DAA
7.7 ± 0.2a 7.4 ± 0.2a 7.6 ± 0.3a
19.7 ± 0.5a 16.8 ± 0.4b –
108.2 ± 4.6a 103.6 ± 4.7a 116.2 ± 2.2a
33.6 ± 3b 47.5 ± 2.3a –
9.8 ± 0.3a 9.2 ± 0.1a 9.9 ± 0.3a
23.5 ± 0.7a 16.1 ± 0.1b –
192.0 ± 6.4a 195.7 ± 7.7a 219.3 ± 17a
34.8 ± 2b 56.3 ± 0.9a –
CT2
20 DAA 40 DAA 60 DAA
8.4 ± 0.1a 8.0 ± 0.1a 7.6 ± 0.2b
21.2 ± 0.8a 18.2 ± 0.7b –
153.3 ± 5.2a 156.0 ± 5.5a 148.5 ± 6.2a
31.5 ± 2.6b 57.2 ± 2.8a –
8.7 ± 0.2a 7.8 ± 0.3ab 8.1 ± 0.2b
20.2 ± 0.8a 17.9 ± 0.9ab –
262.6 ± 10.4a 224.6 ± 9.7b 249.8 ± 10.8ab
48.8 ± 2.7b 87.4 ± 7.6a –
LN3
20 DAA 40 DAA 60 DAA
8.2 ± 0.2a 7.7 ± 0.1a 6.0 ± 0.2b
24.3 ± 0.6a 20.8 ± 0.5b –
184.4 ± 5.9a 171.9 ± 3.0a 152.2 ± 4.7b
26.7 ± 1.1b 52.8 ± 1.3a –
9.4 ± 0.1a 8.1 ± 0.2b 8.3 ± 0.4b
23.1 ± 0.7a 19.8 ± 0.6b –
286.6 ± 2.9a 256.4 ± 9.0b 258.0 ± 10.9b
30.8 ± 0.8b 82.4 ± 2.8a –
M-81E
20 DAA 40 DAA 60 DAA
6.9 ± 0.3a 6.2 ± 0.2a 6.4 ± 0.3a
22.1 ± 0.3a 18.9 ± 0.2b –
129.2 ± 6.9a 129.3 ± 4.7a 111.4 ± 3.8b
19.8 ± 1.5b 43.0 ± 1.7a –
8.6 ± 0.1a 6.9 ± 0.1b 6.5 ± 0.1c
21.8 ± 0.4a 18.3 ± 0.3b –
214.4 ± 7.5a 195.5 ± 3.8b 174.2 ± 5.0c
29.3 ± 1.1b 52.6 ± 0.7a –
–: Data is not available because the grain was harvested on 40 DAA.
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Fig. 4. Changes in accumulation rate of nitrogen (N), phosphorus (P) and potassium (K) of the sweet sorghum cultivars Italy (ITY), Zaoshu-1 (ZS1), Chuntian-2 (CT2), Lvneng-3 (LN3) and M-81E between sowing and elongation ( ), elongation and anthesis ( ), anthesis and 20 days after anthesis (DAA) ( ), 20 and 40 DAA ( ), and 40 and 60 DAA (). The vertical bars indicate standard errors. The different small letters indicate significant differences within each cultivar and each year at a P < 0.05 level.
varieties, and the reverse for the late varieties (Table 1). The concentration of N in leaves was 1.7–3.9 times higher (P < 0.01) than in stems on 0, 20, 40, and 60 DAA for all the varieties in both years (Table 2). However, N accumulated in stems was comparable with that in leaves.
3.6. P partitioning Similarly to the pattern of the N concentration, the five sweet sorghum varieties exhibited a significantly higher P concentration (P < 0.01) in grains (3.9–6.7 g kg−1 ) than in straw (0.9–2.5 g kg−1 )
Table 2 Changes in concentration and accumulation of nitrogen (N) in stem and leaf of the sweet sorghum cultivars Italy (ITY), Zaoshu-1 (ZS1), Chuntian-2 (CT2), Lvneng-3 (LN3) and M-81E on 0, 20, 40, and 60 days after anthesis (DAA) in 2006. The different small letters indicate significant differences within each cultivar at a P < 0.05 level. Variety
Harvest date
N in stem Concentration (g kg−1 )
N in leaf Accumulation (kg ha−1 )
Concentration (g kg−1 )
Accumulation (kg ha−1 )
ITL
0 DAA 20 DAA 40 DAA 60 DAA
6.9 6.4 4.8 4.9
± ± ± ±
0.2a 0.3a 0.2b 0.1b
42.2 51.5 38.8 54.5
± ± ± ±
0.7b 2.2a 0.9b 2.6a
23.0 17.8 17.9 14.6
± ± ± ±
0.3a 0.8b 0.6b 0.3c
66.9 51.9 56.1 57.1
± ± ± ±
3.1a 6.4b 2.0ab 2.6ab
ZS1
0 DAA 20 DAA 40 DAA 60 DAA
5.4 4.5 4.3 5.1
± ± ± ±
0.1a 0.4bc 0.1c 0.2ab
40.4 47.1 44.5 57.9
± ± ± ±
1.9b 4.2b 3.9b 1.1a
18.9 17.3 15.6 15.2
± ± ± ±
0.7a 0.2b 0.4c 0.3c
68.4 61.1 59.1 58.3
± ± ± ±
5.4a 1.0ab 2.0b 1.6b
CT2
0 DAA 20 DAA 40 DAA 60 DAA
8.0 5.2 4.8 4.4
± ± ± ±
0.4a 0.2b 0.2b 0.4b
85.7 67.3 64.8 60.3
± ± ± ±
3.9a 2.4b 4.3b 6.6b
16.8 16.0 15.4 14.8
± ± ± ±
0.3a 0.2ab 0.3b 0.6b
90.2 86.1 91.2 88.2
± ± ± ±
5.8a 4.2a 3.4a 6.6a
LN3
0 DAA 20 DAA 40 DAA 60 DAA
6.7 5.7 6.5 4.9
± ± ± ±
0.1a 0.1b 0.1a 0.2c
86.6 95.1 106.5 93.2
± ± ± ±
1.7b 3.2b 4.5a 2.2b
16.7 15.6 10.8 9.8
± ± ± ±
0.3a 0.4b 0.3c 0.4d
95.0 89.3 65.3 59.0
± ± ± ±
2.2a 2.7a 2.1b 2.6b
M81E
0 DAA 20 DAA 40 DAA 60 DAA
5.7 4.6 4.2 4.0
± ± ± ±
0.2a 0.2b 0.1bc 0.1c
55.6 65.7 63.2 46.9
± ± ± ±
4.5ab 6.9a 3.1a 2.2b
13.5 14.1 11.4 11.1
± ± ± ±
0.4a 0.6a 0.4b 0.6b
49.1 63.5 66.1 64.0
± ± ± ±
1.8b 3.8a 4.2a 3.8a
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Table 3 Changes in concentration and accumulation of phosphorus (P) in straw and grain of the sweet sorghum cultivars Italy (ITY), Zaoshu-1 (ZS1), Chuntian-2 (CT2), Lvneng-3 (LN3) and M-81E on 20, 40, and 60 days after anthesis (DAA). The different small letters indicate significant differences within each cultivar and each year at a P < 0.05 level. Variety
Harvest date
2006
2007
P concentration (g kg−1 )
P accumulation (kg ha−1 )
P concentration (g kg−1 )
P accumulation (kg ha−1 )
Straw
Straw
Grain
Straw
Grain
Straw
Grain
ITL
20 DAA 40 DAA 60 DAA
2.1 ± 0.06a 2.0 ± 0.02a 1.8 ± 0.06b
5.3 ± 0.04a 3.9 ± 0.13b –
Grain
22.8 ± 1.1b 23.0 ± 0.6b 27.6 ± 1.7a
4.3 ± 0.2b 7.3 ± 0.1a –
2.5 ± 0.04a 2.2 ± 0.05b 2.0 ± 0.05c
4.8 ± 0.04a 4.6 ± 0.09b –
31.6 ± 0.4a 28.0 ± 0.5b 30.8 ± 1.3ab
4.9 ± 0.5b 8.9 ± 0.4a –
ZS1
20 DAA 40 DAA 60 DAA
1.5 ± 0.04a 1.4 ± 0.02ab 1.4 ± 0.03b
5.2 ± 0.12a 4.1 ± 0.04b –
19.8 ± 1.0a 19.3 ± 1.2a 20.8 ± 0.7a
9.0 ± 0.7b 11.7 ± 0.5a –
2.2 ± 0.04a 2.0 ± 0.09ab 1.9 ± 0.04b
4.7 ± 0.11a 4.1 ± 0.04b –
42.4 ± 0.4a 43.2 ± 3.2a 41.3 ± 2.7a
7.0 ± 0.1b 14.5 ± 0.4a –
CT2
20 DAA 40 DAA 60 DAA
1.6 ± 0.03a 1.3 ± 0.03b 1.2 ± 0.04b
6.7 ± 0.08a 4.6 ± 0.05b –
28.4 ± 1.5a 25.9 ± 0.9ab 24.3 ± 0.9b
9.9 ± 0.5b 14.6 ± 0.7a –
1.5 ± 0.03a 1.5 ± 0.02a 1.4 ± 0.03a
6.0 ± 0.08a 4.2 ± 0.1b –
43.6 ± 1.0a 41.8 ± 1.0a 43.5 ± 1.4a
14.7 ± 0.8b 20.6 ± 1.2a –
LN3
20 DAA 40 DAA 60 DAA
1.6 ± 0.02a 1.3 ± 0.05b 1.3 ± 0.01b
5.8 ± 0.14a 5.8 ± 0.15a –
34.7 ± 0.8a 28.7 ± 1.5b 31.5 ± 0.9ab
6.4 ± 0.3b 14.7 ± 0.7a –
1.7 ± 0.03a 1.7 ± 0.04ab 1.6 ± 0.02b
5.0 ± 0.2b 5.5 ± 0.11a –
51.0 ± 1.9a 52.4 ± 0.8a 48.7 ± 1.4a
6.7 ± 0.2b 22.8 ± 0.8a –
M-81E
20 DAA 40 DAA 60 DAA
1.2 ± 0.07a 1.1 ± 0.03ab 0.9 ± 0.03b
5.2 ± 0.07a 4.5 ± 0.18b –
22.7 ± 2.1a 22.4 ± 0.8a 16.3 ± 0.8b
4.6 ± 0.3b 10.3 ± 0.7a –
1.4 ± 0.02a 1.1 ± 0.01b 1.1 ± 0.04b
4.7 ± 0.06a 4.6 ± 0.16a –
34.9 ± 0.5a 29.8 ± 0.5b 28.6 ± 1.5b
6.3 ± 0.2b 13.1 ± 0.5a –
–: Data is not available because the grain was harvested on 40 DAA.
on 20 and 40 DAA in the two years (Table 3). A trend of reduction in P concentration after 20 DAA was found for straw and for grain, whereas the accumulation of P in straw (16–52 kg ha−1 ) was 1.7–7.7 times higher (P < 0.01) than in grains (4–23 kg ha−1 ) in both years, due to the much higher biomass of straw (Zhao et al., 2009). The accumulation of P in grains increased significantly (P < 0.01) from 20 DAA to 40 DAA for each variety in both years. However, changes in P accumulation in straw with harvest date from 20 DAA to 60 DAA were not consistent between varieties and between years (Table 3). A significantly higher P concentration (P < 0.01) after anthesis was found in leaves (1.4–4.4 g kg−1 ) than in stems across the varieties (0.7–1.5 g kg−1 ) (Table 4). There was a trend of reduction in P concentration in stems and in leaves with harvest time from 0 DAA to 60 DAA, whereas variations in accumulation of P in stems or in leaves with the harvest dates were not consistent between varieties. All the varieties, with the exception of ITL, exhibited a significantly higher P accumu-
lation in stems (P < 0.05) than in leaves for most harvest dates in 2006. 3.7. K partitioning Contrary to the patterns of N and P concentrations, sweet sorghum exhibited a significantly higher K concentration (P < 0.05) in straw (4.5–10.6 g kg−1 ) than in grains (4.2–6.3 g kg−1 ), with the exception of LN3 and M-81E in 2006 (Table 5). The accumulation of K was 8.1–30.5 times higher (P < 0.001) in straw (81–284 kg ha−1 ) than in grains (3.7–25 kg ha−1 ) across all varieties on 20 DAA and 40 DAA in both years. Accumulation of K in grains increased significantly (P < 0.01) from 20 DAA to 40 DAA. K concentration or accumulation in straw decreased significantly during the delay harvest period from 40 DAA to 60 DAA in both years. Each variety exhibited a significantly higher accumulation of K in grains (P < 0.01) on 40 DAA than on 20 DAA (Table 5). The variations in K
Table 4 Changes in concentration and accumulation of phosphorus (P) in stems and leaves of the sweet sorghum cultivars Italy (ITY), Zaoshu-1 (ZS1), Chuntian-2 (CT2), Lvneng-3 (LN3) and M-81E on 0, 20, 40, and 60 days after anthesis (DAA). The different small letters indicate significant differences within each cultivar at a P < 0.05 level. Variety
Harvest date
P in stem
P in leaf −1
Concentration (g kg
)
−1
Accumulation (kg ha
)
Concentration (g kg−1 )
ITL
0 DAA 20 DAA 40 DAA 60 DAA
1.4 1.3 1.2 1.2
± ± ± ±
0.03a 0.03b 0.01b 0.09b
8.9 10.1 9.6 13.0
± ± ± ±
0.3b 0.4b 0.3b 1.4a
4.4 4.4 4.2 3.7
± ± ± ±
0.05a 0.03a 0.08a 0.06b
ZS1
0 DAA 20 DAA 40 DAA 60 DAA
1.3 1.0 1.0 1.0
± ± ± ±
0.04a 0.05b 0.03b 0.06b
9.9 10.5 10.4 11.6
± ± ± ±
0.5a 0.8a 0.9a 0.8a
2.4 2.6 2.3 2.4
± ± ± ±
0.08ab 0.03a 0.04b 0.10b
CT2
0 DAA 20 DAA 40 DAA 60 DAA
1.5 1.2 1.0 1.0
± ± ± ±
0.02a 0.07b 0.02bc 0.08c
16.6 15.0 13.8 12.8
± ± ± ±
0.8a 1.2ab 0.3b 0.7b
2.7 2.5 2.0 1.9
± ± ± ±
LN3
0 DAA 20 DAA 40 DAA 60 DAA
1.2 1.3 1.1 1.1
± ± ± ±
0.01b 0.03a 0.04c 0.01c
15.8 22.2 17.7 21.6
± ± ± ±
0.4b 0.7a 1.0b 0.7a
3.3 2.2 1.8 1.6
M81E
0 DAA 20 DAA 40 DAA 60 DAA
1.1 1.0 1.0 0.7
± ± ± ±
0.02a 0.06b 0.03b 0.02c
11.1 14.6 14.5 8.4
± ± ± ±
0.8ab 1.9a 0.9a 0.5b
2.5 1.8 1.4 1.4
Accumulation (kg ha−1 ) 12.9 12.7 13.3 14.6
± ± ± ±
0.7a 1.2a 0.4a 0.8a
8.7 9.3 8.8 9.2
± ± ± ±
0.4a 0.2a 0.3a 0.4a
0.12a 0.05a 0.12b 0.15b
14.5 13.3 12.1 11.4
± ± ± ±
0.9a 0.4ab 0.7ab 1.1b
± ± ± ±
0.02a 0.05b 0.09c 0.01d
18.9 12.5 11.0 9.9
± ± ± ±
0.6a 0.1b 0.6c 0.2c
± ± ± ±
0.03a 0.13b 0.05c 0.06c
9.1 8.2 7.9 7.9
± ± ± ±
0.5a 0.6a 0.3a 0.5a
L.P. Han et al. / Field Crops Research 120 (2011) 230–240
237
Table 5 Changes in concentration and accumulation of potassium (K) in straw and grain of the sweet sorghum cultivars Italy (ITY), Zaoshu-1 (ZS1), Chuntian-2 (CT2), Lvneng-3 (LN3) and M-81E on 20, 40, and 60 days after anthesis (DAA). The different small letters indicate significant differences within each cultivar and each year at a P < 0.05 level. Variety
Harvest date
2006
2007
K concentration (g kg−1 )
K accumulation (kg ha−1 )
K concentration (g kg−1 )
K accumulation (kg ha−1 )
Straw
Grain
Straw
ITL
20 DAA 40 DAA 60 DAA
8.9 ± 0.1a 8.9 ± 0.2a 6.4 ± 0.2b
4.6 ± 0.2a 4.4 ± 0.2a –
97.2 ± 3.9a 100.8 ± 3.1a 95.2 ± 5.2a
Grain
Straw
Grain
Straw
3.7 ± 0.2b 8.3 ± 0.5a –
8.7 ± 0.1a 8.8 ± 0.0a 7.2 ± 0.2b
4.5 ± 0.1b 4.9 ± 0.1a –
114.6 ± 4.2a 111.7 ± 3.7a 109.2 ± 4.5a
ZS1
20 DAA 40 DAA 60 DAA
9.5 ± 0.6a 10.6 ± 0.3a 7.3 ± 0.5b
4.8 ± 0.1a 4.6 ± 0.1a –
CT2
20 DAA 40 DAA 60 DAA
10.0 ± 0.6a 9.7 ± 0.4a 7.0 ± 0.2b
LN3
20 DAA 40 DAA 60 DAA
M-81E
20 DAA 40 DAA 60 DAA
Grain 4.6 ± 0.5b 9.6 ± 0.5a –
133.4 ± 7.5ab 149.7 ± 8.1a 113.1 ± 9.3b
8.1 ± 0.4b 12.9 ± 0.3a –
9.7 ± 0.1a 9.1 ± 0.2b 7.3 ± 0.1c
4.2 ± 0.1b 4.5 ± 0.0a –
189.9 ± 4.6a 193.8 ± 9.1a 161.0 ± 7.1b
6.2 ± 0.1b 15.8 ± 0.3a –
5.3 ± 0.1a 5.1 ± 0.1ab –
182.3 ± 16.0a 187.7 ± 11.7a 135.8 ± 3.4b
7.8 ± 0.3b 16.0 ± 0.6a –
9.5 ± 0.3a 9.7 ± 0.1a 8.7 ± 0.3b
5.3 ± 0.2a 5.0 ± 0.5a –
284.1 ± 5.7a 276.3 ± 3.7a 265.5 ± 10.7a
12.9 ± 1.2b 24.0 ± 1.7a –
5.5 ± 0.1a 5.6 ± 0.1a 4.9 ± 0.1b
6.3 ± 0.1a 6.1 ± 0.1ab –
123.6 ± 2.0a 125.1 ± 2.2a 124.2 ± 1.2a
6.9 ± 0.2b 15.4 ± 0.3a –
6.4 ± 0.1a 6.5 ± 0.1a 5.8 ± 0.2b
6.2 ± 0.1a 6.0 ± 0.1ab –
197.5 ± 7.3ab 205.6 ± 2.8a 181.4 ± 8.9b
8.4 ± 0.3b 25.0 ± 0.6a –
5.7 ± 0.3a 4.9 ± 0.2ab 4.6 ± 0.4b
5.5 ± 0.1a 5.3 ± 0.0b –
106.3 ± 3.2a 102.8 ± 4.6a 80.7 ± 7.8b
4.9 ± 0.4b 12.1 ± 0.4a –
7.4 ± 0.2a 6.0 ± 0.2b 4.5 ± 0.1c
4.9 ± 0.2a 4.7 ± 0.1a –
184.7 ± 4.6a 171.2 ± 6.6a 122.3 ± 6.0b
6.6 ± 0.5b 13.4 ± 0.3a –
–: Data is not available because the grain was harvested on 40 DAA.
concentration between stems and leaves were different with varieties in 2006 (Table 6). It was significantly higher in leaves (P < 0.05) on each harvest date for the early maturity variety ITL and the late varieties LN3 and M-81E, with a reverse trend for the early variety ZS1 and middle variety CT2. However, accumulation of K in stems was significantly higher (P < 0.05) than in leaves across all varieties and harvest dates.
grain for both years; whereas the interaction had highly significant effects (P < 0.001) on all the parameters with the exception of nonsignificant effects (P < 0.05) on N concentration and accumulation in grains in 2006. 4. Discussion 4.1. N, P, and K concentrations and accumulation
3.8. ANOVA analysis All sweet sorghum varieties used in this study exhibited an obvious trend of decrease in concentrations of N, P and K in aboveground plants from elongation to grain maturity (ca. 40 DAA) in both years. Conversely, the increase in nutrient accumulation was found to be due to biomass accumulation with advancement of the crop growth. This is expected and in agreement with the findings for all annual crop species (Barker and Pilbeam, 2007). Because a sig-
Effects of harvest time and variety on either concentrations or the accumulations of N, P, and K in straw and grain were highly significant (P < 0.001) in 2006 and 2007 with the exception of a non-significant effect (P < 0.05) of harvest time on K concentration in grains (Table 7). The year × harvest time interaction did not exhibit a significant effect (P < 0.05) on K concentration in
Table 6 Changes in concentration and accumulation of potassium (K) in stem and leaf of the sweet sorghum cultivars Italy (ITY), Zaoshu-1 (ZS1), Chuntian-2 (CT2), Lvneng-3 (LN3) and M-81E on 0, 20, 40, and 60 days after anthesis (DAA) in 2006. The different small letters indicate significant differences within each cultivar at a P < 0.05 level. Variety
Harvest date
K in stem
K in leaf −1
Concentration (g kg
)
−1
Accumulation (kg ha
)
Concentration (g kg−1 )
Accumulation (kg ha−1 )
ITL
0 DAA 20 DAA 40 DAA 60 DAA
9.7 8.2 8.1 5.7
± ± ± ±
0.3a 0.1b 0.2b 0.2c
59.7 65.9 66.1 63.3
± ± ± ±
1.9a 1.6a 2.5a 4.3a
12.1 10.8 11.0 8.2
± ± ± ±
0.2a 0.1b 0.4b 0.3c
35.3 31.3 34.7 31.9
± ± ± ±
2.2a 3.1a 1.3a 1.2a
ZS1
0 DAA 20 DAA 40 DAA 60 DAA
10.0 9.9 11.3 7.7
± ± ± ±
0.5a 0.7a 0.3a 0.5b
75.2 103.6 116.4 88.9
± ± ± ±
1.3c 6.3ab 7.0a 8.6bc
10.1 8.4 8.8 6.3
± ± ± ±
0.2a 0.3b 0.4b 0.6c
36.5 29.8 33.3 24.3
± ± ± ±
2.4a 1.3bc 2.2ab 2.1c
CT2
0 DAA 20 DAA 40 DAA 60 DAA
12.0 10.3 10.2 6.8
± ± ± ±
0.5a 0.7b 0.5b 0.3c
128.1 132.8 137.9 92.1
± ± ± ±
1.1a 11.6a 9.6a 4.9b
10.6 9.2 8.4 7.4
± ± ± ±
0.3a 0.5b 0.1b 0.2c
57.0 49.6 49.8 43.7
± ± ± ±
3.3a 4.4ab 2.4ab 2.8b
LN3
0 DAA 20 DAA 40 DAA 60 DAA
4.8 4.6 4.8 4.5
± ± ± ±
0.0a 0.1ab 0.1a 0.2b
62.7 77.7 79.1 85.3
± ± ± ±
1.7c 1.0b 2.0b 0.9a
10.0 8.0 7.6 6.4
± ± ± ±
0.4a 0.0b 0.2b 0.2c
57.1 45.9 46.0 38.9
± ± ± ±
2.1a 1.1b 0.3b 1.7c
M81E
0 DAA 20 DAA 40 DAA 60 DAA
4.6 5.0 3.8 3.9
± ± ± ±
0.2a 0.2a 0.1b 0.3b
44.0 71.2 57.7 45.7
± ± ± ±
1.7c 3.4a 2.9b 4.0c
11.3 7.8 7.8 6.0
± ± ± ±
0.1a 0.5b 0.3b 0.7c
41.4 35.1 45.0 35.0
± ± ± ±
2.4a 2.8a 3.0a 4.8a
238
L.P. Han et al. / Field Crops Research 120 (2011) 230–240
Table 7 Results of a two-way ANOVA for the analysis of the main effects of harvest date (H), variety (V) or their interaction (H × V) on concentration and accumulation of nitrogen (N), phosphorus (P), and potassium (K). Parameter
2006
N concentration in straw N concentration in grain N accumulation in straw N accumulation in grain P concentration in straw P concentration in grain P accumulation in straw P accumulation in grain K concentration in straw K concentration in grain K accumulation in straw K accumulation in grain
2007
H
V
H×V
H
V
***
***
***
***
***
H×V **
***
***
ns
***
***
***
***
***
***
***
***
***
***
***
ns
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
**
***
***
***
***
***
ns
ns
***
ns
***
***
***
***
***
***
***
***
***
***
***
***
ns: denotes no significant effects. ** Significant effect at P < 0.01 level. *** Significant effect at P < 0.001 level.
nificantly higher level (P < 0.05) of biomass production (Zhao et al., 2009) and the same level of N, P, and K concentration in the plants, the results of this study also indicated that sweet sorghum hybrids had a higher nutrient accumulation than the inbred varieties. Although fertilizer requirement of sweet sorghum is much lower than sugarcane (Almodares and Hadi, 2009), partially because sugarcane has a much longer growth duration than sweet sorghum, we found that the middle and late maturity sweet sorghum varieties took up a higher quantity of N, P, and K than with the main crops of maize, wheat and rice in China (Table 8). With the exception of the late maturity varieties with a significantly lower in K concentration (P < 0.05) than the early and middle varieties, there were no significantly differences in N, P, and K concentrations on the whole plant basis between varieties used in this study. The concentrations of N, P, and K in sweet sorghum are comparable with those in maize, wheat, and rice, respectively (Table 8). The reason for the high nutrient accumulation is thus the relatively high sweet sorghum aboveground biomass level which ranges between 23 and 35 t ha−1 for the middle and late varieties, as reported from the same field as this study (Zhao et al., 2009). Therefore, because the entire aboveground part of sweet sorghum could be harvested for ethanol production, it is important to maintain soil nutrient balance for a sustainable and high productivity. 4.2. N, P, and K partitioning N and P concentrations in straw were significantly lower than in grain; whereas K concentrations were the reverse. The N and
P concentrations in leaves were higher than in stems after anthesis for all sweet sorghum varieties. The findings are in agreement with a previous study on grain sorghum (Lu et al., 1999). However, because sweet sorghum had a higher biomass in straw than in grains (Zhao et al., 2009), accumulation of N, P and K in straw was 2.2–9.3 times, 1.7–7.7 times, and 8.1–30.5 times higher than in grains, respectively. Stem biomass was much higher than leaf biomass, and resulted in a significantly higher accumulation of P and K in stems than in leaves. Due to the higher N concentration in leaves, N accumulation in leaves was comparable with that in stems. Therefore, it suggests to screening varieties with lower nutrient concentrations in a higher yield of straw, particularly in stem, during further genetic improvement for higher nutrient use efficiency of the “nutrient depletion crop” sweet sorghum. It should be noted that the effects of variety on the nutrient concentration or the accumulation in straw were significant, suggesting the possibility of genetic improvement. 4.3. N, P, and K accumulation ratio and rate All varieties exhibited significantly larger fractions of N (50–82%), P (40–83%), and K (55–88%) accumulated from elongation to anthesis in this study. This is in agreement with the findings on grain sorghum cultivated in China (Yu et al., 2003). However, sweet sorghum accumulated more nutrients, particularly N and K, from emergence to elongation than grain sorghum. Sweet sorghum also exhibited only one important K uptake stage, from elongation to thesis, according to the accumulation ratio and rate. The stage
Table 8 Comparison of concentrations and accumulation of nitrogen (N), phosphorus (P), and potassium (K) in the aboveground part at grain maturity between sweet sorghum and the main crops under conventional cultivation in China. Crop
Concentration (g kg−1 ) N
Sweet sorghum (early varieties) Sweet sorghum (middle and late varieties) Summer maize Summer maize Summer maize Winter wheat Winter wheat Winter wheat Lowland rice Lowland rice Lowland rice
P
Accumulation (kg ha−1 ) K
Reference
N
P
K
9–10
1.8–2.5
8–10
128–252
30–58
109–209
This study
8–10
1.4–2.1
5–9
172–339
33–75
115–300
This study
13 10–13 10–11 13 12 9–10 8–10 18–19 10–12
1.8 1.9–2.3 2.1–2.2 1.9 2.8 1.7–2.8 1.7–2.3 2.8–2.9 2.2–3.1
– 5–7 10–16 9 – 7–9 10–11 5–6 8–10
246 201–273 190–205 181 157 93–108 89–109 179–207 –
32 35–47 40–41 25 35 21–30 19–24 27–36 –
– 90–149 182–287 128 – 70–80 121–138 93–110 –
Dai et al. (2008) Yuan et al. (2010) Gao et al. (2008) Dai et al. (2010) Dai et al. (2008) Liu et al. (2003) Liu et al. (2003) Cheng et al. (2003) Chen et al. (2008)
–: Data is not available in the literature cited.
L.P. Han et al. / Field Crops Research 120 (2011) 230–240
from anthesis to grain maturity was the second important N and P uptake period. 4.4. Changes in N, P, and K during delay harvest period The changes in N, P, and K in aboveground plants of sweet sorghum during the delay harvest period between 40 and 60 DAA was different between varieties. The early varieties exhibited increases in N accumulation, and late varieties exhibited the opposite. K accumulation decreased across all varieties in both years. Generally, the later the variety maturity, the higher the nutrient loss when delaying the harvest beyond grain maturity. This is because the early varieties had more days between grain maturity and the first killing frost date, when sweet sorghum still was alive and took up nutrients from the soil, whereas the late varieties died soon after grain maturity close to the first killing frost date. Reduction in mineral nutrient content during the delay harvest period of energy crops could maintain nutrient cycling in the soil–crop ecosystem, because less nutrients could be removed from soil. Also, it has been recognized that reduction in ash content could improve the quality of biomass feedstock for conversion processes (Monti et al., 2008). Xiong et al. (2008) investigated the influence of harvest time on fuel characteristics of the potential energy crops indigo bush (Amorpha fruticosa), sand willow (Salix cheilophila), switch grass (Panicum virgatum), reed canary grass (Phalaris arundinacea), and sainfoin (Onobrychis viciifolia). The authors reported that N, P, and K contents of the five energy crops tended to decrease during the delay harvest period from September to March for most plants in northern China. Therefore, it is worthwhile to examine the dynamics of minerals in sorghum in the longer delay harvest stage. 5. Conclusion This investigation confirms a decrease in concentrations of N, P and K in sweet sorghum aboveground plants from elongation to harvest, and the nutrients’ accumulation with the reverse from elongation to grain maturity. There was only one important K uptake stage from elongation to thesis. The stage from anthesis to grain maturity was the second important N and P uptake period, following the first from elongation to thesis. The uptakes of N, P, and K in sweet sorghum are higher, particularly for the middle and late maturity varieties, than those in the main crops of maize, wheat and rice in China. Although concentrations of N and P in straw were significantly lower than in grains, the accumulation of N, P and K in straw was much higher than in grains. The concentrations of N and P in leaves were higher than in stems after anthesis, comparable N accumulation and significantly higher P and K accumulation in stems were found than in leaves. During the delay harvest period between 40 and 60 days after anthesis, early varieties exhibited significant increase in N accumulation and late varieties exhibited the opposite trend. P accumulation did not decrease significantly, whereas K accumulation decreased during the delay harvest period. Besides suggesting a further genetic improvement for optimizing nutrient use of sweet sorghum, the findings of this study are helpful to make a fertilization recommendation for its production as a bioethanol crop in North China. Acknowledgements This study was co-funded by the “Eleventh-Five Supporting Program” of China (2006BAD07A04) and Commonweal Section (Agriculture) Research Program (nyhyzx07-11). It is conducted in the Key Laboratory of Crop Farming, Ministry of Agriculture, PR China. We gratefully acknowledge Ms. J. Bai for her help in sample collection and chemical analysis.
239
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Accumulation and partitioning of nitrogen, phosphorus and potassium in different varieties of sweet sorghum Li Pu Han a , Yosef Steinberger c , Ya Li Zhao a,d , Guang Hui Xie a,b,∗ a
College of Agronomy and Biotechnology, China Agricultural University, 100193 Beijing, PR China Biomass Engineering Center, China Agricultural University, 100193 Beijing, PR China The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, 52900 Ramat-Gan, Israel d Agronomy College, Henan Agricultural University, 450002 Zhengzhou, PR China b c
a r t i c l e
i n f o
Article history: Received 22 June 2010 Received in revised form 21 October 2010 Accepted 21 October 2010 Keywords: Energy crop Nutrient uptake Harvest time Bio-fuel
a b s t r a c t This study investigated changes in accumulation and partitioning of nitrogen (N), phosphorus (P), and potassium (K) with harvest dates of early, middle, and late maturity sweet sorghum varieties in 2006 and 2007 in North China. All the varieties exhibited an obvious trend of decrease in concentrations of N, P and K in aboveground plants from elongation to 60 days after anthesis (DAA). The reduction in nutrient concentrations was found in the order of K (14.5 − 4.5 g kg−1 ) > N (13.3 − 7.4 g kg−1 ) > P (2.40 − 0.96 g kg−1 ). Conversely, N, P, and K accumulation significantly increased from elongation to anthesis, and continued to increase until 40 DAA. The accumulation of N, P, and K at maturity (40 DAA) was 128–339 kg ha−1 , 30–75 kg ha−1 and 109–300 kg ha−1 , respectively. Between elongation and anthesis, the middle and late maturity varieties had a higher ratio of N (50–82%), P (55–83%), and K (62–88%) accumulation than the early varieties (51–64% for N, 40–62% for P, and 55–75% for K). Sweet sorghum exhibited only one important K uptake stage from elongation to thesis according to the accumulation ratio (percentage of the nutrient accumulated at a given stage relative to that at physiological maturity) and rate (kilogram of nutrient accumulated per day per hectare). The stage from anthesis to grain maturity was the second important N and P uptake period. During the delay harvest period between 40 and 60 DAA, the early varieties exhibited significant increases in N accumulation; and the late varieties exhibited the reverse. P accumulation did not decrease significantly, whereas K accumulation decreased for all varieties in both years. Although of the N and P concentrations in straw were significantly lower than in grains, the N, P and K accumulation in straw was 2.2–9.3, 1.7–7.7, and 8.1–30.5 times higher than in grains, respectively. The concentrations of N and P in leaves were higher than in stems after anthesis. We found significantly higher accumulation of P and K in stems than in leaves, with a comparable N accumulation. The findings are helpful to make a fertilization regime recommendation for sweet sorghum production as a bioethanol crop in North China. It also suggests a further genetic improvement for optimizing nutrient use. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Sweet sorghum (Sorghum biocolor (L.) Moench) is a C4 plant characterized by high biomass and sugar yield (Amaducci et al., 2004; Antonopoulou et al., 2008; Gnansounou et al., 2005; Zhao et al., 2009). The high carbohydrate content of its stalk is similar to sugarcane, but its water requirement is much lower (Almodares and Hadi, 2009). Its wide adaptability (Gnansounou et al., 2005; Kangama and Rumei, 2005) and resistance to salinity and drought
∗ Corresponding author at: College of Agronomy and Biotechnology, China Agricultural University, No. 2 Yuanmingyuan West Road, Haidian, 100193 Beijing, PR China. Tel.: +86 10 62734888; fax: +86 10 62731298. E-mail address: [email protected] (G.H. Xie). 0378-4290/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2010.10.007
(Tsuchihashi and Goto, 2004; Rajagopal, 2008; Wortmann et al., 2010) indicate less competition with food security for human beings, as a result of the possibility to exploit less resources such as productive land and irrigation water for food crops. Sweet sorghum therefore has been widely considered a feedstock for producing fuel ethanol (Buxton et al., 1999; Liu et al., 2008; Almodares and Hadi, 2009; Yu et al., 2008; Liu and Lin, 2009) and biodiesel (Gao et al., 2010). China is not only currently facing an energy shortage, but is also pressured to reduce CO2 emission from the international community. Sweet sorghum plantations are among the most promising solutions (FAO, 2002; Cheng et al., 2009; Li and Chan-Halbrendt, 2009; Tian et al., 2009). Although the dry matter and chemical composition, particularly soluble and insoluble carbohydrates, have been well documented in sweet sorghum, little is known about its mineral nutrient accu-
L.P. Han et al. / Field Crops Research 120 (2011) 230–240
mulation. Sorghum has been recognized as a “nutrient depletion crop” by farmers, compared with cereals in China. The dynamics of mineral element uptake and partitioning are essential for forming a high biomass yield, and are closely related to nutrient cycling in the soil–plant-processing system (Epstein and Bloom, 2005). For the most field crops, some organs (e.g. grains, tuber, etc.) are harvested and the field residues are possibly incorporated into soils and compensate partially the nutrient losses. It is different that the entire aboveground part of sweet sorghum, as a bio-fuel feedstock, are considered to be harvested for ethanol production from sugar, starch, and cellulosic materials. The understanding of nutrient dynamics of the energy crop will be helpful to maintain soil nutrient balance via genetic improvement or/and fertilization. Of the essential mineral nutrients, nitrogen (N), phosphorus (P), and potassium (K) are the most important macro-nutrients affecting crop yields on one hand, fertilization for the three elements constitutes a considerable proportion of production cost on the other. It is essentially important for bio-ethanol production to reduce its feedstock cost. Information of N, P, and K uptakes and partitioning of sweet sorghum could serve for optimizing fertilization application for a high biomass yield. In our previous study we investigated the dynamics of biomass and chemical composition of sweet sorghum varieties differing in physiological maturity in North China during in growth (Zhao et al., 2009). In the present study we tested the N, P, and K contents in five sweet sorghum cultivars with a crop cycle length that varied between 111 and 165 days (the same field experiment as our previous study) in North China. The objectives of this study were: (1) to investigate the changes in accumulation and partitioning of N, P, and K with the harvest date of sweet sorghum varieties; and (2) to determine the differences in accumulation and partitioning of N, P, and K in sweet sorghum between early, middle, and late maturity varieties. 2. Materials and methods 2.1. Study site A field study was conducted in 2006 and 2007 at the Shangzhuang Experimental Station (39◦ 56 N, 116◦ 20 E) of China Agricultural University in Beijing, China. The site has a continental monsoon type climate, with an average multi-annual solar radiation of 2423 h and average multi-annual temperature of 11.5 ◦ C. Annual mean precipitation is 554.2 mm, falling mostly in July and August. Monthly precipitation and air temperature data during the study period and main physical and chemical properties of the soils in the two years are presented in Zhao et al. (2009).
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2.3. Sampling and measurements Ten aboveground sweet sorghum plants were taken on the date of elongation and 0, 20, 40, and 60 DAA from each plot. In 2006, each plant was divided into stems, leaves and a panicle for biomass estimation. One internode was taken after every two internodes from the base of each plant and was cut into 10–15 cm long pieces. The grains were threshed and the panicle axis and rachis branches were cut and mixed with stem pieces proportionately on a basis of oven-dried weight. In 2007, apart from grains, the tissues were not separated and a mixed plant sample of the whole plant was made. After being placed in an individual paper bag, it was oven dried at 70 ◦ C to constant weight in order to gravimetrically estimate plant biomass. The changes in biomass with harvest time are presented in Zhao et al. (2009). The dried samples were ground with a Wiley mill to pass through 0.5 mm mesh for nutrient determination. The ground samples were stored at 4 ◦ C for qualitative analyses. 2.4. Chemical analysis Grains, leaves and stems were separated, oven-dried to constant weight at 70 ◦ C and ground for N, P, and K analyses following Kjeldahl digestion with H2 SO4 –H2 O2 (Wolf, 1982). N concentration was determined by semimicro-Kjeldahl digestion and distillation (Nelson and Sommers, 1980). P concentration was determined by the vanadomolybdate yellow method (Jackson, 1958). K concentration was measured using a flame spectrophotometer. All analyses were performed in duplicate. The chemical composition of the plant parts is presented as nutrient concentration (g kg−1 ). 2.5. Calculation and statistical analysis The nutrient accumulation in grains, leaves and stems was computed as the product of the concentration multiplied by the dry weight of biomass. The nutrient accumulation ratio (%) at different growth stages was the percentage of the nutrient accumulation at a given stage relative to that at physiological maturity (40 DAA). The nutrient accumulation rate (kg ha−1 day−1 ) at each growth stage was obtained from the nutrient accumulation divided by the number of days of the growth stage. Means and standard errors were calculated for the four replicates from each treatment. ANOVA was conducted using SAS (SAS Institute, 1999). The statistical significance of the differences between means was determined by the least significant difference. All significant results are reported at the P < 0.05 level. 3. Results
2.2. Experiment design and crop cultivation
3.1. N, P, and K concentrations
Sweet sorghum hybrid Zaoshu-1 (ZS1), Chuntian-2 (CT2), and inbreed Italy (ITY), Lvneng-3 (LN3), M-81E were tested using a randomized block design with four replications. It was sown on April 26 in 2006 and 2007. The ITY and ZS1 varieties exhibited early maturity (111–116 days), CT2 exhibited middle maturity (138–143 days), and LN3 and M-81E exhibited late maturity (160–165 days). Basal fertilizer of 48 kg N ha−1 as urea, 90 kg P2 O5 ha−1 as diammonium phosphate and 50 kg K2 O ha−1 as potassium sulfate were applied just before sowing. 48 kg N ha−1 as urea and 50 kg K2 O ha−1 as potassium sulfate were applied at elongation, and 24 kg N ha−1 as urea were applied at anthesis. Sweet sorghum grains matured around 30 days after anthesis (DAA) for the early varieties and 36–44 DAA for the middle and late varieties. Further details of the crop management and the main morphological phases of sweet sorghum were described by Zhao et al. (2009).
Sweet sorghum exhibited an obvious trend of decrease in N, P and K concentrations in aboveground plants from elongation to 60 DAA across all the early, middle, and late maturity varieties we used in 2006 and 2007 (Fig. 1). N and K concentrations ranged between 23.7–32.4 g kg−1 and 19.6–29.7 g kg−1 at elongation and were significantly (2.3–3.2 times and 1.6–3.5 times) higher (P < 0.001) than at anthesis (0 DAA) on the whole plant basis. The variations in P concentrations between elongation (2.1–3.3 g kg−1 ) and anthesis (1.5–2.4 g kg−1 ) were smaller than the N or K concentration (Fig. 1). The N, P, and K concentration in aboveground plants at grain maturity (40 DAA) was 7.5–10.2 g kg−1 , 1.4–2.5 g kg−1 and 5.0–9.6 g kg−1 , respectively. The reduction in nutrient concentrations from anthesis to 60 DAA was in the order of K (14.5 − 4.5 g kg−1 ) > N (13.3 − 7.4 g kg−1 ) > P (2.40 − 0.96 g kg−1 ) for all the varieties in both years. Although the K concentration in
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Fig. 1. Changes in concentration of nitrogen (N), phosphorus (P) and potassium (K) of the sweet sorghum cultivars Italy (ITY), Zaoshu-1 (ZS1), Chuntian-2 (CT2), Lvneng-3 (LN3) and M-81E on elongation stage () and 0 ( ), 20 ( ), 40 ( ) and 60 ( ) days after anthesis (DAA). The vertical bars indicate standard errors. The different small letters indicate significant differences within each cultivar and each year at a P < 0.05 level.
plants of the late maturity varieties LN3 and M-81E was significantly (P < 0.05, statistical analysis not shown) lower than each of the early or middle varieties on the same harvest date, there was generally no significant difference (P < 0.05) in N and P concentrations on the whole plant basis between varieties. 3.2. N, P, and K accumulation Although the nutrient concentrations at elongation were much higher than at anthesis (Fig. 1), it was obvious that the nutrient accumulation significantly (P < 0.001) increased from elongation to anthesis for all varieties in both years (Fig. 2) due to the highest fraction of biomass accumulation from elongation (0.6–1.5 t ha−1 , data not presented) to anthesis (5.5–27.1 t ha−1 , see Zhao et al., 2009). Afterwards, all the varieties with different maturity continuously exhibited increases in nutrient accumulation from 0 DAA (anthesis) to 40 DAA (maturity). The accumulation of N, P, and K in aboveground plants at maturity (40 DAA) was 128–339 kg ha−1 , 30–75 kg ha−1 and 109–300 kg ha−1 , respectively. The early varieties ITL, ZS1 and middle variety CT2 exhibited significant increases (P < 0.05) in N accumulation from 40 DAA to 60 DAA, with the exception of CT2 in 2006; whereas the late varieties LN3 and M-81E showed significant decreases (P < 0.05) in N accumulation during the delay harvest period. P accumulation did not decrease significantly (P < 0.05) from 40 DAA to 60 DAA for all varieties with the only exception of M-81E in 2006. How-
ever, K accumulation mostly decreased for the varieties in both years. Generally, similar to the pattern of the nutrient concentrations, N had similar accumulation ranges with K, whereas P accumulation was significantly lower (P < 0.001) for the same harvest date (Fig. 2). Accumulation of N and K ranged between 105–339 kg ha−1 and 85–300 kg ha−1 , respectively. P accumulation ranged between 19 and 75 kg ha−1 from 0 DAA to 40 DAA in both years. In the early variety group, hybrid ZS1 exhibited a significantly higher N, P, and K accumulation (P < 0.05) than the inbred ITL. The middle hybrid variety CT2 exhibited similar N and K accumulation levels with the late inbred LN3, and significantly higher levels (P < 0.05) than inbred M81E for the same harvest date. CT2 also had a significantly higher K accumulation (P < 0.05) than either LN3 or M-81E. The findings indicated that sweet sorghum hybrid varieties had a higher N, P, and K accumulation than the inbred varieties. 3.3. N, P, and K accumulation ratio All the sweet sorghum varieties exhibited significantly larger fractions (P < 0.05) of N, P, and K that accumulated from elongation to anthesis in the two years (Fig. 3). In the period between elongation and anthesis, the middle and late maturity varieties had a higher ratio of N (50–82%), P (55–83%), and K (62–88%) accumulation than the early varieties (51–61% for N, 40–62% for P, and 55–75% for K). The second largest fraction of N was accumulated in
L.P. Han et al. / Field Crops Research 120 (2011) 230–240
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Fig. 2. Changes in accumulation of nitrogen (N), phosphorus (P) and potassium (K) of the sweet sorghum cultivars Italy (ITY), Zaoshu-1 (ZS1), Chuntian-2 (CT2), Lvneng-3 (LN3) and M-81E on elongation stage () and 0 ( ), 20 ( ), 40 ( ) and 60 ( ) days after anthesis (DAA). The vertical bars indicate standard errors. The different small letters indicate significant differences within each cultivar and each year at a P < 0.05 level.
the period from sowing to elongation or in the period between 0 and 20 DAA, depending on different varieties and years, with the exception of CT2 in 2006. The P accumulation ratio in the period from sowing to elongation was significantly lower than in the period between 0 and 20 DAA, and K accumulation ratio exhibited the reverse. There was a trend that the varieties had the lowest N, P and K accumulation ratio between 20 and 40 DAA. In the period of delay harvest between 40 and 60 DAA, N accumulation increased by 8–19% for the early maturity varieties ITL and ZS1; whereas it decreased by −11 to −0.21% for the late varieties LN3 and M-81E in the delay harvest period (Fig. 3). The minus values indicate percentage of the nutrient lost from the aboveground sweet sorghum plants after grain maturity. All the varieties exhibited loss of K, ranging from −26% to −0.8% after grain maturity in both years. P either accumulated or was lost, depending on varieties and years. A generalization of the above results had illustrated the importance of maturity and nutrient relation—the later the variety maturity, the higher the nutrient loss when delaying the harvest beyond grain maturity.
3.4. N, P, and K accumulation rate Accumulation rates of N (1.3–4.3 kg ha−1 day−1 ) and K (1.1–4.6 kg ha−1 day−1 ) were significantly higher (P < 0.05) in the period from elongation to anthesis in the two years for all five
varieties with the exception of M-81E in 2006 (Fig. 4). P accumulation rates were significantly lower (P < 0.01) than those of N or K for the same harvest dates. The highest P accumulation rate was between elongation and anthesis (0.27–0.94 kg ha−1 day−1 ) or between 0 and 20 DAA (0.16–1.08 kg ha−1 day−1 ). It should be noted that N and K were lost at rates comparable to the highest accumulation rates in the delay harvest period between 40 and 60 DAA for the middle and late maturity varieties.
3.5. N partitioning The concentration of N in grains was 1.7–3.2 times higher (P < 0.01) than in straw on 20 and 40 DAA for all sweet sorghum varieties in both years (Table 1). However, because most of the biomass was found in straw (Zhao et al., 2009), N accumulation in grains was 2.2–9.3 times lower (P < 0.01). Although there was a slight reduction in the N concentration in straw from 20 DAA (7.9–13.3 g kg−1 ) to 40 DAA (6.2–9.2 g kg−1 ), the differences were not significant (P < 0.05) between 20 DAA (105–274 kg ha−1 ) and 40 DAA (95–256 kg ha−1 ) for all varieties. The N concentration in grains decreased from 20 DAA to 40 DAA (P < 0.05) for each of the varieties, whereas N accumulated in grains increased significantly (P < 0.05) during the same period resulted from a considerable increase in grain biomass. There was also a trend that N accumulated in straw on 60 DAA was higher than on 40 DAA for each early maturity
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Fig. 3. Changes in accumulation ratio of nitrogen (N), phosphorus (P) and potassium (K) of the sweet sorghum cultivars Italy (ITY), Zaoshu-1 (ZS1), Chuntian-2 (CT2), Lvneng-3 (LN3) and M-81E between sowing and elongation ( ), elongation and anthesis ( ), anthesis and 20 days after anthesis (DAA) ( ), 20 and 40 DAA ( ), and 40 and 60 DAA (). The vertical bars indicate standard errors. The different small letters indicate significant differences within each cultivar and each year at a P < 0.05 level.
Table 1 Changes in concentration and accumulation of nitrogen (N) in straw and grains of the sweet sorghum cultivars Italy (ITY), Zaoshu-1 (ZS1), Chuntian-2 (CT2), Lvneng-3 (LN3) and M-81E on 20, 40, and 60 days after anthesis (DAA). The different small letters indicate significant differences within each cultivar and each year at a P < 0.05 level. Variety
Harvest date
2006
2007 −1
N concentration (g kg
)
−1
N accumulation (kg ha
Straw
Grain
Straw
)
Grain
N concentration (g kg−1 )
N accumulation (kg ha−1 )
Straw
Grain
Straw
Grain
ITL
20 DAA 40 DAA 60 DAA
9.4 ± 0.3a 8.4 ± 0.3b 7.5 ± 0.1c
20.2 ± 0.8a 17.3 ± 0.7b –
103.3 ± 5.4ab 94.9 ± 2.9b 111.6 ± 4.4a
16.3 ± 1.2b 32.8 ± 2.7a –
9.1 ± 0.3a 8.4 ± 0.2a 8.9 ± 0.3a
20.6 ± 0.3a 17.8 ± 0.3b –
119.4 ± 5.3b 106.6 ± 1.6c 134.7 ± 1.7a
21.0 ± 2.1b 34.7 ± 0.7a –
ZS1
20 DAA 40 DAA 60 DAA
7.7 ± 0.2a 7.4 ± 0.2a 7.6 ± 0.3a
19.7 ± 0.5a 16.8 ± 0.4b –
108.2 ± 4.6a 103.6 ± 4.7a 116.2 ± 2.2a
33.6 ± 3b 47.5 ± 2.3a –
9.8 ± 0.3a 9.2 ± 0.1a 9.9 ± 0.3a
23.5 ± 0.7a 16.1 ± 0.1b –
192.0 ± 6.4a 195.7 ± 7.7a 219.3 ± 17a
34.8 ± 2b 56.3 ± 0.9a –
CT2
20 DAA 40 DAA 60 DAA
8.4 ± 0.1a 8.0 ± 0.1a 7.6 ± 0.2b
21.2 ± 0.8a 18.2 ± 0.7b –
153.3 ± 5.2a 156.0 ± 5.5a 148.5 ± 6.2a
31.5 ± 2.6b 57.2 ± 2.8a –
8.7 ± 0.2a 7.8 ± 0.3ab 8.1 ± 0.2b
20.2 ± 0.8a 17.9 ± 0.9ab –
262.6 ± 10.4a 224.6 ± 9.7b 249.8 ± 10.8ab
48.8 ± 2.7b 87.4 ± 7.6a –
LN3
20 DAA 40 DAA 60 DAA
8.2 ± 0.2a 7.7 ± 0.1a 6.0 ± 0.2b
24.3 ± 0.6a 20.8 ± 0.5b –
184.4 ± 5.9a 171.9 ± 3.0a 152.2 ± 4.7b
26.7 ± 1.1b 52.8 ± 1.3a –
9.4 ± 0.1a 8.1 ± 0.2b 8.3 ± 0.4b
23.1 ± 0.7a 19.8 ± 0.6b –
286.6 ± 2.9a 256.4 ± 9.0b 258.0 ± 10.9b
30.8 ± 0.8b 82.4 ± 2.8a –
M-81E
20 DAA 40 DAA 60 DAA
6.9 ± 0.3a 6.2 ± 0.2a 6.4 ± 0.3a
22.1 ± 0.3a 18.9 ± 0.2b –
129.2 ± 6.9a 129.3 ± 4.7a 111.4 ± 3.8b
19.8 ± 1.5b 43.0 ± 1.7a –
8.6 ± 0.1a 6.9 ± 0.1b 6.5 ± 0.1c
21.8 ± 0.4a 18.3 ± 0.3b –
214.4 ± 7.5a 195.5 ± 3.8b 174.2 ± 5.0c
29.3 ± 1.1b 52.6 ± 0.7a –
–: Data is not available because the grain was harvested on 40 DAA.
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Fig. 4. Changes in accumulation rate of nitrogen (N), phosphorus (P) and potassium (K) of the sweet sorghum cultivars Italy (ITY), Zaoshu-1 (ZS1), Chuntian-2 (CT2), Lvneng-3 (LN3) and M-81E between sowing and elongation ( ), elongation and anthesis ( ), anthesis and 20 days after anthesis (DAA) ( ), 20 and 40 DAA ( ), and 40 and 60 DAA (). The vertical bars indicate standard errors. The different small letters indicate significant differences within each cultivar and each year at a P < 0.05 level.
varieties, and the reverse for the late varieties (Table 1). The concentration of N in leaves was 1.7–3.9 times higher (P < 0.01) than in stems on 0, 20, 40, and 60 DAA for all the varieties in both years (Table 2). However, N accumulated in stems was comparable with that in leaves.
3.6. P partitioning Similarly to the pattern of the N concentration, the five sweet sorghum varieties exhibited a significantly higher P concentration (P < 0.01) in grains (3.9–6.7 g kg−1 ) than in straw (0.9–2.5 g kg−1 )
Table 2 Changes in concentration and accumulation of nitrogen (N) in stem and leaf of the sweet sorghum cultivars Italy (ITY), Zaoshu-1 (ZS1), Chuntian-2 (CT2), Lvneng-3 (LN3) and M-81E on 0, 20, 40, and 60 days after anthesis (DAA) in 2006. The different small letters indicate significant differences within each cultivar at a P < 0.05 level. Variety
Harvest date
N in stem Concentration (g kg−1 )
N in leaf Accumulation (kg ha−1 )
Concentration (g kg−1 )
Accumulation (kg ha−1 )
ITL
0 DAA 20 DAA 40 DAA 60 DAA
6.9 6.4 4.8 4.9
± ± ± ±
0.2a 0.3a 0.2b 0.1b
42.2 51.5 38.8 54.5
± ± ± ±
0.7b 2.2a 0.9b 2.6a
23.0 17.8 17.9 14.6
± ± ± ±
0.3a 0.8b 0.6b 0.3c
66.9 51.9 56.1 57.1
± ± ± ±
3.1a 6.4b 2.0ab 2.6ab
ZS1
0 DAA 20 DAA 40 DAA 60 DAA
5.4 4.5 4.3 5.1
± ± ± ±
0.1a 0.4bc 0.1c 0.2ab
40.4 47.1 44.5 57.9
± ± ± ±
1.9b 4.2b 3.9b 1.1a
18.9 17.3 15.6 15.2
± ± ± ±
0.7a 0.2b 0.4c 0.3c
68.4 61.1 59.1 58.3
± ± ± ±
5.4a 1.0ab 2.0b 1.6b
CT2
0 DAA 20 DAA 40 DAA 60 DAA
8.0 5.2 4.8 4.4
± ± ± ±
0.4a 0.2b 0.2b 0.4b
85.7 67.3 64.8 60.3
± ± ± ±
3.9a 2.4b 4.3b 6.6b
16.8 16.0 15.4 14.8
± ± ± ±
0.3a 0.2ab 0.3b 0.6b
90.2 86.1 91.2 88.2
± ± ± ±
5.8a 4.2a 3.4a 6.6a
LN3
0 DAA 20 DAA 40 DAA 60 DAA
6.7 5.7 6.5 4.9
± ± ± ±
0.1a 0.1b 0.1a 0.2c
86.6 95.1 106.5 93.2
± ± ± ±
1.7b 3.2b 4.5a 2.2b
16.7 15.6 10.8 9.8
± ± ± ±
0.3a 0.4b 0.3c 0.4d
95.0 89.3 65.3 59.0
± ± ± ±
2.2a 2.7a 2.1b 2.6b
M81E
0 DAA 20 DAA 40 DAA 60 DAA
5.7 4.6 4.2 4.0
± ± ± ±
0.2a 0.2b 0.1bc 0.1c
55.6 65.7 63.2 46.9
± ± ± ±
4.5ab 6.9a 3.1a 2.2b
13.5 14.1 11.4 11.1
± ± ± ±
0.4a 0.6a 0.4b 0.6b
49.1 63.5 66.1 64.0
± ± ± ±
1.8b 3.8a 4.2a 3.8a
236
L.P. Han et al. / Field Crops Research 120 (2011) 230–240
Table 3 Changes in concentration and accumulation of phosphorus (P) in straw and grain of the sweet sorghum cultivars Italy (ITY), Zaoshu-1 (ZS1), Chuntian-2 (CT2), Lvneng-3 (LN3) and M-81E on 20, 40, and 60 days after anthesis (DAA). The different small letters indicate significant differences within each cultivar and each year at a P < 0.05 level. Variety
Harvest date
2006
2007
P concentration (g kg−1 )
P accumulation (kg ha−1 )
P concentration (g kg−1 )
P accumulation (kg ha−1 )
Straw
Straw
Grain
Straw
Grain
Straw
Grain
ITL
20 DAA 40 DAA 60 DAA
2.1 ± 0.06a 2.0 ± 0.02a 1.8 ± 0.06b
5.3 ± 0.04a 3.9 ± 0.13b –
Grain
22.8 ± 1.1b 23.0 ± 0.6b 27.6 ± 1.7a
4.3 ± 0.2b 7.3 ± 0.1a –
2.5 ± 0.04a 2.2 ± 0.05b 2.0 ± 0.05c
4.8 ± 0.04a 4.6 ± 0.09b –
31.6 ± 0.4a 28.0 ± 0.5b 30.8 ± 1.3ab
4.9 ± 0.5b 8.9 ± 0.4a –
ZS1
20 DAA 40 DAA 60 DAA
1.5 ± 0.04a 1.4 ± 0.02ab 1.4 ± 0.03b
5.2 ± 0.12a 4.1 ± 0.04b –
19.8 ± 1.0a 19.3 ± 1.2a 20.8 ± 0.7a
9.0 ± 0.7b 11.7 ± 0.5a –
2.2 ± 0.04a 2.0 ± 0.09ab 1.9 ± 0.04b
4.7 ± 0.11a 4.1 ± 0.04b –
42.4 ± 0.4a 43.2 ± 3.2a 41.3 ± 2.7a
7.0 ± 0.1b 14.5 ± 0.4a –
CT2
20 DAA 40 DAA 60 DAA
1.6 ± 0.03a 1.3 ± 0.03b 1.2 ± 0.04b
6.7 ± 0.08a 4.6 ± 0.05b –
28.4 ± 1.5a 25.9 ± 0.9ab 24.3 ± 0.9b
9.9 ± 0.5b 14.6 ± 0.7a –
1.5 ± 0.03a 1.5 ± 0.02a 1.4 ± 0.03a
6.0 ± 0.08a 4.2 ± 0.1b –
43.6 ± 1.0a 41.8 ± 1.0a 43.5 ± 1.4a
14.7 ± 0.8b 20.6 ± 1.2a –
LN3
20 DAA 40 DAA 60 DAA
1.6 ± 0.02a 1.3 ± 0.05b 1.3 ± 0.01b
5.8 ± 0.14a 5.8 ± 0.15a –
34.7 ± 0.8a 28.7 ± 1.5b 31.5 ± 0.9ab
6.4 ± 0.3b 14.7 ± 0.7a –
1.7 ± 0.03a 1.7 ± 0.04ab 1.6 ± 0.02b
5.0 ± 0.2b 5.5 ± 0.11a –
51.0 ± 1.9a 52.4 ± 0.8a 48.7 ± 1.4a
6.7 ± 0.2b 22.8 ± 0.8a –
M-81E
20 DAA 40 DAA 60 DAA
1.2 ± 0.07a 1.1 ± 0.03ab 0.9 ± 0.03b
5.2 ± 0.07a 4.5 ± 0.18b –
22.7 ± 2.1a 22.4 ± 0.8a 16.3 ± 0.8b
4.6 ± 0.3b 10.3 ± 0.7a –
1.4 ± 0.02a 1.1 ± 0.01b 1.1 ± 0.04b
4.7 ± 0.06a 4.6 ± 0.16a –
34.9 ± 0.5a 29.8 ± 0.5b 28.6 ± 1.5b
6.3 ± 0.2b 13.1 ± 0.5a –
–: Data is not available because the grain was harvested on 40 DAA.
on 20 and 40 DAA in the two years (Table 3). A trend of reduction in P concentration after 20 DAA was found for straw and for grain, whereas the accumulation of P in straw (16–52 kg ha−1 ) was 1.7–7.7 times higher (P < 0.01) than in grains (4–23 kg ha−1 ) in both years, due to the much higher biomass of straw (Zhao et al., 2009). The accumulation of P in grains increased significantly (P < 0.01) from 20 DAA to 40 DAA for each variety in both years. However, changes in P accumulation in straw with harvest date from 20 DAA to 60 DAA were not consistent between varieties and between years (Table 3). A significantly higher P concentration (P < 0.01) after anthesis was found in leaves (1.4–4.4 g kg−1 ) than in stems across the varieties (0.7–1.5 g kg−1 ) (Table 4). There was a trend of reduction in P concentration in stems and in leaves with harvest time from 0 DAA to 60 DAA, whereas variations in accumulation of P in stems or in leaves with the harvest dates were not consistent between varieties. All the varieties, with the exception of ITL, exhibited a significantly higher P accumu-
lation in stems (P < 0.05) than in leaves for most harvest dates in 2006. 3.7. K partitioning Contrary to the patterns of N and P concentrations, sweet sorghum exhibited a significantly higher K concentration (P < 0.05) in straw (4.5–10.6 g kg−1 ) than in grains (4.2–6.3 g kg−1 ), with the exception of LN3 and M-81E in 2006 (Table 5). The accumulation of K was 8.1–30.5 times higher (P < 0.001) in straw (81–284 kg ha−1 ) than in grains (3.7–25 kg ha−1 ) across all varieties on 20 DAA and 40 DAA in both years. Accumulation of K in grains increased significantly (P < 0.01) from 20 DAA to 40 DAA. K concentration or accumulation in straw decreased significantly during the delay harvest period from 40 DAA to 60 DAA in both years. Each variety exhibited a significantly higher accumulation of K in grains (P < 0.01) on 40 DAA than on 20 DAA (Table 5). The variations in K
Table 4 Changes in concentration and accumulation of phosphorus (P) in stems and leaves of the sweet sorghum cultivars Italy (ITY), Zaoshu-1 (ZS1), Chuntian-2 (CT2), Lvneng-3 (LN3) and M-81E on 0, 20, 40, and 60 days after anthesis (DAA). The different small letters indicate significant differences within each cultivar at a P < 0.05 level. Variety
Harvest date
P in stem
P in leaf −1
Concentration (g kg
)
−1
Accumulation (kg ha
)
Concentration (g kg−1 )
ITL
0 DAA 20 DAA 40 DAA 60 DAA
1.4 1.3 1.2 1.2
± ± ± ±
0.03a 0.03b 0.01b 0.09b
8.9 10.1 9.6 13.0
± ± ± ±
0.3b 0.4b 0.3b 1.4a
4.4 4.4 4.2 3.7
± ± ± ±
0.05a 0.03a 0.08a 0.06b
ZS1
0 DAA 20 DAA 40 DAA 60 DAA
1.3 1.0 1.0 1.0
± ± ± ±
0.04a 0.05b 0.03b 0.06b
9.9 10.5 10.4 11.6
± ± ± ±
0.5a 0.8a 0.9a 0.8a
2.4 2.6 2.3 2.4
± ± ± ±
0.08ab 0.03a 0.04b 0.10b
CT2
0 DAA 20 DAA 40 DAA 60 DAA
1.5 1.2 1.0 1.0
± ± ± ±
0.02a 0.07b 0.02bc 0.08c
16.6 15.0 13.8 12.8
± ± ± ±
0.8a 1.2ab 0.3b 0.7b
2.7 2.5 2.0 1.9
± ± ± ±
LN3
0 DAA 20 DAA 40 DAA 60 DAA
1.2 1.3 1.1 1.1
± ± ± ±
0.01b 0.03a 0.04c 0.01c
15.8 22.2 17.7 21.6
± ± ± ±
0.4b 0.7a 1.0b 0.7a
3.3 2.2 1.8 1.6
M81E
0 DAA 20 DAA 40 DAA 60 DAA
1.1 1.0 1.0 0.7
± ± ± ±
0.02a 0.06b 0.03b 0.02c
11.1 14.6 14.5 8.4
± ± ± ±
0.8ab 1.9a 0.9a 0.5b
2.5 1.8 1.4 1.4
Accumulation (kg ha−1 ) 12.9 12.7 13.3 14.6
± ± ± ±
0.7a 1.2a 0.4a 0.8a
8.7 9.3 8.8 9.2
± ± ± ±
0.4a 0.2a 0.3a 0.4a
0.12a 0.05a 0.12b 0.15b
14.5 13.3 12.1 11.4
± ± ± ±
0.9a 0.4ab 0.7ab 1.1b
± ± ± ±
0.02a 0.05b 0.09c 0.01d
18.9 12.5 11.0 9.9
± ± ± ±
0.6a 0.1b 0.6c 0.2c
± ± ± ±
0.03a 0.13b 0.05c 0.06c
9.1 8.2 7.9 7.9
± ± ± ±
0.5a 0.6a 0.3a 0.5a
L.P. Han et al. / Field Crops Research 120 (2011) 230–240
237
Table 5 Changes in concentration and accumulation of potassium (K) in straw and grain of the sweet sorghum cultivars Italy (ITY), Zaoshu-1 (ZS1), Chuntian-2 (CT2), Lvneng-3 (LN3) and M-81E on 20, 40, and 60 days after anthesis (DAA). The different small letters indicate significant differences within each cultivar and each year at a P < 0.05 level. Variety
Harvest date
2006
2007
K concentration (g kg−1 )
K accumulation (kg ha−1 )
K concentration (g kg−1 )
K accumulation (kg ha−1 )
Straw
Grain
Straw
ITL
20 DAA 40 DAA 60 DAA
8.9 ± 0.1a 8.9 ± 0.2a 6.4 ± 0.2b
4.6 ± 0.2a 4.4 ± 0.2a –
97.2 ± 3.9a 100.8 ± 3.1a 95.2 ± 5.2a
Grain
Straw
Grain
Straw
3.7 ± 0.2b 8.3 ± 0.5a –
8.7 ± 0.1a 8.8 ± 0.0a 7.2 ± 0.2b
4.5 ± 0.1b 4.9 ± 0.1a –
114.6 ± 4.2a 111.7 ± 3.7a 109.2 ± 4.5a
ZS1
20 DAA 40 DAA 60 DAA
9.5 ± 0.6a 10.6 ± 0.3a 7.3 ± 0.5b
4.8 ± 0.1a 4.6 ± 0.1a –
CT2
20 DAA 40 DAA 60 DAA
10.0 ± 0.6a 9.7 ± 0.4a 7.0 ± 0.2b
LN3
20 DAA 40 DAA 60 DAA
M-81E
20 DAA 40 DAA 60 DAA
Grain 4.6 ± 0.5b 9.6 ± 0.5a –
133.4 ± 7.5ab 149.7 ± 8.1a 113.1 ± 9.3b
8.1 ± 0.4b 12.9 ± 0.3a –
9.7 ± 0.1a 9.1 ± 0.2b 7.3 ± 0.1c
4.2 ± 0.1b 4.5 ± 0.0a –
189.9 ± 4.6a 193.8 ± 9.1a 161.0 ± 7.1b
6.2 ± 0.1b 15.8 ± 0.3a –
5.3 ± 0.1a 5.1 ± 0.1ab –
182.3 ± 16.0a 187.7 ± 11.7a 135.8 ± 3.4b
7.8 ± 0.3b 16.0 ± 0.6a –
9.5 ± 0.3a 9.7 ± 0.1a 8.7 ± 0.3b
5.3 ± 0.2a 5.0 ± 0.5a –
284.1 ± 5.7a 276.3 ± 3.7a 265.5 ± 10.7a
12.9 ± 1.2b 24.0 ± 1.7a –
5.5 ± 0.1a 5.6 ± 0.1a 4.9 ± 0.1b
6.3 ± 0.1a 6.1 ± 0.1ab –
123.6 ± 2.0a 125.1 ± 2.2a 124.2 ± 1.2a
6.9 ± 0.2b 15.4 ± 0.3a –
6.4 ± 0.1a 6.5 ± 0.1a 5.8 ± 0.2b
6.2 ± 0.1a 6.0 ± 0.1ab –
197.5 ± 7.3ab 205.6 ± 2.8a 181.4 ± 8.9b
8.4 ± 0.3b 25.0 ± 0.6a –
5.7 ± 0.3a 4.9 ± 0.2ab 4.6 ± 0.4b
5.5 ± 0.1a 5.3 ± 0.0b –
106.3 ± 3.2a 102.8 ± 4.6a 80.7 ± 7.8b
4.9 ± 0.4b 12.1 ± 0.4a –
7.4 ± 0.2a 6.0 ± 0.2b 4.5 ± 0.1c
4.9 ± 0.2a 4.7 ± 0.1a –
184.7 ± 4.6a 171.2 ± 6.6a 122.3 ± 6.0b
6.6 ± 0.5b 13.4 ± 0.3a –
–: Data is not available because the grain was harvested on 40 DAA.
concentration between stems and leaves were different with varieties in 2006 (Table 6). It was significantly higher in leaves (P < 0.05) on each harvest date for the early maturity variety ITL and the late varieties LN3 and M-81E, with a reverse trend for the early variety ZS1 and middle variety CT2. However, accumulation of K in stems was significantly higher (P < 0.05) than in leaves across all varieties and harvest dates.
grain for both years; whereas the interaction had highly significant effects (P < 0.001) on all the parameters with the exception of nonsignificant effects (P < 0.05) on N concentration and accumulation in grains in 2006. 4. Discussion 4.1. N, P, and K concentrations and accumulation
3.8. ANOVA analysis All sweet sorghum varieties used in this study exhibited an obvious trend of decrease in concentrations of N, P and K in aboveground plants from elongation to grain maturity (ca. 40 DAA) in both years. Conversely, the increase in nutrient accumulation was found to be due to biomass accumulation with advancement of the crop growth. This is expected and in agreement with the findings for all annual crop species (Barker and Pilbeam, 2007). Because a sig-
Effects of harvest time and variety on either concentrations or the accumulations of N, P, and K in straw and grain were highly significant (P < 0.001) in 2006 and 2007 with the exception of a non-significant effect (P < 0.05) of harvest time on K concentration in grains (Table 7). The year × harvest time interaction did not exhibit a significant effect (P < 0.05) on K concentration in
Table 6 Changes in concentration and accumulation of potassium (K) in stem and leaf of the sweet sorghum cultivars Italy (ITY), Zaoshu-1 (ZS1), Chuntian-2 (CT2), Lvneng-3 (LN3) and M-81E on 0, 20, 40, and 60 days after anthesis (DAA) in 2006. The different small letters indicate significant differences within each cultivar at a P < 0.05 level. Variety
Harvest date
K in stem
K in leaf −1
Concentration (g kg
)
−1
Accumulation (kg ha
)
Concentration (g kg−1 )
Accumulation (kg ha−1 )
ITL
0 DAA 20 DAA 40 DAA 60 DAA
9.7 8.2 8.1 5.7
± ± ± ±
0.3a 0.1b 0.2b 0.2c
59.7 65.9 66.1 63.3
± ± ± ±
1.9a 1.6a 2.5a 4.3a
12.1 10.8 11.0 8.2
± ± ± ±
0.2a 0.1b 0.4b 0.3c
35.3 31.3 34.7 31.9
± ± ± ±
2.2a 3.1a 1.3a 1.2a
ZS1
0 DAA 20 DAA 40 DAA 60 DAA
10.0 9.9 11.3 7.7
± ± ± ±
0.5a 0.7a 0.3a 0.5b
75.2 103.6 116.4 88.9
± ± ± ±
1.3c 6.3ab 7.0a 8.6bc
10.1 8.4 8.8 6.3
± ± ± ±
0.2a 0.3b 0.4b 0.6c
36.5 29.8 33.3 24.3
± ± ± ±
2.4a 1.3bc 2.2ab 2.1c
CT2
0 DAA 20 DAA 40 DAA 60 DAA
12.0 10.3 10.2 6.8
± ± ± ±
0.5a 0.7b 0.5b 0.3c
128.1 132.8 137.9 92.1
± ± ± ±
1.1a 11.6a 9.6a 4.9b
10.6 9.2 8.4 7.4
± ± ± ±
0.3a 0.5b 0.1b 0.2c
57.0 49.6 49.8 43.7
± ± ± ±
3.3a 4.4ab 2.4ab 2.8b
LN3
0 DAA 20 DAA 40 DAA 60 DAA
4.8 4.6 4.8 4.5
± ± ± ±
0.0a 0.1ab 0.1a 0.2b
62.7 77.7 79.1 85.3
± ± ± ±
1.7c 1.0b 2.0b 0.9a
10.0 8.0 7.6 6.4
± ± ± ±
0.4a 0.0b 0.2b 0.2c
57.1 45.9 46.0 38.9
± ± ± ±
2.1a 1.1b 0.3b 1.7c
M81E
0 DAA 20 DAA 40 DAA 60 DAA
4.6 5.0 3.8 3.9
± ± ± ±
0.2a 0.2a 0.1b 0.3b
44.0 71.2 57.7 45.7
± ± ± ±
1.7c 3.4a 2.9b 4.0c
11.3 7.8 7.8 6.0
± ± ± ±
0.1a 0.5b 0.3b 0.7c
41.4 35.1 45.0 35.0
± ± ± ±
2.4a 2.8a 3.0a 4.8a
238
L.P. Han et al. / Field Crops Research 120 (2011) 230–240
Table 7 Results of a two-way ANOVA for the analysis of the main effects of harvest date (H), variety (V) or their interaction (H × V) on concentration and accumulation of nitrogen (N), phosphorus (P), and potassium (K). Parameter
2006
N concentration in straw N concentration in grain N accumulation in straw N accumulation in grain P concentration in straw P concentration in grain P accumulation in straw P accumulation in grain K concentration in straw K concentration in grain K accumulation in straw K accumulation in grain
2007
H
V
H×V
H
V
***
***
***
***
***
H×V **
***
***
ns
***
***
***
***
***
***
***
***
***
***
***
ns
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
**
***
***
***
***
***
ns
ns
***
ns
***
***
***
***
***
***
***
***
***
***
***
***
ns: denotes no significant effects. ** Significant effect at P < 0.01 level. *** Significant effect at P < 0.001 level.
nificantly higher level (P < 0.05) of biomass production (Zhao et al., 2009) and the same level of N, P, and K concentration in the plants, the results of this study also indicated that sweet sorghum hybrids had a higher nutrient accumulation than the inbred varieties. Although fertilizer requirement of sweet sorghum is much lower than sugarcane (Almodares and Hadi, 2009), partially because sugarcane has a much longer growth duration than sweet sorghum, we found that the middle and late maturity sweet sorghum varieties took up a higher quantity of N, P, and K than with the main crops of maize, wheat and rice in China (Table 8). With the exception of the late maturity varieties with a significantly lower in K concentration (P < 0.05) than the early and middle varieties, there were no significantly differences in N, P, and K concentrations on the whole plant basis between varieties used in this study. The concentrations of N, P, and K in sweet sorghum are comparable with those in maize, wheat, and rice, respectively (Table 8). The reason for the high nutrient accumulation is thus the relatively high sweet sorghum aboveground biomass level which ranges between 23 and 35 t ha−1 for the middle and late varieties, as reported from the same field as this study (Zhao et al., 2009). Therefore, because the entire aboveground part of sweet sorghum could be harvested for ethanol production, it is important to maintain soil nutrient balance for a sustainable and high productivity. 4.2. N, P, and K partitioning N and P concentrations in straw were significantly lower than in grain; whereas K concentrations were the reverse. The N and
P concentrations in leaves were higher than in stems after anthesis for all sweet sorghum varieties. The findings are in agreement with a previous study on grain sorghum (Lu et al., 1999). However, because sweet sorghum had a higher biomass in straw than in grains (Zhao et al., 2009), accumulation of N, P and K in straw was 2.2–9.3 times, 1.7–7.7 times, and 8.1–30.5 times higher than in grains, respectively. Stem biomass was much higher than leaf biomass, and resulted in a significantly higher accumulation of P and K in stems than in leaves. Due to the higher N concentration in leaves, N accumulation in leaves was comparable with that in stems. Therefore, it suggests to screening varieties with lower nutrient concentrations in a higher yield of straw, particularly in stem, during further genetic improvement for higher nutrient use efficiency of the “nutrient depletion crop” sweet sorghum. It should be noted that the effects of variety on the nutrient concentration or the accumulation in straw were significant, suggesting the possibility of genetic improvement. 4.3. N, P, and K accumulation ratio and rate All varieties exhibited significantly larger fractions of N (50–82%), P (40–83%), and K (55–88%) accumulated from elongation to anthesis in this study. This is in agreement with the findings on grain sorghum cultivated in China (Yu et al., 2003). However, sweet sorghum accumulated more nutrients, particularly N and K, from emergence to elongation than grain sorghum. Sweet sorghum also exhibited only one important K uptake stage, from elongation to thesis, according to the accumulation ratio and rate. The stage
Table 8 Comparison of concentrations and accumulation of nitrogen (N), phosphorus (P), and potassium (K) in the aboveground part at grain maturity between sweet sorghum and the main crops under conventional cultivation in China. Crop
Concentration (g kg−1 ) N
Sweet sorghum (early varieties) Sweet sorghum (middle and late varieties) Summer maize Summer maize Summer maize Winter wheat Winter wheat Winter wheat Lowland rice Lowland rice Lowland rice
P
Accumulation (kg ha−1 ) K
Reference
N
P
K
9–10
1.8–2.5
8–10
128–252
30–58
109–209
This study
8–10
1.4–2.1
5–9
172–339
33–75
115–300
This study
13 10–13 10–11 13 12 9–10 8–10 18–19 10–12
1.8 1.9–2.3 2.1–2.2 1.9 2.8 1.7–2.8 1.7–2.3 2.8–2.9 2.2–3.1
– 5–7 10–16 9 – 7–9 10–11 5–6 8–10
246 201–273 190–205 181 157 93–108 89–109 179–207 –
32 35–47 40–41 25 35 21–30 19–24 27–36 –
– 90–149 182–287 128 – 70–80 121–138 93–110 –
Dai et al. (2008) Yuan et al. (2010) Gao et al. (2008) Dai et al. (2010) Dai et al. (2008) Liu et al. (2003) Liu et al. (2003) Cheng et al. (2003) Chen et al. (2008)
–: Data is not available in the literature cited.
L.P. Han et al. / Field Crops Research 120 (2011) 230–240
from anthesis to grain maturity was the second important N and P uptake period. 4.4. Changes in N, P, and K during delay harvest period The changes in N, P, and K in aboveground plants of sweet sorghum during the delay harvest period between 40 and 60 DAA was different between varieties. The early varieties exhibited increases in N accumulation, and late varieties exhibited the opposite. K accumulation decreased across all varieties in both years. Generally, the later the variety maturity, the higher the nutrient loss when delaying the harvest beyond grain maturity. This is because the early varieties had more days between grain maturity and the first killing frost date, when sweet sorghum still was alive and took up nutrients from the soil, whereas the late varieties died soon after grain maturity close to the first killing frost date. Reduction in mineral nutrient content during the delay harvest period of energy crops could maintain nutrient cycling in the soil–crop ecosystem, because less nutrients could be removed from soil. Also, it has been recognized that reduction in ash content could improve the quality of biomass feedstock for conversion processes (Monti et al., 2008). Xiong et al. (2008) investigated the influence of harvest time on fuel characteristics of the potential energy crops indigo bush (Amorpha fruticosa), sand willow (Salix cheilophila), switch grass (Panicum virgatum), reed canary grass (Phalaris arundinacea), and sainfoin (Onobrychis viciifolia). The authors reported that N, P, and K contents of the five energy crops tended to decrease during the delay harvest period from September to March for most plants in northern China. Therefore, it is worthwhile to examine the dynamics of minerals in sorghum in the longer delay harvest stage. 5. Conclusion This investigation confirms a decrease in concentrations of N, P and K in sweet sorghum aboveground plants from elongation to harvest, and the nutrients’ accumulation with the reverse from elongation to grain maturity. There was only one important K uptake stage from elongation to thesis. The stage from anthesis to grain maturity was the second important N and P uptake period, following the first from elongation to thesis. The uptakes of N, P, and K in sweet sorghum are higher, particularly for the middle and late maturity varieties, than those in the main crops of maize, wheat and rice in China. Although concentrations of N and P in straw were significantly lower than in grains, the accumulation of N, P and K in straw was much higher than in grains. The concentrations of N and P in leaves were higher than in stems after anthesis, comparable N accumulation and significantly higher P and K accumulation in stems were found than in leaves. During the delay harvest period between 40 and 60 days after anthesis, early varieties exhibited significant increase in N accumulation and late varieties exhibited the opposite trend. P accumulation did not decrease significantly, whereas K accumulation decreased during the delay harvest period. Besides suggesting a further genetic improvement for optimizing nutrient use of sweet sorghum, the findings of this study are helpful to make a fertilization recommendation for its production as a bioethanol crop in North China. Acknowledgements This study was co-funded by the “Eleventh-Five Supporting Program” of China (2006BAD07A04) and Commonweal Section (Agriculture) Research Program (nyhyzx07-11). It is conducted in the Key Laboratory of Crop Farming, Ministry of Agriculture, PR China. We gratefully acknowledge Ms. J. Bai for her help in sample collection and chemical analysis.
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