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Effects of partial root-zone irrigation on the nitrogen absorption and utilization of maize
agricultural water management 96 (2009) 208–214
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Effects of partial root-zone irrigation on the nitrogen absorption and utilization of maize Tiantian Hu a, Shaozhong Kang b,*, Fusheng Li c,a, Jianhua Zhang d a
Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas, Ministry of Education, Northwest Sci-Tec University of Agriculture and Forestry, Yangling, Shaanxi 712100, China b Center for Agricultural Water Research in China, China Agricultural University, Beijing 100083, China c Agricultural College, Guangxi University, Nanning, Guangxi 530005, China d Department of Biology, Hong Kong Baptist University, Hong Kong, China
article info
abstract
Article history:
To investigate the dynamic change of plant nitrogen (N) absorption and accumulation from
Received 20 May 2008
different root zones under the partial root-zone irrigation (PRI), maize plants were raised in
Accepted 30 July 2008
split-root containers and irrigated on both halves of the container (conventional irrigation,
Published on line 9 September 2008
CI), on one side only (fixed partial root-zone irrigation, FPRI), or alternatively on one of two sides (alternate partial root-zone irrigation, APRI). And the isotope-labeled
15
N-(NH4)2SO4
14
Keywords:
was applied to one half of the container with ( NH4)2SO4 to the other half so that N inflow
Maize (Zea mays L.)
rates can be tracked. Results showed that APRI treatment increased root N absorption in the
15
irrigated zone significantly when compared to that of CI treatment. The re-irrigated half
N use efficiency
resumed high N inflow rate within 5 days after irrigation in APRI, suggesting that APRI had
Alternate partial root-zone irrigation
significant compensatory effect on N uptake. The amount of N absorption from two root
Water use efficiency
zones of APRI was equal after two rounds of alternative irrigation (20 days). The recovery
N-Fertilizer
rate, residual and loss percentages of fertilizer-N applied to two zones were similar. As for FPRI treatment, the N accumulation in plant was mainly from the irrigated root zone. The recovery rate and loss percentage of fertilizer-N applied to the irrigated zone was higher and the residual percentage of fertilizer-N in soil was lower if compared to those of the nonirrigated zone. The recovery rate of fertilizer-N in APRI treatment was higher than that of the non-irrigated zone but lower than that of the irrigated zone in FPRI treatment. In total, both FPRI and APRI treatments increased N and water use efficiencies but only consumed about 70% of the irrigated water when compared to CI treatment. # 2008 Elsevier B.V. All rights reserved.
1.
Introduction
Available water resources for agriculture have been decreasing in recent years with the increased demands for irrigation and other non-agricultural water uses (Bacon, 2004). New water-saving methods and techniques such as the partial root-zone irrigation (PRI) or partial root-zone drying (PRD) have been proposed as an agronomic practice for more efficient use
of the limited water resources (Dry and Loveys, 1998; Gu et al., 2000; Kang et al., 1997; Kang and Zhang, 2004; Kirda et al., 2004; Mingo et al., 2004; Zegbe et al., 2004). PRD can be applied in two ways, i.e. alternate partial root-zone irrigation (APRI) and fixed partial root-zone irrigation (FPRI). Earlier results indicated that PRI induces compensatory water absorption from wetted zone (Poni et al., 1992; Tan and Buttery, 1982), reduces transpiration and maintains higher level of photosynthesis (Duan et al.,
* Corresponding author. Fax: +86 10 62737611. E-mail addresses: [email protected] (S. Kang), [email protected] (F. Li). 0378-3774/$ – see front matter # 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2008.07.011
agricultural water management 96 (2009) 208–214
1999; Kang et al., 1997, 1998; Kirda et al., 2004; Mingo et al., 2004; Zegbe et al., 2004). In addition to substantial saving of irrigated water, PRI also reduces excessive vegetative growth of crops (Dry and Loveys, 1998; Graterol et al., 1993; Kang and Cai, 2002) and maintains or even increases crop yield (Graterol et al., 1993; Liang et al., 1998; Stone and Nofziger, 1993). Water shortage in soil may affect nutrient availability and absorption by plant roots. Therefore, the combined improvement of water and nutrient use efficiencies under conditions of locally restricted irrigation should be an important research topic. PRI causes heterogeneous distribution of soil moisture and therefore causes uneven availability of nutrients in soil and uneven absorptions by the roots in different root zones (Hu et al., 2006; Li et al., 2007). Skinner et al. (1999) indicated that alternate furrow irrigation successfully increased N uptake and reduced the potential for NO3 leaching when environmental conditions allowed adequate root development in the nonirrigated furrow, and when the growing season was long enough to allow the crop to reach physiological maturity. The objectives of this study therefore aimed to investigate the dynamic changes of plant N absorption and accumulation from different root zones and the possible influence of partial root-zone irrigation (PRI) on them. Different PRIs, fixed partial root-zone irrigation (FPRI) and alternate partial root-zone irrigation (APRI), were applied and compared to conventional irrigation (CI). The results should give information for crop management practices of PRI in combination with nitrogen fertilization.
2.
Materials and methods
2.1.
Experimental material and growth conditions
The experiment was conducted in a greenhouse under natural light conditions in Northwest Agriculture & Forestry University in northwest China from July to October in 2002, where no temperature controlling equipment was available. The photon flux density ranged from 450 to 800 mmol m 2 s 1. The average day and night temperatures were 27 8C and 18 8C and relative humidity ranged from 30% to 60%. Maize plants (Zea mays L. cv. Shanndan No. 9, a local variety) were grown in pots (28 cm in diameter at the top edge, 24 cm in diameter at the bottom, 26 cm in depth) filled with soil. The loam soil had a field capacity of 26% (mass by mass), soil pH of 7.87, an organic matter content of 16.9 g kg 1, total N content of 0.98 g kg 1, available N (i.e. hydrolytic N at 1 mol L 1 NaOH hydrolysis) of 69.8 mg kg 1, available P (at 0.5 mol L 1 NaHCO3) of 15.1 mg kg 1, and available K (at 1 mol L 1 neutral NH4OAc) of 163.0 mg kg 1 soil. A basal dressing of 0.123 g KH2PO4 per kg soil was added. Each pot was evenly separated with plastic sheets into two sub-parts of equal volume, between which no water exchange occurred. Each sub-part was filled with 6 kg air-dry soil and 3 cm thick sand layer at the bottom of the pot. In order to reduce bare soil evaporation and prevent soil surface hardening, a perforated PVC tube (2 cm diameter) was vertically installed in each sub-part down to a depth of 15.4 cm and used for irrigation. Each PVC tube was wrapped with two layers of window mesh to help water dispersal. All pots were irrigated up to water holding capacity
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before seeding. Three pre-germinated seeds were placed at the middle of the pot so that their primary roots were fairly evenly distributed into the two separated sub-parts.
2.2.
Experimental treatment and implementation
Treatments were three irrigation methods and two application methods of 15N-fertilizer (isotope-labeled 15N-(NH4)2SO4, 15 N abundance at 10.273%). Three irrigation methods included conventional irrigation (CI, irrigated on both sub-parts of the pot in each watering), alternate partial root-zone irrigation (APRI, watering was alternately applied to the two sub-parts of the pot in consecutive watering every 10 days) and fixed partial root-zone irrigation (FPRI, watering was fixed to one of the two sub-parts). In order to separate N uptake from drying and wetting root zones, the two halves of root zone were respectively applied with the same amount of (14NH4)2SO4 or (15NH4)2SO4, i.e. (15NH4)2SO4 was applied to one half of the pot and (14NH4)2SO4 to the other half of the pot. This experimental plan yielded five treatments, i.e. 15N-Fertilizer applied to one of two root zones for CI treatment (Cf), 15Nfertilizer applied to the non-irrigated root zone (Fd) and the irrigated root zone (Fw) for FPRI treatment, 15N-fertilizer applied to the late (Ab) and early (Aa) irrigated root zone for APRI treatment. The applied N amount was 0.2 g N kg 1 soil. (14NH4)2SO4 and (15NH4)2SO4 fertilizers were respectively applied with 500 mL irrigation water for each sub-part at 36 days after seedling emergence. Irrigation treatment started at 42 days after seedling emergence and the period for the irrigation treatment lasted for 40 days. Soil water contents were kept at the range of 65– 95% of field capacity. Maize was irrigated when the soil water content decreased to or was near to the lower limit of soil moisture threshold (65% of field capacity). All treatments had the same irrigation time. The amount of irrigated water was calculated by the difference of upper limit of irrigation (95% of field capacity) and actual soil water content measured by timedomain reflectometry (TDR) and the soil volume concerned. The water used for the irrigation was tap water with negligible concentrations of nutrients. Irritation water was applied through installed PVC tubes.
2.3.
Measurements and methods
Plants were sampled at the 0, 5, 10, 15, 20 and 40th days of irrigation treatment. In each sampling, each treatment was replicated three times. Plant samples were divided into three parts, i.e. shoots and two sub-roots from two root zones, and dried at 70 8C to constant weight for the measurements of N contents and 15N abundance. At the end of experiment, soil samples applied with 15N-fertilizer were taken and analyzed for the residual 15N content. Dried plant and soil samples were digested with concentrated H2SO4, which mixed with K2SO4–CuSO4 catalyzer. Subsequently, the digested solution was used to determine N content (on a dry mass basis) according to the Kjehldahl method. After the determination of N content, the titrated solution acidified by 6 mol L 1 H2SO4 was concentrated to 2– 3 mL solution in 100 8C boiling water. 15N abundance of the
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agricultural water management 96 (2009) 208–214
titrated solution was analyzed using Finnigan MAT 251 mass spectrometer (USA). Sub-root samples were scanned for root lengths with a CI400 computer image analysis system (CID Ltd., USA). The obtained root length/dried mass ratios were used to calculate the total root lengths for all harvested root samples. Root N inflow rate from 15N fertilizer (I, mg m 1 root length d 1) was calculated according to van Vuuren et al. (1996). The recovery rate of fertilizer-N, residual percentage of fertilizer-N in soil and loss percentage of fertilizer-N were calculated according to Mao (1994).
2.4.
partial root-zone irrigation (APRI) reduced irrigation water by 11.7%, 18.5%, 22.8%, 25.8% and 29.5%, respectively during these periods when compared to CI.
Analysis of variance (ANOVA) was performed using one-way ANOVA using SPSS software. Treatment means were compared for significant differences (P0.05 level) using the Duncan’s multiple range tests.
Results
3.1.
Water consumption for different irrigation methods
Variations of N absorption from different root zones
3.2.1.
Root N inflow rate
In order to separate root N uptake from different root zones, isotope-labeled 15N-(NH4)2SO4 (15N-fertilizer) was applied in this study. As shown in Table 2, there were significant variations of root N inflow rates between two root zones with respect to the same irrigation methods. As expected, root N inflow rate in the irrigated zone was constantly greater than that of the non-irrigated zone in FPRI treatment. The difference of root N inflow rates between the two root zones increased with increasing time after the onset of treatments. While in APRI treatment, root N inflow rate from two root zones alternately varied in the first two treatment periods (I0– I10, II0–II10) but root N inflow rate in the irrigated zone was constantly greater than those of the non-irrigated zone. The difference of root N inflow rate between two root zones of APRI was significantly lower than that of FPRI. Mean N inflow rates during the periods of I–II and III–IV indicated that mean N inflow rate of two root zones was constantly equal in APRI treatment while differed greatly in FPRI treatment, indicating that soil moisture content significantly affected root N inflow rate. Table 2 also shows that root N inflow rate had a significant difference among different root zones of three irrigation
Statistical analysis
3.
3.2.
The amount of total irrigated water during different periods for all treatments was shown in Table 1. During the irrigation treatment of 0–5, 0–10, 0–15, 0–20 and 0–40 days, FPRI reduced total irrigation water by 11.7%, 18.5%, 26.0%, 29.9% and 33.0%, respectively when compared to CI treatment. The alternate
Table 1 – Amounts of total irrigated water (L potS1) during different periods for three irrigation methods Irrigation method
Days after irrigation treatment (d) 0–5
CI FPRI APRI
a
8.40 0.12 (100) 7.42 0.13 (88.3) 7.42 0.13 (88.3)
0–10
0–15
0–20
9.90 0.27 (100) 8.07 0.13 (81.5) 8.07 0.13 (81.5)
11.87 0.29 (100) 8.78 0.15 (74.0) 9.16 0.13 (77.2)
13.01 0.24 (100) 9.12 0.11 (70.1) 9.65 0.10 (74.2)
0–40 15.64 0.28 (100) 10.48 0.21 (67.0) 11.02 0.17 (70.5)
Maize seedlings were raised in split-root containers and irrigated on both halves of the container (conventional irrigation, CI), on one side only (fixed partial root-zone irrigation, FPRI), or alternatively on both sides (alternate partial root-zone irrigation, APRI). a Values are means S.E. (% of CI).
Table 2 – Root N inflow rates (mg N mS1 root length dS1) from maize under three irrigation methods Treatment period
I0–I5 I5–I10 II0–II5 II5–II10 I–II III–IV
Cf
61.93 1.73b 56.63 1.58a 55.47 1.56b 68.94 1.66a 47.91 1.19a 16.63 0.68a
15
N-fertilizer applied to different root zones of pot-grown
FPRI
APRI
Fd
Fw
Ab
26.82 0.98c 23.48 0.77b 21.15 0.67d 10.40 0.56c 16.38 0.65c 2.45 0.18d
70.75 1.85a 54.27 1.52a 52.14 1.56b 61.51 1.68a 48.11 1.23a 14.74 0.61b
26.82 0.98c 23.48 0.77b 62.70 1.78a 64.22 1.83a 35.58 0.98b 12.04 0.59c
Aa 70.75 1.85a 54.27 1.52a 47.83 1.21c 19.55 0.76b 38.22 1.06b 11.67 0.44c
FPRI, fixed partial root-zone irrigation; APRI, alternate partial root-zone irrigation. Note: (1) Values are means S.E. Different letters in the same row indicate significant difference (P < 0.05). (2) Cf represents 15N-fertilizer applied in one of two root zones for CI treatment. In FPRI treatment, Fd and Fw represent 15N-fertilizer applied in the non-irrigated half zone (dry) and the irrigated half zone (wet), respectively. In APRI treatment, Ab and Aa represent 15N-fertilizer applied in the late and early irrigated half zone, respectively. I, II, III and IV respectively represent four treatment stages, i.e. 0–10, 10–20, 20–30 and 30–40 days. I0, I5, I10, II0, II5 and II10 respectively represent 0, 5 and 10 days in periods I and II. Here the symbols in the following tables and figure are the same as those in this table.
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agricultural water management 96 (2009) 208–214
methods. Within the first 5 days after treatment, partial rootzone irrigation (PRI) treatments increased root N inflow rate in the irrigated zone significantly when compared to that of nonirrigated zone and CI treatment, suggesting that PRI had a significant effect on N uptake from the irrigated zone. During 10–15 d of treatment, APRI increased root N inflow rate from the re-irrigated zone by 166.5% when compared to that during 5–10 d of treatment, while in other root zones, root N inflow rate was reduced or kept at the original level. Moreover, the root N inflow rate was significantly greater than that of CI treatment and the other root zones, indicating that APRI had a significant effect on N uptake from the re-irrigated zone. During the 5–10 and 15–20 d of APRI treatment, root N inflow rate in the irrigated zone was not significantly different from that of CI treatment, but root N inflow rate in the non-irrigated zone was significantly lower than that of CI treatment. During the 5–20 d of FPRI treatment, root N inflow rate in the irrigated zone was not significantly different from that of CI treatment, but root N inflow rate in the non-irrigated zone was constantly lower than that of CI treatment, and the reduction in FPRI was significantly greater than that of APRI. After 20 days of treatment, although the reduction of root N inflow rate in the irrigated zone of FPRI was lower than that of APRI treatment, the reduction in the non-irrigated zone was opposite. These results indicate that when compared to FPRI treatment, APRI not only induced a significant compensatory effect on N uptake from the irrigated zone, but also did not significantly reduce root N inflow rate from the non-irrigated zone. Thus APRI can maintain higher N accumulation rate in a long period.
3.2.2.
Fig. 1 – Time courses of N accumulation from the 15Nfertilizer in pot-grown maize in different irrigation treatments. Vertical bars represent one standard error of the mean. Codes are the same as in Tables 1 and 2.
the second alternate watering, the variation of N accumulation for Aa and Ab was similar and the values were not significantly different. At the end of treatment, the N accumulation for different sub-treatments showed that Cf and Fw were the greatest, then Aa and Ab, and Fd the lowest, indicating that crop N uptake from different root zones was closely related to methods of irrigation and APRI was beneficial for crop N uptake from whole root zones.
Nitrogen accumulation
When the 15N-fertilizer was applied to different root zones of three irrigation methods, time course of plant N accumulated from the 15N-fertilizer (N accumulation) for all sub-treatments was evident (Fig. 1). Results indicated that the N accumulation for Fw (15N-fertilizer applied to the irrigated zone of FPRI) was similar to that of Cf (15N-fertilizer applied to one of two root zones of CI) and both significantly increased with the time. For Fd (15N-fertilizer applied to the non-irrigated zone of FPRI), the N accumulation increased slightly, and N accumulation for Fw was constantly greater than that for Fd. As for APRI treatment, before the second alternate watering, the N accumulation for Aa (15N-fertilizer applied to the early irrigated zone) was significantly greater than that for Ab (15N-fertilizer applied to the late irrigated zone), while the N accumulation difference between Aa and Ab firstly increased and then gradually decreased. After
3.3. Effects of partial root-zone irrigation on the source of N absorption in maize Table 3 shows that the percentage of plant N accumulated from the 15N-fertilizer in the non-irrigated zone of FPRI decreased with time, in contrast to the increased percentage of the N accumulation from the irrigated zone. Moreover, the percentage of N accumulation from the irrigated zone of FPRI was significantly greater than that from any other root zones. The percentage of N accumulation from both root zones of APRI treatment was nearly equal and not different from that of CI. Results illustrate that both root zones of APRI treatment had similar contribution to crop N uptake as CI treatment, but the irrigated zone of FPRI treatment had major contribution to N uptake.
Table 3 – Percentages of N accumulation (%) from the 15N-fertilizer during different treatment periods in pot-grown maize Treatment period
I–II III–IV
Cf
38.47 1.18b 38.89 1.19b
FPRI
APRI
Fd
Fw
Ab
14.49 1.12c 11.52 0.89c
58.06 1.23a 76.25 1.31a
34.61 1.26b 34.18 1.15b
Aa 37.80 1.27b 33.77 1.05b
Cf, 15N-fertilizer applied in one of two root zones for CI treatment; FPRI, fixed partial root-zone irrigation; APRI, alternate partial root-zone irrigation. Fd, 15N-fertilizer applied in the non-irrigated half zone (dry); Fw, 15N-fertilizer applied in the irrigated half zone (wet); Ab, 15Nfertilizer applied in the late irrigated half zone; Aa, 15N-fertilizer applied in the early irrigated half zone. Values are means S.E. Different letters in the same row indicate significant difference (P < 0.05).
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agricultural water management 96 (2009) 208–214
Table 4 – N content and N and water use efficiencies of pot-grown maize under different irrigation methods Items 1
Shoot dry mass (g pot ) Root dry mass (g pot 1) Shoot N concentration (g N kg 1 dry mass) Root N concentration (g N kg 1 dry mass) N use efficiency (g dry mass g 1 N) Water use efficiency (g dry mass L 1 water)
CI
FPRI
43.37 1.03a 11.18 0.85a 18.95 0.04a 20.31 0.05ab 52.14 1.00b 3.49 0.12c
31.49 1.02c 9.15 0.30c 16.94 0.01b 20.78 0.04a 56.31 0.17a 3.88 0.14b
APRI 34.79 0.82b 10.27 0.62b 18.05 0.04ab 19.37 0.03b 54.56 0.81a 4.09 0.18a
FPRI, fixed partial root-zone irrigation; APRI, alternate partial root-zone irrigation; CI, conventional irrigation. Notes: Analysis of variance (ANOVA) indicated there was no significant difference in N concentration between two sides of half root zones for three irrigation methods, thus N concentration in two root zones was considered as one level of each irrigation method to statistically analyze the difference among three irrigation methods. Values are means S.E. Different letters in the same row indicate significant difference (P < 0.05).
Table 5 – Fates of treatments
15
N fertilizer applied to different root zones of pot-grown maize after 40 days of different irrigation
Items
Cf
15
Recovery rate of N fertilizer (Nf%p) Loss percentage of 15N fertilizer (Nf%1) Residual percentage of 15N fertilizer (Nf%r)
29.30 2.36a 47.69 0.29ab 22.37 3.64c
FPRI
APRI
Fd
Fw
Ab
6.42 0.17c 32.36 1.57c 61.23 1.41a
27.16 2.42a 52.29 1.86a 21.58 1.94c
20.75 0.15b 45.74 1.77b 33.58 1.99b
Aa 19.59 1.48b 45.87 0.05b 34.55 1.54b
Cf, 15N-fertilizer applied in one of two root zones for CI treatment; FPRI, fixed partial root-zone irrigation; APRI, alternate partial root-zone irrigation. Fd, 15N-fertilizer applied in the non-irrigated half zone (dry); Fw, 15N-fertilizer applied in the irrigated half zone (wet); Ab, 15Nfertilizer applied in the late irrigated half zone; Aa, 15N-fertilizer applied in the early irrigated half zone. Values are means S.E. Different letters in the same row indicate significant difference (P < 0.05).
3.4. Effects of partial root-zone irrigation on N and water use efficiencies of maize Table 4 shows that the root and shoot dry masses in APRI treatment were higher than that of FPRI treatment but lower than that of CI treatment. FPRI treatment reduced shoot N concentration significantly but APRI treatment reduced shoot N concentration slightly, which was between CI treatment and FPRI treatment. As for root N concentration, APRI reduced it when compared to the FPRI and CI treatments. Nitrogen use efficiency (defined by the amount of total biomass accumulated per unit N uptake) in both partial root-zone irrigation treatments increased significantly when compared to CI treatment. Thus, partial root-zone irrigation reduced N concentration and had less N luxury uptake, which produced more dry matter with less N uptake, i.e. increased N use efficiency. As shown in Table 4, FPRI and APRI treatments also significantly increased crop water use efficiency (defined by the amount of total biomass accumulated per unit water used) when compared to CI treatment. Moreover, the water use efficiency of APRI treatment was higher than that of FPRI treatment.
3.5.
Fates of fertilizer-N applied to different root zones
In FPRI treatment, the recovery rate and loss percentage of fertilizer-N applied to the irrigated zone increased substantially and the residual percentage of fertilizer-N in soil decreased when compared to those of the non-irrigated zone (Table 5). In APRI treatment, the recovery rate and loss percentage of fertilizer-N applied to two root zones was similar, and they were higher than that of the non-irrigated
zone and lower than that of the irrigated zone in FPRI. Soil residual fertilizer-N in APRI treatment was also in the middle place when compared to the two zones of FPRI treatment. The recovery rate, loss and residual percentages of fertilizer-N in CI were similar to those of the irrigated zone in FPRI. Put together, the recovery rate and loss percentage of fertilizer-N in different treatments showed that Cf and Fw were the greatest, then Aa and Ab, and Fd the lowest. The residual fertilizer-N in soil showed the opposite, suggesting that irrigation methods determined the fate of N fertilizer application.
4.
Discussion
Our results showed that when compared to the conventional whole root-zone irrigation, the two partial root-zone irrigations saved water in the pot-grown maize plants by 29.5–33.0% during different treatment periods, confirming that partial root-zone irrigation can reduce water consumption and enhance water use efficiency without much reduction in yield or dry mass (Kang et al., 1998, 2001; Stone and Nofziger, 1993; Stoll et al., 2000). Mingo et al. (2003) also showed that tomato plants responded to uneven distribution of water in the soil by reducing their stomatal conductance while the whole shoot remained hydrated when compared to whole root zone irrigation. Such effect should be due to the action of a root-sourced soil-drying signal that is generated in the roots in drying soil and transported to shoots where transpiration is restricted (Davies and Zhang, 1991). Such regulation was shown as the enhanced ABA synthesis in the roots in the drying zone and its appearance in the xylem to the shoots (Zhang and Davies, 1989, 1991) and/or the synergistic effect of a lifted pH in the xylem (Wilkinson and Davies, 2002). In
agricultural water management 96 (2009) 208–214
addition to its enhancement of root hydraulic conductivity (Hose et al., 2000; Zhang et al., 1995), ABA has an important role in controlling stomatal aperture (Wilkinson and Davies, 2002) and achieving optimization of water use for CO2 uptake and plant survival over drought stress (Jones, 1980). Plants have the potential to adapt to the environment by self-regulation. Some studies showed that under the condition of nutrient-localized supply, root-absorbing capacity in the nutrient-supplied zone was significantly increased, which may compensate nutrient uptake in the whole (Anghinoni and Barber, 1980; Robinson, 1994). In this study, PRI treatment had a significant compensatory effect on the root N inflow rate in the irrigated zone within the first 5 days after supplying irrigation water. In APRI treatment, within the first 5 days after irrigation-side alternating, root N inflow rate in the irrigated zone was significantly greater than that of CI treatment and the other root zones, indicating that APRI had significant effect on N uptake from the irrigated zone. Such effects possibly resulted from the mechanism of unevenly N supply in the root zone induced by partial root-zone irrigation. Under PRI condition, root N inflow rate in the non-irrigated zone was reduced significantly. In FPRI treatment, total N uptake of 15Nfertilizer from the irrigated zone was far greater than that of the non-irrigated zone, suggesting that nutrient supply in different root zones was not the same under PRI condition. Growth conditions, N availability and water consumption by plants greatly affect the total N accumulation in the plants. In our study, PRI treatments consumed less water (67.0–70.5% of CI, Table 1) but also accumulated less total nitrogen. N contents in plant tissues in the PRI treatments were lower than that of CI treatment, although their N use efficiencies were higher than CI (Table 4). Less N accumulation might be caused by lower N uptake from the relatively dry soil zones. Such reduced N uptake is obviously related to the uneven distribution of soil moisture that is manipulated by the partial rootzone irrigation. Soil moisture content determines the soil N availability and its transport to the roots. Soil nutrient availability is a function of soil chemistry and regulated by the dynamic changes of soil moisture. For the nutrient transport from the soil to the root surface, mass flow and diffusion are two different mechanisms. Water deficit reduces both mass flow and diffusion rates and the release rate of slowly released nutrient into available nutrient. In addition, water deficit limits crop root growth and reduces root absorbing area and capacity. In our study and earlier reports, indeed PRI reduced plant vegetative growth and also possibly reduced the total nutrient absorption as a consequence (Kang and Zhang, 2004). This study indicates that partial root-zone irrigation reduced a possible N luxury uptake and increased N use efficiency. This is because reduced N supply and absorption from the dry zones of PRI may result in N stress in this zone, and thus induce the plant adaptation to the nutrient stress (Robinson, 1994). Apparently the detailed mechanism involved needs further investigation. In the FPRI treatment, the recovery rate and loss percentage of fertilizer-N applied to the irrigated zone were similar to those of CI treatment and significantly greater than those of the non-irrigated zone (Table 5), indicating that crop N uptake and loss increased with the more soil water content. Such
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phenomenon should be noted. In this study, soil water content was kept 65–95% of field capacity and NO3 leaching was impossible. The N loss may be through denitrification and NH3 volatilization. Gao and Zhang (2001) also indicated that higher soil water content increased soil evaporation, which may enhance NH3 volatilization from the soil. In summary, PRI treatment had compensatory effect on N inflow rate in the irrigated zone during the early period of water treatment, and APRI stimulated compensatory effect of N uptake in longer period during the cycle of alterative wetting and drying of different root zones. As a result, different root zones in APRI had similar contribution to crop N absorption, but in FPRI treatment, N uptake was mainly from the irrigated zone. Moreover, the recovery rate, residual and loss percentages of fertilizer-N applied to both zones of APRI treatment were similar, but there were significant differences of recovery rate, residual and loss percentages between the two zones in FPRI. For both methods, partial root-zone irrigation reduced N luxury uptake but increased N use efficiency of maize. This was achieved at much reduced irrigation and higher water use efficiency.
Acknowledgments We are grateful to the research grants from the State Key Basic Research and Development Plan of China (2006CB403406), the National Natural Science Fund of China (50339030), Visiting scholar fund from Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas, Ministry of Education, Northwest Sci-Tec University, Guangxi Education Department Project (2006-26), Hong Kong Research Grant Council (HKBU 262307) and Hong Kong University Grants Committee (AoE/B-07/99).
references
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Mao, D.R., 1994. Methods of Plant Nutrition Research. Beijing Agriculture University Press, Beijing (in Chinese). Mingo, D.M., Bacon, M.A., Davies, W.J., 2003. Non-hydraulic regulation of fruit growth in tomato plants (Lycopersicon esculentum cv. Solairo) growing in drying soil. J. Exp. Bot. 54, 1205–1212. Mingo, D.M., Theobald, J.C., Bacon, M.A., Davies, W.J., Dodd, I.C., 2004. Biomass allocation in tomato (Lycopersicon esculentum) plants grown under partial root zone drying: enhancement of root growth. Funct. Plant Biol. 31 (10), 971–978. Poni, S., Tagliavini, M., Neri, D., Scudellari, D., Toselli, M., 1992. Influence of root pruning and water stress on growth and physiological factors of potted apple, grape, peach and pear trees. Sci. Hortic. 52, 223–226. Robinson, D., 1994. The responses of plants to non-uniform supplies of nutrients. New Phytol. 127, 635–674. Skinner, R.H., Hanson, J.D., Benjamin, J.G., 1999. Nitrogen uptakes and partitioning under alternate- and every-furrow irrigation. Plant Soil 210, 11–20. Stoll, M., Loveys, B., Dry, P., 2000. Hormonal changes induced by partial root zone drying of irrigated grapevine. J. Exp. Bot. 51, 1627–1634. Stone, J.F., Nofziger, D.L., 1993. Water use and yields of cotton grown under wide-spaced furrow irrigation. Agric. Water Manage. 24, 27–28. Tan, C.S., Buttery, B.R., 1982. The effects of soil moisture stress to various fraction of the root system on transpiration, photosynthesis and internal water relation of peach seedlings. Am. Soc. Hortic. Sci. 107, 845–849. van Vuuren, M.M., Robinson, D., Grifiths, B.S., 1996. Nutrient inflow and root proliferation during the exploitation of a temporally and spatially discrete source of nitrogen in soil. Plant Soil 178, 185–192. Wilkinson, S., Davies, W.J., 2002. ABA-based chemical signaling: the co-ordination of responses to stress in plants. Plant Cell Environ. 25, 195–210. Zegbe, J.A., Behboudian, M.H., Clothier, B.E., 2004. Partial root zone drying is a feasible option for irrigating processing tomatoes. Agric. Water Manage. 68, 195–206. Zhang, J., Davies, W.J., 1989. Abscisic acid produced in dehydrating roots may enable the plant to measure the water status of the soil. Plant Cell Environ. 12, 73–81. Zhang, J., Davies, W.J., 1991. Antitranspirant activity in the xylem sap of maize plants. J. Exp. Bot. 42, 317–321. Zhang, J., Zhang, X., Liang, J., 1995. Exudation rate and hydraulic conductivity of maize roots are enhanced by soil drying and abscisic acid treatment. New Phytol. 131, 329–336.
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/agwat
Effects of partial root-zone irrigation on the nitrogen absorption and utilization of maize Tiantian Hu a, Shaozhong Kang b,*, Fusheng Li c,a, Jianhua Zhang d a
Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas, Ministry of Education, Northwest Sci-Tec University of Agriculture and Forestry, Yangling, Shaanxi 712100, China b Center for Agricultural Water Research in China, China Agricultural University, Beijing 100083, China c Agricultural College, Guangxi University, Nanning, Guangxi 530005, China d Department of Biology, Hong Kong Baptist University, Hong Kong, China
article info
abstract
Article history:
To investigate the dynamic change of plant nitrogen (N) absorption and accumulation from
Received 20 May 2008
different root zones under the partial root-zone irrigation (PRI), maize plants were raised in
Accepted 30 July 2008
split-root containers and irrigated on both halves of the container (conventional irrigation,
Published on line 9 September 2008
CI), on one side only (fixed partial root-zone irrigation, FPRI), or alternatively on one of two sides (alternate partial root-zone irrigation, APRI). And the isotope-labeled
15
N-(NH4)2SO4
14
Keywords:
was applied to one half of the container with ( NH4)2SO4 to the other half so that N inflow
Maize (Zea mays L.)
rates can be tracked. Results showed that APRI treatment increased root N absorption in the
15
irrigated zone significantly when compared to that of CI treatment. The re-irrigated half
N use efficiency
resumed high N inflow rate within 5 days after irrigation in APRI, suggesting that APRI had
Alternate partial root-zone irrigation
significant compensatory effect on N uptake. The amount of N absorption from two root
Water use efficiency
zones of APRI was equal after two rounds of alternative irrigation (20 days). The recovery
N-Fertilizer
rate, residual and loss percentages of fertilizer-N applied to two zones were similar. As for FPRI treatment, the N accumulation in plant was mainly from the irrigated root zone. The recovery rate and loss percentage of fertilizer-N applied to the irrigated zone was higher and the residual percentage of fertilizer-N in soil was lower if compared to those of the nonirrigated zone. The recovery rate of fertilizer-N in APRI treatment was higher than that of the non-irrigated zone but lower than that of the irrigated zone in FPRI treatment. In total, both FPRI and APRI treatments increased N and water use efficiencies but only consumed about 70% of the irrigated water when compared to CI treatment. # 2008 Elsevier B.V. All rights reserved.
1.
Introduction
Available water resources for agriculture have been decreasing in recent years with the increased demands for irrigation and other non-agricultural water uses (Bacon, 2004). New water-saving methods and techniques such as the partial root-zone irrigation (PRI) or partial root-zone drying (PRD) have been proposed as an agronomic practice for more efficient use
of the limited water resources (Dry and Loveys, 1998; Gu et al., 2000; Kang et al., 1997; Kang and Zhang, 2004; Kirda et al., 2004; Mingo et al., 2004; Zegbe et al., 2004). PRD can be applied in two ways, i.e. alternate partial root-zone irrigation (APRI) and fixed partial root-zone irrigation (FPRI). Earlier results indicated that PRI induces compensatory water absorption from wetted zone (Poni et al., 1992; Tan and Buttery, 1982), reduces transpiration and maintains higher level of photosynthesis (Duan et al.,
* Corresponding author. Fax: +86 10 62737611. E-mail addresses: [email protected] (S. Kang), [email protected] (F. Li). 0378-3774/$ – see front matter # 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2008.07.011
agricultural water management 96 (2009) 208–214
1999; Kang et al., 1997, 1998; Kirda et al., 2004; Mingo et al., 2004; Zegbe et al., 2004). In addition to substantial saving of irrigated water, PRI also reduces excessive vegetative growth of crops (Dry and Loveys, 1998; Graterol et al., 1993; Kang and Cai, 2002) and maintains or even increases crop yield (Graterol et al., 1993; Liang et al., 1998; Stone and Nofziger, 1993). Water shortage in soil may affect nutrient availability and absorption by plant roots. Therefore, the combined improvement of water and nutrient use efficiencies under conditions of locally restricted irrigation should be an important research topic. PRI causes heterogeneous distribution of soil moisture and therefore causes uneven availability of nutrients in soil and uneven absorptions by the roots in different root zones (Hu et al., 2006; Li et al., 2007). Skinner et al. (1999) indicated that alternate furrow irrigation successfully increased N uptake and reduced the potential for NO3 leaching when environmental conditions allowed adequate root development in the nonirrigated furrow, and when the growing season was long enough to allow the crop to reach physiological maturity. The objectives of this study therefore aimed to investigate the dynamic changes of plant N absorption and accumulation from different root zones and the possible influence of partial root-zone irrigation (PRI) on them. Different PRIs, fixed partial root-zone irrigation (FPRI) and alternate partial root-zone irrigation (APRI), were applied and compared to conventional irrigation (CI). The results should give information for crop management practices of PRI in combination with nitrogen fertilization.
2.
Materials and methods
2.1.
Experimental material and growth conditions
The experiment was conducted in a greenhouse under natural light conditions in Northwest Agriculture & Forestry University in northwest China from July to October in 2002, where no temperature controlling equipment was available. The photon flux density ranged from 450 to 800 mmol m 2 s 1. The average day and night temperatures were 27 8C and 18 8C and relative humidity ranged from 30% to 60%. Maize plants (Zea mays L. cv. Shanndan No. 9, a local variety) were grown in pots (28 cm in diameter at the top edge, 24 cm in diameter at the bottom, 26 cm in depth) filled with soil. The loam soil had a field capacity of 26% (mass by mass), soil pH of 7.87, an organic matter content of 16.9 g kg 1, total N content of 0.98 g kg 1, available N (i.e. hydrolytic N at 1 mol L 1 NaOH hydrolysis) of 69.8 mg kg 1, available P (at 0.5 mol L 1 NaHCO3) of 15.1 mg kg 1, and available K (at 1 mol L 1 neutral NH4OAc) of 163.0 mg kg 1 soil. A basal dressing of 0.123 g KH2PO4 per kg soil was added. Each pot was evenly separated with plastic sheets into two sub-parts of equal volume, between which no water exchange occurred. Each sub-part was filled with 6 kg air-dry soil and 3 cm thick sand layer at the bottom of the pot. In order to reduce bare soil evaporation and prevent soil surface hardening, a perforated PVC tube (2 cm diameter) was vertically installed in each sub-part down to a depth of 15.4 cm and used for irrigation. Each PVC tube was wrapped with two layers of window mesh to help water dispersal. All pots were irrigated up to water holding capacity
209
before seeding. Three pre-germinated seeds were placed at the middle of the pot so that their primary roots were fairly evenly distributed into the two separated sub-parts.
2.2.
Experimental treatment and implementation
Treatments were three irrigation methods and two application methods of 15N-fertilizer (isotope-labeled 15N-(NH4)2SO4, 15 N abundance at 10.273%). Three irrigation methods included conventional irrigation (CI, irrigated on both sub-parts of the pot in each watering), alternate partial root-zone irrigation (APRI, watering was alternately applied to the two sub-parts of the pot in consecutive watering every 10 days) and fixed partial root-zone irrigation (FPRI, watering was fixed to one of the two sub-parts). In order to separate N uptake from drying and wetting root zones, the two halves of root zone were respectively applied with the same amount of (14NH4)2SO4 or (15NH4)2SO4, i.e. (15NH4)2SO4 was applied to one half of the pot and (14NH4)2SO4 to the other half of the pot. This experimental plan yielded five treatments, i.e. 15N-Fertilizer applied to one of two root zones for CI treatment (Cf), 15Nfertilizer applied to the non-irrigated root zone (Fd) and the irrigated root zone (Fw) for FPRI treatment, 15N-fertilizer applied to the late (Ab) and early (Aa) irrigated root zone for APRI treatment. The applied N amount was 0.2 g N kg 1 soil. (14NH4)2SO4 and (15NH4)2SO4 fertilizers were respectively applied with 500 mL irrigation water for each sub-part at 36 days after seedling emergence. Irrigation treatment started at 42 days after seedling emergence and the period for the irrigation treatment lasted for 40 days. Soil water contents were kept at the range of 65– 95% of field capacity. Maize was irrigated when the soil water content decreased to or was near to the lower limit of soil moisture threshold (65% of field capacity). All treatments had the same irrigation time. The amount of irrigated water was calculated by the difference of upper limit of irrigation (95% of field capacity) and actual soil water content measured by timedomain reflectometry (TDR) and the soil volume concerned. The water used for the irrigation was tap water with negligible concentrations of nutrients. Irritation water was applied through installed PVC tubes.
2.3.
Measurements and methods
Plants were sampled at the 0, 5, 10, 15, 20 and 40th days of irrigation treatment. In each sampling, each treatment was replicated three times. Plant samples were divided into three parts, i.e. shoots and two sub-roots from two root zones, and dried at 70 8C to constant weight for the measurements of N contents and 15N abundance. At the end of experiment, soil samples applied with 15N-fertilizer were taken and analyzed for the residual 15N content. Dried plant and soil samples were digested with concentrated H2SO4, which mixed with K2SO4–CuSO4 catalyzer. Subsequently, the digested solution was used to determine N content (on a dry mass basis) according to the Kjehldahl method. After the determination of N content, the titrated solution acidified by 6 mol L 1 H2SO4 was concentrated to 2– 3 mL solution in 100 8C boiling water. 15N abundance of the
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titrated solution was analyzed using Finnigan MAT 251 mass spectrometer (USA). Sub-root samples were scanned for root lengths with a CI400 computer image analysis system (CID Ltd., USA). The obtained root length/dried mass ratios were used to calculate the total root lengths for all harvested root samples. Root N inflow rate from 15N fertilizer (I, mg m 1 root length d 1) was calculated according to van Vuuren et al. (1996). The recovery rate of fertilizer-N, residual percentage of fertilizer-N in soil and loss percentage of fertilizer-N were calculated according to Mao (1994).
2.4.
partial root-zone irrigation (APRI) reduced irrigation water by 11.7%, 18.5%, 22.8%, 25.8% and 29.5%, respectively during these periods when compared to CI.
Analysis of variance (ANOVA) was performed using one-way ANOVA using SPSS software. Treatment means were compared for significant differences (P0.05 level) using the Duncan’s multiple range tests.
Results
3.1.
Water consumption for different irrigation methods
Variations of N absorption from different root zones
3.2.1.
Root N inflow rate
In order to separate root N uptake from different root zones, isotope-labeled 15N-(NH4)2SO4 (15N-fertilizer) was applied in this study. As shown in Table 2, there were significant variations of root N inflow rates between two root zones with respect to the same irrigation methods. As expected, root N inflow rate in the irrigated zone was constantly greater than that of the non-irrigated zone in FPRI treatment. The difference of root N inflow rates between the two root zones increased with increasing time after the onset of treatments. While in APRI treatment, root N inflow rate from two root zones alternately varied in the first two treatment periods (I0– I10, II0–II10) but root N inflow rate in the irrigated zone was constantly greater than those of the non-irrigated zone. The difference of root N inflow rate between two root zones of APRI was significantly lower than that of FPRI. Mean N inflow rates during the periods of I–II and III–IV indicated that mean N inflow rate of two root zones was constantly equal in APRI treatment while differed greatly in FPRI treatment, indicating that soil moisture content significantly affected root N inflow rate. Table 2 also shows that root N inflow rate had a significant difference among different root zones of three irrigation
Statistical analysis
3.
3.2.
The amount of total irrigated water during different periods for all treatments was shown in Table 1. During the irrigation treatment of 0–5, 0–10, 0–15, 0–20 and 0–40 days, FPRI reduced total irrigation water by 11.7%, 18.5%, 26.0%, 29.9% and 33.0%, respectively when compared to CI treatment. The alternate
Table 1 – Amounts of total irrigated water (L potS1) during different periods for three irrigation methods Irrigation method
Days after irrigation treatment (d) 0–5
CI FPRI APRI
a
8.40 0.12 (100) 7.42 0.13 (88.3) 7.42 0.13 (88.3)
0–10
0–15
0–20
9.90 0.27 (100) 8.07 0.13 (81.5) 8.07 0.13 (81.5)
11.87 0.29 (100) 8.78 0.15 (74.0) 9.16 0.13 (77.2)
13.01 0.24 (100) 9.12 0.11 (70.1) 9.65 0.10 (74.2)
0–40 15.64 0.28 (100) 10.48 0.21 (67.0) 11.02 0.17 (70.5)
Maize seedlings were raised in split-root containers and irrigated on both halves of the container (conventional irrigation, CI), on one side only (fixed partial root-zone irrigation, FPRI), or alternatively on both sides (alternate partial root-zone irrigation, APRI). a Values are means S.E. (% of CI).
Table 2 – Root N inflow rates (mg N mS1 root length dS1) from maize under three irrigation methods Treatment period
I0–I5 I5–I10 II0–II5 II5–II10 I–II III–IV
Cf
61.93 1.73b 56.63 1.58a 55.47 1.56b 68.94 1.66a 47.91 1.19a 16.63 0.68a
15
N-fertilizer applied to different root zones of pot-grown
FPRI
APRI
Fd
Fw
Ab
26.82 0.98c 23.48 0.77b 21.15 0.67d 10.40 0.56c 16.38 0.65c 2.45 0.18d
70.75 1.85a 54.27 1.52a 52.14 1.56b 61.51 1.68a 48.11 1.23a 14.74 0.61b
26.82 0.98c 23.48 0.77b 62.70 1.78a 64.22 1.83a 35.58 0.98b 12.04 0.59c
Aa 70.75 1.85a 54.27 1.52a 47.83 1.21c 19.55 0.76b 38.22 1.06b 11.67 0.44c
FPRI, fixed partial root-zone irrigation; APRI, alternate partial root-zone irrigation. Note: (1) Values are means S.E. Different letters in the same row indicate significant difference (P < 0.05). (2) Cf represents 15N-fertilizer applied in one of two root zones for CI treatment. In FPRI treatment, Fd and Fw represent 15N-fertilizer applied in the non-irrigated half zone (dry) and the irrigated half zone (wet), respectively. In APRI treatment, Ab and Aa represent 15N-fertilizer applied in the late and early irrigated half zone, respectively. I, II, III and IV respectively represent four treatment stages, i.e. 0–10, 10–20, 20–30 and 30–40 days. I0, I5, I10, II0, II5 and II10 respectively represent 0, 5 and 10 days in periods I and II. Here the symbols in the following tables and figure are the same as those in this table.
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agricultural water management 96 (2009) 208–214
methods. Within the first 5 days after treatment, partial rootzone irrigation (PRI) treatments increased root N inflow rate in the irrigated zone significantly when compared to that of nonirrigated zone and CI treatment, suggesting that PRI had a significant effect on N uptake from the irrigated zone. During 10–15 d of treatment, APRI increased root N inflow rate from the re-irrigated zone by 166.5% when compared to that during 5–10 d of treatment, while in other root zones, root N inflow rate was reduced or kept at the original level. Moreover, the root N inflow rate was significantly greater than that of CI treatment and the other root zones, indicating that APRI had a significant effect on N uptake from the re-irrigated zone. During the 5–10 and 15–20 d of APRI treatment, root N inflow rate in the irrigated zone was not significantly different from that of CI treatment, but root N inflow rate in the non-irrigated zone was significantly lower than that of CI treatment. During the 5–20 d of FPRI treatment, root N inflow rate in the irrigated zone was not significantly different from that of CI treatment, but root N inflow rate in the non-irrigated zone was constantly lower than that of CI treatment, and the reduction in FPRI was significantly greater than that of APRI. After 20 days of treatment, although the reduction of root N inflow rate in the irrigated zone of FPRI was lower than that of APRI treatment, the reduction in the non-irrigated zone was opposite. These results indicate that when compared to FPRI treatment, APRI not only induced a significant compensatory effect on N uptake from the irrigated zone, but also did not significantly reduce root N inflow rate from the non-irrigated zone. Thus APRI can maintain higher N accumulation rate in a long period.
3.2.2.
Fig. 1 – Time courses of N accumulation from the 15Nfertilizer in pot-grown maize in different irrigation treatments. Vertical bars represent one standard error of the mean. Codes are the same as in Tables 1 and 2.
the second alternate watering, the variation of N accumulation for Aa and Ab was similar and the values were not significantly different. At the end of treatment, the N accumulation for different sub-treatments showed that Cf and Fw were the greatest, then Aa and Ab, and Fd the lowest, indicating that crop N uptake from different root zones was closely related to methods of irrigation and APRI was beneficial for crop N uptake from whole root zones.
Nitrogen accumulation
When the 15N-fertilizer was applied to different root zones of three irrigation methods, time course of plant N accumulated from the 15N-fertilizer (N accumulation) for all sub-treatments was evident (Fig. 1). Results indicated that the N accumulation for Fw (15N-fertilizer applied to the irrigated zone of FPRI) was similar to that of Cf (15N-fertilizer applied to one of two root zones of CI) and both significantly increased with the time. For Fd (15N-fertilizer applied to the non-irrigated zone of FPRI), the N accumulation increased slightly, and N accumulation for Fw was constantly greater than that for Fd. As for APRI treatment, before the second alternate watering, the N accumulation for Aa (15N-fertilizer applied to the early irrigated zone) was significantly greater than that for Ab (15N-fertilizer applied to the late irrigated zone), while the N accumulation difference between Aa and Ab firstly increased and then gradually decreased. After
3.3. Effects of partial root-zone irrigation on the source of N absorption in maize Table 3 shows that the percentage of plant N accumulated from the 15N-fertilizer in the non-irrigated zone of FPRI decreased with time, in contrast to the increased percentage of the N accumulation from the irrigated zone. Moreover, the percentage of N accumulation from the irrigated zone of FPRI was significantly greater than that from any other root zones. The percentage of N accumulation from both root zones of APRI treatment was nearly equal and not different from that of CI. Results illustrate that both root zones of APRI treatment had similar contribution to crop N uptake as CI treatment, but the irrigated zone of FPRI treatment had major contribution to N uptake.
Table 3 – Percentages of N accumulation (%) from the 15N-fertilizer during different treatment periods in pot-grown maize Treatment period
I–II III–IV
Cf
38.47 1.18b 38.89 1.19b
FPRI
APRI
Fd
Fw
Ab
14.49 1.12c 11.52 0.89c
58.06 1.23a 76.25 1.31a
34.61 1.26b 34.18 1.15b
Aa 37.80 1.27b 33.77 1.05b
Cf, 15N-fertilizer applied in one of two root zones for CI treatment; FPRI, fixed partial root-zone irrigation; APRI, alternate partial root-zone irrigation. Fd, 15N-fertilizer applied in the non-irrigated half zone (dry); Fw, 15N-fertilizer applied in the irrigated half zone (wet); Ab, 15Nfertilizer applied in the late irrigated half zone; Aa, 15N-fertilizer applied in the early irrigated half zone. Values are means S.E. Different letters in the same row indicate significant difference (P < 0.05).
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agricultural water management 96 (2009) 208–214
Table 4 – N content and N and water use efficiencies of pot-grown maize under different irrigation methods Items 1
Shoot dry mass (g pot ) Root dry mass (g pot 1) Shoot N concentration (g N kg 1 dry mass) Root N concentration (g N kg 1 dry mass) N use efficiency (g dry mass g 1 N) Water use efficiency (g dry mass L 1 water)
CI
FPRI
43.37 1.03a 11.18 0.85a 18.95 0.04a 20.31 0.05ab 52.14 1.00b 3.49 0.12c
31.49 1.02c 9.15 0.30c 16.94 0.01b 20.78 0.04a 56.31 0.17a 3.88 0.14b
APRI 34.79 0.82b 10.27 0.62b 18.05 0.04ab 19.37 0.03b 54.56 0.81a 4.09 0.18a
FPRI, fixed partial root-zone irrigation; APRI, alternate partial root-zone irrigation; CI, conventional irrigation. Notes: Analysis of variance (ANOVA) indicated there was no significant difference in N concentration between two sides of half root zones for three irrigation methods, thus N concentration in two root zones was considered as one level of each irrigation method to statistically analyze the difference among three irrigation methods. Values are means S.E. Different letters in the same row indicate significant difference (P < 0.05).
Table 5 – Fates of treatments
15
N fertilizer applied to different root zones of pot-grown maize after 40 days of different irrigation
Items
Cf
15
Recovery rate of N fertilizer (Nf%p) Loss percentage of 15N fertilizer (Nf%1) Residual percentage of 15N fertilizer (Nf%r)
29.30 2.36a 47.69 0.29ab 22.37 3.64c
FPRI
APRI
Fd
Fw
Ab
6.42 0.17c 32.36 1.57c 61.23 1.41a
27.16 2.42a 52.29 1.86a 21.58 1.94c
20.75 0.15b 45.74 1.77b 33.58 1.99b
Aa 19.59 1.48b 45.87 0.05b 34.55 1.54b
Cf, 15N-fertilizer applied in one of two root zones for CI treatment; FPRI, fixed partial root-zone irrigation; APRI, alternate partial root-zone irrigation. Fd, 15N-fertilizer applied in the non-irrigated half zone (dry); Fw, 15N-fertilizer applied in the irrigated half zone (wet); Ab, 15Nfertilizer applied in the late irrigated half zone; Aa, 15N-fertilizer applied in the early irrigated half zone. Values are means S.E. Different letters in the same row indicate significant difference (P < 0.05).
3.4. Effects of partial root-zone irrigation on N and water use efficiencies of maize Table 4 shows that the root and shoot dry masses in APRI treatment were higher than that of FPRI treatment but lower than that of CI treatment. FPRI treatment reduced shoot N concentration significantly but APRI treatment reduced shoot N concentration slightly, which was between CI treatment and FPRI treatment. As for root N concentration, APRI reduced it when compared to the FPRI and CI treatments. Nitrogen use efficiency (defined by the amount of total biomass accumulated per unit N uptake) in both partial root-zone irrigation treatments increased significantly when compared to CI treatment. Thus, partial root-zone irrigation reduced N concentration and had less N luxury uptake, which produced more dry matter with less N uptake, i.e. increased N use efficiency. As shown in Table 4, FPRI and APRI treatments also significantly increased crop water use efficiency (defined by the amount of total biomass accumulated per unit water used) when compared to CI treatment. Moreover, the water use efficiency of APRI treatment was higher than that of FPRI treatment.
3.5.
Fates of fertilizer-N applied to different root zones
In FPRI treatment, the recovery rate and loss percentage of fertilizer-N applied to the irrigated zone increased substantially and the residual percentage of fertilizer-N in soil decreased when compared to those of the non-irrigated zone (Table 5). In APRI treatment, the recovery rate and loss percentage of fertilizer-N applied to two root zones was similar, and they were higher than that of the non-irrigated
zone and lower than that of the irrigated zone in FPRI. Soil residual fertilizer-N in APRI treatment was also in the middle place when compared to the two zones of FPRI treatment. The recovery rate, loss and residual percentages of fertilizer-N in CI were similar to those of the irrigated zone in FPRI. Put together, the recovery rate and loss percentage of fertilizer-N in different treatments showed that Cf and Fw were the greatest, then Aa and Ab, and Fd the lowest. The residual fertilizer-N in soil showed the opposite, suggesting that irrigation methods determined the fate of N fertilizer application.
4.
Discussion
Our results showed that when compared to the conventional whole root-zone irrigation, the two partial root-zone irrigations saved water in the pot-grown maize plants by 29.5–33.0% during different treatment periods, confirming that partial root-zone irrigation can reduce water consumption and enhance water use efficiency without much reduction in yield or dry mass (Kang et al., 1998, 2001; Stone and Nofziger, 1993; Stoll et al., 2000). Mingo et al. (2003) also showed that tomato plants responded to uneven distribution of water in the soil by reducing their stomatal conductance while the whole shoot remained hydrated when compared to whole root zone irrigation. Such effect should be due to the action of a root-sourced soil-drying signal that is generated in the roots in drying soil and transported to shoots where transpiration is restricted (Davies and Zhang, 1991). Such regulation was shown as the enhanced ABA synthesis in the roots in the drying zone and its appearance in the xylem to the shoots (Zhang and Davies, 1989, 1991) and/or the synergistic effect of a lifted pH in the xylem (Wilkinson and Davies, 2002). In
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addition to its enhancement of root hydraulic conductivity (Hose et al., 2000; Zhang et al., 1995), ABA has an important role in controlling stomatal aperture (Wilkinson and Davies, 2002) and achieving optimization of water use for CO2 uptake and plant survival over drought stress (Jones, 1980). Plants have the potential to adapt to the environment by self-regulation. Some studies showed that under the condition of nutrient-localized supply, root-absorbing capacity in the nutrient-supplied zone was significantly increased, which may compensate nutrient uptake in the whole (Anghinoni and Barber, 1980; Robinson, 1994). In this study, PRI treatment had a significant compensatory effect on the root N inflow rate in the irrigated zone within the first 5 days after supplying irrigation water. In APRI treatment, within the first 5 days after irrigation-side alternating, root N inflow rate in the irrigated zone was significantly greater than that of CI treatment and the other root zones, indicating that APRI had significant effect on N uptake from the irrigated zone. Such effects possibly resulted from the mechanism of unevenly N supply in the root zone induced by partial root-zone irrigation. Under PRI condition, root N inflow rate in the non-irrigated zone was reduced significantly. In FPRI treatment, total N uptake of 15Nfertilizer from the irrigated zone was far greater than that of the non-irrigated zone, suggesting that nutrient supply in different root zones was not the same under PRI condition. Growth conditions, N availability and water consumption by plants greatly affect the total N accumulation in the plants. In our study, PRI treatments consumed less water (67.0–70.5% of CI, Table 1) but also accumulated less total nitrogen. N contents in plant tissues in the PRI treatments were lower than that of CI treatment, although their N use efficiencies were higher than CI (Table 4). Less N accumulation might be caused by lower N uptake from the relatively dry soil zones. Such reduced N uptake is obviously related to the uneven distribution of soil moisture that is manipulated by the partial rootzone irrigation. Soil moisture content determines the soil N availability and its transport to the roots. Soil nutrient availability is a function of soil chemistry and regulated by the dynamic changes of soil moisture. For the nutrient transport from the soil to the root surface, mass flow and diffusion are two different mechanisms. Water deficit reduces both mass flow and diffusion rates and the release rate of slowly released nutrient into available nutrient. In addition, water deficit limits crop root growth and reduces root absorbing area and capacity. In our study and earlier reports, indeed PRI reduced plant vegetative growth and also possibly reduced the total nutrient absorption as a consequence (Kang and Zhang, 2004). This study indicates that partial root-zone irrigation reduced a possible N luxury uptake and increased N use efficiency. This is because reduced N supply and absorption from the dry zones of PRI may result in N stress in this zone, and thus induce the plant adaptation to the nutrient stress (Robinson, 1994). Apparently the detailed mechanism involved needs further investigation. In the FPRI treatment, the recovery rate and loss percentage of fertilizer-N applied to the irrigated zone were similar to those of CI treatment and significantly greater than those of the non-irrigated zone (Table 5), indicating that crop N uptake and loss increased with the more soil water content. Such
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phenomenon should be noted. In this study, soil water content was kept 65–95% of field capacity and NO3 leaching was impossible. The N loss may be through denitrification and NH3 volatilization. Gao and Zhang (2001) also indicated that higher soil water content increased soil evaporation, which may enhance NH3 volatilization from the soil. In summary, PRI treatment had compensatory effect on N inflow rate in the irrigated zone during the early period of water treatment, and APRI stimulated compensatory effect of N uptake in longer period during the cycle of alterative wetting and drying of different root zones. As a result, different root zones in APRI had similar contribution to crop N absorption, but in FPRI treatment, N uptake was mainly from the irrigated zone. Moreover, the recovery rate, residual and loss percentages of fertilizer-N applied to both zones of APRI treatment were similar, but there were significant differences of recovery rate, residual and loss percentages between the two zones in FPRI. For both methods, partial root-zone irrigation reduced N luxury uptake but increased N use efficiency of maize. This was achieved at much reduced irrigation and higher water use efficiency.
Acknowledgments We are grateful to the research grants from the State Key Basic Research and Development Plan of China (2006CB403406), the National Natural Science Fund of China (50339030), Visiting scholar fund from Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas, Ministry of Education, Northwest Sci-Tec University, Guangxi Education Department Project (2006-26), Hong Kong Research Grant Council (HKBU 262307) and Hong Kong University Grants Committee (AoE/B-07/99).
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