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Effects of different fertilizer strategies on soil water utilization and maize yield in the ridge and furrow rainfall harvesting system in semiarid regions of China
Agricultural Water Management 208 (2018) 414–421
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Effects of different fertilizer strategies on soil water utilization and maize yield in the ridge and furrow rainfall harvesting system in semiarid regions of China
T
Yan Zhanga,b, Qian Maa,b, Donghua Liua,b, Lefeng Suna,b, Xiaolong Rena,b, Shahzad Alia,b, ⁎ ⁎ Peng Zhanga,b, , Zhikuan Jiaa,b, a
College of Agronomy, Northwest A&F University, Yangling, 712100, Shaanxi, China Key Laboratory of Crop Physi-Ecology and Tillage Science in Northwestern Loess Plateau, Minister of Agriculture, Northwest A&F University, Yangling, 712100, Shaanxi, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Fertilizer rate Maize yield Ridge and furrow rainfall harvesting system Semi-arid area Soil water consumption properties
Shortages of water resources and low soil fertility are two key factors that limit crop production in semiarid areas. The ridge and furrow rainfall harvesting (RFRH) system is an effective method for enhancing the efficiency of rainfall water use and fertility. In this study, we conducted a field experiment over five years (2012–2016) to determine the effects of different fertilizer application rates on the soil water consumption properties, water use efficiency, and maize yield under RFRH. We found that the evapotranspiration (ET), maize dry matter (DM), water consumption strength (CD), and soil water use rate (SP) increased with the fertilizer application rate. Compared with the no fertilizer treatment (RCK), ET, DM, CD, and SP increased significantly by 7.2%, 38.3%, 16.4%, and 37.6% under high fertilizer (RH) treatment, respectively, by 6.7%, 35.8%, 18.0%, and 39.1% with medium fertilizer (RM) treatment, and by 5.5%, 31.1%, 16.1%, and 32.6% with low fertilizer (RL) treatment. RM achieved the highest average yield of 11.3 t ha–1 and the lowest coefficient of variation at 12.9%. The yield, DM, and water use efficiency did not differ significantly between RH and RM. Regression analysis showed that the highest yield could be obtained by applying nitrogen at 265.0 kg ha–1 combined with P2O5 at 132.5 kg ha–1. The yield and water use efficiency were significantly higher under RL compared with RH and RM in wet year. However, in both normal and drought years, the grain yield and water use efficiency was significantly higher under RM. These results indicate that the RFRH system can promote crop use of fertilizers by regulating soil moisture. The best fertilization strategy for planting maize with RFRH system was 265.0 kg ha–1 of pure nitrogen combined with 132.5 kg ha–1 of P2O5 in the semiarid area of the Loess Plateau, in China.
1. Introduction The semiarid region of northwestern China is a typical rain-fed farming area with annual rainfall of 300–550 mm (Xiao and Wang, 2003). The uneven spatial and temporal distribution of rainfall can lead to a mismatch between the water supply and crop water demands, thereby causing water deficits during the crop growth period, which severely hinders the capacity to improve crop production in this area (Hu et al., 2014; Zhao et al., 2014). In addition, poor soil quality and low fertility are other key factors that limit crop production in semiarid areas (Liu and Zhang, 2007; Dai et al., 2015). Film mulching is an effective agricultural treatment that is applied worldwide to improve the soil temperature and water conditions, which
⁎
can increase the crop yield and economic efficiency (Steinmetz et al., 2016). The ridge and furrow rainfall harvesting (RFRH) system is widely used in the rain-fed areas of northwestern China which it is an effective tillage measure for improving the rainfall use efficiency (RUE) and crop yield in dry farming areas (Li et al., 2000; Zhang et al., 2007a, b; Hu et al., 2014; Zhang et al., 2017). The RFRH system significantly improves the rhizosphere soil water conditions by guiding precipitation into furrows and suppressing the evaporation of water from the ridged soil (Li et al., 2001; Zhou et al., 2009; Li et al., 2012; Lian et al., 2016). The RFRH system can enhance the growth of crop roots and improve the water use efficiency (WUE) and fertilizer use efficiency, thereby significantly increasing the plant height, dry matter, and economic yield (Ren et al., 2008; Wang et al., 2009), especially in areas with
Corresponding authors at: College of Agronomy, Northwest A&F University, Yangling, 712100, Shaanxi, China. Tel.: +86-29-87080168, fax: +86-29-87080168. E-mail addresses: [email protected] (Y. Zhang), [email protected] (P. Zhang), [email protected] (Z. Jia).
https://doi.org/10.1016/j.agwat.2018.06.032 Received 31 March 2018; Received in revised form 24 June 2018; Accepted 25 June 2018 Available online 20 July 2018 0378-3774/ © 2018 Elsevier B.V. All rights reserved.
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rainfall of 230–440 mm where the effect on increasing the yield is most significant (Ren et al., 2010, 2016). Since the 1980s, the nutrients used in traditional agriculture in the northwestern region of China have gradually changed from a single application of manure to the use of various chemical fertilizers (Roelcke et al., 2004; Hao et al., 2005; Liu and Zhang, 2007). Studies have shown that the application of appropriate fertilizers can increase the water retention capacity, inhibit soil evaporation, enhance the WUE, and improve crop yields (Hao et al., 2005; Dang et al., 2006). However, the application of excessive amounts of fertilizers can adversely affect the soil physics, chemistry, and biodiversity, as well as leading to nitrate leaching and excessive soil water consumption (Perego et al., 2012; Yang et al., 2017; Lian et al., 2016). Thus, it is very important to develop a scientific and reasonable fertilizer use strategy for the RFRH system in order to fully exploit its potential for increasing production in arid areas and reducing agricultural pollution, where this is a key focus of dry-land farming research. The effects of soil water content and nutrients on crop growth and development are not irrelevant, but interact with each other (Liu and Zhang, 2007). Therefore, using the special water regulation method of the RFRH system to formulate a fertilization scheme suitable for the system, tapping the potential water uses efficiency is an important issue for crop cultivation and management in the arid area. The previous research about the RFRH system were mainly focused on the effects of soil water content, temperature, covering materials, ridges and furrows ratio and crop yields (Liu et al., 2009; Li et al., 2013; Wang et al., 2015; Wu et al., 2017; Ren et al., 2017). However, little is known about the appropriate fertilization strategy for the RFRH system. We conducted a 5-year field experiment in order to (1) determine the effects of different nitrogen and phosphorus fertilizer application rates on the soil water consumption properties, WUE, and maize yield under the RFRH system, (2) investigate the relationship between nitrogen and phosphorus application rate and water consumption and maize yield under the RFRH system, (3) provide a scientific basis for the sustainable development of the RFRH and provide an effective solution to alleviate the agro-ecological problems caused by excessive application of chemical fertilizers in semiarid areas of the Loess Plateau, in China.
Table 1 Precipitation (mm) distribution and typical drought levels during 2012–2016 at Pengyang Experimental Station, Ningxia Province, China. Precipitation distribution character
Year 2012
2013
2014
2015
2016
Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec. GP Typical years Rainfall times (T) < 5 mm times (RT) RT/T (%) Total rainfall (TA, mm) RA (mm) Ra (mm) RA/TA (%) Ra/TA (%)
8.4 3.4 16.0 30.2 48.0 86.0 59.8 136.7 73.0 12.3 1.4 1.1 411.4 Normal 96 62 64.6 476.3
0.2 10.2 5.7 29.5 91.9 54.4 267.3 42.1 108.9 32.7 15.2 0.0 594.1 Wet 81 51 63.0 643.1
0.5 13.6 7.0 58.5 7.5 24.7 41.3 63.6 146.3 33.8 11.6 0.1 375.7 Normal 40 14 35.0 408.5
2.2 1.2 26.7 62.8 61.0 72.7 29.0 86.1 93.0 27.9 9.6 1.8 333.2 Normal 103 75 72.8 474.0
2.4 5.6 18.0 49.7 30.7 35.2 123.3 31.7 20.5 21.2 0.2 0.2 251.6 Drought 110 71 64.5 338.7
81.0 38.2 17.0 8.0
92.9 110.1 14.4 17.1
14.6 48.7 3.6 11.9
92.0 0.0 19.4 0.0
94.3 111.3 27.8 32.9
Note: GP is the amount of rainfall (mm) during the whole maize growth period. RA is precipitation < 5 mm (mm); Ra is the amount of rainfall > 35 mm (mm).
2.2. Experimental design and field management Four fertilizer rates (control, RCK = no fertilizer; low fertilizer, RL = N:P2O5 at 150:75 kg ha–1; medium fertilizer, RM = N:P2O5 at 300:150 kg ha–1; high fertilizer, RH = N:P2O5 at 450:225 kg ha–1) were evaluated in the experiment. The field experiment employed a completely randomized block design with three replicates where each plot area measured 91.8 m2 (17.0 × 5.4 m). In order to reduce the impacts of different treatments, each plot was separated by a 90 cm-wide border. The RFRH system used ridge and furrow widths of 60 cm, where the height of each ridge was 15 cm and the ridges were covered by plastic film (0.8 m wide × 0.008 mm, clear and impermeable film; TianshuiTianbao Plastic Industry Ltd, Gansu, China). The fertilizer comprised urea (N 46%; China Petroleum Ningxia Petrochemical Production Company) with diammonium phosphate (P2O5 46.0%, N 18.0%; Yunnan Three Circles Sinochem Fertilizer Co. Ltd, US-sheng). All of the phosphorus and 60% of the nitrogen were applied at the time of sowing by spreading the materials evenly over the planting zone and plowing into the soil layer (about 25 cm), while the other 40% of the nitrogen was applied at 69–75 days after sowing. Spring maize (Dafeng 30) was planted at a rate of 75,000 plants ha–1. The seeds were sown on April 29 in 2012, April 16 in 2013, April 28 in 2014, April 22 in 2015, and April 22 in 2016 with a row distance of 60 cm. The maize was harvested on October 14 in 2012, September 27 in 2013, October 4 in 2014, October 2 in 2015, and September 20 in 2016. Weeds were controlled manually in each growing season. No obvious diseases and pest damages were observed during the years of the experiment. Irrigation was not applied throughout each year. The growth and developmental progress of maize in 2012–2016 were shown in Table S1.
2. Materials and methods 2.1. Site description The study was performed between 2012 and 2016 at the Dry-land Agricultural Experiment Station, Pengyang city, Ningxia Province, China (35°51′E, 106°48′N; 1658 m above sea level). The average annual evaporation was 1753.2 mm, the average annual temperature was 6.1 °C, the frost-free season lasted 150 days, and the average annual rainfall was 430 mm, where over 60.0% of the rainfall occurred during July–September. The rainfall distribution characteristics for 2012–2016 and the rainfall during the growth period are shown in Table 1. Based on the annual rainfall in 2012–2016 (Table 1), we divided the separate years into normal years (2012, 2014, and 2015), a wet year (2013) and a drought year (2016) by calculating the standardized precipitation index (Tigkas et al., 2013; Mpelasoka et al., 2018). The rainfall during the growing seasons from 2012 to 2016 ranged from 251.6 to 594.1 mm, where the frequency of rainfall < 5 mm was as high as 66.0%, except in the wet year (2013). The maximum one-off rainfall in 2013 was 71.8 mm. In the drought year (2016), the total amount of invalid rainfall comprised 27.7% of the annual rainfall, and there were two consecutive > 50 mm high-intensity precipitation events in July. The soil at the experimental site was loess soil with a mean bulk density at a depth of 2 m of 1.3 g cm–3. The main physical and chemical properties for each soil layer before sowing in 2012 are shown in Table 2.
2.3. Sampling and measurements 2.3.1. Plant sampling Crop growth stages including emergence, V4 (fourth leaf), V6 (sixth leaf), V8 (eighth leaf), VT (tasseling), R3 (milk), and R6 (physiological maturity) were recorded when 75% plants were with the appearance 415
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Table 2 Physico-chemical properties of the loess soil (0–60 cm depth) before sowing in 2012 at the Dryland Agricultural Research Station, Pengyang County, China. Soil layer (cm)
Organic carbon (g kg–1)
Available nitrogen (mg kg–1)
Available phosphorus (mg kg–1)
Available potassium (mg kg–1)
Total nitrogen (g kg–1)
Bulk density (g cm–1)
Porosity (%)
Saturated moisture (%)
0-20 20-40 40-60
8.65 7.95 7.57
63.6 44.9 46.8
12.6 7.9 6.0
161.2 117.2 102.7
1.19 0.94 1.05
1.33 1.34 1.41
49.8 49.4 46.8
37.4 36.4 38.4
Note: Values represent the mean of three samples. Organic carbon was determined using the Walkley–Black method. Available nitrogen was determined by the alkaline hydrolysis method. Available phosphorus was determined using the molybdenum blue method. Available potassium was determined with the flame photometric method. Total nitrogen was determined by Kjeldah.
as follows (Zhong and Shang, 2014):
characteristics of the stage in each plot. Fifteen representative plants were sampled from each treatment were cut at ground level and measured at 35, 55, 75, 105, and 129 days after sowing and R6 stage in the five experimental years. The aboveground total dry matter was determined after oven drying at 65 °C until constant weight. All plants of four planted rows (2.4 m wide and 14 m long, except border rows) were selected to obtain yield measurements in each plot, where maize ears were manually threshed and the seed weight was determined (14% standard water content). The coefficient of variation (CV) for the yield was calculated using Eq. (1) (Singh et al., 1990):
CV = S / y
PP = 100 × GP / ET
(5)
SP = 100 × ΔSWS/ET
(6)
where PP is the soil water use rate (%), SP is the rainfall use rate (%), ET is the evapotranspiration (mm) during the whole growth period, GP is the amount of rainfall (mm) during the whole maize growth period, and ΔSWC is the change in the amount of SWS (mm). The WUE and RUE were calculated using Eqs. (7) and (8), respectively (Xie et al., 2005; Wu et al., 2017): (7)
WUE = GY / ET
(1)
(8)
RUE = GY / GP
where S is the standard deviation (kg ha–1) and y y is the average yield (kg ha–1).
–1
–1
–1
–1
where WUE is in kg mm ha , RUE is in kg mm ha , GY is the maize grain yield (kg ha–1), ET is in mm during the whole growth period, and GP is the amount of rainfall (mm) during the whole maize growth period.
2.3.2. Soil water and ET Soil water was measured gravimetrically to a depth of 200 cm at 10 cm intervals in the top 0–20 cm soil layer and at 20 cm intervals in the 20–200 cm layer. The soil samples were obtained randomly using a 54 mm-diameter steel-core sampling drill at location between plants at the side of ridge. Each plot repeats 3 times. The samples were collected at the sowing, V4, V8, VT, R3, and R6 stages in the five experimental years and the gravimetric (g g–1) soil water content of the 0–200 cm profile was measured by drying the soil to a constant weight at 105 °C. The soil water storage (SWS) was calculated using Eq. (2) (Wu et al., 2015):
2.3.3. Statistical analysis Analysis of variance, regression and correlation were performed using SAS 9.2 where the data from each sampling event were analyzed separately. Means among treatments were compared based on the least significant difference test (LSD0.05) if the F-tests were significant at P < 0.05. Figures were prepared using SigmaPlot 12.0. 3. Results
n
SWS =
∑ ci × di × hi/10
3.1. Water consumption strength (2)
i
During the sowing–V4 stage, Water consumption strength (CD) did not differ significantly between the treatments. However, during the sowing–V4 stage, CD decreased as the fertilizer rate increased in 2015 and 2016. In the V4–R3 stage, CD (5-year average) increased with the fertilizer rate (Fig. 1); compared with RCK, CD increased under RH, RM, and RL by 15.5% (P < 0.05), 18.7% (P < 0.05), and 15.9% (P < 0.05), respectively; in the wet year, CD was 11.9% (P < 0.05) and 11.7% (P < 0.05) higher under RH compared with RM and RL, respectively, and here were no significant differences in CD between RM and RL; in the normal years, CD was 8.6% (P < 0.05) and 6.5% (P > 0.05) higher under RH and RM compared with RL, respectively, and there were no significant differences between RH and RM. In the drought year, CD was 22.9% and 22.5% higher (P < 0.05) under RM and RL in the VT–R3 stage compared with RH, respectively. In the R3–R6 stage, CD (5-year average) did not differ significantly between the treatments. However, in the normal years, CD was 20.0% (P < 0.05), 21.5% (P < 0.05), and 18.0% (P < 0.05) higher under RM, RL, and RCK compared with RH, respectively, but there were no significant differences between the other treatments.
where ci is the soil gravimetric water content (%), di is the soil bulk density (g cm–3), hi is the soil depth (cm), n is the number of soil layers, and i = 10, 20, 40,…200. In this area, a simplified formula Eq. (3) is normally used to estimate the seasonal evapotranspiration (ET) (Xie et al., 2005; Zhao et al., 2014; Lian et al., 2016): (3)
ET = P + ΔSWS + C − D − S
where P is the amount of rainfall (mm), ΔSWC is the change in the amount of SWS (mm), C is the upward flow into the root zone, D is the downward drainage out of the root zone, and S is the surface runoff. At the experimental site, the upward flow, downward drainage, and runoff were negligible (Wu et al., 2017). CD in each growth stage was calculated according to Eq. (4) (Wang et al., 2013): (4)
CDi = ETi / D –1
where CDi is the water consumption strength (mm d ), ETi is the ET in each stage (mm), D is the number of days between each growth stage, and i is the growth stage for maize (sowing–V4, V4–V8, V8–VT, VT–R3, and R3–R6). The soil water use rate and rainfall use rate were calculated based on the ratios of the change in the amounts of SWS and rainfall during the growth period relative to the ET from the maize field (respectively),
3.2. Soil water consumption properties ET increased with the fertilizer application rate (Table 3). Compared with RCK, the 5-year average ET was 36.0, 32.5, and 22.3 mm higher 416
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Fig. 1. Water consumption strength under different fertilizer application rates with ridge and furrow rainfall harvesting system during 2012–2016. Horizontal bars represent the LSD at p = 0.05 (n = 3).Treatments RCK, RL, RM, and RH represent applied N:P2O5 rates of 0:0, 150:75, 300:150, and 450:225 kg ha–1, respectively.
31.2% under the RH, RM, and RL treatments compared with RCK, respectively. The dry matter of RH was 3.7% (P > 0.05) and 10.1% (P < 0.05) higher than RM and RL, respectively. There was no significant difference between the dry matter under RM and RL. In the wet year, the dry matter increased by 7.6% (P < 0.05) and 18.8% (P < 0.05) under RH in the R6 stage compared with RM and RL, respectively. There were no significant differences in the dry matter between the other treatments. In the normal years and drought year, the dry matter increased significantly (P < 0.05) by 10.0% and 11.5% under the RH and RM treatments compared with RL, respectively. The increase in the dry matter was higher in the normal years than the drought year. In the V4 stage, during 2015 and 2016, the dry matter were 44.3% (P < 0.05) and 48.3% (P < 0.05), and 19.5% (P < 0.05) and 12.5% (P < 0.05) lower under RH and RM than RL, respectively. Due to the cumulative effect of fertilizer application, the dry matter in the R3–R6 stage was lower under RH than RM during 2016.
under the RH, RM, and RL treatments, respectively. ET was higher (P < 0.05) under the RH and RM treatments compared with RL in the wet year and normal years. However, in the drought year, ET was 14.9 (P < 0.05) and 7.5 mm (P > 0.05) higher under RM compared with RH and RL, respectively. There were no significant differences between ET under RH and RM in all years. SP increased with the fertilizer application rate. Compared with RCK, the average SP increased by 37.6% (P < 0.05), 39.1% (P < 0.05) and 36.6% (P < 0.05) under the RH, RM, and RL treatments, respectively, but there were no significant differences among the fertilizer treatments. In the wet year (2013) and normal years (2012 and 2014), the rainfall basically met the water demand for maize, where SP ranged between 0.0% and 19.4%, and it improved gradually as the fertilizer rate application increased. SWS had major effects on maize growth in the drought year (2016) and in 2015 when the summer drought was very severe, where SP ranged from 31.4% to 37.2%. Compared with RCK, SP increased by 9.0% (P < 0.05), 11.3% (P < 0.05), and 9.9% (P < 0.05) under RH, RM, and RL, respectively. In the drought year, SP increased by 7.0% (P < 0.05) and 3.5% (P > 0.05) under RM compared with RH and RL, respectively. SP was 3.6% (P > 0.05) higher under RL than RH.
3.4. Grain yield The grain yield (5-year average) increased by 45.8% (P < 0.05), 47.9% (P < 0.05), and 45.6% (P < 0.05) under RH, RM, and RL compared with RCK, respectively. The average grain yield was highest under RM with 11.3 t ha–1. Compared with RH and RL, the average grain yield increased by 4.0% and 4.2% under RM, respectively, and the CV was the lowest at 12.9%. The yield was most stable under RM. In the
3.3. Dry matter The dry matter increased with the fertilizer application rate (Fig. 2). The dry matter increased significantly (P < 0.05) by 38.3%, 35.8%, and
Table 3 Evapotranspiration (ET), rainfall use rate (PP), and soil water use rate (SP) under different fertilizer rates with RFRH during 2012–2016. Treatments
2012
2013
ET (mm) RH RM RL RCK
456.5 457.8 444.6 441.1
± ± ± ±
1.0ab 1.2a 0.5c 1.3c
PP (%)
SP (%)
ET (mm)
90.1 89.9 92.5 93.3
9.9 10.1 7.5 6.7
487.8 473.8 470.1 456.0
2014
± ± ± ±
2.7a 2.4b 2.5b 2.1c
PP (%)
SP (%)
ET (mm)
100.0 100.0 100.0 100.0
0.0 0.0 0.0 0.0
466.1 452.1 424.6 375.3
2015
± ± ± ±
15.0a 20.4b 20.2c 17.2d
PP (%)
SP (%)
ET (mm)
80.6 83.1 88.5 100.0
19.4 16.9 11.5 0.0
514.5 508.7 509.5 485.4
2016
± ± ± ±
2.6a 3.0b 2.9b 3.2c
PP (%)
SP (%)
ET (mm)
64.8 65.5 65.4 68.6
35.2 34.5 34.6 31.4
367.5 382.4 375.0 354.4
± ± ± ±
4.8a 2.3a 3.9a 1.2a
PP (%)
SP (%)
65.4 62.8 64.1 67.9
34.6 37.2 35.9 32.1
Note: Values represent the means ± standard deviation (n = 3). Treatments RCK, RL, RM, and RH denotes applied N:P2O5 rates of 0:0, 150:75, 300:150, and 450:225 kg ha–1, respectively. Different lower case letters in the same line indicate significant differences at P < 0.05. 417
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Fig. 2. Dynamic changes in dry matter under different fertilizer application rates with ridge and furrow rainfall harvesting system during 2012–2016. Data are means ± SD (n = 3). Bars with different lower case letters indicate significant differences at P < 0.05. Note: Treatments RCK, RL, RM, and RH represent applied N:P2O5 rates of 0:0, 150:75, 300:150, and 450:225 kg ha–1, respectively.
Table 4 Maize yield (t ha–1) and coefficient of variation (%) of different fertilizer rates under RFRH during 2012–2016. Treatments
2012
RH RM RL RCK Analysis of Variance Year F Year × F
12.1 13.3 12.2 11.0
± ± ± ±
162.4 308.6 19.9
0.5c 0.4a 0.4b 0.4d
2013
2014
2015
2016
12.4 ± 0.1ab 12.0 ± 0.1b 12.8 ± 0.1a 9.7 ± 0.3c
10.8 ± 0.1ab 11.1 ± 0.3a 10.2 ± 0.3b 4.0 ± 0.1c
10.3 ± 0.2b 10.9 ± 0.6a 10.3 ± 0.4b 2.6 ± 0.1c
8.9 9.4 8.9 1.8
± ± ± ±
CV 0.2b 0.1a 0.2b 0.1c
12.9 12.9 14.7 72.6
< .0001 < .0001 < .0001
Note: Values represent the means ± SD (n = 3). Treatments RCK, RL, RM, and RH denote applied N:P2O5 rates of 0:0, 150:75, 300:150, and 450:225 kg ha–1, respectively. Different lower case letters in the same line indicate significant differences at P < 0.05.
wet year (2013), the grain yield was 3.2% (P > 0.05) and 6.0% (P < 0.05) higher under RL than RH and RM, respectively. During the normal yearsand drought year, the grain yield were 5.6% (P < 0.05) and 6.4% (P < 0.05) higher under RM than RH and RL, respectively. In addition, analysis of variance showed that year, fertilizer rate and their interaction had a significant effect on maize yield (Table 4). Regression analysis showed that the rainfall during growing period, fertilizer rates, and their interaction effect on the maize yield were significant (R2 = 0.9109, P < 0.01,). The effects of rainfall and fertilizer rate clearly increased the maize yield, where the effect of the fertilizer application rate (t = 1.95) was higher than that of rainfall (t = 5.06). Due to the mismatch between water and fertilizer, the interaction between rainfall and fertilizer was negative. After calculating the partial derivative of the regression equation, we found that the optimum rate for pure nitrogen was 265.0 kg ha–1 and that for P2O5 was 132.5 kg ha–1 (Fig. 3). Correlation analysis showed that there was a significant positive correlation between CD and the maize yield during the sowing–V4, V8–VT, and VT–R3 stages. In the R3–R6 stage, the maize grain began to dehydrate and the demand for water decreased, so there was a poor
Fig. 3. Maize yield under different N fertilizer application rates and rainfall during growing season (GP) with ridge and furrow rainfall harvesting system. The corresponding equation is: Y = –11,354.72 + 66.2268 X1 + 51.6749 X2 – 0.0348 X1 X2 – 0.0518 X12 – 0.0613 X22 (R2 = 0.9119, P < 0.01) where Z is the grain yield (kg ha−1), X is GP (mm), and Y is the N application rate (kg ha−1). 418
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4. Discussion
Table 5 Correlations between water consumption strength at different growth stages and maize yield (5-year averages).
P value R2
Sowing-V4
V4-V8
V8-VT
VT-R3
R3-R6
0.03 0.999
0.17 0.970
0.05 0.997
0.05 0.998
0.87 0.248
4.1. Soil water consumption properties of RFRH system The ET and nitrogen fertilizer application amount showed a quadratic curve relationship in the normal years and drought year, and it showed linear relationship in the wet year (Fig. 5). The changing trend of ET in normal years and drought year is consistent with previous research results what showed that the water consumption does not increase further after the fertilizer application rate reaches a certain threshold (Zhou et al., 2009; Hunsaker et al., 2000). The result of wet year is different from those obtained by Zhou et al. (2009). This difference may be explained by the high ratio of ineffective rainfall and the high intensity precipitation relative (> 15.5%) to the total rainfall in the present study (Table 1). In addition, the soil water use rate increased with the amount of fertilizer applied. Especially when there is drought during the growing season or less rainfall, the soil water use rate exceed 31.0%, leading a significant consumption of soil water (Table 2). This is because e the application of fertilizer can increase the accumulated dry matter and root growth as well as enhancing the water absorption capacity, and it can also effectively increase the leaf area index and transpiration rate of crops thereby improving the soil water use rate (Rahman et al., 2005, 2005; Zhong and Shang, 2014).
correlation between CD and the yield in this stage (R2 = 0.248) (Table 5).
3.5. Water use efficiency and rainfall use efficiency As shown in Table 6, year, fertilizer rate and their interaction had a significant effect on WUE and RUE. The grain WUE increased significantly (P < 0.05) by 44.6%, 46.7%, and 47.2% under RH, RM, and RL compared with RCK, respectively. In each experimental year (except 2013), the order of the WUE under the fertilizer treatments was: RM > RH > RL. Compared with RH and RL, WUE (5-year average) increased by 4.5% and 2.0% under RM, respectively. WUE was 3.2% higher under RL than RH. In the wet year, WUE decreased by 7.2% (P < 0.05) and 7.2% (P < 0.05) under RH and RM compared with RL, respectively, but there was no significant difference between WUE under RH and RM. In the normal years, WUE increased by 7.5% (P < 0.05) and 4.6% (P > 0.05) under RM compared with RL and RH, respectively. There was no significant difference between WUE under RH and RL. In the drought year, there was no significant difference in WUE under all of the treatments. The five-year average RUE was higher under all the fertilizer treatments than RCK. Thus, compared with RCK, RUE increased significantly (P < 0.05) by 48.6%, 50.9%, and 49.2% under RH, RM, and RL respectively. The order of RUE in each year under the fertilizer treatments was: RM > RL > RH. RUE was 5.3% and 4.3% higher under RM than RH and RL, respectively. RUE was highest in the drought year. Compared with RH and RL, RUE increased by 11.5% (P < 0.05) and 5.2% (P < 0.05) under RM, respectively. RUE was 6.4% higher under RH than RL (P < 0.05). There were no significant differences in RUE under the fertilizer treatments during the wet year. In the drought year, RUE was 6.3% (P < 0.05) and 7.4% (P < 0.05) higher under RM than RH and RL, respectively. RUE did not differ significantly under RH and RL. The effects of rainfall during growing period (X1), fertilizer rate (X2), and their interaction were significant on the grain WUE (R2 = 0.7033, P < 0.01) and RUE (R2 = 0.7589, P < 0.01) (Fig. 4). The fertilizer rate had quadratic relationships with the WUE and RUE, whereas the rainfall had linear relationships with the WUE and RUE.
4.2. Yield effects of growth period rainfall in RFRH system The RFRH system can increase the yield and WUE, where it is influenced by the regional rainfall levels and other natural factors (Guo et al., 2012; Ren et al., 2010). 5-year consecutive field experiments shown that the low fertilizer treatment (N 150 kg ha–1, P2O5 75 kg ha–1) obtained the highest yield (12.8 t ha–1) in the wet year. Yield of medium fertilizer treatment (N 300 kg ha–1, P2O5 150 kg ha–1) was highest (average 11.3 t ha–1) in normal years and drought year and the CV was lowest (Table 4). This result is consistent with that of Li et al. (2015) what showed that when the nitrogen application rate reached 300 kg ha–1, the maize yield was the highest. The regression analysis showed (Fig. 3) that there was a quadratic curve relationship between the growing period rainfall and yield, and when the growing period rainfall was about 550 mm, the maize yield was the highest. The rainfall during the growth period in the range of 251.6–594.1 mm, and the WUE increased with the growing period rainfall (Fig. 4a). If the rainfall is uneven or insufficient during the growing season, the crop yield can be enhanced by increasing the amount of nitrogen fertilizer applied to an appropriate level (Zhong and Shang, 2014). 4.3. Yield effects of fertilizer rate in RFRH system The application of fertilizer can effectively improve the crop growth, and increase the yield and WUE in arid areas (Li and Gong, 2002; Wang et al., 2015, 2016; Zand-Parsa et al., 2006; Zhou et al.,
Table 6 Rainfall use efficiency (RUE) and water use efficiency (WUE) under different fertilizer rates with RFRH during 2012–2016. Treatments
WUE (kg mm–1 ha–1) 2012
RH 26.4 ± RM 29.1 ± RL 27.5 ± RCK 24.9 ± Analysis of Variance Year 176.6 F 396.2 Year × F 33.7
RUE (kg mm–1 ha–1)
2013 1.0c 0.9a 0.9b 0.9d
25.3 25.3 27.2 21.4
2014 ± ± ± ±
1.0b 1.1b 0.8a 1.7c
23.2 24.5 24.0 10.7
± ± ± ±
0.3b 0.4a 0.5ab 0.4c
2015
2016
2012
20.1 ± 0.8b 21.5 ± 0.3a 20.2 ± 0.9b 5.3 ± 0.3c
24.3 ± 0.4a 24.5 ± 0.3a 23.7 ± 0.5a 6.3 ± 0.6b
29.3 32.4 29.7 26.7
< .0001 < .0001 < .0001
2013 ± ± ± ±
1.1c 1.0a 1.0b 1.0d
Year F Year × F
21.9 21.2 22.6 17.2
2014 ± ± ± ±
112.4 509.6 57.4
0.9a 1.0a 0.6a 0.8b
28.8 29.6 27.1 10.7
± ± ± ±
0.3a 0.7a 0.3b 0.1c
2015
2016
31.1 ± 0.8b 33.2 ± 0.1a 30.9 ± 0.4b 7.7 ± 0.2c
37.1 ± 0.7c 42.2 ± 0.2a 39.7 ± 0.9b 9.3 ± 0.5d
< .0001 < .0001 < .0001
Note: Values represent the means ± standard deviation (n = 3). Treatments RCK, RL, RM and RH represent applied N:P2O5 rates of 0:0, 150:75, 300:150 and 450:225 kg ha–1, respectively. Different lower case letters in the same line indicate significant differences at P < 0.05. 419
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Fig. 4. Water use efficiency (WUE) (a) and rainfall use efficiency (RUE) (b) under different N fertilizer application rates and rainfall during growing season (GP) with ridge and furrow rainfall harvesting system. The corresponding equations are: Y = –3.0079 + 0.04307 X1 + 0.1204 X2 – 0.0001 X1 X2 – 0.0001 X22 (R2 = 0.7033, P < 0.01) (a); Y = 14.5295 + 0.1748 X2 – 0.0001 X1 X2 – 0.0002 X22 (R2 = 0.8571, P < 0.01) (b); where Z is WUE/ RUE (kg mm–1 ha−1), X is GP (mm), and Y is the N application rate (kg ha−1).
Shang, 2014), and reduces the increasing production effect (Ren et al., 2010; Payero et al., 2009; Teixeira et al., 2014). Moreover, the reduction of rainfall in 2012–2016 is another reason for dry matter and yield are decreasing annually. The mismatch between water availability and the application of fertilizer supply had a negative effect on the water–fertilizer interaction. 5. Conclusions Five years consecutive experiment showed that high fertilizers levels (> 300 kg ha–1) can cause excessive consumption of soil moisture. In the wet year, the low fertilizer level achieved the best yield and WUE, whereas the medium fertilizer level obtained the highest yields and WUE in the normal years and the dry year. Regression analysis showed that the application of N at 265.0 kg ha–1 with P2O5 at 132.5 kg ha–1 could obtain the highest yield and WUE under RFRH farming. The RFRH system can effectively coordinate the relationship between water and fertilizer, promote the absorption and utilization of fertilizers by crops, and provide an effective solution to the problem of over-application of chemical fertilizers in the semi-arid regions of the Loess Plateau, China.
Fig. 5. The relationship between N fertilizer application rate and evapotranspiration (ET) under ridge and furrow rainfall harvesting system.
2011). Numerous studies have shown that there is a parabolic relationship between the application of nitrogen fertilizer and the crop yield, where the grain yield declines when the nitrogen application rate exceeds a certain threshold (Timsina et al., 2001; Morell et al., 2011; Lian et al., 2016). Under the RFRH system, growing period rainfall, fertilizer rates, and their interaction effect on the maize yield (R2 = 0.9101, P < 0.001) and WUE (R2 = 0.7033, P < 0.01) (Figs. 3 and 4). When the fertilizer rate reached 265.0 kg ha–1, the maize yield reached the maximum, and when the fertilization amount reached 430 kg ha–1, the WUE began to decline. In China, based on a large number of fields in the early stages, it was shown that the best fertilization rate for yield (about 8.50 t ha–1) is 180–225 kg ha–1 (Guo et al., 2008; Zhang et al., 2007a, b). Our result is slightly higher than previous studies. This indicates that the RFRH system can effectively coordinate the relationship between water and fertilizer, promote the absorption and utilization of fertilizers by crops, improves crop yield and water use efficiency.
Funding This work was supported by the Fundamental Research Fund for Universities and Colleges (2452017051 and 2452016014), the Project Supported by Natural Science Basic Research Plan in Shaanxi Province of China (2018JQ3024), China Support Program for Dry-land Farming in the 12th 5-year plan period (2012BAD09B03, 2015BAD22B02), the National High-Tech Research and Development Programs of China (“863 Program”) for the 12th 5-Year Plans (2013AA102902), the Program of Introducing Talents of Discipline to Universities (B12007), the China Postdoctoral Science Foundation funded project (2016M602870), and the Agricultural Science and Technology Innovation and Key Project of Shaanxi Province (2015NY115).
4.4. Inhibition of excessive fertilization Acknowledgements Under the high fertilizers rate, the yields, WUE and RUE significantly show decreased trend with increasing the fertilizers rates. (Tables 4 and 5). From 2014 onwards, the growth of maize in high fertilizer treatment of was suppressed during the sowing-V4 period, and this inhibition continued until physiological maturity in 2015–2016 (Fig. 1). This results are mainly caused by the application of fertilizer in successive years may have increased the nitrogen concentration in the soil solution to cause physiological drought by inhibiting water absorption via the root system (Zhong and Shang, 2014), thereby affecting the dry matter, yield, and water use efficiency of maize (Zhong and
The manuscript was reviewed and approved for publication by all authors. Zhikuan Jia and Peng Zhangy conceived and designed the experiments. Yan Zhang, Qian Ma, Xiaolong Ren, Lefeng Sun, Shahzad Ali and Donghua Liu performed the experiments. Yan Zhang, Peng Zhang and Zhikuan Jia analyzed the data. Yan Zhang, Peng Zhang wrote the paper. Yan Zhang, Peng Zhang and Zhikuan Jia reviewed and revised the paper. Zhikuan Jia and Shahzad Ali corrected the English language for the paper. We are also grateful to Nie Junfeng, Yang Baoping and Ding Ruixia for help during experimental period. 420
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Appendix A. Supplementary data
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Effects of different fertilizer strategies on soil water utilization and maize yield in the ridge and furrow rainfall harvesting system in semiarid regions of China
T
Yan Zhanga,b, Qian Maa,b, Donghua Liua,b, Lefeng Suna,b, Xiaolong Rena,b, Shahzad Alia,b, ⁎ ⁎ Peng Zhanga,b, , Zhikuan Jiaa,b, a
College of Agronomy, Northwest A&F University, Yangling, 712100, Shaanxi, China Key Laboratory of Crop Physi-Ecology and Tillage Science in Northwestern Loess Plateau, Minister of Agriculture, Northwest A&F University, Yangling, 712100, Shaanxi, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Fertilizer rate Maize yield Ridge and furrow rainfall harvesting system Semi-arid area Soil water consumption properties
Shortages of water resources and low soil fertility are two key factors that limit crop production in semiarid areas. The ridge and furrow rainfall harvesting (RFRH) system is an effective method for enhancing the efficiency of rainfall water use and fertility. In this study, we conducted a field experiment over five years (2012–2016) to determine the effects of different fertilizer application rates on the soil water consumption properties, water use efficiency, and maize yield under RFRH. We found that the evapotranspiration (ET), maize dry matter (DM), water consumption strength (CD), and soil water use rate (SP) increased with the fertilizer application rate. Compared with the no fertilizer treatment (RCK), ET, DM, CD, and SP increased significantly by 7.2%, 38.3%, 16.4%, and 37.6% under high fertilizer (RH) treatment, respectively, by 6.7%, 35.8%, 18.0%, and 39.1% with medium fertilizer (RM) treatment, and by 5.5%, 31.1%, 16.1%, and 32.6% with low fertilizer (RL) treatment. RM achieved the highest average yield of 11.3 t ha–1 and the lowest coefficient of variation at 12.9%. The yield, DM, and water use efficiency did not differ significantly between RH and RM. Regression analysis showed that the highest yield could be obtained by applying nitrogen at 265.0 kg ha–1 combined with P2O5 at 132.5 kg ha–1. The yield and water use efficiency were significantly higher under RL compared with RH and RM in wet year. However, in both normal and drought years, the grain yield and water use efficiency was significantly higher under RM. These results indicate that the RFRH system can promote crop use of fertilizers by regulating soil moisture. The best fertilization strategy for planting maize with RFRH system was 265.0 kg ha–1 of pure nitrogen combined with 132.5 kg ha–1 of P2O5 in the semiarid area of the Loess Plateau, in China.
1. Introduction The semiarid region of northwestern China is a typical rain-fed farming area with annual rainfall of 300–550 mm (Xiao and Wang, 2003). The uneven spatial and temporal distribution of rainfall can lead to a mismatch between the water supply and crop water demands, thereby causing water deficits during the crop growth period, which severely hinders the capacity to improve crop production in this area (Hu et al., 2014; Zhao et al., 2014). In addition, poor soil quality and low fertility are other key factors that limit crop production in semiarid areas (Liu and Zhang, 2007; Dai et al., 2015). Film mulching is an effective agricultural treatment that is applied worldwide to improve the soil temperature and water conditions, which
⁎
can increase the crop yield and economic efficiency (Steinmetz et al., 2016). The ridge and furrow rainfall harvesting (RFRH) system is widely used in the rain-fed areas of northwestern China which it is an effective tillage measure for improving the rainfall use efficiency (RUE) and crop yield in dry farming areas (Li et al., 2000; Zhang et al., 2007a, b; Hu et al., 2014; Zhang et al., 2017). The RFRH system significantly improves the rhizosphere soil water conditions by guiding precipitation into furrows and suppressing the evaporation of water from the ridged soil (Li et al., 2001; Zhou et al., 2009; Li et al., 2012; Lian et al., 2016). The RFRH system can enhance the growth of crop roots and improve the water use efficiency (WUE) and fertilizer use efficiency, thereby significantly increasing the plant height, dry matter, and economic yield (Ren et al., 2008; Wang et al., 2009), especially in areas with
Corresponding authors at: College of Agronomy, Northwest A&F University, Yangling, 712100, Shaanxi, China. Tel.: +86-29-87080168, fax: +86-29-87080168. E-mail addresses: [email protected] (Y. Zhang), [email protected] (P. Zhang), [email protected] (Z. Jia).
https://doi.org/10.1016/j.agwat.2018.06.032 Received 31 March 2018; Received in revised form 24 June 2018; Accepted 25 June 2018 Available online 20 July 2018 0378-3774/ © 2018 Elsevier B.V. All rights reserved.
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rainfall of 230–440 mm where the effect on increasing the yield is most significant (Ren et al., 2010, 2016). Since the 1980s, the nutrients used in traditional agriculture in the northwestern region of China have gradually changed from a single application of manure to the use of various chemical fertilizers (Roelcke et al., 2004; Hao et al., 2005; Liu and Zhang, 2007). Studies have shown that the application of appropriate fertilizers can increase the water retention capacity, inhibit soil evaporation, enhance the WUE, and improve crop yields (Hao et al., 2005; Dang et al., 2006). However, the application of excessive amounts of fertilizers can adversely affect the soil physics, chemistry, and biodiversity, as well as leading to nitrate leaching and excessive soil water consumption (Perego et al., 2012; Yang et al., 2017; Lian et al., 2016). Thus, it is very important to develop a scientific and reasonable fertilizer use strategy for the RFRH system in order to fully exploit its potential for increasing production in arid areas and reducing agricultural pollution, where this is a key focus of dry-land farming research. The effects of soil water content and nutrients on crop growth and development are not irrelevant, but interact with each other (Liu and Zhang, 2007). Therefore, using the special water regulation method of the RFRH system to formulate a fertilization scheme suitable for the system, tapping the potential water uses efficiency is an important issue for crop cultivation and management in the arid area. The previous research about the RFRH system were mainly focused on the effects of soil water content, temperature, covering materials, ridges and furrows ratio and crop yields (Liu et al., 2009; Li et al., 2013; Wang et al., 2015; Wu et al., 2017; Ren et al., 2017). However, little is known about the appropriate fertilization strategy for the RFRH system. We conducted a 5-year field experiment in order to (1) determine the effects of different nitrogen and phosphorus fertilizer application rates on the soil water consumption properties, WUE, and maize yield under the RFRH system, (2) investigate the relationship between nitrogen and phosphorus application rate and water consumption and maize yield under the RFRH system, (3) provide a scientific basis for the sustainable development of the RFRH and provide an effective solution to alleviate the agro-ecological problems caused by excessive application of chemical fertilizers in semiarid areas of the Loess Plateau, in China.
Table 1 Precipitation (mm) distribution and typical drought levels during 2012–2016 at Pengyang Experimental Station, Ningxia Province, China. Precipitation distribution character
Year 2012
2013
2014
2015
2016
Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec. GP Typical years Rainfall times (T) < 5 mm times (RT) RT/T (%) Total rainfall (TA, mm) RA (mm) Ra (mm) RA/TA (%) Ra/TA (%)
8.4 3.4 16.0 30.2 48.0 86.0 59.8 136.7 73.0 12.3 1.4 1.1 411.4 Normal 96 62 64.6 476.3
0.2 10.2 5.7 29.5 91.9 54.4 267.3 42.1 108.9 32.7 15.2 0.0 594.1 Wet 81 51 63.0 643.1
0.5 13.6 7.0 58.5 7.5 24.7 41.3 63.6 146.3 33.8 11.6 0.1 375.7 Normal 40 14 35.0 408.5
2.2 1.2 26.7 62.8 61.0 72.7 29.0 86.1 93.0 27.9 9.6 1.8 333.2 Normal 103 75 72.8 474.0
2.4 5.6 18.0 49.7 30.7 35.2 123.3 31.7 20.5 21.2 0.2 0.2 251.6 Drought 110 71 64.5 338.7
81.0 38.2 17.0 8.0
92.9 110.1 14.4 17.1
14.6 48.7 3.6 11.9
92.0 0.0 19.4 0.0
94.3 111.3 27.8 32.9
Note: GP is the amount of rainfall (mm) during the whole maize growth period. RA is precipitation < 5 mm (mm); Ra is the amount of rainfall > 35 mm (mm).
2.2. Experimental design and field management Four fertilizer rates (control, RCK = no fertilizer; low fertilizer, RL = N:P2O5 at 150:75 kg ha–1; medium fertilizer, RM = N:P2O5 at 300:150 kg ha–1; high fertilizer, RH = N:P2O5 at 450:225 kg ha–1) were evaluated in the experiment. The field experiment employed a completely randomized block design with three replicates where each plot area measured 91.8 m2 (17.0 × 5.4 m). In order to reduce the impacts of different treatments, each plot was separated by a 90 cm-wide border. The RFRH system used ridge and furrow widths of 60 cm, where the height of each ridge was 15 cm and the ridges were covered by plastic film (0.8 m wide × 0.008 mm, clear and impermeable film; TianshuiTianbao Plastic Industry Ltd, Gansu, China). The fertilizer comprised urea (N 46%; China Petroleum Ningxia Petrochemical Production Company) with diammonium phosphate (P2O5 46.0%, N 18.0%; Yunnan Three Circles Sinochem Fertilizer Co. Ltd, US-sheng). All of the phosphorus and 60% of the nitrogen were applied at the time of sowing by spreading the materials evenly over the planting zone and plowing into the soil layer (about 25 cm), while the other 40% of the nitrogen was applied at 69–75 days after sowing. Spring maize (Dafeng 30) was planted at a rate of 75,000 plants ha–1. The seeds were sown on April 29 in 2012, April 16 in 2013, April 28 in 2014, April 22 in 2015, and April 22 in 2016 with a row distance of 60 cm. The maize was harvested on October 14 in 2012, September 27 in 2013, October 4 in 2014, October 2 in 2015, and September 20 in 2016. Weeds were controlled manually in each growing season. No obvious diseases and pest damages were observed during the years of the experiment. Irrigation was not applied throughout each year. The growth and developmental progress of maize in 2012–2016 were shown in Table S1.
2. Materials and methods 2.1. Site description The study was performed between 2012 and 2016 at the Dry-land Agricultural Experiment Station, Pengyang city, Ningxia Province, China (35°51′E, 106°48′N; 1658 m above sea level). The average annual evaporation was 1753.2 mm, the average annual temperature was 6.1 °C, the frost-free season lasted 150 days, and the average annual rainfall was 430 mm, where over 60.0% of the rainfall occurred during July–September. The rainfall distribution characteristics for 2012–2016 and the rainfall during the growth period are shown in Table 1. Based on the annual rainfall in 2012–2016 (Table 1), we divided the separate years into normal years (2012, 2014, and 2015), a wet year (2013) and a drought year (2016) by calculating the standardized precipitation index (Tigkas et al., 2013; Mpelasoka et al., 2018). The rainfall during the growing seasons from 2012 to 2016 ranged from 251.6 to 594.1 mm, where the frequency of rainfall < 5 mm was as high as 66.0%, except in the wet year (2013). The maximum one-off rainfall in 2013 was 71.8 mm. In the drought year (2016), the total amount of invalid rainfall comprised 27.7% of the annual rainfall, and there were two consecutive > 50 mm high-intensity precipitation events in July. The soil at the experimental site was loess soil with a mean bulk density at a depth of 2 m of 1.3 g cm–3. The main physical and chemical properties for each soil layer before sowing in 2012 are shown in Table 2.
2.3. Sampling and measurements 2.3.1. Plant sampling Crop growth stages including emergence, V4 (fourth leaf), V6 (sixth leaf), V8 (eighth leaf), VT (tasseling), R3 (milk), and R6 (physiological maturity) were recorded when 75% plants were with the appearance 415
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Table 2 Physico-chemical properties of the loess soil (0–60 cm depth) before sowing in 2012 at the Dryland Agricultural Research Station, Pengyang County, China. Soil layer (cm)
Organic carbon (g kg–1)
Available nitrogen (mg kg–1)
Available phosphorus (mg kg–1)
Available potassium (mg kg–1)
Total nitrogen (g kg–1)
Bulk density (g cm–1)
Porosity (%)
Saturated moisture (%)
0-20 20-40 40-60
8.65 7.95 7.57
63.6 44.9 46.8
12.6 7.9 6.0
161.2 117.2 102.7
1.19 0.94 1.05
1.33 1.34 1.41
49.8 49.4 46.8
37.4 36.4 38.4
Note: Values represent the mean of three samples. Organic carbon was determined using the Walkley–Black method. Available nitrogen was determined by the alkaline hydrolysis method. Available phosphorus was determined using the molybdenum blue method. Available potassium was determined with the flame photometric method. Total nitrogen was determined by Kjeldah.
as follows (Zhong and Shang, 2014):
characteristics of the stage in each plot. Fifteen representative plants were sampled from each treatment were cut at ground level and measured at 35, 55, 75, 105, and 129 days after sowing and R6 stage in the five experimental years. The aboveground total dry matter was determined after oven drying at 65 °C until constant weight. All plants of four planted rows (2.4 m wide and 14 m long, except border rows) were selected to obtain yield measurements in each plot, where maize ears were manually threshed and the seed weight was determined (14% standard water content). The coefficient of variation (CV) for the yield was calculated using Eq. (1) (Singh et al., 1990):
CV = S / y
PP = 100 × GP / ET
(5)
SP = 100 × ΔSWS/ET
(6)
where PP is the soil water use rate (%), SP is the rainfall use rate (%), ET is the evapotranspiration (mm) during the whole growth period, GP is the amount of rainfall (mm) during the whole maize growth period, and ΔSWC is the change in the amount of SWS (mm). The WUE and RUE were calculated using Eqs. (7) and (8), respectively (Xie et al., 2005; Wu et al., 2017): (7)
WUE = GY / ET
(1)
(8)
RUE = GY / GP
where S is the standard deviation (kg ha–1) and y y is the average yield (kg ha–1).
–1
–1
–1
–1
where WUE is in kg mm ha , RUE is in kg mm ha , GY is the maize grain yield (kg ha–1), ET is in mm during the whole growth period, and GP is the amount of rainfall (mm) during the whole maize growth period.
2.3.2. Soil water and ET Soil water was measured gravimetrically to a depth of 200 cm at 10 cm intervals in the top 0–20 cm soil layer and at 20 cm intervals in the 20–200 cm layer. The soil samples were obtained randomly using a 54 mm-diameter steel-core sampling drill at location between plants at the side of ridge. Each plot repeats 3 times. The samples were collected at the sowing, V4, V8, VT, R3, and R6 stages in the five experimental years and the gravimetric (g g–1) soil water content of the 0–200 cm profile was measured by drying the soil to a constant weight at 105 °C. The soil water storage (SWS) was calculated using Eq. (2) (Wu et al., 2015):
2.3.3. Statistical analysis Analysis of variance, regression and correlation were performed using SAS 9.2 where the data from each sampling event were analyzed separately. Means among treatments were compared based on the least significant difference test (LSD0.05) if the F-tests were significant at P < 0.05. Figures were prepared using SigmaPlot 12.0. 3. Results
n
SWS =
∑ ci × di × hi/10
3.1. Water consumption strength (2)
i
During the sowing–V4 stage, Water consumption strength (CD) did not differ significantly between the treatments. However, during the sowing–V4 stage, CD decreased as the fertilizer rate increased in 2015 and 2016. In the V4–R3 stage, CD (5-year average) increased with the fertilizer rate (Fig. 1); compared with RCK, CD increased under RH, RM, and RL by 15.5% (P < 0.05), 18.7% (P < 0.05), and 15.9% (P < 0.05), respectively; in the wet year, CD was 11.9% (P < 0.05) and 11.7% (P < 0.05) higher under RH compared with RM and RL, respectively, and here were no significant differences in CD between RM and RL; in the normal years, CD was 8.6% (P < 0.05) and 6.5% (P > 0.05) higher under RH and RM compared with RL, respectively, and there were no significant differences between RH and RM. In the drought year, CD was 22.9% and 22.5% higher (P < 0.05) under RM and RL in the VT–R3 stage compared with RH, respectively. In the R3–R6 stage, CD (5-year average) did not differ significantly between the treatments. However, in the normal years, CD was 20.0% (P < 0.05), 21.5% (P < 0.05), and 18.0% (P < 0.05) higher under RM, RL, and RCK compared with RH, respectively, but there were no significant differences between the other treatments.
where ci is the soil gravimetric water content (%), di is the soil bulk density (g cm–3), hi is the soil depth (cm), n is the number of soil layers, and i = 10, 20, 40,…200. In this area, a simplified formula Eq. (3) is normally used to estimate the seasonal evapotranspiration (ET) (Xie et al., 2005; Zhao et al., 2014; Lian et al., 2016): (3)
ET = P + ΔSWS + C − D − S
where P is the amount of rainfall (mm), ΔSWC is the change in the amount of SWS (mm), C is the upward flow into the root zone, D is the downward drainage out of the root zone, and S is the surface runoff. At the experimental site, the upward flow, downward drainage, and runoff were negligible (Wu et al., 2017). CD in each growth stage was calculated according to Eq. (4) (Wang et al., 2013): (4)
CDi = ETi / D –1
where CDi is the water consumption strength (mm d ), ETi is the ET in each stage (mm), D is the number of days between each growth stage, and i is the growth stage for maize (sowing–V4, V4–V8, V8–VT, VT–R3, and R3–R6). The soil water use rate and rainfall use rate were calculated based on the ratios of the change in the amounts of SWS and rainfall during the growth period relative to the ET from the maize field (respectively),
3.2. Soil water consumption properties ET increased with the fertilizer application rate (Table 3). Compared with RCK, the 5-year average ET was 36.0, 32.5, and 22.3 mm higher 416
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Fig. 1. Water consumption strength under different fertilizer application rates with ridge and furrow rainfall harvesting system during 2012–2016. Horizontal bars represent the LSD at p = 0.05 (n = 3).Treatments RCK, RL, RM, and RH represent applied N:P2O5 rates of 0:0, 150:75, 300:150, and 450:225 kg ha–1, respectively.
31.2% under the RH, RM, and RL treatments compared with RCK, respectively. The dry matter of RH was 3.7% (P > 0.05) and 10.1% (P < 0.05) higher than RM and RL, respectively. There was no significant difference between the dry matter under RM and RL. In the wet year, the dry matter increased by 7.6% (P < 0.05) and 18.8% (P < 0.05) under RH in the R6 stage compared with RM and RL, respectively. There were no significant differences in the dry matter between the other treatments. In the normal years and drought year, the dry matter increased significantly (P < 0.05) by 10.0% and 11.5% under the RH and RM treatments compared with RL, respectively. The increase in the dry matter was higher in the normal years than the drought year. In the V4 stage, during 2015 and 2016, the dry matter were 44.3% (P < 0.05) and 48.3% (P < 0.05), and 19.5% (P < 0.05) and 12.5% (P < 0.05) lower under RH and RM than RL, respectively. Due to the cumulative effect of fertilizer application, the dry matter in the R3–R6 stage was lower under RH than RM during 2016.
under the RH, RM, and RL treatments, respectively. ET was higher (P < 0.05) under the RH and RM treatments compared with RL in the wet year and normal years. However, in the drought year, ET was 14.9 (P < 0.05) and 7.5 mm (P > 0.05) higher under RM compared with RH and RL, respectively. There were no significant differences between ET under RH and RM in all years. SP increased with the fertilizer application rate. Compared with RCK, the average SP increased by 37.6% (P < 0.05), 39.1% (P < 0.05) and 36.6% (P < 0.05) under the RH, RM, and RL treatments, respectively, but there were no significant differences among the fertilizer treatments. In the wet year (2013) and normal years (2012 and 2014), the rainfall basically met the water demand for maize, where SP ranged between 0.0% and 19.4%, and it improved gradually as the fertilizer rate application increased. SWS had major effects on maize growth in the drought year (2016) and in 2015 when the summer drought was very severe, where SP ranged from 31.4% to 37.2%. Compared with RCK, SP increased by 9.0% (P < 0.05), 11.3% (P < 0.05), and 9.9% (P < 0.05) under RH, RM, and RL, respectively. In the drought year, SP increased by 7.0% (P < 0.05) and 3.5% (P > 0.05) under RM compared with RH and RL, respectively. SP was 3.6% (P > 0.05) higher under RL than RH.
3.4. Grain yield The grain yield (5-year average) increased by 45.8% (P < 0.05), 47.9% (P < 0.05), and 45.6% (P < 0.05) under RH, RM, and RL compared with RCK, respectively. The average grain yield was highest under RM with 11.3 t ha–1. Compared with RH and RL, the average grain yield increased by 4.0% and 4.2% under RM, respectively, and the CV was the lowest at 12.9%. The yield was most stable under RM. In the
3.3. Dry matter The dry matter increased with the fertilizer application rate (Fig. 2). The dry matter increased significantly (P < 0.05) by 38.3%, 35.8%, and
Table 3 Evapotranspiration (ET), rainfall use rate (PP), and soil water use rate (SP) under different fertilizer rates with RFRH during 2012–2016. Treatments
2012
2013
ET (mm) RH RM RL RCK
456.5 457.8 444.6 441.1
± ± ± ±
1.0ab 1.2a 0.5c 1.3c
PP (%)
SP (%)
ET (mm)
90.1 89.9 92.5 93.3
9.9 10.1 7.5 6.7
487.8 473.8 470.1 456.0
2014
± ± ± ±
2.7a 2.4b 2.5b 2.1c
PP (%)
SP (%)
ET (mm)
100.0 100.0 100.0 100.0
0.0 0.0 0.0 0.0
466.1 452.1 424.6 375.3
2015
± ± ± ±
15.0a 20.4b 20.2c 17.2d
PP (%)
SP (%)
ET (mm)
80.6 83.1 88.5 100.0
19.4 16.9 11.5 0.0
514.5 508.7 509.5 485.4
2016
± ± ± ±
2.6a 3.0b 2.9b 3.2c
PP (%)
SP (%)
ET (mm)
64.8 65.5 65.4 68.6
35.2 34.5 34.6 31.4
367.5 382.4 375.0 354.4
± ± ± ±
4.8a 2.3a 3.9a 1.2a
PP (%)
SP (%)
65.4 62.8 64.1 67.9
34.6 37.2 35.9 32.1
Note: Values represent the means ± standard deviation (n = 3). Treatments RCK, RL, RM, and RH denotes applied N:P2O5 rates of 0:0, 150:75, 300:150, and 450:225 kg ha–1, respectively. Different lower case letters in the same line indicate significant differences at P < 0.05. 417
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Fig. 2. Dynamic changes in dry matter under different fertilizer application rates with ridge and furrow rainfall harvesting system during 2012–2016. Data are means ± SD (n = 3). Bars with different lower case letters indicate significant differences at P < 0.05. Note: Treatments RCK, RL, RM, and RH represent applied N:P2O5 rates of 0:0, 150:75, 300:150, and 450:225 kg ha–1, respectively.
Table 4 Maize yield (t ha–1) and coefficient of variation (%) of different fertilizer rates under RFRH during 2012–2016. Treatments
2012
RH RM RL RCK Analysis of Variance Year F Year × F
12.1 13.3 12.2 11.0
± ± ± ±
162.4 308.6 19.9
0.5c 0.4a 0.4b 0.4d
2013
2014
2015
2016
12.4 ± 0.1ab 12.0 ± 0.1b 12.8 ± 0.1a 9.7 ± 0.3c
10.8 ± 0.1ab 11.1 ± 0.3a 10.2 ± 0.3b 4.0 ± 0.1c
10.3 ± 0.2b 10.9 ± 0.6a 10.3 ± 0.4b 2.6 ± 0.1c
8.9 9.4 8.9 1.8
± ± ± ±
CV 0.2b 0.1a 0.2b 0.1c
12.9 12.9 14.7 72.6
< .0001 < .0001 < .0001
Note: Values represent the means ± SD (n = 3). Treatments RCK, RL, RM, and RH denote applied N:P2O5 rates of 0:0, 150:75, 300:150, and 450:225 kg ha–1, respectively. Different lower case letters in the same line indicate significant differences at P < 0.05.
wet year (2013), the grain yield was 3.2% (P > 0.05) and 6.0% (P < 0.05) higher under RL than RH and RM, respectively. During the normal yearsand drought year, the grain yield were 5.6% (P < 0.05) and 6.4% (P < 0.05) higher under RM than RH and RL, respectively. In addition, analysis of variance showed that year, fertilizer rate and their interaction had a significant effect on maize yield (Table 4). Regression analysis showed that the rainfall during growing period, fertilizer rates, and their interaction effect on the maize yield were significant (R2 = 0.9109, P < 0.01,). The effects of rainfall and fertilizer rate clearly increased the maize yield, where the effect of the fertilizer application rate (t = 1.95) was higher than that of rainfall (t = 5.06). Due to the mismatch between water and fertilizer, the interaction between rainfall and fertilizer was negative. After calculating the partial derivative of the regression equation, we found that the optimum rate for pure nitrogen was 265.0 kg ha–1 and that for P2O5 was 132.5 kg ha–1 (Fig. 3). Correlation analysis showed that there was a significant positive correlation between CD and the maize yield during the sowing–V4, V8–VT, and VT–R3 stages. In the R3–R6 stage, the maize grain began to dehydrate and the demand for water decreased, so there was a poor
Fig. 3. Maize yield under different N fertilizer application rates and rainfall during growing season (GP) with ridge and furrow rainfall harvesting system. The corresponding equation is: Y = –11,354.72 + 66.2268 X1 + 51.6749 X2 – 0.0348 X1 X2 – 0.0518 X12 – 0.0613 X22 (R2 = 0.9119, P < 0.01) where Z is the grain yield (kg ha−1), X is GP (mm), and Y is the N application rate (kg ha−1). 418
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4. Discussion
Table 5 Correlations between water consumption strength at different growth stages and maize yield (5-year averages).
P value R2
Sowing-V4
V4-V8
V8-VT
VT-R3
R3-R6
0.03 0.999
0.17 0.970
0.05 0.997
0.05 0.998
0.87 0.248
4.1. Soil water consumption properties of RFRH system The ET and nitrogen fertilizer application amount showed a quadratic curve relationship in the normal years and drought year, and it showed linear relationship in the wet year (Fig. 5). The changing trend of ET in normal years and drought year is consistent with previous research results what showed that the water consumption does not increase further after the fertilizer application rate reaches a certain threshold (Zhou et al., 2009; Hunsaker et al., 2000). The result of wet year is different from those obtained by Zhou et al. (2009). This difference may be explained by the high ratio of ineffective rainfall and the high intensity precipitation relative (> 15.5%) to the total rainfall in the present study (Table 1). In addition, the soil water use rate increased with the amount of fertilizer applied. Especially when there is drought during the growing season or less rainfall, the soil water use rate exceed 31.0%, leading a significant consumption of soil water (Table 2). This is because e the application of fertilizer can increase the accumulated dry matter and root growth as well as enhancing the water absorption capacity, and it can also effectively increase the leaf area index and transpiration rate of crops thereby improving the soil water use rate (Rahman et al., 2005, 2005; Zhong and Shang, 2014).
correlation between CD and the yield in this stage (R2 = 0.248) (Table 5).
3.5. Water use efficiency and rainfall use efficiency As shown in Table 6, year, fertilizer rate and their interaction had a significant effect on WUE and RUE. The grain WUE increased significantly (P < 0.05) by 44.6%, 46.7%, and 47.2% under RH, RM, and RL compared with RCK, respectively. In each experimental year (except 2013), the order of the WUE under the fertilizer treatments was: RM > RH > RL. Compared with RH and RL, WUE (5-year average) increased by 4.5% and 2.0% under RM, respectively. WUE was 3.2% higher under RL than RH. In the wet year, WUE decreased by 7.2% (P < 0.05) and 7.2% (P < 0.05) under RH and RM compared with RL, respectively, but there was no significant difference between WUE under RH and RM. In the normal years, WUE increased by 7.5% (P < 0.05) and 4.6% (P > 0.05) under RM compared with RL and RH, respectively. There was no significant difference between WUE under RH and RL. In the drought year, there was no significant difference in WUE under all of the treatments. The five-year average RUE was higher under all the fertilizer treatments than RCK. Thus, compared with RCK, RUE increased significantly (P < 0.05) by 48.6%, 50.9%, and 49.2% under RH, RM, and RL respectively. The order of RUE in each year under the fertilizer treatments was: RM > RL > RH. RUE was 5.3% and 4.3% higher under RM than RH and RL, respectively. RUE was highest in the drought year. Compared with RH and RL, RUE increased by 11.5% (P < 0.05) and 5.2% (P < 0.05) under RM, respectively. RUE was 6.4% higher under RH than RL (P < 0.05). There were no significant differences in RUE under the fertilizer treatments during the wet year. In the drought year, RUE was 6.3% (P < 0.05) and 7.4% (P < 0.05) higher under RM than RH and RL, respectively. RUE did not differ significantly under RH and RL. The effects of rainfall during growing period (X1), fertilizer rate (X2), and their interaction were significant on the grain WUE (R2 = 0.7033, P < 0.01) and RUE (R2 = 0.7589, P < 0.01) (Fig. 4). The fertilizer rate had quadratic relationships with the WUE and RUE, whereas the rainfall had linear relationships with the WUE and RUE.
4.2. Yield effects of growth period rainfall in RFRH system The RFRH system can increase the yield and WUE, where it is influenced by the regional rainfall levels and other natural factors (Guo et al., 2012; Ren et al., 2010). 5-year consecutive field experiments shown that the low fertilizer treatment (N 150 kg ha–1, P2O5 75 kg ha–1) obtained the highest yield (12.8 t ha–1) in the wet year. Yield of medium fertilizer treatment (N 300 kg ha–1, P2O5 150 kg ha–1) was highest (average 11.3 t ha–1) in normal years and drought year and the CV was lowest (Table 4). This result is consistent with that of Li et al. (2015) what showed that when the nitrogen application rate reached 300 kg ha–1, the maize yield was the highest. The regression analysis showed (Fig. 3) that there was a quadratic curve relationship between the growing period rainfall and yield, and when the growing period rainfall was about 550 mm, the maize yield was the highest. The rainfall during the growth period in the range of 251.6–594.1 mm, and the WUE increased with the growing period rainfall (Fig. 4a). If the rainfall is uneven or insufficient during the growing season, the crop yield can be enhanced by increasing the amount of nitrogen fertilizer applied to an appropriate level (Zhong and Shang, 2014). 4.3. Yield effects of fertilizer rate in RFRH system The application of fertilizer can effectively improve the crop growth, and increase the yield and WUE in arid areas (Li and Gong, 2002; Wang et al., 2015, 2016; Zand-Parsa et al., 2006; Zhou et al.,
Table 6 Rainfall use efficiency (RUE) and water use efficiency (WUE) under different fertilizer rates with RFRH during 2012–2016. Treatments
WUE (kg mm–1 ha–1) 2012
RH 26.4 ± RM 29.1 ± RL 27.5 ± RCK 24.9 ± Analysis of Variance Year 176.6 F 396.2 Year × F 33.7
RUE (kg mm–1 ha–1)
2013 1.0c 0.9a 0.9b 0.9d
25.3 25.3 27.2 21.4
2014 ± ± ± ±
1.0b 1.1b 0.8a 1.7c
23.2 24.5 24.0 10.7
± ± ± ±
0.3b 0.4a 0.5ab 0.4c
2015
2016
2012
20.1 ± 0.8b 21.5 ± 0.3a 20.2 ± 0.9b 5.3 ± 0.3c
24.3 ± 0.4a 24.5 ± 0.3a 23.7 ± 0.5a 6.3 ± 0.6b
29.3 32.4 29.7 26.7
< .0001 < .0001 < .0001
2013 ± ± ± ±
1.1c 1.0a 1.0b 1.0d
Year F Year × F
21.9 21.2 22.6 17.2
2014 ± ± ± ±
112.4 509.6 57.4
0.9a 1.0a 0.6a 0.8b
28.8 29.6 27.1 10.7
± ± ± ±
0.3a 0.7a 0.3b 0.1c
2015
2016
31.1 ± 0.8b 33.2 ± 0.1a 30.9 ± 0.4b 7.7 ± 0.2c
37.1 ± 0.7c 42.2 ± 0.2a 39.7 ± 0.9b 9.3 ± 0.5d
< .0001 < .0001 < .0001
Note: Values represent the means ± standard deviation (n = 3). Treatments RCK, RL, RM and RH represent applied N:P2O5 rates of 0:0, 150:75, 300:150 and 450:225 kg ha–1, respectively. Different lower case letters in the same line indicate significant differences at P < 0.05. 419
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Fig. 4. Water use efficiency (WUE) (a) and rainfall use efficiency (RUE) (b) under different N fertilizer application rates and rainfall during growing season (GP) with ridge and furrow rainfall harvesting system. The corresponding equations are: Y = –3.0079 + 0.04307 X1 + 0.1204 X2 – 0.0001 X1 X2 – 0.0001 X22 (R2 = 0.7033, P < 0.01) (a); Y = 14.5295 + 0.1748 X2 – 0.0001 X1 X2 – 0.0002 X22 (R2 = 0.8571, P < 0.01) (b); where Z is WUE/ RUE (kg mm–1 ha−1), X is GP (mm), and Y is the N application rate (kg ha−1).
Shang, 2014), and reduces the increasing production effect (Ren et al., 2010; Payero et al., 2009; Teixeira et al., 2014). Moreover, the reduction of rainfall in 2012–2016 is another reason for dry matter and yield are decreasing annually. The mismatch between water availability and the application of fertilizer supply had a negative effect on the water–fertilizer interaction. 5. Conclusions Five years consecutive experiment showed that high fertilizers levels (> 300 kg ha–1) can cause excessive consumption of soil moisture. In the wet year, the low fertilizer level achieved the best yield and WUE, whereas the medium fertilizer level obtained the highest yields and WUE in the normal years and the dry year. Regression analysis showed that the application of N at 265.0 kg ha–1 with P2O5 at 132.5 kg ha–1 could obtain the highest yield and WUE under RFRH farming. The RFRH system can effectively coordinate the relationship between water and fertilizer, promote the absorption and utilization of fertilizers by crops, and provide an effective solution to the problem of over-application of chemical fertilizers in the semi-arid regions of the Loess Plateau, China.
Fig. 5. The relationship between N fertilizer application rate and evapotranspiration (ET) under ridge and furrow rainfall harvesting system.
2011). Numerous studies have shown that there is a parabolic relationship between the application of nitrogen fertilizer and the crop yield, where the grain yield declines when the nitrogen application rate exceeds a certain threshold (Timsina et al., 2001; Morell et al., 2011; Lian et al., 2016). Under the RFRH system, growing period rainfall, fertilizer rates, and their interaction effect on the maize yield (R2 = 0.9101, P < 0.001) and WUE (R2 = 0.7033, P < 0.01) (Figs. 3 and 4). When the fertilizer rate reached 265.0 kg ha–1, the maize yield reached the maximum, and when the fertilization amount reached 430 kg ha–1, the WUE began to decline. In China, based on a large number of fields in the early stages, it was shown that the best fertilization rate for yield (about 8.50 t ha–1) is 180–225 kg ha–1 (Guo et al., 2008; Zhang et al., 2007a, b). Our result is slightly higher than previous studies. This indicates that the RFRH system can effectively coordinate the relationship between water and fertilizer, promote the absorption and utilization of fertilizers by crops, improves crop yield and water use efficiency.
Funding This work was supported by the Fundamental Research Fund for Universities and Colleges (2452017051 and 2452016014), the Project Supported by Natural Science Basic Research Plan in Shaanxi Province of China (2018JQ3024), China Support Program for Dry-land Farming in the 12th 5-year plan period (2012BAD09B03, 2015BAD22B02), the National High-Tech Research and Development Programs of China (“863 Program”) for the 12th 5-Year Plans (2013AA102902), the Program of Introducing Talents of Discipline to Universities (B12007), the China Postdoctoral Science Foundation funded project (2016M602870), and the Agricultural Science and Technology Innovation and Key Project of Shaanxi Province (2015NY115).
4.4. Inhibition of excessive fertilization Acknowledgements Under the high fertilizers rate, the yields, WUE and RUE significantly show decreased trend with increasing the fertilizers rates. (Tables 4 and 5). From 2014 onwards, the growth of maize in high fertilizer treatment of was suppressed during the sowing-V4 period, and this inhibition continued until physiological maturity in 2015–2016 (Fig. 1). This results are mainly caused by the application of fertilizer in successive years may have increased the nitrogen concentration in the soil solution to cause physiological drought by inhibiting water absorption via the root system (Zhong and Shang, 2014), thereby affecting the dry matter, yield, and water use efficiency of maize (Zhong and
The manuscript was reviewed and approved for publication by all authors. Zhikuan Jia and Peng Zhangy conceived and designed the experiments. Yan Zhang, Qian Ma, Xiaolong Ren, Lefeng Sun, Shahzad Ali and Donghua Liu performed the experiments. Yan Zhang, Peng Zhang and Zhikuan Jia analyzed the data. Yan Zhang, Peng Zhang wrote the paper. Yan Zhang, Peng Zhang and Zhikuan Jia reviewed and revised the paper. Zhikuan Jia and Shahzad Ali corrected the English language for the paper. We are also grateful to Nie Junfeng, Yang Baoping and Ding Ruixia for help during experimental period. 420
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Appendix A. Supplementary data
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