Effect of irrigation and fertilization regimes on grain yield, water and nitrogen productivity of mulching cultivated maize (Zea mays L.) in the Hetao Irrigation District of China

Agricultural Water Management 232 (2020) 106065

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Effect of irrigation and fertilization regimes on grain yield, water and nitrogen productivity of mulching cultivated maize (Zea mays L.) in the Hetao Irrigation District of China

T

Changjian Lia,b, Yunwu Xionga,b,*, Zhen Cuia,b, Quanzhong Huanga,b, Xu Xua,b, Wenguang Hanc, Guanhua Huanga,b a b c

Chinese-Israeli International Center for Research and Training in Agriculture, China Agricultural University, Beijing 100083, PR China Center for Agricultural Water Research in China, College of Water Resources & Civil Engineering, China Agricultural University, Beijing 100083 PR China Yongji Experimental Station, Bureau of the Hetao Irrigation District, Bayannaoer, 015000, PR China

A R T I C LE I N FO

A B S T R A C T

Keywords: Drip irrigation Border irrigation Crop water productivity Partial factor productivity of nitrogen

Irrigation and fertilizer management are essential for sustainable development of agriculture in the arid and semiarid regions. In order to obtain high yield production, over irrigation and fertilization are frequently conducted by the farmer which results in a series of environmental problems in particular in the shallow groundwater areas. In this paper, two-year field experiments were conducted to investigate the effect of irrigation and fertilization regimes on grain yield, water and nitrogen productivity of mulching cultivated maize (Zea mays L.) in the Hetao Irrigation District of China. Two irrigation methods, i.e., drip and border irrigation, with different schedules were manipulated in silt loam soil. The border irrigation included two/three different water levels and drip irrigation was triggered by a tensiometer located at a depth of 25 cm with different matric potentials (−15, −25 and −35 kPa). Three different nitrogen fertilization levels (350, 250 and 150 kg ha−1) were applied under drip irrigation controlled by the matric potential of −25 kPa. Soil water storage variation indicated that the active root zone concentrated at a depth of 35−60 cm in the border irrigated plots and 25−45 cm in the drip irrigated plots. Around 16 % of irrigated water (71 out of 450 mm) and 18 % of supplied nitrogen fertilizer (64 out of 350 kg ha−1) were percolated into deeper zone for the farmer’s irrigation and fertilization schedules. Border irrigation water reduced from 450 to 315 mm could decrease the deep percolation without yield reduction. Almost no deep percolation was detected in drip irrigation for three different matric potential controls. The highest yield, water and nitrogen productivity obtained from the drip irrigated plots triggered by matric potential of −15 kPa. Considering yield, water and nitrogen productivity, environmental factors and farmer’s net-profit, drip irrigation at the matric potential of −15 kPa with 250 kg ha−1 nitrogen fertilizer or border irrigation of 315 mm is recommended for mulching cultivated maize in silt loam soil in the Hetao Irrigation District. The nitrogen fertilizer schedule in border irrigation is desirable for optimal application.

1. Introduction Maize (Zea mays L.) is one of the main field crops throughout the world. Global maize production was around 1.1 × 1012 kg in 2016 (Yang et al., 2017). China is one of the top three (the other two countries are US and Brazil) maize production and consumption countries, which produced approximately 2.6 × 1011 kg and consumed 2.3 × 1011 kg in 2017. The maize cultivated area in China was around 4.2 × 107 ha with a wide variation of climate and geography (Statistics, 2018). The Hetao Irrigation District (HID), the third largest irrigation district in China, is one of the major maize production regions. The

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maize planting area was around 2.6 × 105 ha in the HID which accounted for 35.6 % of the crop planting area (around 7.3 × 105 ha) in 2017. The annual maize production in the HID is around 3.0 × 109 kg. The HID is located in the arid and semiarid region of China with a temperate continental climate condition. The annual precipitation is around 160 mm, but the annual potential evaporation is around 2300 mm (Feng et al., 2005; Ren et al., 2016). The large gap between the precipitation and evaporation implies that irrigation is essential for maize production and agriculture development. Currently, water used for irrigation in the HID is mainly diverted from the Yellow River (annual 4.4 × 109 m3) and the irrigation method is basin irrigation for

Corresponding author at: Chinese-Israeli International Center for Research and Training in Agriculture, China Agricultural University, Beijing 100083, PR China. E-mail address: [email protected] (Y. Xiong).

https://doi.org/10.1016/j.agwat.2020.106065 Received 26 April 2019; Received in revised form 30 January 2020; Accepted 31 January 2020 0378-3774/ © 2020 Elsevier B.V. All rights reserved.

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provide desirable growth environment for maize in sandy loam soil, and maize suffered from water-stress when it was irrigated 50 % and 25 % of field capacity at a daily interval. Kang et al. (2000) found that the yield of maize was not significantly reduced when the plant suffered from water-stress (67 % full irrigation) at the seeding stage for loamy soil in the Loess Plateau of China, but it reduced by 30 % when waterstress happened at the stem-elongation stage. Wang et al. (2017) found that water use efficiency of maize enhanced by 5 % in moderate waterstress (60 % of soil water holding capacity) in sandy loam soil under the humid tropical savannah climate compared with full irrigation (100 % of soil water holding capacity). El-Wahed and Ali (2013) found that irrigation at 85 % of crop evapotranspiration (with 20 t ha−1 farmyard manure mulching) could obtain the same maize yield as 100 % crop evapotranspiration in sandy soil under drip irrigation, while grain yield and irrigation water use efficiency for irrigation at 70 % of crop evapotranspiration reduced by 68 % and 18 %, respectively. Therefore, the impact of reduced irrigation on the yield and water productivity varies with soil, climate and growth stage of maize. In addition to irrigation, fertilization is another critical factor to ensure high crop production. Fertilizer in particular nitrogen is frequently excessively supplied by the farmer aiming at high yield (Burney et al., 2010; Huang et al., 2001; Sylvester-Bradley and Kindred, 2009; Xu et al., 2017). The annual nitrogen fertilizer application reaches 600 kg ha−1 in some area of China, and around 45–50 % of nitrogen fertilizer is detected to be leached into groundwater (Ju et al., 2004). In the HID, nitrogen use efficiency is extremely low (35 %) resulting from the low-efficient basin irrigation and excessive fertilization, thus nonpoint source pollution is serious and the sustainability of agriculture and ecology is threatened. Therefore, to achieve the green and sustainable maize production as well as agriculture development, it is essential to understand the effect of irrigation and fertilization regimes on grain yield, water and nitrogen use efficiency of maize and propose proper irrigation and fertilization regimes in the HID. Despite a large amount of research conducted on the effect of irrigation and fertilization regimes on crop production in the last few decades (He et al., 2018; Miyauchi et al., 2012; Tiwari et al., 2003; Wang et al., 2011), the optimum irrigation and fertilization differs with the crop, soil and climate. The purposes of this paper are: 1) to investigate the impact of irrigation and fertilization regimes on soil water conditions and growth of maize in silt loam; (2) to quantify the fate of nitrogen under different irrigation and fertilization regimes in the arid region; (3) to analyze water-nitrogen productivity under different irrigation and fertilization regimes and propose a proper application strategy for maize production in the HID.

most areas. The irrigation depth is 400−500 mm during the maize growing season and 220−260 mm for post-harvest autumn irrigation (Liu et al., 2016). Due to a large amount of water from irrigation, groundwater is shallow and the depth of water table varies from 0.5 to 3 m during the growing season (Zhang et al., 2017b). In addition, excessive fertilizer is frequently supplied to obtain high yield production. The average supplied nitrogen fertilizer is around 350 kg ha−1 in the HID. The use efficiency of nitrogen is reported to be only 35 % in the HID (Du et al., 2011), thus a large fraction of fertilizer is leached into the drainage ditches and groundwater. The drainage water flows to the downstream of the HID and is pumped into the Wuliangsuhai Lake, which results in a series of environmental problems such as eutrophication and swamping (Guo et al., 2015). Therefore, proper irrigation and fertilization regimes are desired for improving water-fertilizer productivity and the sustainable development of agriculture and ecology in the HID. Diversely effective water and fertilizer use strategies and techniques have been proposed for maize production, such as mulching cultivation, reduced irrigation and drip irrigation. Mulching with polypropylene film or crop residue is widely used for the field and cash crops due to the benefit of increasing soil accumulated temperature, reducing soil evaporation and hindering weed growth (Chakraborty et al., 2010; Romic et al., 2003; Zhang et al., 2017a, 2012). The mulching cultivation is frequently combined with basin irrigation in the HID where the cultivation pattern of maize is narrow-wide alternation model. Maize is usually sowed inside the mulched plastic film. These types of cultivation and irrigation may limit the availability of water and fertilizer to plants thus reducing the water-fertilizer productivity. Drip irrigation provides the required quantity of water directly to the root zone of plants. Drip irrigation can minimize the surface runoff and deep percolation thus promoting water and fertilizer use efficiencies (Singandhupe et al., 2003). Drip irrigation with film mulching, which combines the advantages of mulching cultivation and drip irrigation, becomes widely accepted in the arid and cold regions of China (Wang et al., 2011; Zhang et al., 2018). The application of drip irrigation with film mulching is mainly for cash crops (Vázquez et al., 2006; Wang et al., 2014; Zhang et al., 2017b) and partially for maize and other cereals (Zhang et al., 2018). Proper irrigation scheduling (frequency, duration of watering and quantity of water) is an important aspect of irrigation water management. Irrigation schedule of maize may be estimated through the reference crop evapotranspiration, soil moisture and potential, and pan evaporation (Cavero et al., 2008; Lv et al., 2011; Reddy et al., 1983). Soil water content or matric potential is frequently used as the criterion for triggering irrigation. Soil matric potential is a realistic criterion for irrigation scheduling as it constitutes the force with which water is held by soil matrix and measures soil water availability to the crop. Optimum soil matric potential can build a favorable water and nutrition environment for plant. Previous research showed that high yield of maize could be obtained when soil matric potential in the plow layer (15 cm) was maintained below 33.3 kPa in sandy loam soil (Rhoads and Stanley, 1973). Kang et al. (2010) found that soil matric potential above −20 kPa at a depth of 20 cm could be used as an indicator for maize irrigation (subsurface drip irrigation) in silt soil under the temperate semi-humid monsoon climate. A large amount of research on drip irrigation scheduling was conducted in the North of China (Kang et al., 2004; Wan et al., 2010; Yuan et al., 2001), where the authors established the drip irrigation schedule using soil matric potential at a depth of 20 cm for different crops and soils. Irrigation schedule design should consider the variation of soil, climate and crop species. Therefore, it is essential to investigate drip irrigation management for the specific crop in different regions. In the last few decades, reduced irrigation has been proposed with consideration of water productivity in water scarcity regions (Igbadun et al., 2008; Mbagwu and Osuigwe, 1985). Mbagwu and Osuigwe (1985) reported that irrigation 75 % of field capacity every day may

2. Materials and methods 2.1. Experimental site description Field experiments were conducted at the Fenzidi Experimental Station in the HID of Inner Mongolia in 2016 and 2017 (latitude 41°09′ N, longitude 107°39′ E, altitude 1031 m, Fig. 1). Climate condition in the study area is semi-arid temperate continental climate characterized by low rainfall and high evaporation. Annual rainfall is around 160 mm with marked seasonality and the potential evaporation is 2300 mm. The mean annual temperature is 6.8 °C and the annual total sunshine duration is 3230 h. Monthly meteorological data during the growing season of maize are presented in Table 1. The daily reference evapotranspiration (ET0) was calculated through the FAO56 Penman-Monteith equation (Allen et al., 1998). Soil at a depth of 0−100 cm was sampled and analyzed using the Mastersizer 2000 laser diffraction particle size analyzer. Texture analysis indicated that soil at a depth of 0−70 cm was silt loam and loam in 70−100 cm according to the US textural classification triangle. Table 2 presents the detailed physical and chemical properties of soil in the study site. Groundwater depth varied from 0.7 to 2.3 m in the 2

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Fig. 1. Location of experimental site in the Hetao Irrigation District of China.

in 2016, and 450, 315 and 180 mm in 2017 (Table 3). The amount of irrigation was measured by the water meter in each treatment. The irrigation depth of 450 mm (irrigation 3–4 times) in growing season was commonly supplied by local farmer. Three irrigation events at the jointing, tasseling and milking stages were usually adopted. The irrigation depth was about 150 mm each time. The timing for border irrigation was consistent with that of the local farmer. Drip irrigation was triggered by a tensiometer located at a depth of 25 cm with three different matric potentials (−15, −25 and −35 kPa). The detailed irrigation schedule of each treatment is shown in Fig. 4. The irrigation depth, I (mm), for each drip irrigation event was calculated by

Table 1 Monthly meteorological data at the experimental site during the maize growing season in 2016 and 2017. Year

Meteorological factors

May

June

July

August

September

2016

Temperature (°C) Relative humidity (%) Wind speed (m s−1) Rainfall (mm) ET0 (mm day−1) Temperature (°C) Relative humidity (%) Wind speed (m s−1) Rainfall (mm) ET0 (mm day−1)

16.1 33.8 2.9 5.15 4.1 21.3 37.7 3.7 4.2 6.0

19.3 50.6 2.6 8.9 4.7 21.5 54.1 3.3 17.4 5.3

22.9 68.4 2.4 36.8 5.1 24.2 67.9 2.4 26.2 4.8

22.9 65.7 2.4 52.1 5.0 21.6 61.5 2.4 6.2 4.3

16.2 61.3 2.4 3.2 4.3 18.4 50.9 2.7 10.2 3.5

2017

I = AH (0.95θ fc − θ mp) ρ η

(1)

where A is the experimental plot area (m2); H is the irrigation design rooting depth (m); θfc is the field capacity (m3 m−3); θmp is the soil water content corresponding to matric potential before irrigation (cm3 cm−3); ρ is the wetting ratio of drip irrigation, in this study wetting ratio is 0.65; η is the irrigation water use efficiency of drip irrigation (0.95 according to the Technical Code for Micro-Irrigation Engineering). Roots of maize are mainly distributed at the depth of 0−60 cm and 90 % concentrated in the 0−40 cm (Nicoullaud et al., 1994). Thus irrigation design rooting depth was set to be 20 cm in the seeding stage and 40 cm in the other stages. The seasonal irrigation depth of each treatment is tabulated in Table 3. Three nitrogen fertilization levels including 350, 250 and 150 kg ha−1 were applied for the drip irrigation treatments triggered by matric potential of −25 kPa. 250 kg ha−1 nitrogen fertilizer was supplied for the other drip irrigation treatments (Table 3). The nitrogen fertilization for each border irrigated plot was 350 kg ha−1 which was referred to the farmer. Fertilization prior to seeding was consisted of 135 kg ha−1 of phosphorus fertilizer (diammonium phosphate, P = 50 %) and 60 kg

growing season which was influenced by the irrigation of surrounding farms (Fig. 2). The test maize (Zea mays L.) was the cultivar Zeyu No.19 which was widely planted in the HID. The maize was sowed on May 15th and harvested on September 26th in two experimental years. The planting pattern for maize was wide-narrow rows with a width of 70 and 50 cm (Fig. 3). The wide row was mulched with polypropylene film with a breadth of 90 cm. The maize seedlings were sowed close to the border of wide rows with plant spacing of 30 cm. The planting density was 67,500 plants per hectare.

2.2. Irrigation and fertilization treatment Two irrigation methods, i.e., drip irrigation and border irrigation, with different schedules were implemented in 2016 and 2017, respectively. The irrigation depth for border irrigation was 450 and 315 mm Table 2 Physical, chemical and hydrological properties of soil profile in experimental site. Soil depth (cm)

Clay (%)

Silt (%)

Sand (%)

Soil texture

Bulk density (g cm−3)

Field capacity (cm−3 cm-3)

Wilting point (cm

0-25 25-50 50-70 70-100

14.0 4.2 17.4 11.5

72.6 59.8 80.3 43.7

13.4 36.0 2.3 44.8

Silt loam Silt loam Silt loam Loam

1.44 1.39 1.38 1.53

0.35 0.26 0.39 0.28

0.08 0.03 0.10 0.07

3

3

cm−3)

EC (μS cm−1)

pH

331 226 224 223

7.9 8.1 8.1 8.2

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Fig. 2. Daily variation of groundwater depth during the growing season of maize.

ha−1 potassium fertilizer (potassium oxide, K = 50 %) for all treatments. The nitrogen fertilizer supplied prior to seeding and supplemental in different growing stages is presented in Table 3. The nitrogen fertilizer was dissolved in water and transported to root zone (fertigation) in drip irrigated plots. For the plots with border irrigation, nitrogen fertilizer was uniformly spread between the polypropylene films prior to each irrigation event and then dissolved into irrigated water. The experimental design was a randomized complete block with three replicates to minimize the influence of spatial heterogeneity. Each plot had a size of 96 m2 (4.8 m × 20 m).

samples were collected using an auger every 10 cm for the 20 cm upper soil and every 20 cm from 20 to 100 cm in the middle of wide and narrow rows. Soil was sampled every 7 days in 2016 and 10 days in 2017. Three replicates were taken for each treatment. Soil solution was extracted from the mixture of soil and 2 mol L−1 KCl solution at a ratio of 1:5. The available nitrogen (ammonium and nitrate) in the soil were measured within 48 h using a continuous flow analyzer (Auto Analyzer 3, SEAL ANALYTICAL Inc, German). The deep percolated soil solution was collected using a steel bucket with a diameter of 40 cm (called leakage bucket). The bucket was composed of a 100 cm cylinder and a 20 cm conical-shape container in the bottom. The 100 cm cylinder of bucket was filled with soil at the same bulk density as in the field, and the conical part was emptied to collect the percolated soil solution (Fig. 3). Percolated solution was pumped after each irrigation and precipitation event, and the volume of water as well as the concentration of inorganic nitrogen was measured.

2.3. Measurements Leaf area index (LAI) of maize was measured by the ceptometer (AccuPAR L80; Decagon Devices, Pullman, WA). Three plants were cut off in each plot to measure the aboveground biomass accumulation prior to harvest. The plants were first dried at 105 °C for 1 h to inactivate enzyme and then dried to constant weight at 75 °C. Thirty plants were sampled in each plot to evaluate the yield as well as its components (including the traits of ears per hectare, kernels per ear, ear weight, grain yield per plant and the 100-kernel weight of maize). The grains with water content of 14 % were considered as the standard yield of maize. Soil water content was measured by the gravimetric method. Soil

2.4. Calculation and data analysis The actual evapotranspiration (ETa) was estimated through soil water balance equation

ETa = Pe + I + ΔS − R − F

(2)

where Pe is the precipitation in the growing season (mm); △S is the

Fig. 3. Schematic illustration of maize cultivation pattern in drip (a) and border (b) irrigated plots and leakage bucket (c). 4

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Table 3 Irrigation and fertilization treatment design and seasonal irrigation depth of each treatment. Year

Treatment

Fertilization (kg ha−1)

Irrigation Irrigation method

2016

2017

DI1-250 DI2-350 DI2-250 DI2-150 DI3-250 BI1-350 BI2-350 DI1-250 DI2-350 DI2-250 DI2-150 DI3-250 BI1-350 BI2-350 BI3-350

Trigger point (kPa)

Drip Drip Drip Drip Drip Border Border Drip Drip Drip Drip Drip Border Border Border

15 25 25 25 35 — — 15 25 25 25 35 — — —

Seasonal irrigation depth (mm)

320 260 260 260 200 450 315 234 176 176 176 175 450 315 180

Phosphorus

Potassium

Nitrogen

Prior to seeding

Prior to seeding

Prior to seeding

Jointing stage

Tasseling stage

Milking stage

Total of nitrogen

135 135 135 135 135 135 135 135 135 135 135 135 135 135 135

60 60 60 60 60 60 60 60 60 60 60 60 60 60 60

75 105 75 45 75 105 105 75 105 75 45 75 105 105 105

75 105 75 45 75 105 105 75 105 75 45 75 105 105 105

50 70 50 30 50 70 70 50 70 50 30 50 70 70 70

50 70 50 30 50 70 70 50 70 50 30 50 70 70 70

250 350 250 150 250 350 350 250 350 250 150 250 350 350 350

no great variation for soil water content in soil layer of 70−90 cm because of less rainfall and the controlled irrigation depths, thus soil water content between measurements was linearly interpolated using the measured soil water contents. The cumulative leached nitrogen was calculated by

change of soil water storage at a depth of 0−80 cm (mm); R is the surface runoff (mm); F is the vertical soil water flux in bottom boundary (positive means deep percolation and negative means compensation by capillary rise). No runoff was detected during the growing season; thus R was zero. The vertical soil water flux F at a depth of 80 cm was estimated by Darcy’s equation using soil water content in 60−80 cm and 80−100 cm. The vertical water flux was calculated by the following equations

F = −K (θ)[

ψm,z 1 − ψm,z2 Z1 − Z2

− 1] 1

m 2

(4)

θ − θr 1 = θs − θr [1 + (α |ϕm|)n]m

(5)

⎟

⎜

1 1000

n

∑ i= 1

Ci × Vi A0

(6)

where M is the cumulative leachate N (kg ha−1); Ci is the concentration of nitrate in leached soil solution for each sampling event (mg L−1); Vi is the volume for each sampling event (L); A0 is the cross-sectional area of the leakage bucket (m2). Crop water productivity (CWP) is a quantitative term used to define the relationship between crop produced and the amount of water involved in crop production. Crop water productivity can be expressed in terms of actual evapotranspiration (CWPET) and in terms of the volume of supplied irrigation water (CWPIrrig), i.e.,

(3)

0.5 ⎡ θ − θr ⎞ ⎧ θ − θr ⎞ m ⎤ ⎫ K (θ) = Ks × ⎛ 1 − ⎢1 − ⎛ ⎥ ⎨ − θ θ θ r⎠ ⎝ s − θr ⎠ ⎦ ⎬ ⎝ s ⎣ ⎭ ⎩ ⎜

M=

⎟

where θ is the soil water content (cm3 cm−3); K(θ) is the hydraulic conductivity (cm day-1); Ks is the saturated hydraulic conductivity (cm day-1), Ks = 16.6 cm day-1; Z is soil depth (cm); ψm is the matric potential at depth of Z (cm); α, n, m, θr and θs are the parameters of van Genuchten model, and they are 0.01 cm-1, 1.46, 0.31, 0.42 cm3 cm−3 and 0.04 cm3 cm−3, respectively. Soil water content was converted to soil matric potential using the soil water characteristics curve Eq. (5). Both K(θ) and soil water characteristics curve were regressed using the soil particles distribution (Table 2) by the RETC. The vertical water flux was estimated daily using measured and interpolated data. There was

CWPET =

CWPIrrig =

Yield of maize ET a Yield of maize Irrigation depth

(7)

(8)

Partial factor productivity (PFP) is a useful measure of nutrient use efficiency in agriculture production. Partial factor productivity of nitrogen fertilizer (PFPn) was calculated by

Fig. 4. Cumulated irrigation depth in the maize growing season for different irrigation and nitrogen treatments in 2016 and 2017. 5

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Fig. 5. Variation of water storage in the soil profile with different irrigation and fertilization regimes in 2017: (a) border irrigation with 350 kg ha−1 nitrogen fertilizer, (b) drip irrigation with 250 kg ha−1 nitrogen fertilizer, and (c) drip irrigation with three different fertilization levels (150, 250 and 350 kg ha−1 nitrogen fertilizer).

PFPn =

Yield of maize The applied rate of nitrogen fertilizer

irrigation due to the large gap between two irrigation events, so roots extracted water in the deeper soil. In contrast, water content was higher in the upper zone in the drip irrigated plots, thus roots took water from the upper zone of soil. Therefore, the depth of water storage variation was higher in the drip irrigated plots than the border irrigated ones.

(9)

Net profit is an important indicator for crop production and agricultural activities. The components of cost included the investment of agricultural machinery for plough, sow and harvest, labour costs for field management, fertilizer, seed and pesticide, drip tape and water for irrigation. Only income from the sale of maize grain yield is considered as the benefits. The benefits are calculated from the current price and grain yield. Data were statistically analyzed by one-way ANOVA using the SPSS 20.0 (SPSS Inc., Chicago, USA). Least significant difference (LSD) was used to test the differences among experimental treatments at a significant level of P < 0.05.

3.2. Soil nitrogen leaching and residue Fig. 6 shows soil water and inorganic nitrogen cumulated leakage of 1 m soil horizon during the whole growing season for different treatments. Without exception, the cumulative leakage of nitrogen in the plots of border irrigation was much larger than those of drip irrigation. The cumulative percolation in plots of border irrigation varied from 35 to 71 mm. The largest irrigation depth of 450 mm (refers to the farmer’s irrigation) had around 70 mm deep percolation which accounted for 15.6 % of irrigated water. The reduced irrigation (315 and 180 mm) plots had percolation of 55 and 35 mm, which accounted for 17.4 % and 19.4 % of irrigation, respectively. The deep percolation of drip irrigation was only a few millimeters during the whole growing season and there was no significant (P > 0.05) difference among treatments. Thus deep percolation was trivial and could be neglected in the drip irrigated plots. Soil nitrogen was leached out of root zone with soil water percolation. The NO3−-N accounted for more than 96 % and dominated the content of inorganic nitrogen in the soil solution. The NH4+-N was less mobile because it was strongly adsorbed by the clay due to its positive charge. Thus the leaching of NH4+-N could be ignored. The cumulative leakage of NO3–N increased with the increase in irrigation depth (Fig. 6b). The cumulative leakage of NO3−-N in the border irrigation treatments was in the range of 21 to 64 kg ha-1. The largest cumulative leakage of NO3−-N was observed in 450 mm irrigation plots which accounted for 18 % of the nitrogen fertilization. Cumulative leakage of NO3−-N in reduced irrigation (315 and 180 mm) plots was around 50 and 21 kg ha-1 which accounted for 14 % and 6 % of the nitrogen fertilization, respectively. In contrast, the cumulative leakage of NO3−N was only 0.2-0.4 kg ha-1 in the drip irrigated plots which could be neglected. Hence drip irrigation can effectively minimize the leakage of nitrogen and reduce the risk of groundwater pollution.

3. Results 3.1. Soil moisture Fig. 5 illustrates the change of water storage in soil profile during the growing season. Different irrigation and fertilization regimes have different impacts on the variation of soil water storage. The change of soil moisture mainly concentrated at a depth of 35−60 cm in all plots of border irrigation. There was no evident difference in the change of water storage for different irrigation depth. In contrast, variation of soil moisture was mainly at a depth of 25−45 cm for all plots of drip irrigation. The change of soil water storage in drip irrigated plots varied with trigger matric potential, i.e., the plots with high trigger matric potential had less variation of soil water storage. The impact of nitrogen fertilizer on the change of water storage varied with the quantity of fertilizer supplied for the identical irrigation regime. The plots of 250 kg ha−1 nitrogen obtained the relatively small variation (around 70 mm), while there was no clear difference in the plots of 150 and 350 kg ha−1 nitrogen treatments (around 100 mm). The change of soil water storage is the balance of irrigation, precipitation, evaporation, percolation and root uptake, etc. Soil moisture affects the distribution of roots, and root distribution influences water uptake as well as water distribution. Soil in the upper zone was always dry in plots of border 6

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Fig. 6. Accumulation of percolated water and leached nitrogen (NO3−-N and NH4+-N) for different irrigation treatments in 2017 (a–c) border irrigation and (d–f) drip irrigation.

The NO3−-N residue in soil post-harvest of maize is shown in Fig. 7. Panels a–c show the residual NO3−-N in soil covered by polypropylene film, and panels d–f display the residual NO3−-N in inter-row. In general, the residual NO3−-N accounted for more than 85 % of the inorganic nitrogen in the soil profile. Thus, only the variation of NO3−-N in soil profile was analyzed. Initial soil nitrogen was around 22.5 mg kg1 and almost uniformly distributed in soil profile. For border irrigated plots, there was no evident difference in NO3−-N resident in the film covered area for different irrigation treatments. The residual NO3−-N decreased with soil depth in the inter-row area. The average soil NO3−N at a depth of 0−40 cm in the non-mulching area was around 95 mg kg-1, which was much larger than that in the film covered area (around 20 mg kg-1). In contrast, soil NO3−-N in the mulching area was higher than that in non-mulching area for the drip irrigated plots. In vertical profile, soil NO3−-N reduced with depth in the mulching area. But in the area without film, soil NO3−-N was almost uniformly distributed similar to the initial condition. The impact of nitrogen fertilizer on concentration of soil NO3−-N increased with the supplemental rate under the identical irrigation condition (matric potential of −25 kPa). The distribution of soil nitrogen was similar for two experimental years.

3.3. Plant growth and biomass production The leaf area index was used as an indicator to evaluate the growth of maize. Fig. 8 shows the LAI of maize under different irrigation and fertilization regimes. The LAI steadily increased before milking stage and then reduced at the maturity stage for all treatments. There was no evident difference in LAI prior to tasseling stage. For the border irrigated plots, relatively larger LAI was detected in the plots with larger irrigation depth. For the drip irrigated plots, the LAI slightly varied with irrigation depth and frequency as well as fertilizer applied. The larger LAI was detected in higher matric potential treatments under the same nitrogen fertilization condition after tasseling stage. For the identical irrigation condition (matric potential of −25 kPa), the LAI increased with nitrogen fertilizer application. The decrease of LAI was delayed around 10 days in 2016 due to the larger rainfall in August (Table 1). The dry aboveground biomass in the late maturity stage is presented in Fig. 9. Dry aboveground biomass varied with yearly irrigation depth under border irrigation condition. In general, large dry aboveground biomass obtained from the plots of high irrigation depth. For drip irrigation, the plots with high matric potential had significant larger dry 7

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Fig. 7. Residual NO3−-N in the soil profile post-harvest of maize for different irrigation and fertilization regimes (a–c) the NO3−-N at the wide inter-row with plastic film mulch and (d–f) the NO3−-N at the narrow inter-row without plastic film mulch.

treatment plots, which suggested that the treatment of 450 mm was over-irrigated. The influence of yield components (the kernel per ear, ear weight, grain yield per plant and 100-kernel weight) was consistent with the grain yield. For the identical drip irrigation treatment (matric potential of −25 kPa), grain yield slightly increased with application rate of nitrogen fertilizer. The kernel per ear, grain yield per plant and 100-kernel weight increased with the increase in nitrogen fertilizer, but the amount of ears per hectare was not significantly influenced. The CWPET of maize generally increased with trigger matric potential under the drip irrigation (Table 4). Significant differences (P < 0.05) were found in CWPET between two experimental years. The maximum CWPET of drip irrigated plots was 3.47 and 3.44 kg m−3 in 2016 and 2017, respectively. The CWPIrrig was generally inversely correlated to trigger matric potential. The maximum CWPIrrig of maize was 6.65 and 7.20 kg m−3 in 2016 and 2017, respectively. For the border irrigated plots, the CWPET and CWPIrrig decreased with increase in water amount. For identical drip irrigation, the effects of nitrogen fertilizer on CWPET and CWPIrrig varied with the experimental years. The PFPn of maize generally increased with the increase in irrigation quantity for both drip and border irrigation (Table 4). The maximum PFPn was 62.1 and 52.1 kg kg−1 for drip irrigated plots, and 41.9 and 36.4 kg kg−1 for border irrigated plots in 2016 and 2017, respectively. However, over-irrigation would not significantly improve the PFPn for border irrigated plots. The PFPn varied with the rate of

biomass (P < 0.05). The maximum dry aboveground biomass was around 510 and 470 g per plant in 2016 and 2017, respectively. No significant difference (P > 0.05) in dry aboveground biomass was found between the 250 and 350 kg ha−1 nitrogen treatments under the same irrigation condition (matric potential of −25 kPa). The difference of biomass between experimental years may be attributed to the variation of climate. 3.4. Grain yield, water and fertilizer productivity Grain yield of maize was significantly influenced by the matric potential controlled in the drip irrigation (Table 4). The grain yield ranged from 13.3 to 15.5 t ha−1 in 2016 and 10.6 to 13.0 t ha−1 in 2017, respectively. The highest grain yield obtained in the plots triggered by matric potential of −15 kPa. Table 5 presents the traits of yield components for different irrigation and nitrogen fertilizer treatments. The kernel per ear, ear weight and grain yield per plant increased with matric potential, but there was no significant difference in ears per hectare and 100-kernel weight. For border irrigation, grain yield varied with quantity of irrigation. The grain yield of 450 and 315 mm irrigation depth treatments increased by around 17 % compared with 180 mm. It indicated that the treatment of 180 mm was deficient in irrigation, and the plant suffered from water-stress to certain extent. But no significant difference was observed between 450 and 315 mm 8

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Fig. 8. Leaf area index (LAI) of maize for different irrigation and fertilization regimes during 2016 (a–c) and 2017 (d–f) crop cycles.

yield. Thus only proper fertilization can promote both yield and fertilizer use efficiency.

nitrogen fertilizer, i.e., the higher PFPn was obtained in the lower nitrogen fertilization plots. The PFPn of 150 kg ha−1 nitrogen treatment increased by 113 % and 107 % compared with 350 kg ha−1 nitrogen treatment. Low nitrogen fertilization improved PFPn but reduced grain

Fig. 9. Dry aboveground biomass of maize for different water and fertilizer treatments in 2016 (a–c) and 2017 (d–f). 9

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Table 4 Grain yield, actual evapotranspiration (ETa), crop water productivity in terms of actual evapotranspiration (CWPET) and in terms of the volume of supplied irrigation water (CWPIrrig), partial factor productivity of nitrogen (PFPn), and net profit analysis for different irrigation and nitrogen fertilizer treatments (mean ± standard deviation). Year

Treatment

ETa (mm)

Yield (t ha−1)

CWPET (kg m−3)

CWPIrrig (kg m−3)

PFPn (kg kg−1)

Net profit (×104 CNY ha−1)

2016

DI1-250 DI2-250 DI3-250 DI2-350 DI2-150 BI1-350 BI2-350 DI1-250 DI2-250 DI3-250 DI2-350 DI2-150 BI1-350 BI2-350 BI3-350

447.2 424.6 390.7 442.1 396.7 600.3 518.5 378 372.5 354.25 397.3 343.2 520.6 401.4 305.1

15.5 ± 0.5 14.5 ± 0.5 13.3 ± 0.4 15.0 ± 0.1 13.8 ± 0.5 14.7 ± 0.9 13.7 ± 0.2 13.0 ± 0.2 11.8 ± 0.1 10.6 ± 0.1 12.7 ± 0.3 11.3 ± 0.1 12.7 ± 0.1 12.7 ± 0.1 10.9 ± 0.2

3.47 ± 0.12 3.42 ± 0.12 3.41 ± 0.11 3.40 ± 0.02 3.47 ± 0.12 2.45 ± 0.15 2.63 ± 0.03 3.44 ± 0.01 3.17 ± 0.02 3.00 ± 0.02 3.19 ± 0.08 3.28 ± 0.03 2.45 ± 0.02 3.17 ± 0.02 3.59 ± 0.08

4.85 ± 0.17 c 5.58 ± 0.20 de 6.65 ± 0.23 f 5.79 ± 0.03 e 5.29 ± 0.19 d 3.26 ± 0.2 a 4.34 ± 0.05 b 5.56 ± 0.01 e 6.70 ± 0.04 b 6.08 ± 0.03 d 7.20 ± 0.18 a 6.39 ± 0.06 c 2.83 ± 0.03 g 4.04 ± 0.02 f 6.09 ± 0.14 d

62.1 ± 2.1 58.0 ± 2.1 53.2 ± 1.9 43.0 ± 0.3 91.7 ± 3.2 41.9 ± 2.6 39.0 ± 0.5 52.1 ± 0.7 47.2 ± 0.3 42.6 ± 2.0 36.2 ± 0.9 75.0 ± 6.8 36.4 ± 3.2 36.4 ± 1.6 31.3 ± 0.7

1.48 ± 0.07 1.34 ± 0.08 1.18 ± 0.07 1.38 ± 0.01 1.27 ± 0.07 1.47 ± 0.14 1.35 ± 0.02 1.52 ± 0.01 1.31 ± 0.01 1.10 ± 0.01 1.43 ± 0.06 1.26 ± 0.02 1.56 ± 0.02 1.60 ± 0.01 1.32 ± 0.04

2017

a ab c a bc ab bc a c f b d b b e

a a a ab a b b b d e d c f d a

b c d e a e e b c d e a e e f

a ab c ab bc a ab b d f c e ab a d

CNY is the abbreviated of Chinese Yuan.

4. Discussion

In contrast, little deep percolation (around 0.6 %) was observed during the growing season in drip irrigated plots where the maximum irrigation design rooting depth was 40 cm (Fig. 6). The results agree with the findings of Kang et al. (2012), who have measured the deep percolation under different matric potential controlled drip irrigation and found that the proportion of deep percolation is small for all treatments (range from 0.4 % to 3.4 %). Nitrogen is leached out of the root zone with deep percolation. The variation tendency of nitrogen leakage is consistent with deep percolation of soil solution (Fig. 6). The result agrees with earlier studies conducted by Gheysari et al. (2009) and Jia et al. (2014) who have found that the nitrogen leakage increases due to the large amount of irrigation under the same application rate of nitrogen fertilizer. Nitrogen leakage is an important factor for non-point source pollution in shallow groundwater area. The average nitrogen fertilizer application is around 350 kg ha−1 in the HID. The measured leakage of nitrogen is around 64 kg ha−1 in growing season under the border irrigation of 450 mm (Fig. 6), which indicates that 18 % of supplied nitrogen is leached out of root zone. So the estimated annual leaching of nitrogen is 1.8 × 107 kg from the maize field on the basis of planting area. As groundwater table is shallow, the nitrogen is directly leached into the groundwater and drainage ditches. It is noted that the leaching of nitrogen is estimated from the leakage bucket where the reuse of leached soil solution through capillary rise is not considered. The drainage water with nitrogen flows to the downstream of the HID and is pumped into the Wuliangsuhai Lake (the largest freshwater lake in the Yellow River basin). The measured input of nitrogen to the lake is 2.7 × 106 kg

The agro-ecosystem in the arid and semiarid region is vulnerable due to the scarcity of water resource and soil salinity. Excessive irrigation and nitrogen fertilizer are frequently applied by the farmer in order to obtain high-yield production. Thus a large amount of nitrogen fertilizer either remains in the soil profile or leaches into groundwater or drainage ditches, which has the potential to result in a series of environmental problems such as the desertification and degradation of farmland, pollution of groundwater in the shallow groundwater region, and eutrophication and swamping of wetland in the downstream of catchment. Border irrigation is widely used in the HID. The average irrigation depth is 110−150 mm each time which is much larger than the storage of soil and crop requirement. The measured deep percolation was around 70 mm accounting for 16 % of total irrigation, which resulted in the rise of groundwater table (the depth is less than 1 m, Fig. 2). While the deep percolation of soil water in plots irrigated 315 and 180 mm reduced by 22.5 % and 50.7 % compared with the irrigation plots of 450 mm. The planting area of maize is around 2.8 × 105 ha in the HID, so approximately 2.0 × 108 m3 water (around 5 % of total diversion from the Yellow River) is lost every year through deep percolation in maize field under border irrigation. It is noted that this estimation is just a rough calculation without consideration of soil spatial heterogeneity and the reuse of percolated water. Deep percolation is correlated with ponding time of irrigation water, and generally long pounding time results in high deep percolation (Bethune et al., 2008).

Table 5 Yield components of maize for different irrigation and nitrogen fertilizer treatments (mean ± standard deviation). Year

Treatment

Ears per hectare

Kernel per ear

Ear weight (g)

Grain yield (g plant−1)

100-Kernel weight (g)

2016

DI1-250 DI2-250 DI3-250 DI2-350 DI2-150 BI1-350 BI2-350 DI1-250 DI2-250 DI3-250 DI2-350 DI2-150 BI1-350 BI2-350 BI3-350

69728 67500 67500 69728 67500 69728 67500 67500 67500 67500 67500 67500 67500 67500 67500

673 ± 36 650 ± 33 611 ± 13 674 ± 36 642 ± 35 694 ± 17 601 ± 19 708 ± 51 636 ± 13 600 ± 17 686 ± 37 624 ± 23 669 ± 22 679 ± 26 608 ± 25

286.4 ± 18.4 b 265.2 ± 11.5 ab 244.9 ± 12.2 a 290.5 ± 17.1 b 245.8 ± 9.0 a 281.5 ± 31.5 b 272.5 ± 6.8 ab 327.3 ± 16.2 b 280.7 ± 7.7 a 268.7 ± 16.9 a 307.8 ± 11.2 b 269.9 ± 8.4 a 312.9 ± 2.1 b 316.7 ± 9.7 b 267.7 ± 6.0 a

234.9 ± 14.7 b 220.6 ± 7.1 ab 203.0 ± 11.3 a 242.3 ± 15.1 b 205.1 ± 4.8 a 235.0 ± 27.4 b 227.0 ± 7.9 ab 201.0 ± 11.2 a 182.2 ± 5.4 bc 164.3 ± 12.0 d 192.8 ± 10.7 ab 160.9 ± 7.4 d 203.5 ± 5.1 a 202.5 ± 21.4 a 172.0 ± 9.8 cd

37.6 ± 0.4 36.7 ± 0.2 35.8 ± 0.7 37.9 ± 1.8 35.1 ± 1.1 36.0 ± 2.4 35.5 ± 0.3 40.5 ± 0.9 39.6 ± 0.7 40.6 ± 0.9 41.4 ± 0.9 39.2 ± 0.9 41.4 ± 0.9 40.4 ± 1.3 39.2 ± 0.3

2017

a ab b a ab a b a bcd d ab cd abc ab d

10

ab ab ab b a ab a ab a ab b a b ab a

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drip irrigation with film mulching triggered by matric potential of −15 kPa and 250 kg ha-1 nitrogen fertilization is considered an acceptable irrigation and fertilization strategy for maize planting in silt loam soil of the HID. If drip irrigation is not available, border irrigation of 315 mm is recommended according to the experiments. Unfortunately, we didn’t conduct border with different fertilization treatment. So the recommendation for fertilization regime is desirable for the future research under different border irrigation schedules.

annually (Liu et al., 2007), and the total nitrogen from agricultural sector accounts for 51 % of the total load (Guo et al., 2015). Input of nitrogen causes the eutrophication and swamping of Wuliangsuhai Lake. Reduction of irrigation and nitrogen fertilization is one of the effective ways to reduce the risk of eutrophication and swamping of Wuliangsuhai Lake. The leaching of nitrogen (50 and 21 kg ha−1) reduces by 20 % and 67 % when irrigation depth decreases from 450 mm to 315 and 180 mm, respectively. Thus the annual nitrogen leaching from maize field can reduce by 4.0 × 106 kg if the reduced irrigation (315 mm) is carried out instead of traditional border irrigation. Almost no deep percolation is observed from the drip irrigated plots triggered by different matric potential which has demonstrated the reduction of non-point source pollution risk. In addition to the impact on the environment, plant growth and yield are great concern to the grower. Irrigation is the main driving factor affecting water and nutrient dynamics in the root zone. The distribution of soil water determines root distribution, and inversely the root development influences on water and nutrient uptake which translates into biomass, LAI and grain yield (Guan et al., 2014; Kang et al., 2000). Drip irrigation can keep more water and nutrients in the root zone. Therefore, more available water and nutrients are absorbed by maize plants, and increase crop yield. However, plant growth is affected by many factors including soil moisture, nitrogen content, aeration and temperature. Optimal soil matric potential can create favorable soil water, fertilizer, gas conditions, and promote crop growth. In contrast, a large amount of water and fertilizer is leached out of root zone in border irrigation that may cause water- and nutrients-stress and eventually reduce yield. In addition, the large gap between two irrigation events may result in water-stress of plants and inhibit growth and yield production. Water and fertilizer productivities are critical indicators to evaluate water and fertilizer management. In crop systems, water productivity is used to characterize the relationship between crop production and water consumption. Crop water productivity of drip irrigation treatments is much higher than that of border irrigated plots (Table 4). Drip irrigation enhances crop water productivity through the reduction of irrigation depth and the decrease in deep percolation. In addition, irrigation water is directly delivered to the root zone through drip irrigation tape, and this can lead to an increase in crop water productivity. In contrast, in border irrigated plots, over-irrigation causes water percolation thus reducing crop water productivity (Table 4). Drip irrigation with mulching significantly enhances partial factor productivity of nitrogen. The improvement of partial factor productivity of nitrogen may result from three aspects: delivering the nitrogen directly to the root zone and reducing leakage (Fig. 5); establishing a proper soil and water environment and promoting nitrogen uptake; reducing the nitrogen loss by mulching. In contrast, nitrogen is leached out of root zone due to over-irrigation thus reducing the partial factor productivity of nitrogen in the border irrigated plots. Partial factor productivity of nitrogen decreases with nitrogen fertilizer supply under the drip irrigation triggered by matric potential of −25 kPa. Numerous research demonstrated that reduction of nitrogen application could improve nitrogen fertilizer use efficiency, while excessive nitrogen application would reduce nitrogen use efficiency (Singh et al., 1998; Wang et al., 2016). Even though a relatively appropriate irrigation and nitrogen fertilization strategy can be proposed with consideration of yield, water and fertilizer productivity and environment impact, the net-profit is the main concerned issue to the farmer. Here we analyzed the cost and benefit of maize planting under different irrigation and fertilization regimes. The highest net profit for drip irrigated plots obtained from the plots triggered by matric potential of −15 kPa and nitrogen fertilizer application of 250 kg ha−1. For border irrigation, the highest net profit obtained in 315 mm irrigation depth treatment with 350 kg ha-1 nitrogen fertilizer. Therefore, comprehensively considering yield, water and nitrogen productivity, economic benefit and environment factors,

5. Conclusion Two-year field experiments were conducted in the HID to investigate the effects of irrigation and fertilization regimes on grain yield, water and nitrogen productivity of mulching cultivated maize. Border and drip irrigation with different irrigation and fertilization schedules have been studied in silt loam soil. The traditional border irrigation causes a large amount of deep percolation and nitrogen leaching during the maize growing season. Groundwater has high risk to be polluted under the current irrigation and fertilization regimes implemented by the farmer. The irrigation and fertilizer application strategy need to be improved to maintain sustainable agriculture and ecology development. Drip irrigation can effectively decrease deep percolation and nitrogen leaching thus promote water and nitrogen use efficiency. If drip irrigation is available, soil matric potential-based irrigation trigger value −15 kPa at a depth of 25 cm and 250 kg ha−1nitrogen fertilizer are recommended for maize cultivation. If drip irrigation is not available, border irrigation with water quantity of 315 mm is recommended for mulching cultivated maize in silt loam in the HID. The nitrogen fertilizer schedule in border irrigation is desirable for optimal application. Declaration of Competing Interest We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted. Acknowledgements This research is partially supported by National Key R&D Program of China (Grant No.: 2017YFC0403305 and 2017YFC0403301) and National Natural Science Foundation of China (Grant No.:51639009). References Allen, R.G., Pereira, L.S., Raes, D., Smith, M., 1998. Crop Evapotranspiration-Guidelines for Computing Crop Water Requirements-FAO Irrigation and Drainage Paper 56. Food and Agriculture Organization of the United Nations, Rome,Italy. Bethune, M., Selle, B., Wang, Q., 2008. Understanding and predicting deep percolation under surface irrigation. Water Resour. Res. 44, 1–16. Burney, J.A., Davis, S.J., Lobell, D.B., 2010. Greenhouse gas mitigation by agricultural intensification. Proc. Natl. Acad. Sci. 107, 12052–12057. Cavero, J., Jiménez, L., Puig, M., Faci, J.M., Martínez-Cob, A., 2008. Maize growth and yield under daytime and nighttime solid-set sprinkler irrigation. Agron. J. 100, 1573–1579. Chakraborty, D., Garg, R.N., Tomar, R.K., Singh, R., Sharma, S.K., Singh, R.K., Trivedi, S.M., Mittal, R.B., Sharma, P.K., Kamble, K.H., 2010. Synthetic and organic mulching and nitrogen effect on winter wheat (Triticum aestivum L.) in a semi-arid environment. Agric. Water Manag. 97, 738–748. Du, J., Yang, P., Li, Y., Ren, S., Wang, Y., Li, X., Lin, Y., 2011. Nitrogen balance in the farmland system based on water balance in Hetao Irrigation District, Inner Mongolia. Acta Ecol. Sin. 31, 4549–4559. El-Wahed, M.H.A., Ali, E.A., 2013. Effect of irrigation systems, amounts of irrigation water and mulching on corn yield, water use efficiency and net profit. Agric. Water Manag. 120, 64–71. Feng, Z.Z., Wang, X.K., Feng, Z.W., 2005. Soil N and salinity leaching after the autumn irrigation and its impact on groundwater in Hetao Irrigation District, China. Agric. Water Manag. 71, 131–143. Gheysari, M., Mirlatifi, S.M., Homaee, M., Asadi, M.E., Hoogenboom, G., 2009. Nitrate leaching in a silage maize field under different irrigation and nitrogen fertilizer rates. Agric. Water Manag. 96, 946–954. Guan, D., Al-Kaisi, M.M., Zhang, Y., Duan, L., Tan, W., Zhang, M., Li, Z., 2014. Tillage

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