Modeling of water and nitrogen utilization of layered soil profiles under a wheat–maize cropping system

Improvement of Water and Nitrogen Use Efficiencies by Alternative Cropping Systems Based on a Model Approach

The conventional double cropping system of winter wheat and summer maize (WW-SUM) in the North China Plain (NCP) consumes a large amount of water and chemical fertilizer, threatening the sustainable development of agriculture in this region. This study was based on a three-year field experiment of different cropping systems (2H1Y-two harvests in one year; 3H2Y-three harvests in two years; and 1H1Y-one harvest in one year). The 2H1Y system had three irrigation-fertilization practices (FP-farmer's practice; RI-reduced input; and WQ-Wuqiao pattern in Wuqiao County, Hebei Province). A soil-crop system model (WHCNS-soil water heat carbon nitrogen simulator) was used to quantify the effects of different cropping systems on water and nitrogen use efficiencies (WUE and NUE, respectively), and to explore the trade-offs between crop yields and environmental impacts. The results showed that annual yield, water consumption, and the WUE of 2H1Y were higher than those of the 3H2Y and 1H1Y systems. However, local precipitation during the period of crop growth could only meet 65%, 76%, and 91% of total water consumption for the 2H1Y, 3H2Y and 1H1Y systems, respectively. Nearly 65% of irrigation water (groundwater) was used in the period of wheat growth that contributed to almost 40% of the annual yield. Among the three patterns of the 2H1Y system, the order of the WUE was 2H1Y_RI > 2H1Y_WQ > 2H1Y_FP. Compared to 2H1Y_FP, the total fertilizer N application rates in 2H1Y_WQ, 2H1Y_RI, and 3H2Y were reduced by 25%, 65%, and 74%, respectively. The 3H2Y system had the highest NUE of 34.3 kg kg^-1, 54% greater than the 2H1Y_FP system (22.2 kg kg^-1). Moreover, the 3H2Y system obviously reduced nitrate leaching and gaseous N loss when compared with the other two systems. The order of total N loss of different cropping systems was 2H1Y (261 kg N ha^-1) > 1H1Y (78 kg N ha^-1) > 3H2Y (70 kg N ha^-1). Considering the agronomic and environmental effects as well as economic benefits, the 3H2Y cropping system with optimal irrigation and fertilization would be a promising cropping system in the NCP that could achieve the balance between crop yield and the sustainable use of groundwater and N fertilizer.

Evaluation and simulation of spatial variability of soil property effects on deep percolation and nitrate leaching within a large-scale field in arid Northwest China

Variability of soil properties within large-scale fields not only exists in the horizontal domain, but also in the vertical direction, causing spatial variability in yield. Three yield zones were delineated based on measured yield in 2017 and 2018 within a large field in northwest China. The Soil Water Heat Carbon Nitrogen Simulator (WHCNS) model was calibrated and used to simulate yield, nitrogen uptake (N_u), water use efficiency (WUE), fertilizer N (nitrogen) use efficiency (FNUE), deep percolation (DP), nitrate leaching (NL) and residual nitrate (RN) at each sampling point in different yield zones. Based on the simulations, there were significant differences in N_u, WUE, FNUE, DP, NL and RN in 0-100 cm and 100-160 cm soil layers among the three yield zones. DP, NL and RN in the layers were strongly determined by the interaction of zone and year (p < 0.05), thus yielding consistent patterns mainly determined by soil properties and meteorological factors. The modelled ranges of DP, NL, and RN (0-160 cm) were 25-119 mm, 15-94 kg ha^-1, and 178-476 kg·ha^-1 respectively, across the field. Soil texture in the maize main root zone (0-100 cm) has a great influence on yield and N_u, and in the 100-160 cm layer upon DP and NL. RN was abundant after harvest and should be taken into account to determine the nitrogen fertilization demand for the following crop. The study showed that the process of delineating zones can be based on historical yield, making it feasibly easier than mapping soil properties. In view of the fact that there were large losses of water and nitrogen with uniform irrigation and fertilization management, the effects of vertically variable soil properties should be considered in future precision agriculture research, to achieve higher economic benefits and utilization efficiency.

Evaluating the Sustainable Use of Saline Water Irrigation on Soil Water-Salt Content and Grain Yield under Subsurface Drainage Condition

A sustainable irrigation system is known to improve the farmland soil water-salt environment and increase crop yields. However, the sustainable use of saline irrigation water under proper drainage measures still needs further study. In this study, a two-year experiment was performed to assess the sustainable effects of saline water irrigation under subsurface drainage condition. A coupled model consisting of the HYDRUS-2D model and EPIC module was used to investigate the effects of irrigation water salinity (IWS) and subsurface drainage depth (SDD) on soil water-salt content and summer maize yield when saline water was adopted for irrigation under different subsurface drainage measures. Summer maize in the two-year experiments were irrigated with saline water of three different salinity levels (0.78, 3.75, and 6.25 dS m−1) under three different drainage conditions (no subsurface drainage, drain depth of 80 cm, and drain depth of 120 cm). The field observed data such as soil water content, soil salinity within root zone, ET and grain yield in 2016 and 2017 were used for calibration and validation, respectively. The calibration and validation results indicated that there was good correlation between the field measured data and the HYDRUS-EPIC model simulated data, where RMSE, NSE (> 0.50), and R2 (> 0.70) satisfied the requirements of model accuracy. Based on a seven × seven (IWS × SDD) scenario simulation, the effects of IWS and SDD on summer maize relative grain yield and water use efficiency (WUE) were evaluated in the form of a contour map; the relative grain yield and WUE obtained peak values when drain depth was around 100 cm, where the relative yield of summer maize was about 0.82 and 0.53 at IWS of 8 and 12 dS m−1, and the mean WUE was 1.66 kg m−3. The proper IWS under subsurface drainage systems was also optimized by the scenario simulation results; the summer maize relative yield was still about 0.80 even when the IWS was as high as 8.61 dS m−1. In summary, subsurface drainage measures may provide important support for the sustainable utilization of saline water in irrigation. Moreover, the coupled HYDRUS-EPIC model should be a beneficial tool to evaluate future sustainability of the irrigation system.

Rational trade-offs between yield increase and fertilizer inputs are essential for sustainable intensification: A case study in wheat-maize cropping systems in China

In order to feed a population of nearly 1.4 billion people with limited arable land resources, China's high crop production has been maintained by an intensive cropping system with excessive inputs of chemical fertilizers, resulting in high environmental costs. This study attempted to explore the reasonable balance between yield increase and nitrogen (N) inputs in the intensive wheat-maize cropping system in the North China Plain, which is one of the most important grain production regions in China. Based on yield simulations with the DSSAT-CERES-Wheat and DSSAT-CERES-Maize models and a household survey of 241 farmers' fields, we conducted a coupled analysis of the regional crop yields, N fertilizer inputs, and farmers' technical conversion efficiency with respect to winter wheat and summer maize production in four representative study areas. We also conducted a quantitative analysis of the equilibrium relationship between fertilizer application rates and expected yields, and the optimum N fertilization amounts for wheat and maize were recommended. The results indicated that farmers' average yields had reached almost 80% of the attainable yields, which meant that there was little room for farmers to increase their yields. However, we found that the yield gaps among the different farmers were still large, and most farmers applied excessive amounts of N while obtaining unsatisfactory yields due to poor fertilizer management techniques. Only 15% of winter wheat and 4% of summer maize on farmers' fields had achieved the synergy of high crop yields and efficient fertilization, and farmers' technical conversion efficiency was still relatively low. Therefore, farmers should be guided to appropriately lower their yield expectations and reduce the overuse of N fertilizer. In the future, if farmers receive necessary education and training and adopt advanced fertilizer management techniques, sustainable intensification of agricultural production with lower environmental costs will be feasible in China.