Summer Maize Rotation Research Articles

Stable isotope evidences for identifying crop water uptake in a typical winter wheat–summer maize rotation field in the North China Plain

Better managing agricultural water resources, which are increasingly stressed by climate change and anthropogenic activities, is difficult, particularly because of variations in water uptake patterns associated with crop type and growth stage. Thus, the stable isotopes δ18O and δ2H were employed to investigate the water uptake patterns of a summer maize (Zea mays L.) and winter wheat (Triticum aestivum L.) rotation system in the North China Plain. Based on the soil water content, soil layers were divided into four groups (0–20cm, 20–40cm, 40–120cm, and 120–200cm) using a hierarchical cluster analysis. The main soil layer of water uptake for summer maize was from 0–20cm at the trefoil (77.8%) and jointing (48.6%) stages to 20–40cm at the booting (33.6%) and heading (32.6%) stages, became 40–120cm at the silking (32.0%) and milking (36.7%) stages, and then returned to 0–20cm at the mature (35.0%) and harvest (52.4%) stages. Winter wheat most absorbed water from the 0–20cm soil water at the wintering (86.6%), seedling (83.7%), jointing (45.2%), booting (51.4%), heading (28.8%), and mature (67.8%) stages, but it was 20–40cm at the flowering (34.8%) and milking (25.2%) stages. The dry root weight density was positively correlated with the contributions of the water uptake for winter wheat. However, no similar correlation was found in summer maize. Regression analysis indicated that the soil volumetric water content (SVWC) was negatively correlated with the contribution of the water uptake (CWU) for summer maize (CWU=−0.91×SVWC+57.75) and winter wheat (CWU=−2.03×SVWC+92.73). These different responses to water uptake contributions suggested that a traditional irrigation event should be postponed from the booting to flowering stage of winter wheat. This study provides insights into crop water uptake and agricultural water management.

Improving nitrogen use efficiency with minimal environmental risks using an active canopy sensor in a wheat-maize cropping system

Nitrogen (N) management needs to be significantly improved to address the triple challenge of global food security, environmental pollution and climate change. In addition to being site-specific, dynamic in-season management is needed to respond to temporal variability in soil N supply and crop N demand. Active canopy sensor-based precision N management (CS-PNM) aims to match N supply with crop N demand in both space and time. Studies that systematically compare this strategy with other N management strategies are limited, especially in intensively farmed regions of developing countries. The objective of this study was to compare CS-PNM strategy in terms of agronomic and environmental impacts in comparison with farmer’s N practice, regional optimum N management, modified Green Window-based N Management and soil test-based in-season root zone N management for an intensive winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) rotation system in North China Plain. A field experiment was conducted from 2008 to 2012 in Quzhou, Hebei Province of China to evaluate these systems. The CS-PNM strategy was consistently better for both crops than the other tested strategies. In comparison with farmer’s practice and regional optimum N management, the CS-PNM strategy reduced N fertilizer applications by 62% and 36%, increased N use efficiencies by 68–123% and 20–61%, decreased apparent total N losses by 81% and 57%, and lowered intensities of total N2O emission, greenhouse gas emission and reactive N losses by 54–68% and 20–42%, respectively. Here we demonstrate that relative to current N management strategies, the CS-PNM strategy has significant potential to improve N use efficiencies and mitigate environmental degradation for sustainable intensification of agriculture in developing countries.

Effect of experimental warming on soil respiration under conventional tillage and no-tillage farmland in the North China Plain

Understanding the response of soil respiration to global warming in agro-ecosystem is crucial for simulating terrestrial carbon (C) cycle. We conducted an infrared warming experiment under conventional tillage (CT) and no-tillage (NT) farmland for winter wheat and summer maize rotation system in North China Plain (NCP). Treatments include CT with and without warming (CTW and CTN), NT with and without warming (NTW and NTN). The results indicated that warming had no significant effect on soil moisture in irrigated farmland of NCP (P>0.05). The elevated average soil temperature of 1.1–1.6°C in crop growing periods could increase annual soil CO2 emission by 10.3% in CT filed (P>0.05), but significantly increase it by 12.7% in NT field (P<0.05), respectively. The disturbances such as plowing, irrigation and precipitation resulted in the obvious soil CO2 emission peaks, which contributed 36.6–40.8% of annual soil cumulative CO2 emission. Warming would enhance these soil CO2 emission peaks; it might be associated with the warming-induced increase of autotrophic respiration and heterotrophic respiration. Compared with un-warming treatments, dissolved organic carbon (DOC) and soil microbial biomass carbon (MBC) in warming treatments were significantly increased by 11.6–23.4 and 12.9–23.6%, respectively, indicating that the positive responses of DOC and MBC to warming in both of two tillage systems. Our study highlights that climate warming may have positive effects on soil C release in NCP in association with response of labile C substrate to warming.

Water Leakage and Nitrate Leaching Characteristics in the Winter Wheat–Summer Maize Rotation System in the North China Plain under Different Irrigation and Fertilization Management Practices

Field experiments were carried out in Huantai County from 2006 to 2008 to evaluate the effects of different nitrogen (N) fertilization and irrigation management practices on water leakage and nitrate leaching in the dominant wheat–maize rotation system in the North China Plain (NCP). Two N fertilization (NF1, the traditional one; NF2, fertilization based on soil testing) and two irrigation (IR1, the traditional one; IR2, irrigation based on real-time soil water content monitoring) management practices were designed in the experiments. Water and nitrate amounts leaving the soil layer at a depth of 2.0 m below the soil surface were calculated and compared. Results showed that the IR2 effectively reduced water leakage and nitrate leaching amounts in the two-year period, especially in the winter wheat season. Less than 10 percent irrigation water could be saved in a dry winter wheat season, but about 60 percent could be saved in a wet winter wheat season. Besides, 58.8 percent nitrate under single NF2IR1 and 85.2 percent under NF2IR2 could be prevented from leaching. The IR2 should be considered as the best management practice to save groundwater resources and prevent nitrate from leaching. The amounts of N input play a great role in affecting nitrate concentrations in the soil solutions in the winter wheat–summer maize rotation system. The NF2 significantly reduced N inputs and should be encouraged in ordinary agricultural production. Thus, nitrate leaching and groundwater contamination could be alleviated, but timely N supplement might be needed under high precipitation condition.

Effects of Different Forms of Selenium Fertilizers on Se Accumulation, Distribution, and Residual Effect in Winter Wheat-Summer Maize Rotation System.

Foliar Se fertilizers were applied to investigate the effects of Se forms on Se accumulation and distribution in the wheat-maize rotation system and residual concentration of Se in subsequent crops. Sodium selenite, sodium selenate, selenomethionine, chemical nano-Se, humic acid + sodium selenite, and compound fertilizer + sodium selenite were applied once at the flowering stage of wheat (30 g ha-1) and at the bell stage of maize (60 g ha-1). Compared with the control treatment, foliar Se applications significant increased the grain Se concentration of wheat and maize by 0.02-0.31 and 0.07-1.09 mg kg-1, respectively. Wheat and maize grain Se recoveries were 3.0-10.4 and 4.1-18.5%, respectively. However, Se concentrations in the grain of subsequent wheat and maize significantly decreased by 77.9 and 91.2%, respectively. The change of Se concentration in soil was a dynamic process with Se depletion after harvest of maize.

Spatial Variation of Soil Respiration in a Cropland under Winter Wheat and Summer Maize Rotation in the North China Plain.

Spatial variation of soil respiration (Rs) in cropland ecosystems must be assessed to evaluate the global terrestrial carbon budget. This study aims to explore the spatial characteristics and controlling factors of Rs in a cropland under winter wheat and summer maize rotation in the North China Plain. We collected Rs data from 23 sample plots in the cropland. At the late jointing stage, the daily mean Rs of summer maize (4.74 μmol CO2 m-2 s-1) was significantly higher than that of winter wheat (3.77μmol CO2 m-2 s-1). However, the spatial variation of Rs in summer maize (coefficient of variation, CV = 12.2%) was lower than that in winter wheat (CV = 18.5%). A similar trend in CV was also observed for environmental factors but not for biotic factors, such as leaf area index, aboveground biomass, and canopy chlorophyll content. Pearson’s correlation analyses based on the sampling data revealed that the spatial variation of Rs was poorly explained by the spatial variations of biotic factors, environmental factors, or soil properties alone for winter wheat and summer maize. The similarly non-significant relationship was observed between Rs and the enhanced vegetation index (EVI), which was used as surrogate for plant photosynthesis. EVI was better correlated with field-measured leaf area index than the normalized difference vegetation index and red edge chlorophyll index. All the data from the 23 sample plots were categorized into three clusters based on the cluster analysis of soil carbon/nitrogen and soil organic carbon content. An apparent improvement was observed in the relationship between Rs and EVI in each cluster for both winter wheat and summer maize. The spatial variation of Rs in the cropland under winter wheat and summer maize rotation could be attributed to the differences in spatial variations of soil properties and biotic factors. The results indicate that applying cluster analysis to minimize differences in soil properties among different clusters can improve the role of remote sensing data as a proxy of plant photosynthesis in semi-empirical Rs models and benefit the acquisition of Rs in cropland ecosystems at large scales.

Upscaling plot-scale soil respiration in winter wheat and summer maize rotation croplands in Julu County, North China

Soil respiration (Rs) data from 45 plots were used to estimate the spatial patterns of Rs during the peak growing seasons of winter wheat and summer maize in Julu County, North China, by combining satellite remote sensing data, field-measured data, and a support vector regression (SVR) model. The observed Rs values were well reproduced by the model at the plot scale, with a root-mean-square error (RMSE) of 0.31μmolCO2m−2s−1 and a coefficient of determination (R2) of 0.73. No significant difference was detected between the prediction accuracy of the SVR model for winter wheat and summer maize. With forcing from satellite remote sensing data and gridded soil property data, we used the SVR model to predict the spatial distributions of Rs during the peak growing seasons of winter wheat and summer maize rotation croplands in Julu County. The SVR model captured the spatial variations of Rs at the county scale. The satellite-derived enhanced vegetation index was found to be the most important input used to predict Rs. Removal of this variable caused an RMSE increase from 0.31μmolCO2m−2s−1 to 0.42μmolCO2m−2s−1. Soil properties such as soil organic carbon (SOC) content and soil bulk density (SBD) were the second most important factors. Their removal led to an RMSE increase from 0.31μmolCO2m−2s−1 to 0.37μmolCO2m−2s−1. The SVR model performed better than multiple regression in predicting spatial variations of Rs in winter wheat and summer maize rotation croplands, as shown by the comparison of the R2 and RMSE values of the two algorithms. The spatial patterns of Rs are better captured using the SVR model than performing multiple regression, particularly for the relatively high and relatively low Rs values at the center and northeast study areas. Therefore, SVR shows promise for predicting spatial variations of Rs values on the basis of remotely sensed data and gridded soil property data at the county scale.

Plant and soil fertility characteristics of different winter wheat fields in the Huang-huai-hai plain of China

ABSTRACTHigh-profile nutrient accumulation has caused low nutrient use efficiency and environmental pollution. A total of 140 points in farmers’ wheat fields were investigated and sampled under a typical winter wheat and summer maize rotation system in the Huang-huai-hai Plain of China (HPC). The average wheat yield in the high-yield field is more than 10% relative to the mid-low-yield areas based on historical data. The results showed in the high-yield wheat field the effective spike number was the main yield component, followed by 1000-grain weight. Uptake contents and ratios of N, P2O5 and K2O in the whole wheat plant were also examined. Along the soil depth, organic matter (OM), alkali-hydrolyzable N (AN), available P (AP) and available K (AK) concentration gradually decreased. Soil critical values of AN, AP and AK in the 0–20 cm depth needed to achieve the maximum grain yield were 85.9, 17.7 and 114.2 mg kg−1 calculated by the significant linear-plus-plateau model between wheat grain yield and soil nutrient concentration at harvest, respectively. These results indicated that the rational application of fertilizer based on the soil nutrient supply capacity and residual nutrients in root zone and optimum planting density are key determinants of grain production in the HPC.

Effects of different cultivation patterns on yield, nitrate accumulation and nitrogen balance in winter wheat and summer maize rotation system.

This study investigated the impacts of four cultivation patterns including farmer practice, high yield and high efficiency practice, super high yield practice, and super high yield and high efficiency practice on yields, soil nitrate and nitrogen (N) balances in 3 winter wheat-summer maize rotations with straw returning in Hebei Province. Results showed that the super high yield practice was identified with greatest winter wheat and summer maize yields, followed by high yield and high efficiency practice, and super high yield and high efficiency practice, which were all greater than that of farmer practice. The N use efficiency of high yield and high efficiency practice was significantly greater than the other cultivation patterns. The total nitrate accumulation in 0-400 cm soil of these cultivation patterns reached 768.4-1133.3 kg·hm-2, where 80%-85% of the accumulated nitrate were in 90-400 cm soil. Meanwhile, the nitrate leaching was observed in all cultivation patterns and nitrate accumulation peaks at 120-150 cm and 270-330 cm were found. Soil nitrate content of high yield and high efficiency practice was less than 30 mg·kg-1 and generally lower than other cultivation patterns, which to some extent reduced the environmental risk. In addition, nitrate surplus in 0-90 cm soil during winter wheat season was lower than that during summer maize season, and the high yield and high efficiency practice had the lowest apparent nitrogen loss. Overall, the high yield and high efficiency practice was evaluated to be the best cultivation pattern in consi-deration of yield, nitrogen use efficiency and nitrate accumulation in soil, but there was still certain achievable improvement potential.

Optimal nitrogen input for higher efficiency and lower environmental impacts of winter wheat production in China

Many fertilization guidelines have been established to recommend the proper nitrogen (N) application rate to optimize grain yield. However, environmental impacts and grain nutritional quality such as protein content have not received enough attention. To optimize regional N fertilizer management in China, a total of 1212 and 1110 sets of data from a literature survey and field experiments were used in a regression analysis to determine the relationships of N application rate with winter wheat grain yield and protein content, respectively. Regional N rate recommendations were estimated with the linear-plus-plateau model and were between the N rates used to maximize grain yield and protein content. The recommended N rates for the winter wheat–summer maize rotation (WM), winter wheat–rice rotation (WR), and rainfed winter wheat (RW) regions in China were 208–230kgha−1, 150–195kgha−1, and 117–134kgha−1, respectively. These values were comparable to or lower than the investigated farm average in each region; however, calculated based on the linear-plus-plateau model, the recommended N rate in each region achieved 1–19% greater grain yield and 2–9% greater protein content compared with the farm average yield and protein content. Compared with the excessive N input group, the recommended N rates increased the N partial factor productivity (PFPN) of wheat by 7–11, 8–14, and 18–24kgkg−1 and gained an additional profit of 214–228, 91–354, and 465–476USDha−1 in the three regions, respectively; in addition, the recommended N rates reduced the residual inorganic N, nitrate leaching, and direct nitrous oxide emissions by 8–27%, 29–52%, and 19–36% in the three regions, respectively. These findings suggest that this N recommendation method provides an option to balance the yield, grain quality, income, nitrogen use efficiency, and environmental impacts of winter wheat production in China and similar cropping systems around the world.

Atmospheric deposition as an important nitrogen load to a typical agro-ecosystem in the Huang-Huai-Hai Plain. 2. Seasonal and inter-annual variations and their implications (2008–2012)

Abstract Atmospheric nitrogen (N) deposition, an important N source to agro-ecosystems, has increased intensively in China during recent decades. However, knowledge on temporal variations of total N deposition and their influencing factors is limited due to lack of systematic monitoring data. In this study, total N deposition, including dry and wet components, was monitored using the water surrogate surface method for a typical agro-ecosystem with a winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) rotation system in the Huang-Huai-Hai Plain from May 2008 to April 2012. The results indicated that annual total N deposition ranged from 23.8 kg N ha−1 (2009–2010) to 40.3 kg N ha−1 (2008–2009) and averaged 31.8 kg N ha−1. Great inter-annual variations were observed during the sampling period, due to differences in annual rainfall and gaseous N losses from farmlands. Monthly total N deposition varied greatly, from less than 0.6 kg N ha−1 (January, 2010) to over 8.0 kg N ha−1 (August, 2008), with a mean value of 2.6 kg N ha−1. In contrast to wet deposition, dry portions generally contributed more to the total, except in the precipitation-intensive months, accounting for 65% in average. NH 4 + -N was the dominant species in N deposition and its contribution to total deposition varied from 6% (December, 2009) to 79% (July, 2008), averaging 53%. The role of organic N (O–N) in both dry and wet deposition was equal to or even greater than that of NO 3 − -N. Influencing factors such as precipitation and its seasonal distribution, reactive N sources, vegetation status, field management practices, and weather conditions were responsible for the temporal variations of atmospheric N deposition and its components. These results are helpful for reducing the knowledge gaps in the temporal variations of atmospheric N deposition and their influencing factors in different ecosystems, to improve the understandings on N budget in the typical agro-ecosystem, and to provide references and recommendations for field nutrient management in this region.

Modelling and predicting crop yield, soil carbon and nitrogen stocks under climate change scenarios with fertiliser management in the North China Plain

Changes in field management and climate will alter soil organic carbon (SOC) and nitrogen (SN) cycling in the coming decades. This study is to quantify the effects of various fertilisation strategies and climate change scenarios on crop yield, and soil C and N cycling by the end of this century. Data from a long-term experiment with a winter-wheat (Triticum aestivium L.) and summer maize (Zea mays L.) rotation in Northern China was used to calibrate and validate the SPACSYS model. Five fertiliser practices were used: control (CK); combined mineral nitrogen, phosphorus and potassium (NPK); NPK plus manure (NPKM); high application rate of NPK fertilisers plus manure (hNPKM) and NPK with straw incorporation (NPKS). Crop yields, and SOC and SN stocks by 2100 were predicted under four climate scenarios (Baseline, RCP2.6, RCP4.5 and RCP4.5). Results showed that the SPACSYS model can adequately simulate the dynamics of SOC and SN stocks and the yields of winter wheat and summer maize. An application of NPK plus manure or straw not only enhanced crop yield, but also substantially increased SOC and SN stocks. The predictions showed the positive effects of fertilisation and climate change on crop yields and SOC stocks compared with those under the baseline. However, SN stock under the RCP8.5 decreased by 3–14% by 2100 for various fertilisation strategies compared with that under the baseline. On the other hand, mineral fertiliser plus manure led to a higher soil respiration rate and nitrogen losses through leaching and surface runoff under all the climate scenarios. Therefore, application of mineral fertilisers plus manure could enhance crop productivity and sustain soil fertility but cause more carbon emitted to the atmosphere and nitrogen losses. More attention should be paid on optimising fertilisation in order to increase crop productivity while minimising environmental risks.

Comparison of the DNDC, LandscapeDNDC and IAP-N-GAS models for simulating nitrous oxide and nitric oxide emissions from the winter wheat–summer maize rotation system

The DNDC, LandscapeDNDC and IAP-N-GAS models have been designed to simulate the carbon and nitrogen processes of terrestrial ecosystems. Until now, a comparison of these models using simultaneous observations has not been reported, although such a comparison is essential for further model development and application. This study aimed to evaluate the performance of the models, delineate the strengths and limitations of each model for simulating soil nitrous oxide (N2O) and nitric oxide (NO) emissions, and explore short-comings of these models that may require reconsideration. We conducted comparisons among the models using simultaneous observations of both gases and relevant variables from the winter wheat–summer maize rotation system at three field sites with calcareous soils. Simulations of N2O and NO emissions by the three models agreed well with annual observations, but not with daily observations. All models failed to correctly simulate soil moisture, which could explain some of the incorrect daily fluxes of N2O and NO, especially for intensive fluxes during the growing season. Multi-model ensembles are promising approaches to better simulate daily gas emissions. IAP-N-GAS underestimated the priming effect of straw incorporation on N2O and NO emissions, but better results were obtained with DNDC95 and LandscapeDNDC. LandscapeDNDC and IAP-N-GAS need to improve the simulation of irrigation water allocation and residue decomposition processes, respectively, and together to distinguish different irrigation methods as DNDC95 does. All three models overestimated the emissions of the nitrogenous gases for high nitrogen fertilizer (>430kgNha−1yr−1) addition treatments, and therefore, future research should focus more on the simulation of the limitation of soil dissolvable organic carbon on denitrification in calcareous soils.

Modelling to increase the eco-efficiency of a wheat–maize double cropping system

The winter wheat- summer maize rotation is the main cropping system in the North China Plain (NCP). While its productivity has been constantly increased, the sustainability of the double cropping system has been increasingly questioned due to the high resource use and negative environmental impact. This paper combined field data with scenario modelling to investigate the productivity, resource (water and nitrogen) use efficiency and environmental impact of the wheat–maize rotation in response to management changes at a representative site Wuqiao in NCP. In addition the potential options to increase the system’s eco-efficiency, i.e., producing more with less input and less negative impact on the environment were explored. The results show that 180kg/ha/year of nitrogen could be considered as the optimal N rate for summer maize. For the wheat–maize double cropping rotation, 225mm of irrigation water for wheat and 330kg N/ha (150 for wheat and 180 for maize) are required to maintain the potential grain yield at 18t/ha and to have minimum impact on environment in terms of N leaching to the groundwater and N loss due to denitrification. These derived rates are 175mm/year less and 120kg N/ha less than the highest irrigation and N rates currently practiced. The reduced water and N inputs could reduce the annual totals of drainage, N leaching and denitrification N loss to a minimum of 117mm, 12kg N/ha and 28kg N/ha, respectively. Our simulation results also enabled derivation of yield response curves to water and nitrogen inputs, which can be used to optimise N applications under various levels of irrigation water inputs.

Characteristics of annual nitrous and nitric oxide emissions from major cereal crops in the North China Plain under alternative fertilizer management

Although nitrogen fertilizer is crucially important for China’s crop production, the overuses in the intensive cereal cropping systems of the North China Plain has caused extensive concern for its environmental consequences on nitrous oxide (N2O) and nitric oxide (NO) fluxes. To characterize the integration of environmental and agronomic aspects of fertilizer management, we conducted two annual winter wheat (Triticum aestivum L.)–summer maize (Zea mays L.) rotation cycles under five fertilization treatments, including the farmers’ conventional practice (CP) amended with synthetic nitrogen, three alternative managements of reduced nitrogen inputs with synthetic fertilizers alone (UA), synthetic fertilizers combined with poultry manure (UA+PM) or controlled-release urea combined with poultry manure (CU+PM), and the control without nitrogen fertilization (CK). The N2O and NO fluxes and direct emission factors varied seasonally and annually. These variations could be interpreted mechanically by a revised “hole-in-the-pipe” model and dual Michaelis–Menten and Arrhenius kinetics. The CK, CP, UA, UA+PM, and CU+PM treatments released N2O at 0.65, 4.64, 3.66, 2.88, and 2.40kgNha−1yr−1, respectively, and NO at least 0.42, 2.35, 2.24, 1.30, and 1.18kgNha−1yr−1, respectively. The annual direct emission factors of N2O and NO were 0.41–0.67% and 0.18–0.32%, respectively. The three alternative managements decreased both N2O and NO emissions, expressed either on an area basis or relative to grain yield, without sacrificing crop yields compared to CP. However, their mitigation effects on each gas emission were different. The UA treatment reduced only N2O emission, while UA+PM and CU+PM showed significant mitigation effects on both gases as compared to CP or UA. Overall, our results provide insight into environmental aspect of fertilizer management in major cereal crops and suggest that reducing nitrogen input coupled with organic manure incorporation could be beneficial for simultaneously mitigating nitrogen-containing trace gas fluxes and sustaining cereal grain yields.

The impact of alternative cropping systems on global warming potential, grain yield and groundwater use

The large consumption of groundwater for irrigating winter wheat has resulted in a continuous decline in the groundwater table on the North China Plain in recent decades. Alternative cropping systems have been proposed to substitute for the conventional winter wheat–summer maize rotation system for the sustainable use of groundwater in the future. However, the impact of these cropping systems on net global warming potential (net GWP), and greenhouse gas emissions on the basis of per unit of yield (greenhouse gas intensity, GHGI) is poorly documented. Measurements of greenhouse gases were conducted over a four-year period to gain insight into net GWP and GHGI on a crop rotation scale based on an ongoing long-term field experiment on the North China Plain. The cropping systems investigated include one conventional winter wheat–summer maize system (Chem. W/M) as the control and four alternative cropping systems, namely an optimized winter wheat–summer maize system (Opt. W/M), two winter wheat–summer maize (or soybean)–spring maize system with three crops in two years (W/M–M, W/S–M), and a single spring maize per year (M). Compared with the Chem. W/M control, the grain yields in Opt. W/M increased significantly by 19% while the net GWP, GHGI and fertilizer N decreased by 29%, 40% and 40%, respectively, but still consumed as much groundwater (264mmyr−1) as Chem. W/M. In the two-year rotation cycle fertilizer N, groundwater use, net GWP and GHGI in W/M–M, W/S–M and M declined by 56–70%, 43–63%, 50–58% and 30–50%, respectively, compared to Chem. W/M. Moreover, these cropping systems consumed only 108–159mmyr−1 groundwater for irrigation, a value close to the theoretical value of 150mmyr−1 to avoid a continuing decline in the groundwater table in this region. However, W/S–M treatment had grain yield reductions of −23% and M treatment had −30%, and only W/M–M maintained grain yields relative to Chem. W/M. We therefore recommend the W/M–M management package as a preferred option to maintain grain yields together with low GWP and GHGI while mitigating the decline in the groundwater table in areas with a high water deficit.

Recharge and groundwater use in the North China Plain for six irrigated crops for an eleven year period.

Water tables are dropping by approximately one meter annually throughout the North China Plain mainly due to water withdrawals for irrigating winter wheat year after year. In order to examine whether the drawdown can be reduced we calculate the net water use for an 11 year field experiment from 2003 to 2013 where six irrigated crops (winter wheat, summer maize, cotton, peanuts, sweet potato, ryegrass) were grown in different crop rotations in the North China Plain. As part of this experiment moisture contents were measured each at 20 cm intervals in the top 1.8 m. Recharge and net water use were calculated based on these moisture measurement. Results showed that winter wheat and ryegrass had the least recharge with an average of 27 mm/year and 39 mm/year, respectively; cotton had the most recharge with an average of 211 mm/year) followed by peanuts with 118 mm/year, sweet potato with 76 mm/year, and summer maize with 44 mm/year. Recharge depended on the amount of irrigation water pumped from the aquifer and was therefore a poor indicator of future groundwater decline. Instead net water use (recharge minus irrigation) was found to be a good indicator for the decline of the water table. The smallest amount of net (ground water) used was cotton with an average of 14 mm/year, followed by peanut with 32 mm/year, summer maize with 71 mm/year, sweet potato with 74 mm/year. Winter wheat and ryegrass had the greatest net water use with the average of 198 mm/year and 111 mm/year, respectively. Our calculations showed that any single crop would use less water than the prevalent winter wheat summer maize rotation. This growing one crop instead of two will reduce the decline of groundwater and in some rain rich years increase the ground water level, but will result in less income for the farmers.

Coupled water and nitrogen (N) management as a key strategy for the mitigation of gaseous N losses in the Huang-Huai-Hai Plain

Gaseous nitrogen (N) losses are mainly responsible for low N use efficiency of applied fertilizers and their derivative environmental hazards, while N application rates and soil water regime are important factors regulating these N processes. In this study, gaseous N losses via ammonia volatilization (AV) and denitrification, determined by sponge trapping-KCl extraction and acetylene inhibition-soil core incubation, respectively, were investigated under different coupled water-N management practices with a winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) rotation system in the Huang-Huai-Hai Plain. Ammonia volatilization after urea application, particularly after topdressing during maize growing seasons, was the dominant gaseous N loss, amounting up to 53.2 kg N ha−1 (38.6 % of the applied N). Ammonia volatilization generally decreased by increasing irrigation rate applied immediately after fertilization. Denitrification N losses were lower than ammonia-N losses, accounting for 1.3 to 18.7 kg N ha−1 year−1, with more than 90 % occurring during the maize growing seasons. Total gaseous N losses showed a significant (P < 0.05) positive correlation with N application rates and a negative correlation with irrigation rates applied immediately after fertilization and depended on weather conditions and crop seasons. Temperature and relative humidity were the main influencing factors for both gaseous N losses. The relative importance of weather conditions and field management, such as fertilization and irrigation, on affecting gaseous N losses varied during the five cropping seasons from June 2008 to September 2010. Therefore, the consideration of interannual climate variations, potential nitrate leaching, grain yields, and water-N management could be a promising solution for reducing gaseous N losses and enhancing N use efficiency in this region.

Assessment of climate change impacts on soil organic carbon and crop yield based on long-term fertilization applications in Loess Plateau, China

Climate change may significantly impact crop yields and soil. In this study the DNDC model, together with climatic outputs from Hadley Centre’s general circulation model (HadCM3), was used to investigate the influence of projected climate change and management practices on soil organic carbon (SOC) dynamics and crop yield of the Chinese Loess Plateau. The results identify management practices with the greatest potential to mitigate climate change and to increase SOC in this area. Field experiments on winter-wheat (Triticum aestivum L.) and summer maize (Zea mays L.) rotation included a control and four types of fertilization treatments: T1 (control), T2 (inorganic fertilizer), T3 (NPK inorganic fertilization combined with wheat or maize residue return), T4 (NPK inorganic fertilization combined with low amount of manure) and T5 (NPK inorganic fertilization combined with high amount of manure). DNDC model was calibrated using the field data from 1991 to 2000 and validated from 2001 to 2010. Furthermore, a baseline climate and three future climate scenarios (A1B, A2 and B1) were considered. DNDC model effectively simulated the SOC and crop yields. The findings showed that in 1991–2010, T1 maintained its initial SOC level but reduced crop yields, while T2 promoted crop production with less effect on soil carbon storage. However, T3, T4 and T5 enhanced both crop yield and soil carbon, and the best results were observed under T5. The investigated climate scenarios substantially affect SOC content and crop yields. In terms of SOC content, B1 had great effects on T1, T4 and T5, while A1B on T2 and T3. Considering crop yields, in all treatments, the trends are B1 > A1B > A2 for winter-wheat and A2 > A1B > B1 for summer maize, respectively. The impacts of climate changes on SOC dynamics and crop yields were different depending on the management applied. Thus, the adoption of certain management practices in the Chinese Loess Plateau agroecosystems could be critical in maximizing SOC sequestration and reducing CO2 in the atmosphere. Reasonably low temperature and high precipitation can enhance winter-wheat yields, while maize yields need medium temperature and precipitation. We recommended the combined application of inorganic and organic fertilizers to achieve a balance between food security and soil carbon sequestration objectives.

Effects of Tillage and Straw Returning on Biomass and Water Use Efficiency in a Winter Wheat and Summer Maize Rotation System

Effects of Tillage and Straw Returning on Biomass and Water Use Efficiency in a Winter Wheat and Summer Maize Rotation System