Wheat-summer Maize Double Cropping System Research Articles

Effects of Partial Substitution of Organic Fertilizer for Synthetic N Fertilizer on Yield and N Use Efficiencies in a Semiarid Winter Wheat–Summer Maize Rotation

Finding field management techniques that increase crop output while protecting soil sustainability is essential for maintaining a long-term food supply in a changing environment. However, comprehensive evaluation of the effects of nitrogen (N) reduction combined with organic fertilizer on grain yield, N use efficiency (NUE), water use efficiency (WUE), and soil organic carbon (SOC) and total N (TN) contents of winter wheat–summer maize double cropping systems in drought-prone areas remains limited. Therefore, a 3-year field experiment (2018–2021) was conducted in a winter wheat–summer maize double cropping system with five treatments: no N fertilizer (CK), conventional farmer fertilization (CF), recommended fertilization (R), organic N substitution of 20% of the recommended synthetic N (R20), and organic N substitution of 40% of the recommended synthetic N (R40). When results were averaged from 2018 to 2021, R20 had the highest annual grain yield, which increased by 42.15%, 7.69%, 7.58%, and 12.50% compared with CK, CF, R, and R40, respectively. Compared with CF, R20 increased winter wheat and summer maize NAE, NPFP, NUE, and WUE. In addition, the soil organic carbon content of R20 and R40 treatment increased with the increase in years. In conclusion, R20 was considered ideal for improving crop yield, promoting soil fertility, and increasing the fertilizer utilization rate in a semiarid winter wheat–summer maize rotation.

Supplemental irrigation at the jointing stage of late sown winter wheat for increased production and water use efficiency

ContextThe sowing of winter wheat (Triticum aestivum L.) in the winter wheat-summer maize double cropping system is considerably delayed due to late harvest of the maize. This delayed sowing leads to reduction in spike numbers and ultimately the yield. Supplemental irrigation at the jointing stage (SIJ) can effectively regulate the population of winter wheat, but few studies have reported the impacts of SIJ on water utilization, wheat stem number fluctuations, and yield formation of late sown wheat. ObjectiveThe aim of this study was to determine the effects of sowing scheme accompanied with SIJ on wheat yield and water use efficiency (WUE). MethodsA two-year field experiment with two treatment factors (sowing date and irrigation schemes) in a split-plot design was laid out during 2018–2020 in the wheat growing seasons. The main plots were divided into two levels: normal sown date (A1) and late sown date (A2). The split plots included two irrigation schemes: no SIJ (W0) and SIJ (W1). ResultsThe soil water consumption at 20–120 cm soil depth during sowing to jointing stage in late sown wheat (A2) was significantly lower than the normal sown wheat (A1) but it increased considerably at 100–200 cm soil depth from jointing to maturity in A2. SIJ (W1) in late sown wheat produced better yield and WUE than no SIJ (W0). Under W1 conditions, A2 significantly promoted water consumption from jointing to maturity compared with A1, but, because water consumption from sowing to jointing was very low, seasonal water consumption remained significantly low. Additionally, A2 showed accelerated dry matter accumulation after jointing, increased grain numbers per spike and per unit area, improved net photosynthetic rate (Pn) of flag leaf and post-anthesis assimilate production. ConclusionsSIJ accelerated Pn and dry matter accumulation after jointing in late sown wheat, increased grain numbers per unit area, grain yield, and WUE without increasing seasonal water consumption. The seasonal water consumption in the normal sown period were higher. Although the number of spikes in normal sown wheat with higher water consumption, total stem number and dry matter accumulation before jointing was higher, after SIJ, the yield and WUE were lower than those of late sown wheat owing to the reduction in grain numbers per spike. SignificanceThis study explains how the sowing scheme and SIJ affect wheat yield and WUE, and demonstrates that SIJ was particularly crucial for late sown wheat to achieve the synergistic improvement of grain yield and WUE.

Comparing water related indicators and comprehensively evaluating cropping systems and irrigation strategies in the North China Plain for sustainable production

The fully irrigated winter wheat–summer maize double cropping system (DWM) has caused groundwater overexploitation and aggravated water scarcity in the North China Plain (NCP). Therefore, it is necessary to select alternative cropping systems with effective irrigation strategies to maintain the sustainable use of groundwater and maintain crop productivity. However, the evaluation indicators, especially the water-related indicators of cropping systems and irrigation strategies in current studies are not consistent and it is difficult to obtain a comprehensive evaluation result. Hence, to overcome these challenges, this study reviewed and compared groundwater indicators, water use indicators, water production performance indicators and output indicators, and summarized twelve evaluation combinations. Four evaluation combinations with grain yield as output indicator were selected to comprehensively evaluate the cropping systems and irrigation strategies developed by Agricultural Production Systems sIMulator (APSIM) at a typical site in the NCP in the past 52 years. The indicator weights were determined by analytic hierarchy process, entropy weight method, random forest algorithm and principal component analysis. Evaluation results showed that when the main goal was to guarantee food safety or improve the beneficial water use, the DWM was selected as the best choice and the WMM (winter wheat–summer maize → spring maize system, three crops in two years) was the alternative cropping system. Under this condition, water saving irrigation should be vigorously developed to reduce groundwater exploitation. When the four indicator types had the same weight, the DWM under rainfed was the best choice to improve evapotranspiration use efficiency and precipitation use efficiency; the monocropping spring maize system under normal irrigation strategy was the best choice to reduce water footprint. The WMM under rainfed was the alternative choice to improve evapotranspiration use efficiency, improve precipitation use efficiency and reduce water footprint. The evaluation methods proposed in this study could be used as reference in the comparison of cropping systems and irrigation strategies in other water-related situations.

Optimization of sowing date and irrigation schedule of maize in different cropping systems by APSIM for realizing grain mechanical harvesting in the North China Plain

Grain mechanical harvesting can decrease the harvest cost and improve the efficiency of maize production. However, the optimization of the sowing date and irrigation schedule of maize in existing studies rarely considered the grain mechanical harvesting. Therefore, the sowing date and irrigation schedule of two maize cultivars in three cropping systems was optimized by considering yield, water use efficiency (WUE), and grain mechanical harvesting. The quality of grain mechanical harvesting is mainly influenced by grain moisture content. Thus, Agricultural Production Systems sIMulator (APSIM) was coupled with a grain dry down model to simulate maize production in the northern part of the North China Plain (NCP). The latest date for grain mechanical harvesting of maize was analyzed using the date when the grain moisture content decreased to 25% for the first time (DCM25). The DCM25, yield, WUE, and irrigation amount were used as constraints in the optimization. The results showed that, the optimal sowing dates under full irrigation of spring maize in SM (monocropping maize system), spring maize and summer maize in WMM (winter wheat-summer maize-spring maize system) for Huanong887 were from 6th May to 10th June, from 6th May to 16th May and 10th June, respectively. The optimal sowing dates of spring maize in SM were from 1st May to 5th June for Zhengdan958. The summer maize in DWM (winter wheat-summer maize double cropping system) could not achieve high-quality grain mechanical harvesting when using Huanong887 and Zhengdan958. In different hydrological year types, the optimal irrigation schedule with grain mechanical harvesting involved irrigation (80 mm each time) 1–3 times during sowing, jointing and flowering stages of spring maize in SM and summer maize in WMM. For spring maize in WMM, the optimal irrigation schedule involved irrigation 2–3 times during sowing, jointing, and flowering stages. The optimization method could provide a reference for other sites to promote high-efficient maize production.

An alternative water-fertilizer-saving management practice for wheat-maize cropping system in the North China Plain: Based on a 4-year field study

Developing an alternative water-fertilizer-saving management practice for winter wheat-summer maize double cropping system in the North China Plain (NCP) is urgent to address severe water scarcity and adverse environmental impacts. A four-year field experiment in split plot design was conducted to evaluate the effects of supplemental drip irrigation on grain yield, water use efficiency (WUE), nitrogen use efficiency (NUE), nitrogen (N) loss and economic benefits, keeping three supplemental drip irrigation times (DI0, no irrigation after emergence; DI3, irrigation once at wheat jointing, once at maize seedling and once at maize jointing; DI5, irrigation once at wheat jointing, once at wheat anthesis, once at maize seedling, once at maize jointing and once at maize tasseling) in the main plots and three N fertilizer rates (N0, no N fertilizer; N60%, 60% of the local recommended N fertilizer rate, 272 kg N ha−1 yr−1; N100%, 100% of the local recommended N fertilizer rate, 453 kg N ha−1 yr−1) in the sub plots. The traditional surface irrigation regime was also conducted as control (CK) under local recommended N fertilizer at 453 kg N ha−1 yr−1. The results showed that DI5N60% achieved the highest WUE in wheat (1.93 kg m−3) and maize (3.00 kg m−3) on average, which was 3.0% and 25.3% higher compared to CK, respectively. The highest partial factor productivity from applied N (PEPN) in wheat and maize were also observed in DI5N60% (56.8 kg kg−1 and 56.3 kg kg−1, respectively) on average, which was 54.0% and 74.0% higher compared to CK, respectively. For winter wheat-summer maize double cropping system, DI5N60% can generally achieve similar crop yield and net income but reduce irrigation and N fertilizer use and N loss compared to CK. Therefore, DI5N60% was considered as an alternative water-fertilizer-saving management practice for winter wheat-summer maize double cropping system in the NCP. Moreover, the optimized combination of irrigation amount and N fertilizer rate corresponding simultaneously to higher crop yield, WUE and net income were determined by using the response surface methodology based on binary quadratic regression analysis, and the optimal irrigation amount were 165 mm and 90 mm, optimal N rates were 186 kg N ha−1 and 185 kg N ha−1 for winter wheat and summer maize, respectively.

Responses of Cereal Yields and Soil Carbon Sequestration to Four Long-Term Tillage Practices in the North China Plain

Current tillage practices in the important winter wheat–summer maize double cropping system of the North China Plain are under debate because of negative effects on soil quality and crop yield. Therefore, a long-term experiment was conducted from 2001 to 2018 to determine the effects of soil conservation practices on crop yield and soil quality. The treatments were imposed following maize harvest and prior wheat seeding, and were defined as follows: (1) moldboard ploughing (0–20 cm) following maize straw removal (CK); (2) moldboard ploughing (0–20 cm) following maize straw return (CT); (3) rotary tillage following maize straw return (RT); and (4) no tillage with maize straw covering the soil surface (NT). Wheat straw was chopped and spread on the soil in all treatments and maize seeded without prior tillage. Wheat yields were higher in CT than RT and NT treatments (p < 0.05); NT had 18% lower wheat yields than CT. No significant differences were found between treatments in summer maize yields. The soil organic carbon (SOC) content in the surface layer (0–5 cm) was higher in NT and RT compared to CT and CK. However, SOC content in the 10–20 cm and 20–30 cm layers was lower in NT and RT compared to CT and CK. Similarly, available phosphorus in the surface soil was higher in NT and RT than in CT and CK. but the opposite was true for the lower soil layers. SOC stocks (0–30 cm) increased in all treatments, and were initially faster in NT and RT than in CT and CK. However, SOC stocks were higher in CT than in other treatments at the end of the experiment. This finding indicates that no tillage and reduced tillage decreased both wheat yields and soil C sequestration over time; it also indicates that CT was the most robust in terms of crop yields and soil C sequestration.

Soil physical properties, nutrients, and crop yield with two-year tillage rotations under a winter wheat-summer maize double cropping system

Winter wheat and summer maize were planted from 2015-2017 to study the effects of different rotational tillage patterns on soil physicochemical properties, crop yield, water content, and fertilizer utilization. The tillage treatments were designed as wheat subsoiling-maize no tillage (WS-MN), wheat rotary tillage-maize subsoiling (WR-MS), wheat subsoiling-maize subsoiling (WS-MS), and conventional wheat rotary tillage-maize no tillage (WR-MN) as a control. Among the four treatments, WS-MN and WR-MS were single-season subsoiling treatments, and WS-MS was a two-season subsoiling treatment. The average soil bulk density decreased by 7.6% in the single- and double-season subsoiling groups compared to the WR-MN group, and the total porosity and noncapillary porosity increased by 10.7% and 12.2%, respectively. Single- or double-season subsoiling treatment was not conducive to water storage in the 0-20 cm soil layer but increased the water content of the 20-140 cm soil layer, and the average soil water content of the 0-140 cm layer was increased by 11.6% in the two-growing season treatment groups compared with the WR-MN group. In WS-MS and WS-MN groups compared with the WR-MN group, the soil ammonium nitrogen content was increased by an average of 18.6% in 0-20 cm soil and 16.8% in 20-100 cm soil; soil nitrate-nitrogen content was decreased by 13.5% in 0-100 cm soil; total organic carbon and microbial carbon contents in the 15-30 cm soil were increased by 18.1% and 12.7%, respectively; and soil urease, catalase, and alkaline phosphatase activities were increased by 46.1%, 15.2%, and 23.1%, respectively. Annual crop yield and water use efficiency increased by 8.9% and 15.0%, respectively, in both the single- and double-season subsoiling treatment groups. This study demonstrated the advantages of subsoiling tillage and suggested that it is suitable for crop cultivation in the Haihe Plain, China. Keywords: tillage rotations, wheat-maize double cropping, soil properties, utilization of water and fertilizer, crop yield DOI: 10.25165/j.ijabe.20221501.6855 Citation: Yin B Z, Liu P, Cui Y W, Hu Z H, Li X L, Pan Z H, et al. Soil physical properties, nutrients, and crop yield with two-year tillage rotations under a winter wheat-summer maize double cropping system. Int J Agric & Biol Eng, 2022; 15(1): 172–181.

Reduced groundwater use and increased grain production by optimized irrigation scheduling in winter wheat–summer maize double cropping system—A 16-year field study in North China Plain

Optimizing irrigation strategies to increase water utilization efficiency and achieve higher yield is vital for balancing groundwater use and improving food security during water shortage in the North China Plain (NCP). Based on a 16-year field experiment (2003–2018) using seven irrigation schedules from W0M0 to W4M3 (numbers are irrigation times in wheat (W) and maize (M) season, 75 mm each) in the winter wheat–summer maize double cropping system, we analyzed annual total water consumption ( ET a ) and groundwater table change in terms of net groundwater depletion, annual total grain yield, water productivity (WP), irrigation water productivity (IWP) and marginal benefit of the whole wheat–maize system. Relationship between yield or WP and irrigation or ET a were also revealed. Results showed that (1) total ET a increased as irrigation input increased, ranging from 427.3 mm (Rainfed, W0M0) to 891.0 mm (W4M3). Soil water storage contributed nearly 30% to ET a for winter wheat under water deficit conditions. Pre-sowing soil water storage played an important role in improving the annual yield and WP of both wheat and maize by promoting germination, seedling emergence and root growth; (2) the rainfed treatment (W0M0) was best for mitigating the groundwater table decline (0.1 m yr -1 ), followed by W1M1 (0.5 m yr -1 ) and W2M1 (0.8 m yr -1 ). Groundwater table decline in M2W2 almost overlapped the observed data at the station (1.1 m yr -1 ). In W3M2, the farmers’ traditional practice, the groundwater table declined by 1.4 m yr -1 , obviously over exploitation, while W4M2 and W4M3 declined by almost 2.0 m yr -1 ; (3) the relationship between total annual yield and irrigation (or ET a ) followed a quadratic curve. Total annual yield significantly increased from W0M0 to M1W1 (25%) to M2M1 (5%) and then kept stable. Average annual WP decreased as irrigation increased, from 2.4 kg m -3 (W0M0) to 1.6 kg m -3 (W4M3). Average annual IWP and marginal benefit also declined as irrigation increased. These results over 16 years indicated that the W2M1 is the most balanced irrigation regime for wheat– maize rotation to mitigate groundwater decline, maintain grain production, and improve water use efficiency in the NCP. ● A 16 - year field experiment of seven irrigation regimes for wheat-maize was conducted. ● ET a increased and water productivity decreased with increasing irrigation amount. ● W2M1 was the best optimized irrigation regime for balancing groundwater use and yield.

Optimized fertilizer recommendation method for nitrate residue control in a wheat–maize double cropping system in dryland farming

The recommendations for soil fertilization based on soil testing are time-critical and labor-intensive for farmers in the winter wheat–summer maize double cropping system. Understanding the relationships between the crop yield, nitrogen requirement, and nitrate residue level under the combined N and P fertilizer application is necessary to optimize the fertilizer recommendation method in order to reduce the nitrate residue levels. In 2009, we established a long-term field fertilization experiment with five N application rates and four P application rates in the winter wheat-summer maize double cropping system. The grain yield, N requirement, and soil nitrate residue were determined during 2016–2019 to optimize the N inputs for nitrate residue control. The crop yield was increased by N application and it increased further when combined with P fertilizer. The N requirement of crops increased by N application but decreased when combined with P. The calculated maximum winter wheat yield was 7235 kg ha−1 and the theoretical N requirement for 1000 kg grain formation (NR) was 28.68 kg Mg−1. The maximum summer maize yield was 7866 kg ha−1, and the theoretical NR was determined as 23.43 kg Mg−1. The residual nitrate-N was increased by N application but decreased by combined P fertilizer. The correlation between the nitrate-N content in 0–20 cm top soil (SNC) and nitrate-N residue in 0–100 cm soil (SNR) was linear at the winter wheat harvest but exponential at the summer maize harvest. Thus, the SNR can be predicted by the SNC according to their correlation at the harvest. The predicted SNR at the harvest of the previous crop, the target yield and NR for the subsequent crop obtained from long-term in-situ observations can be used to guide the fertilizer amounts applied to the following crop. Therefore, we developed a convenient method to optimize the fertilizer recommendation method for the winter wheat–summer maize cropping system.

Diversified crop rotations enhance groundwater and economic sustainability of food production

AbstractEarth's water resources are critical for supporting livelihoods and food security but are being increasingly overexploited to support global agriculture. Diversifying cropping systems could potentially resolve unsustainable water use but trade‐offs with other aspects of sustainability and food security have not yet been assessed. We performed a detailed analysis of 31 different field crop rotations conducted during 1990–2019 in the North China Plain, to assess the potential impact of crop diversification on actual evapotranspiration (ETa), changes in regional groundwater table, grain yield, economic output, and water use efficiency (WUE) and to identify configurations that can achieve co‐benefits across multiple dimensions. We found that a combination of lowering the cropping index (i.e., harvest frequency), incorporating fallow periods, and introducing higher‐value crops into the currently dominant winter wheat–summer maize double cropping system can reduce growing season ETa by as much as 31%, mitigate groundwater decline by 19% or more, and increased economic output and economic WUE by more than 11% and 3%, respectively. We also found that multiple diversified wheat‐maize–based rotations—all with rotation lengths greater than 2 years—achieve co‐benefits across all evaluated dimensions. This study provides new empirical evidence of the opportunities for diversified crop rotations to balance the multiple objectives of food production, sustainable groundwater use, and farmer profitability. Extending this solution to other water‐stressed agricultural regions could be an effective strategy in achieving more sustainable food production system globally.

Straw mulching improves soil water content, increases flag leaf photosynthetic parameters and maintaines the yield of winter wheat with different irrigation amounts

In North China Plain, straw mulching is increasingly applied to the succeeding crops with winter wheat-summer maize double cropping system. However, research results on the effect of maize straw mulching on the yield of winter wheat are inconsistent, and the underlying mechanism of the effect remains unclear. Such information is helpful to guide the field water management for higher yield. In this study, soil moisture, plant growth, photosynthesis and yield of winter wheat field treated with no-till and straw mulching (SM) and non- mulching (N) and three irrigation amounts (high, middle and low irrigation, HI, MI and LI) in four growing seasons in 2013–2016. The results showed that straw mulching improved soil moisture by reducing the days of soil moisture less than 60% field capacity for 2–10 days. Straw mulching increased net photosynthetic rate, stomatal conductance, maximum carboxylation rate (Vcmax), and the maximum rate of photosynthetic electron transport (Jmax) of flag leaves, especially at the post-anthesis measurements, during which, the above parameters increased by 20.6%, 21.9%, 28.7% and 25.2%, respectively. Compared with pre-anthesis measurements, the post-anthesis Vcmax and Jmax values decreased, but the decrease percentage of the SM treatments (10.8–25.7% for Vcmax and 22.0%−49.6% for Jmax) was less than those of N treatments (19.6%−41.4% for Vcmax and 29.3%−61.3% for Jmax). Vcmax and Jmax were significantly linear correlating to leaf nitrogen content and the relationships between them were not affected by straw mulching. The yield was not affected by straw mulching. However, straw mulching significantly increased the intercept of the linear relationship between yield and canopy potential photosynthetic capacity (the productions of leaf area index and Vcmax, or Jmax), indicating that straw mulching may improve the harvest index of winter wheat. The overall net effect of straw mulching was a favorable environment that stimulated plant photosynthesis, which compensated the lower LAI and tiller density, in turn, maintained wheat yield. This study elucidated the physiological basis of straw mulching and no-till effect on yield and provided photosynthetic parameters of winter wheat under such soil management.

Will Maize-Based Cropping Systems Reduce Water Consumption without Compromise of Food Security in the North China Plain?

The winter wheat–summer maize double cropping system caused overexploitation of groundwater in the North China Plain; it is unsustainable and threatens food security and the overall wellbeing of humankind in the region. Finding water-saving cropping systems without compromising food security is a more likely solution. In this study, six alternative cropping systems’ water conservation and food supply capacity were compared simultaneously. A combined water footprint method was applied to analyze the cropping systems’ water consumption. The winter wheat–summer maize system had the largest water consumption (16,585 m3/ha on average), followed by the potato/spring maize, spinach–spring maize, rye–spring maize, vetch–spring maize, pea/spring maize, soybean||spring maize and mono-spring maize cropping systems. For the groundwater, the spinach–spring maize, pea/spring maize, soybean||spring maize systems showed a higher degree of synchronization between crop growth period and rainfall, which could reduce use of groundwater by 36.8%, 54.4% and 57.6%, respectively. For food supply capacity, the values for spinach–spring maize, pea/spring maize, soybean||spring maize systems were 73.0%, 60.8% and 48.4% of winter wheat–summer maize, respectively, but they showed a better feeding efficiency than the winter wheat–summer maize system. On the whole, spinach–spring maize may be a good option to prevent further decline in groundwater level and to ensure food security in a sustainable way.

Modeling crop growth and land surface energy fluxes in wheat–maize double cropping system in the North China Plain

The land surface characteristic influences climatic environments by controlling the land surface energy and water fluxes. Although large progresses have been made in coupling detailed crop models into land surface models, there is much room left for improved estimates of surface fluxes in double cropping system, such as the winter wheat (Triticum aestivum L.)–summer maize (Zea mays L.) system under intensive influences of climate change and human activities in the North China Plain (NCP). Here, we modeled the growth and surface fluxes in winter wheat–summer maize double cropping system in the NCP through modified SiBcrop model. The parameters related with the crop growth in winter wheat and maize sub-models were emphasized to better simulate the seasonal dynamics of phenology phase, leaf area index (LAI), and latent (LH) and sensible (SH) heat fluxes. Observational data for phenology, LAI, and energy fluxes were compiled from Yucheng and Guantao stations, to calibrate and validate the SiBcrop model. The results showed that the adjusted SiBcrop captured better the seasonal dynamics of phenology, LAI, LH, and SH, relative to the original code. The largest biases in model results were in SH when horizontal advection prevails and in LH when there is summer maize senescence. Sensitivity analysis illustrated that growth duration, emergence date, LH, SH, and Bowen ratio were quite sensitive to sowing date of wheat, and growth duration and emergence and harvest dates to sowing of maize. The calibrated SiBcrop also simulated the LH and SH well at Guantao station. The adjusted SiBcrop is capable of assessing the responses of surface biophysical processes to the changes of human management and climate change in the double cropping system in the NCP.

Effects of residue management strategies on greenhouse gases and yield under double cropping of winter wheat and summer maize

The North China Plain (NCP) is typically cropped using a winter wheat–summer maize double cropping system, which has huge potential for straw production. The region also experiences atmospheric pollution caused by straw burning, which has become an important contributor to global warming. The goals of this experiment were to resolve the conflict between soil fertility and greenhouse gas emission when using straw return to the field and to identify the best balance between environmental protection and agricultural production. A randomized block design with three replicates was used. The design included three treatments based on the return of all winter wheat stalks to the field: (1) all summer maize stalks were pulverized mechanically and returned to the field (SR); (2) half of the summer maize stalks were pulverized mechanically and returned to the field (1/2 SR); and (3) all summer maize stalks were fully removed (control: CK). This long-term test was performed for 6 years. Straw returned to the field significantly increased greenhouse gas emissions. The cumulative CO2 emissions were higher by 32% under SR and by 17% under 1/2 SR compared with CK. The cumulative N2O emissions were higher by 28% under SR and 15% under 1/2 SR compared with CK. The greenhouse gas efflux increased with increased amounts of straw returned to the field. Compared with SR, 1/2 SR significantly reduced greenhouse gas emissions, while still ensuring sustainable soil fertility. Additionally, our research showed that the upper part of the corn stalk is better for generating biomass energy than the lower part. This study provides a theoretical basis for using the upper stalk for bioenergy and the lower stalk for direct return to the field for fertilization.

Biophysical controls of soil respiration in a wheat-maize rotation system in the North China Plain

Croplands play a vital role in regional carbon budgets. We hypothesized that biophysical factors would be important for soil respiration in a wheat-maize rotation cropping system. Soil CO2 efflux was measured using the closed chamber method, and net CO2 exchange between the cropland and the atmosphere obtained by the eddy covariance technique in a winter wheat-summer maize double cropping system over four years (Oct 2002–Oct 2006). In addition to soil temperature, soil respiration was controlled by leaf area index and soil moisture in the wheat field and soil moisture in the maize field. Temperature sensitivity (Q10) of soil respiration was 2.2 in the wheat and maize growing seasons. In the wheat field, the Q10 value during the sowing–returning green period (4.9) was more than that during the returning green–ripening period (2.0). On a monthly time scale, soil respiration was controlled by gross primary productivity in the wheat field, indicating that soil respiration was coupled with ecosystem photosynthesis. Annual soil respiration was 825±73gCm−2 in the wheat–maize rotation system in 2003–2006. Over a 4–year average, soil respiration was 355±50gCm−2 in the wheat growing season and 470±67gCm−2 in the maize growing season, which accounted for 43% and 57% of the annual value respectively. At an annual time scale, soil respiration contributed to 72% of ecosystem respiration in the winter wheat–summer maize double cropping system.

Effects of saline irrigation on soil salt accumulation and grain yield in the winter wheat-summer maize double cropping system in the low plain of North China

In the dominant winter wheat (WW)-summer maize (SM) double cropping system in the low plain located in the North China, limited access to fresh water, especially during dry season, constitutes a major obstacle to realize high crop productivity. Using the vast water resources of the saline upper aquifer for irrigation during WW jointing stage, may help to bridge the peak of dry season and relieve the tight water situation in the region. A field experiment was conducted during 2009–2012 to investigate the effects of saline irrigation during WW jointing stage on soil salt accumulation and productivity of WW and SM. The experiment treatments comprised no irrigation (T1), fresh water irrigation (T2), slightly saline water irrigation (T3: 2.8 dS m−1), and strongly saline water irrigation (T4: 8.2 dS m−1) at WW jointing stage. With regard to WW yields and aggregated annual WW-SM yields, clear benefits of saline water irrigation (T3 & T4) compared to no irrigation (T1), as well as insignificant yield losses compared to fresh water irrigation (T2) occurred in all three experiment years. However, the increased soil salinity in early SM season in consequence of saline irrigation exerted a negative effect on SM photosynthesis and final yield in two of three experiment years. To avoid the negative aftereffects of saline irrigation, sufficient fresh water irrigation during SM sowing phase (i.e., increase from 60 to 90 mm) is recommended to guarantee good growth conditions during the sensitive early growing period of SM. The risk of long-term accumulation of salts as a result of saline irrigation during the peak of dry season is considered low, due to deep leaching of salts during regularly occurring wet years, as demonstrated in the 2012 experiment year. Thus, applying saline water irrigation at jointing stage of WW and fresh water at sowing of SM is most promising to realize high yield and fresh irrigation water saving.

Effects of different irrigation regimes on soil compaction in a winter wheat–summer maize cropping system in the North China Plain

An adjusted irrigation regime may help to minimize the risk of soil compaction, which is a major yield constraining factor in global crop production, constituting a serious issue in the winter wheat–summer maize double cropping system of the North China Plain. Thus this study aimed to evaluate the natural changes of soil penetration resistance (PR) and soil bulk density (BD) caused by freezing/thawing (FT) and wetting/drying (WD) cycles. This was tested under full irrigation (FI) and deficit irrigation (DI) over three double cropping seasons from 2011 to 2014, following a conventional tillage sequence of shallow, deep and shallow tillage before the first, second and third season, respectively. The results showed that in the deeper soil layer FT during winter reduced the PR by 22.9%, 34.7% and −18.7% under FI for the three seasons, respectively. The values under DI were 4.5%, 8.0% and −33.8% for the three seasons, respectively. However the compaction alleviating effects due to FT were only of temporary nature. Furthermore FI caused a stronger recompaction after deep tillage compared to DI, mainly attributed to increased slumping of soil. On the contrary DI reduced the BD by 8.4% in the deep soil layer by fostering intensive cycles of WD over the three double cropping seasons. Results also showed that DI resulted in a higher physical quality of subsoil, expressed by the value of S, compared to FI. It was concluded that irrigation intensity should be reduced after deep tillage to minimize and slow down subsequent recompaction.

Evaluation of optimal irrigation scheduling and groundwater recharge at representative sites in the North China Plain with SWAP model and field experiments

The application of water saving irrigation is essential to alleviate the rapid depletion of groundwater resources in water crisis areas such as the North China Plain (NCP). The integrated effects of climate, soil and groundwater conditions on water balance and crop response need to be further studied. It is imperative to investigate spatial differences of irrigation scheduling and groundwater recharge within the NCP for regional water management. In this study, three representative sites including Luancheng (LC), Tongzhou (TZ) and Yucheng (YC) with different precipitation, soil and water table conditions were selected. The SWAP model was established at each site to compare optimal irrigation scheduling and groundwater recharge of the winter wheat-summer maize double cropping system under different hydrological years. Largest optimal irrigation amount and additional irrigation at the winter-dormancy stage of wheat were required for the TZ site in each hydrological year. The optimal irrigation scheduling was almost same at the three sites for summer maize, except that no irrigation was needed at filling stage in dry year at the YC site. The average annual groundwater recharge under optimal irrigation was in the order of YC (108.4mm), TZ (63.8mm) and LC (0.4mm). Furthermore, the groundwater recharge occurred throughout the double cropping seasons in YC, but it occurred only in summer maize season at the LC and TZ sites. The net irrigation amount of the optimal irrigation scheduling was reduced by 51.2%, 24.9% and 77.2% compared to reference practice at the LC, TZ and YC sites, respectively. The amount of groundwater recharge depended on the local precipitation and irrigation, while water table depth and soil texture mainly influenced the delay time of groundwater recharge relative to the water input events.

Impact of the shrinking winter wheat sown area on agricultural water consumption in the Hebei Plain

This study firstly analyzed the shrinkage of winter wheat and the changes of crop- ping systems in the Hebei Plain from 1998 to 2010 based on the agricultural statistic data of 11 cities and meteorological data, including daily temperature, precipitation, water vapor, wind speed and minimum relative humidity data from 22 meteorological stations, and then calcu- lated the water deficit and irrigation water resources required by different cropping systems, as well as the irrigation water resources conserved as a result of cropping system changes, using crop coefficient method and every ten-day effective precipitation estimation method. The results are as follows. 1) The sown areas of winter wheat in the 11 cities in the Hebei Plain all shrunk during the study period. The shrinkage rate was 16.07% and the total shrinkage area amounted to 49.62×10 4 ha. The shrinkage was most serious in the Bei- jing-Tianjin-Tangshan metropolitan agglomerate, with a shrinkage rate of 47.23%. 2) The precipitation fill rate of winter wheat was only 20%-30%, while those of spring maize and summer maize both exceeded 50%. The irrigation water resources demanded by the winter wheat-summer maize double cropping system ranged from 400 mm to 530 mm, while those demanded by the spring maize single cropping system ranged only from 160 mm to 210 mm. 3) The water resources conserved as a result of the winter wheat sown area shrinkage during the study period were about 15.96×10 8 m 3 /a, accounting for 27.85% of those provided for Beijing, Tianjin and Hebei by the first phase of the Mid-Route of the South-to-North Water Diversion Project.

Concentration profiles of CH4, CO2 and N2O in soils of a wheat–maize rotation ecosystem in North China Plain, measured weekly over a whole year

Agricultural soils are main sources and sinks of the greenhouse gases carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). The source–sink function depends on soil characteristics, climate and management. Emission measurements usually quantify the net result of production, consumption and transport of these gases in the soil; they do not provide information about the depth distributions of the concentrations of these gases in the soil. Here we report on concentrations of CO2, CH4 and N2O in air of 300cm deep soil profiles, at resolutions of 30–50cm, over a full year. Gas samples were taken weekly in a long-term field experiment with an irrigated winter wheat–summer maize double cropping system, and four fertilizer N application rates (0, 200, 400 and 600kgNha−1year−1). The results showed distinct differences in CH4, CO2 and N2O concentrations profiles with soil depth. The concentrations of CO2 in soil air increased with soil depth and showed a seasonal pattern with relatively high concentrations in the warm and moist maize growing season and relatively low concentrations in the winter-wheat growing season. In contrast, CH4 concentrations decreased with depth, and did not show a distinct seasonal cycle. Urea application did not have a large effect on CH4 or CO2 concentrations, neither in the topsoil nor the subsoil. Concentrations of N2O responded to N fertilizer application and irrigation. Application of fertilizer strongly increased grain and straw yields of both winter wheat and summer maize, relatively to the control, but differences in yield between the treatments N200, N400 and N600 were not statistically significant. However, it significantly increased mean N2O concentrations peaks at basically all soil depths. Interestingly, concentrations of N2O increased almost instantaneously in the whole soil profile, which indicates that the soil had a relatively high diffusivity, despite compacted subsoil layers.In conclusion, the frequent measurements, at high depth resolutions, of concentrations of CH4, CO2 and N2O in soil air under a winter wheat–summer maize double crop rotation provide detailed insight into the production, consumption and transport of these gases in the soil. Concentrations of CH4, CO2 and N2O responded differently to management activities and weather conditions.