Wheat-maize Double Cropping System Research Articles

Dynamic changes in soil organic carbon induced by long-term compost application under a wheat-maize double cropping system in North China

Soil organic carbon (SOC) plays a vital role in improving soil quality and alleviating global warming. Understanding the dynamic changes in SOC is crucial for its accumulation induced by compost application in agroecosystem. In this study, soil samples were collected from three treatments: high-rate bio-compost (BioMh), low-rate bio-compost (BioMl), and control (CK, no fertilization) during 2002–2020 in a wheat-maize double cropping system in North China. The soils were separated into three functional fractions, i.e., coarse particle organic matter (cPOM, >250 μm), microaggregates (μAgg, 53–250 μm) and mineral-associated organic matter (MAOM, < 53 μm), and the associated SOC contents were determined. During 1993–2002, SOC contents in bulk soil significantly increased with the duration in the BioMh and BioMl plots. However, there was no significant correlation between SOC content and duration during 2002–2020. These results suggested that compost application positively improved SOC sequestration, while the duration of SOC sequestration (i.e., the longevity of increased SOC with time) under compost inputs maintained only 9 years. Moreover, there was a significant increase in mean annual SOC contents in bulk soil with compost application rate during 2002–2020, indicating that carbon saturation did not occur. Additionally, the SOC contents in the cPOM fraction increased with time (p < 0.01), but the corresponding μAgg and MAOM associated SOC was insignificant (p > 0.05). The MAOM fraction exhibited no additional carbon accumulation with expanding compost application, confirming a hierarchical carbon saturation in these fractions. We concluded that soils under wheat-maize double cropping system in North China have greater potential to sequester C through additional compost inputs, despite showing hierarchical saturation behavior in the non-protected coarse particulate fraction.

Soil Compaction and Maize Root Distribution under Subsoiling Tillage in a Wheat–Maize Double Cropping System

Huang-Huai-Hai Plain is the most important region for grain production in China. In this area, long-term rotary tillage in winter wheat and no tillage in summer maize have significantly increased soil bulk density, which impede maize root growth and reduce the grain yield. Subsoiling tillage is an effective practice to improve soil properties and crop growth. The objective of this study was to investigate the integrated effects of subsoiling tillage in both winter wheat and summer maize seasons on soil bulk density, maize root growth and spatial distribution. A two-year field experiment was conducted in winter wheat–summer maize rotation system. Tillage treatments included rotary tillage (RT) and subsoiling tillage (ST) in wheat season, and no tillage (NT), inter–row subsoiling tillage (STIR), and on–row subsoiling tillage (STOR) in maize season. It was found that in the second year, i.e., in 2018, ST decreased soil bulk density by 3.87% and increased porosity by 5.86% at 30–40 cm soil depth at maize maturity. Meanwhile, maize root length density at 40–50 cm depth increased by 30.00% and grain yield increased by 4.70% under ST. In maize season tillage treatments, STOR decreased soil bulk density by 4.52% and increased soil porosity by 6.96% at 20–30 cm soil depth. Compared with NT, the STOR significantly increased maize root length density at 20–30 cm soil depth by 78.45%, and increased root length density in a horizontal area 0–10 cm for both years, with a significant increase of 58.89% in 2018. Therefore, this study demonstrated that in the Huang-Huai-Hai Plain, which has a tidal soil type, subsoiling tillage in winter wheat season and on–row subsoiling tillage in maize season can loosen the soil and improve vertical extension of maize root system in the soil.

Optimizing Straw Management to Enhance Carbon and Nitrogen Efficiency and Economic Benefit of Wheat-Maize Double Cropping System

The optimization of annual straw management can improve the yield, income, and carbon and nitrogen efficiency of wheat-maize double cropping systems. Based on a long-term positioning trial started in 2012, five straw management methods were considered, C100 (100% return), C75 (75% return+25% harvest), C50 (50% return+50% harvest), C25 (25% return+75% harvest), and C0 (100% harvest). We analyzed the effects of farmland carbon and nitrogen inputs and their ratios on crop yield, carbon and nitrogen use efficiency, and economic benefits in wheat and maize anniversaries with different straw managements. The results showed that: ① the amount of straw returning to the field resulted in a significant difference in carbon and nitrogen input. The annual carbon and nitrogen inputs from crop residues decreased by 1.76 t·hm-2 and 34.28 kg·hm-2, respectively, with a 25% reduction in straw returning. The C/N ratios under the C100-C0 treatment were 18.62, 17.03, 15.64, 12.54, and 9.61, respectively. ② Grain yield first increased and then decreased with the decrease in the C/N input ratio, and the effect of straw management on wheat yield was greater than that on maize. Compared with that under C100 and C0, the average grain yield of wheat and maize under the C50 treatment increased by 13.34%-13.67% and 16.10%-17.71%, respectively, and the total grain yield of wheat and maize increased by 14.98% and 15.68%. ③ The annual grain yield and carbon agronomy efficiency were the best with the C/N input ratio of 15.64 (in the C50 treatment), which were 15.71% and 0.29 kg·kg-1, respectively. The carbon production efficiency continued to increase with the decrease in the C/N input ratio, and there was a significant negative correlation between them. The nitrogen production efficiency increased first and then decreased with the decrease in the C/N input ratio. The nitrogen production efficiency of the C50 treatment was the highest (0.64 kg·kg-1), which was significantly higher than that of C100 by 32.63%. ④ The C50 treatment had the highest economic income and net income, which were 46200 yuan·hm-2 and 33400 yuan·hm-2, respectively. Compared with that of C100, the economic income of grain and straw feed increased by 5600 yuan·hm-2 and 3200 yuan·hm-2, respectively. In conclusion, the optimal C/N input ratio can be achieved by optimized straw management; 50% straw returning and 50% harvest in a wheat-maize double-cropping intensive production system can promote carbon agricultural efficiency and nitrogen production efficiency and obtain the maximum grain yield and economic benefits.

Nitrogen management to reduce GHG emissions while maintaining high crop productivity in temperate summer rainfall climate

Nitrogen (N) fertilizer management determines the productivity and environmental footprint of intensive wheat-maize double-cropping systems in the North China Plain (NCP). The N fertilizer application rate can be optimized by balancing the trade-off between crop productivity and N 2 O emissions. Applying more N fertilizer to wheat in the dry, cool winter season while less N to summer crops is expected to reduce the N 2 O emissions without scarifying yield, because summer crop (maize) will use the residual N fertilizer from the previous crop season (wheat) to maintain their productivity. We combined four years of experimental data and soil-plant system modeling to assess the productivity and greenhouse gas emissions resulting from various N fertilizer management strategies. The farming systems model APSIM was used to simulate the wheat-maize double cropping system with N fertilizer application rates of 0–920 kg N ha −1 yr −1 . The APSIM model explained 93% variation in biomass (RMSE = 0.88), 82% variation in soil mineral N (RMSE = 34.1), and 70% variation in N 2 O emission (RMSE = 1.37) measured in the experiment. The default IPCC emission factor (0.5% for the wheat season and 1.6% for the maize season) underestimated the N 2 O emission by 7.25 kg ha −1 when the local N fertilizer rates were applied (about 325 kg N ha −1 for wheat and 257 kg N ha −1 for maize). A N rate of 420 kg N ha −1 yr −1 would reduce GHG emission to the minimum (1.15 t CO 2 -eq ha −1 yr −1 ) while achieving more than 90% of the maximum grain yield. Additionally, allocating more N fertilizer to the wheat crop, while reducing the N fertilizer input for maize, did not significantly change grain yield of either crop, but further reduced net GHG emission by 1.07 t CO 2 -eq ha −1 yr −1 . The APSIM model describes the crop growth and soil N dynamics of a wheat-maize double cropping system that receives N fertilizer at rates up to 920 kg N ha −1 yr −1 . The site-specific modeling results indicate that appropriate N fertilizer management, i.e., adjusting the rate and time of N applications, can lower the net GHG emission without impacting crop yields. Our study provides a practical and reliable method to develop a "win-win" strategy for N fertilizer management in double-cropping systems. • There is a trade-off between crop yield and GHG emissions with N fertilizer use. • Long-term impact of N fertilizer use was deduced with a modelling approach. • Lowering N fertilizer rate could reduce GHG emissions while maintaining crop yield. • Allocating more N for wheat and less for maize is a further opportunity. • These scenarios should be used to develop a "win-win" N management strategy.

Application of water-energy-food nexus approach for optimal tillage and irrigation management in intensive wheat-maize double cropping system

Demand for water, energy and food is increasing driven by a rising global population, changing diets, warming climate and economic growth. Wheat-maize double cropping system, as one of the best trials in ensuring sustainable food security, is experiencing various optimizing irrigation management and tillage practices in the North China Plain. However, previous studies mainly focused on their influences on crop yield and water use efficiency. Comprehensive analysis of water-energy-food for the practices was limited. Therefore, a life cycle assessments based water–energy–food (WEF) nexus analysis was conducted using data from a 7-year two-factor split-plot field experiments with four tillage (NT, no-tillage; RT, rotary tillage; PT, plow tillage; CT, local current tillage) and three irrigation managements (W1, pre-planting irrigation for wheat + pre-planting irrigation for maize; W2, pre-planting + jointing irrigation for wheat + pre-planting irrigation for maize; and W3, pre-planting + jointing + anthesis irrigation for wheat + pre-planting irrigation for maize; 75 mm each time). The results indicated that irrigation, fertilizer and diesels input were the top three items for water and energy consumption. Irrigation managements significantly altered wheat and annual yield but not for maize yield. Tillage practices primarily altered diesel input to affect energy mass and energy economic productivity. During wheat season, W3PT obtained the highest yield at 8.69 t ha−1 and highest net income at 8.27 ¥ ha−1. With the same tillage practice, W1 had the best performance in water and energy consumption and mass productivity, while W2 had the highest water and energy economic productivity. In terms of different tillage practices with the same irrigation amount, NT consumed lowest energy, but its lowest wheat yield offset its benefits as well. During maize season, the yields were insensitive for irrigation and tillage practices. NT and CT were substantially beneficial regarding energy input, which further resulted in good performance in terms of energy mass and economic productivity under the same irrigation treatment. Throughout the year, lower water and energy consumption and higher resource productivity offset the yield and income loss under W1CT to accomplish highest value of WEF nexus index. Thus it is the optimal tillage and irrigation management pattern in the wheat-maize double cropping system of the North China Plain achieving cleaner production. This study contributed a new case to using WEF nexus analysis and offered new reference data and effective suggestions for selecting proper filed management in the double cropping system to achieve sustainable development goals with carbon peaking and carbon neutrality.

Partial substitution of urea fertilizers by manure increases crop yield and nitrogen use efficiency of a wheat–maize double cropping system

Partial substitution of urea fertilizers by manure increases crop yield and nitrogen use efficiency of a wheat–maize double cropping system

Combined nitrogen and phosphorus management based on nitrate nitrogen threshold for balancing crop yield and soil nitrogen supply capacity

An appropriate combined nitrogen (N) and phosphorus (P) fertilization strategy is essential for obtaining sustained higher grain yields while maintaining soil fertility. In this study, a long-term split-plot design farmland experiment (initiated in 2009) with five N fertilizer rates combined with four P fertilizer rates was established during 2016–2019 to determine an appropriate nitrate-N (NO3-N) threshold in an intensive managed wheat–maize double cropping system. A fertilization strategy was then proposed based on the NO3-N threshold to balance the crop yields and soil nitrogen supply capacity. The results showed that N fertilizer increased the accumulated NO3-N, and the combined application of phosphate fertilizer with each N rate reduced the accumulated NO3-N to different degrees. The residual soil NO3-N reached a steady-state soil N pool balance after long-term application of N at 150–225 kg ha−1 combined with P at 60–120 kg ha−1. The residual NO3-N threshold in the root zone (0–100 cm soil layer) was determined as about 100 kg ha−1 at the crop harvest to maintain the N supply capacity and prevent leaching into the deep soil (>100 cm soil layer). The fertilization guidelines are 154 kg ha−1 for N fertilizer and 106 kg ha−1 for P fertilizer in the winter wheat season, and 162 kg ha−1 for N fertilizer and 122 kg ha−1 for P fertilizer in the summer maize growing season based on the NO3-N safety threshold. The optimized fertilizer strategy reduced the fertilizer application rate by 67 kg N ha−1 per year and the residual NO3-N by 34.2 % in the deep soil, while only reducing the average yield by 3.1 % across the crops and years. These findings provide a basis for sustainably balancing grain yields and soil nitrogen supply capacity as well as preventing nitrate pollution of farmland.

Interactions between phosphorus availability and microbes in a wheat–maize double cropping system: A reduced fertilization scheme

Mechanisms controlling phosphorus (P) availability and the roles of microorganisms in the efficient utilization of soil P in the wheat–maize double cropping system are poorly understood. In the present study, we conducted a pot experiment for four consecutive wheat–maize seasons (2016–2018) using calcareous soils with high (30.36 mg kg−1) and low (9.78 mg kg−1) initial Olsen-P content to evaluate the effects of conventional P fertilizer application to both wheat and maize (Pwm) along with a reduced P fertilizer application only to wheat (Pw). The microbial community structure along with soil P availability parameters and crop yield were determined. The results showed that the Pw treatment reduces the annual P input by 33.3% without affecting the total yield for at least two consecutive years as compared with the Pwm treatment in the high Olsen-P soil. Soil water-soluble P concentrations in the Pw treatment were similar to those in the Pwm treatment at the 12-leaf collar stage when maize requires the most P. Furthermore, the soil P content significantly affected soil microbial communities, especially fungal communities. Meanwhile, the relative abundances of Proteobacteria and alkaline phosphatase (ALP) activity of Pw were significantly higher (by 11.4 and 13.3%) than those of Pwm in soil with high Olsen-P. The microfloral contribution to yield was greater than that of soil P content in soil with high Olsen-P. Relative abundances of Bacillus and Rhizobium were enriched in the Pw treatment compared with the Pwm treatment. Bacillus showed a significant positive correlation with acid phosphatase (ACP) activity, and Rhizobium displayed significant positive correlations with ACP and ALP in soil with high Olsen-P, which may enhance P availability. Our findings suggested that the application of P fertilization only to wheat is practical in high P soils to ensure optimal production in the wheat and maize double cropping system and that the soil P availability and microbial community may collaborate to maintain optimal yield in a wheat–maize double cropping system.

冬小麦-夏玉米轮作&amp;ldquo;双晚&amp;rdquo;种植模式下的品种匹配与资源效率

<p id="C3">It is of great significance that exploring the characteristics of wheat-maize varieties combination suitable for stress resistance, high yield, and stable yield under the “double delay” system and their matching properties with natural resources, for ensuring the high yield and high efficiency production of winter wheat and summer maize in this region. In this study, field experiments were conducted from 2017 to 2019. Eight winter wheat and eight summer maize varieties were the main varieties in the North China Plain under winter wheat-summer maize “double delay” system with different irrigation treatments. Based on the analysis and evaluation of water use efficiency, grain filling characteristics, growth process, annual light, temperature, and water use efficiency, etc., the characteristics of wheat-maize varieties combination and resource use efficiency under the “double delay” system of winter wheat and summer maize were explored. The results suggested that among the tested wheat varieties, the yields of Jimai 325, Shimai 15, Nongda 3486, and Jimai 22 under conventional water-saving irrigation and rain-fed mode were higher than the average yield of the tested varieties druing the two growing seasons. In addition, the drought resistance index of Jimai 325 and Shimai 15 were higher than that of Jimai 22. Meanwhile, the grain-filling rate, grain number per spike, grain weight, and high stability coefficients of Jimai 22, Jimai 325, and Shimai 15 were higher than the mean of the tested varieties under different irrigation modes. Among the tested maize variaties, the yield and high stability coefficients of Denghai 605, Weike 702, MC670, and Nonghua 816 were all higher than the means of the tested varieties. The grain-filling rate of MC670, Denghai 605, and Xianyu 335 were higher than the means of the tested varieties during the two growing seasons. While, Dika 517 and Xianyu 335 had the lowest grain water content at harvest stage but the highest average dehydration rate among the tested varieties. Based on the comprehensive analysis of the yield and yield stability, drought resistance, grain-filling properties, and dehydration characteristics, the variety combination of Jimai 325-MC670 was selected with the highest annual yield and resource use efficiency. Compared with the local control combination of Jimai 22-Zhengdan 958, the annual yield increased by 17.2% and 17.9%, the light, temperature and irrigation water use efficiency increased by 18.6% and 20.0%, 18.1% and 18.9%, 17.4% and 18.1%, and increased economic benefit 8800 Yuan hm ^-2 and 9600 Yuan hm ^-2, respectively; to fit the whole-process mechanized management mode of wheat-maize double cropping system, maize could use varieties with fast dehydration rate and low grain water content when harvest, such as Dika 517 or Xianyu 335. Compared with the current local combination of Jimai 22-Zhengdan 958, this combination could increase the annual yield by 4.7% and 14.4%, and increase the light, temperature, and irrigation water use efficiency by 5.6% and 16.3%, 4.7% and 15.4%, 5.0% and 14.6%, and increased economic benefit by 2080 Yuan hm ^-2 and 7080 Yuan hm ^-2, respectively. In summary, optimizing the wheat-maize variety combination under the “double delay” cropping system can further improve the annual yield and resource use efficiency synergistically compared with the local staple wheat-maize variety combination.

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.

Model construction for field operation machinery selection and configuration in wheat-maize double cropping system

In order to scientifically and reasonably select the field operation machinery in wheat-maize double cropping system, first, the selection evaluation index system was constructed through the existing national standards and industry standards. Then the selection evaluation model was established based on the improved fuzzy comprehensive evaluation method. And the method of subjective weight and objective weight was used to overcome the drawbacks of the previous single weighting method that could not take into account the subject and object information of each indicator, and the weight value of each index was obtained in the evaluation system. Finally, the tillage process was used as an example, the field experiment was carried out to obtain the evaluation index value, and the model of selection evaluation was verified. The selection results of moldboard plough and rotary cultivator were as follows: the order of the comprehensive evaluation results of the moldboard plough results was ranked from high to low as 1LFK-435 (IIM), 1LFK-535 (IM), 1LF-342 (IIIM), 1LFT-445 (IVM), 1LFT-545 (VM), and the best machine type of the moldboard plough was IIM; the order of the comprehensive evaluation results of the rotary cultivator was ranked from high to low as 1GQKGN-240 (IIIR), 1GKNSM-250 (IVR), 1GKN-230K (IR), 1GKN-250K (IIR), 1GQKGN-220 (VR), and the optimal model of the rotary cultivator was IIIR. The experimental results showed that the results obtained by the evaluation model were in agreement with the local actual situation. The evaluation model will provide a scientific method for the selection of wheat and maize double cropping field operation machinery. Keywords: wheat-maize double cropping system, agricultural machinery, parts selection mode, evaluation system, fuzzy comprehensive evaluation method, combination weight DOI: 10.25165/j.ijabe.20211404.6383 Citation: Zhang F, Chen T H, Teng S, Wang J J, Xu R L, Guo Z J. Model construction for field operation machinery selection and configuration in wheat-maize double cropping system. Int J Agric & Biol Eng, 2021; 14(4): 82–89.

Impact of Tillage and Crop Residue Management on the Weed Community and Wheat Yield in a Wheat–Maize Double Cropping System

Weeds are often harmful to crop growth due to the competition for space and resources. A field experiment containing four treatments with three replications in a complete randomized design was conducted at Yucheng Comprehensive Experiment Station, Chinese Academy of Sciences since 2008 to assess the impact of shifting from conventional tillage to no-till with crop residue management on weeds and wheat production at the North China Plain. We found that both aboveground weed density and species richness were higher under continuous no-till (NT) than conventional tillage (CT) in the regrowth and stem elongation stage of wheat growth. On the other hand, aboveground weed density in the stage of flowering and filling decreased with crop residue mulching. The density of the soil seed bank in crop residue removal treatments was significantly higher than that of crop residue retention. Besides, either crop residue mulching or incorporating into the soil significantly increased the wheat yield compared with crop residue removal regardless of tillage management. In conclusion, crop residue retention could decrease the weed density and species richness both aboveground and in the soil seed bank and inhibit the growth of broadleaf weeds by the residue layer. Moreover, crop residue retention could improve the wheat yield.

Integrated crop residue and subsoiling management strategies influence soil quality and agricultural sustainability

AbstractThe rapid expansion of commercial‐scale cellulosic industries raises the prospect of widespread crop residue harvest. However, the effects of integrated crop residue and tillage management strategies on agricultural sustainability are not fully understood. Here, we investigated the effects of different integrated crop residue and tillage management strategies on crop productivity, economic profit, soil quality, and agricultural sustainability in an intensive wheat (Triticum aestivum L.)–maize (Zea mays L.) double‐cropping system over 7 yr. The treatments included residue return of both crops (WrMr), wheat residue return with harvesting maize residue (WrMh), wheat residue return with stubble at a height of 30∼40 cm and harvesting maize residue (WsMh), maize residue return with harvesting wheat residue (WhMr), maize residue return with subsoiling and harvesting wheat residue (WhMs), and residue harvest of both crops (WhMh). The annual average grain yields of wheat and maize increased by 17.6∼36.1% and 9.9∼22.8% under integrated strategies relative to those in WhMh. Compared with the WhMh, the WsMh and WhMs increased the economic profit (EP) by 9.5 and 6.1%, respectively. The integrated strategies significantly improved the chemical, biological, and physical properties of soil, resulting in higher sustainability indices (SIs) relative to the WhMh. The SIs were 1.59 and 1.33 in WrMr and WhMs, respectively, higher than the lowest value when a sustained system needed. Therefore, the adoption of maize residue return with subsoiling and harvesting wheat residue can maintain agricultural sustainability in the wheat–maize double cropping system under commercial‐scale cellulosic industries’ expansion in the north‐central plain of China.

Model construction for field operation machinery selection and configuration in wheat-maize double cropping system

Model construction for field operation machinery selection and configuration in wheat-maize double cropping system

Impacts of Land Fragmentation and Cropping System on the Productivity and Efficiency of Grain Producers in the North China Plain: Taking Cangxian County of Hebei Province as an Example

Land fragmentation is widely known to have an impact on farm performance. However, previous studies investigating this impact mainly focused on a single crop, and only limited data from China are available. This study considers multiple crops to identify the impact of land fragmentation (LF), as well as cropping system (CS), on farm productivity and the efficiency of grain producers in the North China Plain (NCP), using Cangxian County of Hebei Province as an example. Detailed household- and plot-level survey data are applied and four stochastic frontier and inefficiency models are developed. These models include different sets of key variables in either the production function or the inefficiency models, in order to investigate all possibilities of their influences on farm productivity and efficiency. The results show that LF plays a significant and detrimental role, affecting both productivity and efficiency. A positive effect is evident with respect to the CS variable, i.e., multiple cropping index (MCI), and the wheat-maize double CS, rather than the maize single CS, is usually associated with higher farm productivity and efficiency. In addition to LF and CS, four basic production input variables (labor, seed, pesticide and irrigation), also significantly affect farmers' productivity, while the age of the household head and the ratio of the off-farm labor to total labor are significantly relevant to technical inefficiency. Policies geared toward the promotion of land transfer and the rational adjustment of cropping systems are recommended for boosting farm productivity and efficiency, and thus maintaining the food supply while mitigating the overexploitation of groundwater in the NCP.

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.

Variability and controls of soil CO2 fluxes under different tillage and crop residue managements in a wheat-maize double-cropping system.

The spatial and temporal variability of soil CO2 emissions from agricultural soils is inherently high. While tillage and crop residue practices play vital roles in governing soil CO2 emission, their effects on the variability of soil CO2 fluxes across depths and seasons are still poorly understood. To address this, an experiment consisting of four treatments, namely conventional tillage with (CT+) and without crop residue application (CT-), as well as no tillage with (NT+) and without crop residue application (NT-), was conducted to investigate soil CO2 fluxes at top 40 cm soils with 10-cm depth intervals in a winter wheat-summer maize rotation system in the North China Plain. Our results showed soil CO2 fluxes increased with depth in both the wheat- and maize-growing seasons. However, the dominant factors in regulating soil CO2 fluxes changed with soil depth and seasons. In the wheat-growing season, increase in soil CO2 fluxes with depth was attributed to the increase of dissolved organic carbon-to-nitrogen ratio (DOC/DON) and a decline in soil DON concentration along the soil profile. These factors explained about 55-96% of the total variation in soil CO2 fluxes at different soil depths. In the maize-growing season, the dominant factors were soil DOC/DON ratio, soil DON concentrations, and soil moisture. These factors explained approximately 79-96% of the total variation in soil CO2 fluxes along the soil depth. Greater soil CO2 fluxes (except at 30-40 cm depth) were observed in NT- than CT- treatments. Furthermore, crop residue application enhanced soil CO2 fluxes across different depths, but the enhancement was more prominent in CT+ than NT+. Moreover, soil CO2 fluxes in the maize-growing season were greater than those in the wheat-growing season. Our results demonstrate that the effects of tillage regimes and crop residue management practices on soil CO2 emissions are not confined only to the plough layer but can extend to soils of over 30 cm depths. We also need to revisit the general conventional view that no tillage can significantly reduce soil CO2 emissions compared with conventional tillage for better climate change mitigation.

Impacts of nitrogen fertilizer type and application rate on soil acidification rate under a wheat-maize double cropping system

Nitrogen (N) fertilizer-induced soil acidification in Chinese croplands is well-known, but insight in the impacts of different N fertilizer management approaches (fertilizer type and rate) on soil acidification rates is very limited. Here, we conducted a field experiment on a moderate acid soil to quantify soil acidification rates in response to N fertilization by different fertilizer types and N rates through monitoring the fate of elements (mainly nutrients) related to H+ production and consumption. Two N fertilizer types (urea and NH4Cl) and three N rates (control, optimized and conventional, 0/120/240 kg N ha−1 for wheat, 0/160/320 kg N ha−1 for maize) were included. Nitrogen addition led to an average H+ production of 4.0, 8.7, 11.4, 29.7 and 52.6 keq ha−1 yr−1, respectively, for the control, optimized urea, conventional urea, optimized NH4Cl and conventional NH4Cl plots. This was accompanied with a decline in soil base saturation of 1–10% and in soil pH of 0.1–0.7 units in the topsoil (0–20 cm). Removal of base cations by crop harvesting and N transformations contributed ~70% and ~20% to the H+ production in the urea treated plots, being ~20% and ~75% in the NH4Cl treated plots, respectively. The large NH4+ input via fertilization in the NH4Cl treated plots strongly enhanced the H+ production induced by N transformations. The low contribution of N transformations to the H+ production in the urea treated plots was due to the limited NO3− leaching, induced by the high N losses to air caused by denitrification. Increased N addition by urea, however, strongly increased H+ production by enhanced plant uptake of base cations, mainly due to a large potassium uptake in straw. Our results highlight the important role of optimizing fertilizer form and N rate as well as straw return to the field in alleviating soil acidification.

Soil Water and Nitrogen Fluxes in Response to Climate Change in a Wheat–Maize Double Cropping System

The impact of soil nutrient depletion on crop production is a thoroughly researched issue; however, robust assessments on the impact of climate change on water and N fluxes in agroecosystem are lacking. The complexity of soil water and N fluxes in response to climate change under agroecosystems makes simulation-based approaches to this issue appealing. This study evaluated the responses of crop yield, soil water, and N fluxes of a wheat–maize rotation to two Representative Concentration Pathways climate scenarios (RCP4.5 and RCP8.5) at Tai’an, a representative site on the North China Plain (NCP). Results showed that the mean air temperature and accumulated precipitation for both winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) growing seasons changed in both magnitude and pattern under various climate scenarios. The temperature increases shortened the growth periods of these two crops by more than 13 days and decrease summer maize yields (P &lt; 0.05). These results are illustrated by lower yield results associated with RCP4.5 (20.5%) and RCP8.5 (19.3%) climate scenarios, respectively. During the winter wheat growing season, water drainage examined in the climate scenarios was significantly higher (more than double) than the baseline, and there was no significant change to nitrate leaching and denitrification. In the summer maize growing season, with continuously rising temperatures, the ranking for evaporation was in the order baseline &lt; RCP4.5 &lt; RCP8.5, however, the opposite ranking applied for transpiration and evapotranspiration. The increase in water drainage was 1.4 times higher than the baseline, whereas the nitrate leaching in soil significantly decreased. Our simulation results provide an opportunity to improve the understanding of soil water and N fluxes in agroecosystems, which can lead to deficient or excess N under future climate conditions.

Crop Productivity and Nitrogen Balance as Influenced by Nitrogen Deposition and Fertilizer Application in North China

In spite of the importance of N management in agricultural production, closing the full nitrogen balance remains a challenge, mainly due to the uncertainties in both fluxes of nitrogen input and output. We analyzed N deposition and its influence on crop productivity and field nitrogen balance based on data from three of 15 years (1990–2005) of experiments in North China. The results showed that the average annual nitrogen deposition was 76, 80, and 94 kg N/ha at Changping, Zhengzhou, and Yangling in a wheat-maize rotation system, respectively. The deposited N could support a corresponding total biomass production (wheat plus maize) of 9.6, 10.6, and 8.8 Mg/ha with a total grain yield of 3.8, 4.8, and 3.7 Mg/ha, however, that did not cause a further decline in soil organic matter. N fertilizer application could increase total biomass (grain) by 244% (259%) and 74% (119%) for wheat and maize, respectively. Under optimal N management, N deposition accounted for 17–21% of the total N inputs, which affected significantly the recovery efficiency of applied N. N deposition showed a significant spatial variation in terms of the fraction of dry and wet depositions. On an annual average, N deposition roughly balanced out N losses due to NH3 volatilization and N2O loss from nitrification and denitrification. NH3 volatilization and NO3−-N leaching each accounted for 16–20% of the total N outputs. A system modeling approach is recommended to investigate the spatial variation of N leaching as affected by climatic conditions, and to fully account for the nitrogen fluxes. The N deposition derived from this study can be used as the background N input into the wheat-maize double cropping system for N balance.