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This study aimed to identify whether nitrogen (N) use efficiency in a summer-maize/winter-wheat double-cropping system of the North China Plain (NCP) could be increased by adjusting N supply to crop N demand, and through the use of alternate N fertilizers and application strategies. In a static experiment conducted on a farmers’ field six reduced N treatments were compared to farmers’ practice (FP: 550 kg (N) ha −1 a −1 ) and a control treatment (CK). With few exceptions of single treatments in single cropping-seasons, the optimized fertilization of N did not lead to a yield reduction of either summer-maize or winter-wheat. The grain yield of summer-maize ranged between 5.8 and 7.1 Mg ha −1 . The grain yield of wheat ranged between 4.4 and 6.2 Mg ha −1 . For the first two vegetation periods of summer-maize, the recovery efficiency (RE N : 0.09–0.30 kg kg −1 ) and agronomic efficiency of N (AE N ) were mainly affected by the yield achieved in the control treatment (5.7 and 5.9 Mg ha −1 ), which was not significantly reduced compared to most fertilized treatments. In the third vegetation period of summer-maize, an increase of RE N of the reduced treatments (0.37–0.58 kg kg −1 ) was determined compared to FP (0.21 kg kg −1 ). In both vegetation periods of wheat RE N of the reduced treatments (0.34–1.0 kg kg −1 ) was significantly higher compared to FP (0.26 and 0.27 kg kg −1 ). The highest cumulated AE N , as well as cumulated grain yields were observed when ammonium sulphate nitrate + 3,4-dimethylpyrazolephosphate (ASN DMPP ) was applied according to crop N demand and residual soil mineral N. The highest RE N was observed when urea ammonium nitrate was applied in a shallow, banded depot (UAN DEP ). This research demonstrates that N application rates in a maize/wheat double cropping system may be significantly reduced compared to common farmers’ practice, without negatively affecting grain yield, thereby increasing N use efficiency. [ABSTRACT FROM AUTHOR]

Highlights: [•] Adjusting fertilization to the crop requirements reduces the N balance in a farmer's field. [•] N mineralized in spring is only utilized by the following summer-crop. [•] N application above crop requirements increases the amount of cycling N and apparent N loss. [Copyright &y& Elsevier]

Abstract: A process-based ecosystem model (Vegetation–atmosphere Interface Processes (VIP) model) is expanded, and then validated against three years’ biometric, soil moisture and eddy-covariance fluxes data over a winter wheat–summer maize cropping system in the North China Plain (NCP). The results show that the model is capable of simulating satisfactorily the evolution of crop biomass, phenological development and soil moisture. The computed 30-min estimates of CO2, water and heat fluxes agree well with the eddy-covariance measurements. At daily scale, the root mean square errors (RMSEs) of net radiation, latent heat flux and net ecosystem productivity (NEP) are 1.0MJm−2 day−1, 1.8MJm−2 day−1 and 2.6gCm−2 day−1, respectively. However, systematic errors in sensible heat flux estimates are identified in times of season when daily sensible heat flux is negative due to the horizontal advection. Annually, about 55% of evapotranspiration (ET) is emanated from winter wheat and 45% from maize. The annual NEP varies noticeably, with relative biases of 18, 9 and −29% in each year from 2003 to 2005, respectively. Sensitivity analysis illustrates that ET is quite sensitive to soil resistance parameters contributing to soil evaporation, and NEP to quantum efficiency of photosynthesis. The uncertainties of annual ET and NEP are 16.5% and 35.6% respectively when the key parameters are randomly sampled in their uncertainty ranges. Errors on eddy-covariance measurements and uncertainty on the model parameters may partly explain the discrepancy between the simulations and the measurements. [Copyright &y& Elsevier]

Abstract: Nitrogen amendment followed by flooding irrigation is a general management practice for a wheat–maize rotation in the North China Plain, which may favor nitrification and denitrification. Consequently, high emissions of nitrous oxide (N2O) and nitric oxide (NO) are hypothesized to occur. To test this hypothesis, we performed year-round field measurements of N2O and NO fluxes from irrigated wheat–maize fields on a calcareous soil applied with all crop residues using a static, opaque chamber measuring system. To interpret the field data, laboratory experiments using intact soil cores with added carbon (glucose) and nitrogen (nitrate, ammonium) substrates were performed. Our field measurements showed that pulse emissions after fertilization and irrigation/rainfall contributed to 73% and 88% of the annual N2O and NO emissions, respectively. Soil moisture and mineral nitrogen contents significantly affected the emissions of both gases. Annual emissions from fields fertilized at the conventional rate (600 kg N ha−1 yr−1) totaled 4.0 ± 0.2 and 3.0 ± 0.2 kg N ha−1 yr−1 for N2O and NO, respectively, while those from unfertilized fields were much lower (0.5 ± 0.02 kg N ha−1 yr−1 and 0.4 ± 0.05 kg N ha−1 yr−1, respectively). Direct emission factors (EFds) of N2O and NO for the fertilizer nitrogen were estimated to be 0.59 ± 0.04% and 0.44 ± 0.04%, respectively. By summarizing the results of our study and others, we recommended specific EFds (N2O: 0.54 ± 0.09%; NO: 0.45 ± 0.04%) for estimating emissions from irrigated croplands on calcareous soils with organic carbon ranging from 5 to 16 g kg−1. Nitrification dominated the processes driving the emissions of both gases following fertilization. It was evident that insufficient available carbon limited microbial denitrification and thus N2O emission. This implicates that efforts to enhance carbon sink in calcareous soils likely increase their N2O emissions. [Copyright &y& Elsevier]

Abstract: Plant water status is a key factor impacting crop growth and agricultural water management. Crop water stress may alter canopy temperature, the energy balance, transpiration, photosynthesis, canopy water use efficiency, and crop yield. The objective of this study was to calculate the Crop Water Stress Index (CWSI) from canopy temperature and energy balance measurements and evaluate the utility of CWSI to quantify water stress by comparing CWSI to latent heat and carbon dioxide (CO2) flux measurements over canopies of winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.). The experiment was conducted at the Yucheng Integrated Agricultural Experimental Station of the Chinese Academy of Sciences from 2003 to 2005. Latent heat and CO2 fluxes (by eddy covariance), canopy and air temperature, relative humidity, net radiation, wind speed, and soil heat flux were averaged at half-hour intervals. Leaf area index and crop height were measured every 7 days. CWSI was calculated from measured canopy-air temperature differences using the Jackson method. Under high net radiation conditions (greater than 500Wm−2), calculated values of minimum canopy-air temperature differences were similar to previously published empirically determined non-water-stressed baselines. Valid measures of CWSI were only obtained when canopy closure minimized the influence of viewed soil on infrared canopy temperature measurements (leaf area index was greater than 2.5m2 m−2). Wheat and maize latent heat flux and canopy CO2 flux generally decreased linearly with increases in CWSI when net radiation levels were greater than 300Wm−2. The responses of latent heat flux and CO2 flux to CWSI did not demonstrate a consistent relationship in wheat that would recommend it as a reliable water stress quantification tool. The responses of latent heat flux and CO2 flux to CWSI were more consistent in maize, suggesting that CWSI could be useful in identifying and quantifying water stress conditions when net radiation was greater than 300Wm−2. The results suggest that CWSI calculated by the Jackson method under varying solar radiation and wind speed conditions may be used for irrigation scheduling and agricultural water management of maize in irrigated agricultural regions, such as the North China Plain. [Copyright &y& Elsevier]