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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]

In the North China Plain, the grain yield of irrigated wheat-maize cropping system has been steadily increasing in the past decades under a significant warming climate. This paper combined regional and field data with modeling to analyze the changes in the climate in the last 40 years, and to investigate the influence of changes in crop varieties and management options to crop yield. In particular, we examined the impact of a planned adaptation strategy to climate change -'Double-Delay' technology, i.e., delay both the sowing time of wheat and the harvesting time of maize, on both wheat and maize yield. The results show that improved crop varieties and management options not only compensated some negative impact of reduced crop growth period on crop yield due to the increase in temperature, they have contributed significantly to crop yield increase. The increase in temperature before over-wintering stage enabled late sowing of winter wheat and late harvesting of maize, leading to overall 4-6% increase in total grain yield of the wheat-maize system. Increased use of farming machines and minimum tillage technology also shortened the time for field preparation from harvest time of summer maize to sowing time of winter wheat, which facilitated the later harvest of summer maize. [ABSTRACT FROM AUTHOR]

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]

mospheric nitrogen (N) deposition is a serious problem on the North China Plain (NCP) because it imposes a considerable nutrient burden on the local environment. However, it also makes a substantial contribution to agricultural crop N requirements. The integrated total N input (ITNI) system is a method to quantify total atmospheric N deposition by using N-labeled monitor plants grown in pots. The effect of pot surface area and variety of indicator plant on the amount of airborne N input quantified by the ITNI system was investigated in this study. Total N deposition to the soil-maize/soil-wheat plant system at key growth stages was also quantified to improve N-fertilizer recommendations. When indicator plants having a high space requirement were used a correction factor was needed and this could be obtained only by simulating commercial field conditions, especially plant density, because the factor depends largely on pot area or the difference in plant density between pot conditions and field conditions. The total airborne N input measured by the ITNI system was not influenced by the variety of monitoring plant. N deposition was 20-25 kg N ha during growth from three expanded leaf to ten expanded leaf and also from ten expanded leaf to maturity of maize. N deposition was 29.1 kg N ha between planting and the jointing stage and 10.1 kg N ha from jointing to maturity of wheat. This high measured N deposition indicates that N deposition should be taken into account when calculating the N fertilizer requirements of maize and wheat in this region. [ABSTRACT FROM AUTHOR]

The North China Plain (NCP) is the most important agricultural production area in China. Crop production in the NCP is sensitive to changes in both climate and management practices. While previous studies showed a negative impact of climatic change on crop yield since 1980s, the confounding effects of climatic and agronomic factors have not been separately investigated. This paper used 25 years of crop data from three locations (Nanyang, Zhengzhou and Luancheng) across the NCP, together with daily weather data and crop modeling, to analyse the contribution of changes in climatic and agronomic factors to changes in grain yields of wheat and maize. The results showed that the changes in climate were not uniform across the NCP and during different crop growth stages. Warming mainly occurred during the vegetative (preflowering) growth stage of wheat and maize, while there was a cooling trend or no significant change in temperatures during the postflowering stage of wheat (spring) or maize (autumn). If varietal effects were excluded, warming during vegetative stages would lead to a reduction in the length of the growing period for both crops, generally leading to a negative impact on crop production. However, autonomous adoption of new crop varieties in the NCP was able to compensate the negative impact of climatic change. For both wheat and maize, the varietal changes helped stabilize the length of preflowering period against the shortening effect of warming and, together with the slightly reduced temperature in the postflowering period, extend the length of the grain-filling period. The combined effect led to increased wheat yield at Zhengzhou and Luancheng; increased maize yield at Nanyang and Luancheng; stabilized wheat yield at Nanyang, and a slight reduction in maize yield at Zhengzhou, compared with the yield change caused entirely by climatic change. [ABSTRACT FROM AUTHOR]

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]

The article presents an analysis of the sustainable level of vegetation water use in the climate of the North China Plain (NCP). The study involved mimicking a natural forest ecosystem with an evapotranspiration of 470mm/year in the north and 910 mm/year in the south. It was found that dryland farming should be practiced in order to mimic the natural system, which will mean a water deficit for wheat and corn. Also, irrigation stoppage will result to lower wheat yields and increased variability in yield of wheat and corn.

CO2 flux was measured continuously using the eddy covariance technique in a wheatmaize rotation system in the North China Plains from October 2002 to October 2006. The annual and seasonal variation of ecosystem respiration and the bio-environmental controls on them were investigated. The results show that ecosystem respiration (Rec) in the cropland increased exponentially with soil temperature at 5 cm depth. The temperature sensitivity coefficient (Q10) for ecosystem respiration varied from 3.5 to 5.4 for wheat and from 2.4 to 4.5 for maize. In the wheat growing season, monthly average R0 (ecosystem respiration at 0°C) increased linearly with soil temperature and logarithmically with leaf area index (LAI). Monthly average Q10 decreased logarithmically with R0. Residual Rec was significantly correlated with LAI. After considering LAI, the modified Q10 model could estimate Rec better than before. The simulation results show that annual ecosystem respiration in the wheat-maize rotation system in the North China Plains was 1327, 1348, 1040 and 1171 gC m-2 yr-1 for the 4 years of the study. As a 4-year average, seasonal mean ecosystem respiration in wheat (2.60 gC m-2 day-1) was much lower than in maize (6.09 gC m-2 day-1). However, integrated ecosystem respiration for the wheat growing season (566 gC m-2) was slightly higher than that for maize (520 gC m-2). These account for 46.4 and 42.6% of the annual values, respectively. [ABSTRACT FROM AUTHOR]