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Losses of nutrients, water and soil from sloping farmlands have a large potential to contribute to water eutrophication and land degradation. However, few long-term and multi-site measurements are available to assess the magnitude of effects of cross-ridge tillage on surface runoff and nitrogen (N) and phosphorus (P) losses from sloping farmlands. Field experiments were conducted under natural rainfall conditions for six to seven years across four experimental sites in southern China. Each site-year experiment consisted of three management practices: downslope ridge without fertilizer as control (CK), downslope tillage with fertilizer (DF), and cross-ridge with fertilizer (CF). Results indicated that compared to the downslope tillage practice, cross-ridge tillage reduced the average annual runoff by 6.11% to 64.2%. Compared with DF, CF significantly decreased total N (TN) and total P (TP) losses by 11.3% to 69.7% and 15.9%- to 63.5%, respectively (P

An increasing disconnect between livestock production and croplands has been observed in many world regions, including China, which has the world’s largest livestock production sector. Here we propose a cropland-based livestock production system to rebuild the linkage between livestock and cropland from both agriculture production and human consumption perspectives for China. In 2015, the total excretion nitrogen (N) generated by livestock production operations was 14.6 Tg N, and it would grow to 15.0 Tg in 2030 by extrapolating current trends. The optimal demand of total N by crops in China was estimated to be 23.0 Tg N in 2030, suggesting that Chinese livestock would be within the carrying capacity of cropland on national level, but substantial variations were found across provinces. The carrying capacity of cropland with regard to N input from manure would be exceeded in 74% provinces, under the assumption that manure providing half of the N supply for crops. Furthermore, from the perspective of domestic feed supply for livestock production, about 51% of feed N needs to be imported. If following the optimized dietary structure of China to manage livestock sector, livestock production could be reduced by 37% in excretion nitrogen, which would not only benefit the food security and human health, but also mitigate the agricultural pollution. Accordingly, policy regulations on reduction and spatially reallocation of livestock production on a regional scale could substantially reduce manure N loss from 10.5 Tg yr−1 to 1–1.2 Tg yr−1 under different recoupled scenarios.

Increasing nitrogen (N) application to croplands in order to support growing food demand is a major cause of environmental degradation. However, evaluations of suitable N application rates based on environmental benefit have rarely been carried out for paddy-rice at a national scale in China. To address this challenge, we investigated the current status of N management in 1531 counties, covering the primary agro-ecological regions of Chinese rice production in 2008, and conducted 12 field experiments with six N level practices for 3 years (2011–2013). Results showed that the highest yields for rice were 5.8–8.6 Mg ha−1 with N rates of 209.4–289.8 kg N ha−1. Compared with the N rate for the highest yield (YHN), the environmentally optimal N rate (EnON) was lower by 20–39% and the corresponding N loss was reduced by 21–45%, while ensuring 95–99% of the highest crop yield. In China, the N inputs to paddy fields exceeded the YHN and EnON rates by 10% and 45%, respectively. After adjusting the N rate to paddy fields to the EnON rate, the N amount used in China and the corresponding N lost would be reduced by 0.9 and 0.5 Tg N yr−1, respectively, which enable highly efficient production of food with the lowest N loss possible. Thus, we suggest that N use rates for 45% of rice paddy fields in China, for which N application rates exceed the EnON rate, need to be reduced to mitigate environmental damage, and this can be done while still meeting China’s food demand.

Application of manure is reported to effectively improve agricultural soil fertility. However, the potential of annual manure applications to increase stocks of soil organic carbon (SOC) and total nitrogen (TN) needs to be better understood. In this study, we evaluated the long-term (1991–2012) effects of various fertilization regimes on crop yield, and SOC and TN in the topsoil (0–20 cm) of a fluvo-aquic soil in a wheat (Triticum aestivumL.)-maize (Zea mays L.) cropping system in the North China Plain. The treatments included no N fertilizer (PK), chemical N, P, K fertilizers (NPK), NPK plus 22.5 t ha−1 swine manure (NPKM), and NPK plus 33.75 t ha−1 swine manure (NPKM+). Compared with NPK and PK, both NPKM and NPKM+ significantly increased crop yields, with no significant difference between NPKM and NPKM+. NPKM and NPKM+ treatments had a lower N use efficiency (NUE) than NPK through the whole period and the average NUE were 30.1%, 14.8% and 12.3% in NPK, NPKM and NPKM+ treatments, respectively. Compared with the initial value of 17.2–17.4 Mg C ha−1 and 2.01–2.07 Mg N ha−1, SOC and TN stocks in NPKM and NPKM+ increased by 94.7–114.2% and 83.0–98.0% over the 22 experimental years, respectively, without any indication of C or N saturation in the soil. Furthermore, TN stock was positively correlated to SOC stock (P

Optimizing the nitrogen (N) application rate can increase crop yield while reducing the environmental risks. However, the optimal N rates vary substantially when different targets such as maximum yield or maximum economic benefit are considered. Taking the wheat-maize rotation cropping system on the North China Plain as a case study, we quantified the variation of N application rates when targeting constraints on yield, economic performance, N uptake and N utilization, by conducting field experiments between 2011 and 2013. Results showed that the optimal N application rate was highest when targeting N uptake (240 kg ha− 1 for maize, and 326 kg ha− 1 for wheat), followed by crop yield (208 kg ha− 1 for maize, and 277 kg ha− 1 for wheat) and economic income (191 kg ha− 1 for maize, and 253 kg ha− 1 for wheat). If environmental costs were considered, the optimal N application rates were further reduced by 20–30% compared to those when targeting maximum economic income. However, the optimal N rate, with environmental cost included, may result in soil nutrient mining under maize, and an extra input of 43 kg N ha− 1 was needed to make the soil N balanced and maintain soil fertility in the long term. To obtain a win-win situation for both yield and environment, the optimal N rate should be controlled at 179 kg ha− 1 for maize, which could achieve above 99.5% of maximum yield and have a favorable N balance, and at 202 kg ha− 1 for wheat to achieve 97.4% of maximum yield, which was about 20 kg N ha− 1 higher than that when N surplus was nil. Although these optimal N rates vary on spatial and temporal scales, they are still effective for the North China Plain where 32% of China's total maize and 45% of China's total wheat are produced. More experiments are still needed to determine the optimal N application rates in other regions. Use of these different optimal N rates would contribute to improving the sustainability of agricultural development in China.

The excessive application of manure has caused a high load of phosphorus (P) in the North China Plain. Having an understanding of how manure application affects soil P changes and its transport between different soil layers is crucial to reasonably apply manure P and reduce the associated loss. Based on our 28-year field experiments, the compositions and changes of P species and the risk of P loss under excessive manure treatments were investigated, i.e., no fertilizer (CK), mineral fertilizer NPK (NPK), NPK plus 22.5 t ha−1 yr−1 swine manure (LMNPK), and NPK plus 33.75 t ha−1 yr−1 swine manure (HMNPK). Manure application increased the content of orthophosphate and myo-inositol hexaphosphate (myo-IHP), especially the orthophosphate content exceeded 95%. The amount of orthophosphate in manure and the conversion of organic P to inorganic P in soil were the main reasons for the increased soil orthophosphate. Compared with NPK treatment, soil microbial biomass phosphorus and alkaline phosphatase activity in LMNPK and HMNPK treatments significantly increased. Compared with NPK treatment, a high manure application rate under HMNPK treatment could increase the abundance of organic P-mineralization gene phoD by 60.0% and decrease the abundance of inorganic P-solubilization gene pqqC by 45.9%. Due to the continuous additional manure application, soil P stocks significantly increased under LMNPK and HMNPK treatments. Furthermore, part of the P has been leached to the 60–80 cm soil layer. Segmented regression analysis indicated that CaCl2–P increased sharply when Olsen-P was higher than 25.1 mg kg−1, however the content of Olsen-P did not exceed this value until 10 years after consecutive excessive manure application. In order to improve soil P availability and decrease the risk of P loss, the manure application rate should vary over time based on soil physicochemical conditions, plants requirements, and P stocks from previous years.

Monitoring data collected from rivers are used to support assessments of the quality of the river environment and help decision makes formulate appropriate management plans. Therefore, accurate and precise estimates of constituent fluxes in streams and rivers are important. However, seasonal errors have not received enough attention and the published results have rarely been verified by other methods. In this study, the error associated with sampling frequencies (3 daily, weekly, 2 weekly, 4 weekly, 6 weekly, 8 weekly) and seven load estimation algorithms were examined. Seasonal and annual total N loads were estimated and wavelet coherence was used as a reference. In order to reduce the contingency of the results, three years data were used and total N (with 17.53% particulate N, 58.70% NO3−-N and 23.77% other dissolved N fractions) was chosen to reflect water quality parameters. Results indicated that 2 weekly sampling frequency and algorithm F (linear interpolation) are sufficient for evaluating the characters of annual total N load in Fengyu River Watershed with 5% RMSE (root-mean-square error). There was a large RMSE (3.97–44.66%) in summer with a high CV (coefficient variation) (35.2%) for total N concentration. These results can serve as a useful reference for decision makes who need to establish monitoring programmes in watersheds with similar characteristics.