Shiqi Yang

Biochar amendment reduces paddy soil nitrogen leaching but increases net global warming potential in Ningxia irrigation, China

The efficacy of biochar as an environmentally friendly agent for non-point source and climate change mitigation remains uncertain. Our goal was to test the impact of biochar amendment on paddy rice nitrogen (N) uptake, soil N leaching, and soil CH4 and N2O fluxes in northwest China. Biochar was applied at four rates (0, 4.5, 9 and13.5 t ha−1 yr−1). Biochar amendment significantly increased rice N uptake, soil total N concentration and the abundance of soil ammonia-oxidizing archaea (AOA), but it significantly reduced the soil NO3−-N concentration and soil bulk density. Biochar significantly reduced NO3−-N and NH4+-N leaching. The C2 and C3 treatments significantly increased the soil CH4 flux and reduced the soil N2O flux, leading to significantly increased net global warming potential (GWP). Soil NO3−-N rather than NH4+-N was the key integrator of the soil CH4 and N2O fluxes. Our results indicate that a shift in abundance of the AOA community and increased rice N uptake are closely linked to the reduced soil NO3−-N concentration under biochar amendment. Furthermore, soil NO3−-N availability plays an important role in regulating soil inorganic N leaching and net GWP in rice paddies in northwest China.

Using side-dressing technique to reduce nitrogen leaching and improve nitrogen recovery efficiency under an irrigated rice system in the upper reaches of Yellow River Basin, Northwest China

Abstract The excessive nitrogen (N) fertilizer input coupled with flood irrigation might result in higher N leaching and lower nitrogen recovery efficiency (NRE). Under an intensive rice system in the Ningxia irrigation region, China, environmental friendly N management practices are heavily needed to balance the amount of N input for optimum crop production while minimize the nitrogen loss. The objective of this study was to determine the influences of side-dressing (SD) technique in mechanical transplanting systems on the NRE, N leaching losses and rice yield in anthropogenic-alluvial soil during two rice growing seasons (2010–2011). Four fertilizer N treatments were established, including conventional urea rate (CU, 300 kg ha −1 yr −1 ); higher SD of controlled-release N fertilizer rate (SD1, 176 kg ha −1 yr −1 ); lower SD of controlled-release N fertilizer rate (SD2, 125 kg ha −1 yr −1 ); and control (CK, no N fertilizer). Field lysimeters were used to quantify drainage from undisturbed soil during six rice growing stages. Meanwhile, the temporal variations of total nitrigen (TN), NO 3 − -N, and NH 4 + -N concentrations in percolation water were examined. The results showed that SD1 substantially improved NRE and reduced N leaching losses while maintaining rice yields. Across two years, the averaged NRE under SD1 treatment increased by 25.5% as relative to CU, but yet the rice yield was similar between two treatments. On average, the nitrogen loss defined as TN, NH 4 + -N, and NO 3 − -N under the SD1 treatment reduced by 27.4, 37.2 and 24.1%, respectively, when compared with CU during the study periods. Although the SD2 treatment could further reduce N leaching loss to some extent, this technique would sharply decline rice yield, with the magnitude of as high as 21.0% relative to CU treatment. Additionally, the average NRE under SD2 was 11.2% lower than that under SD1 treatment. Overall, the present study concluded that the SD technique is an effective strategy to reduce N leaching and increase NRE, thus potentially mitigate local environmental threat. We propose SD1 as a novel alternative fertilizer technique under an irrigated rice-based system in Ningxia irrigation region when higher yields are under consideration.

Regulating N Application for Rice Yield and Sustainable Eco-Agro Development in the Upper Reaches of Yellow River Basin, China

High N fertilizer and flooding irrigation applied to rice on anthropogenic-alluvial soil often result in N leaching and low recovery of applied fertilizer N from the rice fields in Ningxia irrigation region in the upper reaches of the Yellow River, which threatens ecological environment, food security, and sustainable agricultural development. This paper reported the regulating N application for rice yield and sustainable Eco-Agro development in the upper reaches of Yellow River basin. The results showed that reducing and postponing N application could maintain crop yields while substantially reducing N leaching losses to the environment and improving the nitrogen use efficiency. Considering the high food production, the minimum environmental threat, and the low labor input, we suggested that regulating N application is an important measure to help sustainable agricultural development in this region.

Effects of straw application on nitrate leaching in fields in the Yellow River irrigation zone of Ningxia, China

A five-year field experiment was conducted to investigate the effects of straw application on nitrate leaching loss. Treatments included soil that was not treated (control), soil treated with straw at a low rate (4,500 kg ha−2, T1) and soil treated with straw at a high rate (9,000 kg ha−2, T2). Nitrate-nitrogen leaching in the 10, 20, 30, 60, and 90 cm soil layers was measured using the resin-core method. The results indicated that straw application could reduce soil nitrate leaching losses in the 0–30 cm layer. In this layer, the nitrate leaching values for T1 (13.76 kg ha−2) and T2 (13.74 kg ha−2) were both significantly lower than those of the control (15.76 kg ha−2) (P < 0.05); the soil nitrate leaching losses decreased by 12.71% and 12.84% for those two treatments, respectively. However, no significant differences in losses were observed (P > 0.05) between T1 and T2. The effects of straw application were apparent only in the ploughing layer (30 cm-depth soil layer). In the deeper layers (60 and 90 cm), no significant differences were observed between the treatments and the control, and the same results were observed in the topsoil layers (10 and 20 cm).

Improved crop yield and reduced nitrate nitrogen leaching with straw return in a rice-wheat rotation of Ningxia irrigation district

Field experiments were conducted in rice-wheat rotation under conventional management to determine the effects of straw return ((half straw return, HS) and (total straw return, TS)) on crop yield, N uptake, soil properties and soil NO3−–N leaching. We found that straw return significantly increased crop yield and N uptake. TS significantly increased soil SOM at depths of 20 cm and 30 cm. Straw return had significantly increased soil NO3−–N leaching at a depth of 10 cm, whereas significantly decreased soil NO3−–N leaching at depths of 30 cm and 90 cm in the rice season. In wheat season, HS and TS performed better than conventional fertilization management without straw return in reducing soil NO3−–N leaching at depth of 90 cm. Soil NO3−–N leaching was significantly decreased through enhancing total N uptake, improving soil aggregation and decreasing soil NO3−–N concentration. Our results indicated that total straw return has the potential to increase crop yield, improve soil aggregation and decrease soil NO3−–N concentration, thus increasing total N uptake and reducing soil NO3−–N leaching in the rice-wheat rotation system of Ningxia Yellow river irrigation district. In the future, the long-term observation of crop yield and nitrate nitrogen leaching are necessary to identify the environmentally friendly straw return practices for rice-wheat rotation.

Effect of Nitrate Leaching Caused by Swine Manure Application in Fields of the Yellow River Irrigation Zone of Ningxia, China

A five-year swine manure application trial and a study of nitrate leaching losses have been conducted. There were three treatments: traditional without manure (CK), traditional matched manure 4500 kg ha−2 (T1) and traditional matched manure 9000 kg ha−2 (T2). Nitrate nitrogen leaching losses at the 30-, 60-, and 90-cm soil layers were measured using the resin core method. The results indicate that the swine manure application did not noticeably increase soil nitrate leaching losses in the 30-cm layer. T1 (16.85 ± 0.40 kg ha−2) and T2 (17.01 °C0.46 kg ha−2) were not significantly different than CK (15.96 ± 0.41 kg ha−2) (P < 0.05), which was also the case at the 60-cm layer. However, there are significant differences between the treatments and CK at the 90-cm layer, although there were no significant differences between T1 and T2 in that layer. The application of manure can increase soil organic matter (SOM) and total nitrogen (TN). The SOM of T1 and T2 were increased to 0.95 g kg−1 and 1.41 g kg−1, respectively. The TN values of CK, T1 and T2 were 0.72, 0.78 and 0.88 g kg−1, respectively, in the 0 to 30 cm layer, and were improved by 7.72% and 22.04%.