Responses of Cereal Yields and Soil Carbon Sequestration to Four Long-Term Tillage Practices in the North China Plain

Current tillage practices in the important winter wheat–summer maize double cropping system of the North China Plain are under debate because of negative effects on soil quality and crop yield. Therefore, a long-term experiment was conducted from 2001 to 2018 to determine the effects of soil conservation practices on crop yield and soil quality. The treatments were imposed following maize harvest and prior wheat seeding, and were defined as follows: (1) moldboard ploughing (0–20 cm) following maize straw removal (CK); (2) moldboard ploughing (0–20 cm) following maize straw return (CT); (3) rotary tillage following maize straw return (RT); and (4) no tillage with maize straw covering the soil surface (NT). Wheat straw was chopped and spread on the soil in all treatments and maize seeded without prior tillage. Wheat yields were higher in CT than RT and NT treatments (p < 0.05); NT had 18% lower wheat yields than CT. No significant differences were found between treatments in summer maize yields. The soil organic carbon (SOC) content in the surface layer (0–5 cm) was higher in NT and RT compared to CT and CK. However, SOC content in the 10–20 cm and 20–30 cm layers was lower in NT and RT compared to CT and CK. Similarly, available phosphorus in the surface soil was higher in NT and RT than in CT and CK. but the opposite was true for the lower soil layers. SOC stocks (0–30 cm) increased in all treatments, and were initially faster in NT and RT than in CT and CK. However, SOC stocks were higher in CT than in other treatments at the end of the experiment. This finding indicates that no tillage and reduced tillage decreased both wheat yields and soil C sequestration over time; it also indicates that CT was the most robust in terms of crop yields and soil C sequestration.

Effects of Straw Return and Feed Addition on the Environment and Nitrogen use Efficiency in the Rice–Crayfish System

Purpose Understanding the direction of nitrogen flow in the rice-crayfish system (RC) and optimizing the rate of nitrogen fertilizer application (ORN) are of great significance for sustainable development of RC. Methods To this end, a field experiment involving straw and feed treatment was conducted to delineate the flow of the nitrogen present in the straw (straw-N) and feed (feed-N). Second, under different feed and straw treatments, we carried out a mesocosm experiment with different rates of 15N-labeled nitrogen fertilizer application to explore the optimal rate under the effects of feed-N and straw-N supply.Results The results showed that at 75 kg N ha-1(75N), 14% and 1.86% of feed-N and 4.3% and 8.78% of straw-N is absorbed by crayfish and rice, respectively. The percentage of feed-N and straw-N lost to the environment was the lowest at 75N, i.e., 84.48% and 86.92%, respectively. Using straw return to the field and feeding as the basic management measures for RC, we observed that the rice yield was the highest under 75N, and the highest nitrogen utilization efficiency (NUE) was 25%, and the highest the percentage of soil storing nitrogen by the fertilizer-derived was 34% (lost to the environment, at least 41%).Conclusions ORN could help in the effective utilization of feed-N and straw-N via a compensation effect, promote the absorption and transport of nitrogen, and ultimately lead to an improvement in NUE in RC.