Effects of mulching practices on soil carbon, nitrogen contents, and grain yield, water and nitrogen use efficiencies of summer maize

Ridge furrows with plastic film mulching (RFM) and straw mulching (SM) are beneficial for improving grain yield and rainwater use efficiency; however, it is not clear whether they can affect the changes in soil carbon and nitrogen under continuous RFM and SM in the Loess Plateau of China. A 2-year field experiment (2019–2020) was established with three treatments, namely, RFM, SM, and no mulching (NM), to study the effects of RFM and SM on soil water and heat conditions, soil organic carbon and nitrate nitrogen contents, soil respiration rate, as well as summer maize nitrogen uptake, aboveground dry matter accumulation, evapotranspiration, soil water and nitrogen use efficiencies, and grain yield. Finally, a mulching method suitable for rainfed agriculture in the semi-arid Loess Plateau was proposed to provide a scientific basis for summer maize planting and environmental protection in this area. The results showed that compared with NM, RFM significantly increased the soil temperature by 0.5–1.0 °C at 5 cm soil depth and by 0.2–0.7 °C at 10 cm soil depth (P<0.05), accelerated the decomposition of soil organic carbon, significantly decreased the soil organic carbon content by 4.2%, and significantly enhanced the soil respiration rate by 33.2% (P<0.05). SM significantly decreased the soil temperature by 0.2–1.5 °C at 5 cm soil depth and by 0.5–1.0 °C at 10 cm soil depth (P<0.05), increased the soil organic carbon content by 21.3% (P<0.05), and decreased the soil respiration rate by 44.0% (P<0.05). Compared with NM, RFM significantly decreased the soil nitrate nitrogen content in the furrow (P<0.05). SM significantly increased the soil nitrate nitrogen content at 0–80 cm depth (P<0.05), but significantly reduced the nitrate nitrogen content in the deeper soil (P<0.05). The results showed that SM significantly increased the nitrate nitrogen content of the soil surface, promoted the supply of nitrogen, and reduced the residual nitrate nitrogen content as well as the leaching loss. SM and RFM significantly increased the soil water content by 23.8% and 15.2% (P<0.05), respectively; increased the plant nitrogen uptake by 37.6% and 11.3% (P<0.05), respectively; transferred more nitrogen to the grains; significantly increased the grain nitrogen uptake, nitrogen harvest index, and grain dry weight (P<0.05); increased the aboveground dry matter accumulation (P<0.05); significantly improved the grain yield of summer maize by 16.8% and 9.2% (P<0.05), respectively; and increased the water use efficiency by 13.0% and 9.1% (P<0.05), respectively. Mulching practices (RFM and SM) can increase the soil water content, plant nitrogen uptake, and grain yield. However, compared with RFM, SM was more effective in conserving soil water, increasing production, and reducing carbon dioxide emissions. SM could increase the summer maize nitrogen uptake and utilization as well as grain yield of summer maize by improving the soil moisture content, soil organic carbon content, and soil nitrogen availability. Therefore, SM is an effective mulching method for rainfed agriculture in the semi-arid Loess Plateau, China.