Nitrate leaching is the main driving factor of soil calcium and magnesium leaching loss in intensive plastic-shed vegetable production systems

Soil pH is important for influencing soil properties. High input of nitrogen (N) fertilizers and irrigation water has accelerated the soil acidification in plastic-shed greenhouses. However, little is known about the dynamics of soil pH buffering system, especially the base cations, and its response mechanisms under different N management practices. In this study, we investigated the responses of soil Ca2+ and Mg2+ leaching loss to nitrate leaching under different N application rate, N forms, or straw addition. Our long-term experiment in typical greenhouses showed that N application significantly decreased soil pH and increased Ca2+ and Mg2+ leaching loss by 43.1-73.6%, which correlated significantly and positively with nitrate leaching loss. However, optimizing N application and straw incorporation alleviated the leaching loss of Ca2+ and Mg2+ not only by alleviating the accompanying nitrate leaching caused by reduced N input, but also by reducing the conversion of exchangeable Ca2+ and Mg2+ to water-soluble Ca2+ and Mg2+ caused by alleviating soil pH reduction. The laboratory microcosm experiment showed that nitrate application did not reduce soil pH, but significantly increased the leaching loss of Ca2+ and Mg2+. Ammonium sulfate application also significantly increased the leaching loss of Ca2+ and Mg2+, whereas the effects were significantly reversed by nitrification inhibitors. These results further supported the importance of nitrate leaching in promoting the Ca2+ and Mg2+ losses. Together, this study revealed new insights into the dynamics of cation losses mainly regulated by nitrate leaching loss, highlighting that optimizing N management is an effective strategy to alleviate base cation losses and subsequent soil acidification for sustainable agricultural management.