Sweet corn significantly increases nitrogen retention and reduces nitrogen leaching as summer catch crop in protected vegetable production systems

Nitrogen (N) leaching is a commonly reported problem in protected vegetable production in China due to poor management. To minimize soil residue N and reduce N leaching, sweet corn is often used as the summer catch crop after the winter-spring growing season. However, the effectiveness of this practice has never been systematically quantified before. Here we reported the effects of sweet corn as catch crop on soil N retention and N leaching in the greenhouse vegetable system, using the data of two 15N isotope micro-plot experiments in soil-bound greenhouse. The results showed that sweet corn removed 11.5% of total residual 15N in soil profile and kept more organic 15N by 39.8% in soil profile, compared to fallow treatment. Root activity increased nitrogen retention due to temporarily immobilizing N as organic form, thereby reducing N leaching. Interestingly, sweet corn significantly reduced N leaching in the later growing stage (August), but not in the earlier stages (July). In total, dissolved organic nitrogen (DON) accounted for 63% of total N leaching. Sweet corn significantly reduced DON leaching, but not mineral N (Nmin) leaching. Hence, reducing N leaching in Chinese greenhouse must distinguish DON and Nmin sources and optimize both. Our study provides quantitative insights in N retention and leaching influenced by sweet corn as catch crop in typical Chinese greenhouse production systems, which provide guidance for searching for better catch crops in further studies.