Chinese cabbage as a catch crop decreases soil soluble N and labile organic N during one-month summer fallow in greenhouse vegetable production

Summer catch crops can reduce soil soluble nitrogen (N) during the summer fallow period in Chinese greenhouse vegetable production. However, the influence of growing fast-growing leafy vegetables as catch crops on soil organic N pools remain insufficiently understood. The aim of this study was to investigate the effects of growing Chinese cabbage (Kuaicai) on soil N pools in the top 0.3 m soil layer during a one-month fallow period in two years. Treatments included Kuaicai cultivation and a fallow treatment for comparison. Results show that soil soluble N pools and non-hydrolysable N (NHN) in the top 0.3 m soil layer were increased during the summer fallow period in the fallow treatment. Kuaicai accumulated 40–114 kg N ha -1 each year, improving N use efficiency by 9.2–26.3%. Growing Kuaicai with drip irrigation to 90% field capacity reduced soil total N (TN) by 12–16% and total soluble N (TSN) by 37–83%. Growing Kuaicai reduced labile N fractions, specifically ammonium N (AN) in the top 0.2 m soil layer by 13–26% and amino acid N (AAN) in the 0.1–0.2 m soil layer by 5–17%. The partial least squares path modelling (a goodness of fit = 0.67) revealed that fallow period management had direct effects on TSN, NHN, and TN, and an indirect effect on labile organic N fractions. The AN and AAN were direct contributors to TSN. These findings suggest that growing Kuaicai as a catch crop is an effective strategy for reducing soluble N pools and labile organic N fractions, thereby lowering the risk of N loss in the next growing season. • Summer fallow increases soil soluble and recalcitrant nitrogen. • Growing Chinese cabbage during the fallow period reduced soil labile organic N fractions and soluble N. • Compared to fallow condition, Chinese cabbage cultivation reduced recalcitrant N.