Nitrogen absorption and mineralization change with cover crop types and greenhouse vegetable planting years in fluvo-aquic soil

Purpose Cover cropping during the summer fallow is a feasible practice for soil residual nitrogen (N) absorption and subsequent N supply in greenhouse vegetables. However, the change in these effects with a progression in the cultivation years of greenhouse vegetables remains unknown. This study aimed to evaluate the effects of different cover crops on the uptake of residual N in soil and N mineralization as affected by the planting years of greenhouse vegetables. Methods Five soil samples were collected from fields that had been cultivated with greenhouse vegetables for different number of years (0, 5, 10, 15, and 20 years); upper layers (0–30 cm) of the soil were sampled from a major vegetable production area in Xinxiang City, Henan Province, China. Three cover crop treatments were included for each soil sample: no cover crop planted during summer fallow with no straw return (CK), summer maize ( Zea mays L.) planted and straw return (SM), and alfalfa ( Medicago sativa L.) planted and straw return (A). Pot and incubation experiments were conducted to determine the amounts of N absorbed by cover crops during the fallow and soil N mineralization after cover crop straw return. Results The effects of cover crops on soil residual N absorption and subsequent N mineralization changed with cover crop types and greenhouse vegetable planting years. SM performed better as a cover crop than A in crop biomass development (on average 6.67 times larger), soil residual N absorption (4.46 times larger), and loss (3.61 times smaller) control, regardless of the greenhouse vegetable planting years. In terms of soil net N mineralization and straw-induced N mineralization, SM was inferior to A (1.15 and 2.12 times smaller). With the increase of planting years, total biomass yield and N uptake by the SM increased, whereas these parameters decreased for treatment A due to the plants’ different tolerance to soil available N and pH (pondus hydrogenii). For all cover crop treatments, with the increase of greenhouse vegetable planting years, net N mineralization of the soil increased due to the positive contribution of soil organic matter, whereas straw-induced N mineralization decreased due to the negative regulation of accumulated soil nitrate nitrogen. Conclusions Non-legumes, as represented by SM, were a good choice for cover cropping regardless of the greenhouse vegetable cultivation years. However, attention should be paid to N supplementation at an early stage of subsequent c