Is planting sorghum as summer catch crop a promising strategy to enhance subsequent eggplant yield and reduce nitrate accumulation in protected-field vegetable system？

Abstract Purpose Summer catch crop (CC) has been introduced into the vegetable rotating system in protected fields to reduce nitrogen (N) losses through crop uptake and residual N immobilization. However, the effects of sorghum with biological nitrification inhibition (BNI) capacity as a CC on soil N dynamics and subsequent crop yield remain unclear. Methods In the two-year protected field experiment, the comprehensive effects of sorghum as CC on subsequent eggplant yield, soil mineral N dynamics, ammonia-oxidizing archaea (AOA) and bacteria (AOB) were determined, in comparison to the sweet corn and fallow treatments. Results Compared to the fallow treatment, sweet corn and sorghum as CC increased subsequent eggplant yield by 12.22% (not significantly) and 18.94%-24.88% (significantly), respectively. CC planting reduced soil nitrate (NO3--N) accumulation during the summer fallow season. Sorghum planting could significantly maintain higher level of ammonium (NH4+-N) concentration during the summer fallow season and the first month of succeeding over-winter season. In addition, sorghum planting reduced soil nitrifying potential, which could be partially attributed to the decreased amoA gene abundance of AOA at the 0–30 and 30–60 cm soil layers and AOB at 0–30 cm soil layer. However, similar results were not observed while planting sweet corn. Conclusion We conclude that planting sorghum with BNI capacity in the summer fallow season is a promising strategy to retain soil NH4+-N, reduce soil NO3--N accumulation, and enhance subsequent eggplant yield.