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Purpose: Summer catch crop (CC) has been introduced into the vegetable rotating system in greenhouse fields to reduce nitrogen (N) losses through crop uptake and residual N immobilization. However, the effects of planting sorghum with high N uptake and biomass, and biological nitrification inhibition (BNI) potential as a CC on soil N dynamics and subsequent crop yield remain unclear. Methods: In the two-year field experiment, the comprehensive effects of planting sorghum as CC on subsequent eggplant yield, soil mineral N dynamics, ammonia-oxidizing archaea (AOA) and bacteria (AOB) amoA gene abundances were determined, in comparison to the sweet corn and fallow treatments. Results: Compared to the fallow and sweet corn, planting sorghum as CC increased subsequent eggplant yield by 24.88% and 18.94% in the 2014–2015 and 2015–2016 over-winter growing season, 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 net 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. Conclusion: We conclude that planting sorghum in the summer fallow season is a promising strategy to retain soil NH4+-N, reduce soil NO3−-N accumulation, and enhance subsequent eggplant yield. [ABSTRACT FROM AUTHOR]

Purpose : Nitrogen (N) transfer from white clover (Trifolium repens cv.) to ryegrass (Lolium perenne cv.) has the potential to meet ryegrass N requirements. This study aimed to quantify N transfer in a mixed pasture and investigate the influence of the microbial community and land management on N transfer. Methods: Split root 15N-labelling of clover quantified N transfer to ryegrass via exudation, microbial assimilation, decomposition, defoliation and soil biota. Incorporation into the microbial protein pool was determined using compound-specific 15N-stable isotope probing approaches. Results: N transfer to ryegrass and soil microbial protein in the model system was relatively small, with one-third arising from root exudation. N transfer to ryegrass increased with no microbial competition but soil microbes also increased N transfer via shoot decomposition. Addition of mycorrhizal fungi did not alter N transfer, due to the source-sink nature of this pathway, whilst weevil grazing on roots decreased microbial N transfer. N transfer was bidirectional, and comparable on a short-term scale. Conclusions: N transfer was low in a model young pasture established from soil from a permanent grassland with long-term N fertilisation. Root exudation and decomposition were major N transfer pathways. N transfer was influenced by soil biota (weevils, mycorrhizae) and land management (e.g. grazing). Previous land management and the role of the microbial community in N transfer must be considered when determining the potential for N transfer to ryegrass. [ABSTRACT FROM AUTHOR]