Continuous Cropping Affects Gross Nitrogen Transformations in Subtropical Acidic Soils Under Greenhouse Cultivation

Abstract

Relationship between gross N transformation rate and continuous cropping years in the greenhouse soil is largely unknown. This study aimed to investigate the mechanism of the gross N transformation rate changes in greenhouse subtropical acidic soils under different continuous cropping years. The 15N isotope tracer method was used to study the effects of greenhouse soil under 4 years of continuous cropping (C4), 5 years of continuous cropping (C5), and 7 years of continuous cropping (C7) of lily (Lilium brownii), respectively, on soil N transformation with the N tracer model. The results showed that the main soil N transformation processes were N mineralization, autotrophic nitrification, and NO3−-N immobilization under the three continuous cropping years. After continuous cropping, the gross N mineralization rate, autotrophic nitrification rate, and NO3−-N immobilization rate increased with the increase of continuous cropping years. Specifically, the gross N mineralization rate was 0.62~0.85 mg N kg−1 day−1, the autotrophic nitrification rate was 1.08~3.24 mg N kg−1 day−1, and the NO3−-N immobilization rate was 0.30~0.62 mg N kg−1 day−1. Moreover, the positive difference between the autotrophic nitrification rate and immobilization rate of NO3−-N became greater with the increase of continuous cropping years, which might have been the main reason for the accumulation of NO3−-N in greenhouse subtropical soils. These findings contribute to the understanding of the mechanism of soil secondary salinization formation and provide ideas for prevention of secondary salinization under long-term continuous cropping.