Nitrogen Dynamics and Environmental Sustainability in Rice-Crab Co-Culture System: Optimal Fertilization for Enhanced Water Quality

Abstract

Rice-crab co-culture system (RC) has emerged as a promising eco-agricultural model for enhancing nitrogen use efficiency and ecosystem services. However, comprehensive understanding of nitrogen dynamics and environmental responses to nitrogen fertilization rates in RC system remains limited. In this study, we investigated nitrogen dynamics under different nitrogen application rates by comparing RC with rice monoculture system (RM). Results showed that nitrogen content in field water increased with nitrogen application rates, with a significant jump in ammonium nitrogen (NH4+-N) concentration when rates exceeded 210 kg·hm−2. Both NH4+-N and nitrate nitrogen (NO3−-N) peaked immediately after fertilization and then declined, returning to levels similar to the no-nitrogen treatment 15 days after basal fertilizer application. Compared to RM, the RC system exhibited enhanced nitrogen retention capacity, with NO3−-N concentrations remaining elevated for an additional two days following tillering fertilization, suggesting a potential critical period for nitrogen loss risk. Nitrogen application significantly increased NH4+-N content in the surface soil layer (0–2 cm) of the RC system, NO3−-N concentrations showed no significant change across the 0–20 cm soil profile. The RM system showed increases in NO3−-N content at 2–10 cm depth with higher nitrogen application rates. At 210 kg·hm−2, rice yields in the RC system were significantly higher than those in the RM system, suggesting this rate as the optimal nitrogen application rate for the RC system, which could balance high yields and minimizing nitrogen loss. These findings provide a scientific basis for nitrogen management in RC systems in paddy aquaculture and emphasize the need to optimize water and fertilizer practices.

Keywords: field water, rice-crab co-culture, nitrogen application rate, nitrogen transformation, environmental sustainability