Optimization of irrigation and N fertilization management profoundly increases soil N retention potential in a greenhouse tomato production agroecosystem of Northeast China

Abstract

Soil nitrogen (N) retention capacity can influence crop production, soil health, and environmental quality, especially in greenhouse agroecosystem with multiple cropping and high N application rate. However, the key N components and indices for predicting greenhouse soil N retention potential and the underlying driving mechanism of soil N retention under different agricultural management practices remain elusive. Here, a three-year tomato field experiment with mulch-film drip irrigation was conducted to investigate the effects of different irrigation and N fertilization regimes on soil organic N fractions and soil-retained N pools in a greenhouse agroecosystem of Northeast China. Three irrigation levels (W1, high, 25 kPa; W2, moderate, 35 kPa; W3, low, 45 kPa) and three N application rates (N1, low, 75 kg N ha−1; N2, moderate, 300 kg N ha−1; N3, high, 525 kg N ha−1) were considered. The results showed irrigation, N fertilization, and their interactions profoundly influenced soil properties, organic N fractions, and soil-retained N pools at 0–30 cm greenhouse vegetable soil layers. The dominant forms of greenhouse soil organic N fractions and soil-retained N pools were acidolysable amino acid N (AAN) and fixed ammonium (FA), respectively. Structural equation modeling and redundancy analysis indicated that there were significant direct effects of soil properties (SOC, Ntotal, and C/N) on FA, acidolysable ammonium N (AN), and AAN; additionally, soil microbial biomass N (SMBN) also exerted a significant direct effect on AN. Our results suggest that soil organic N fractions are closely correlated with soil-retained N pools and soil properties under different irrigation and N fertilization regimes. Furthermore, AAN and FA could be the appropriate indicators for predicting greenhouse soil N retention potential, and the optimization of irrigation and N fertilization application schedule (W3N2 treatment: 45 kPa – 300 kg N ha−1) is conducive to improve soil N retention potential in greenhouse tomato production of Northeast China.