Organic and Inorganic Nitrogen forms as Affected by Phosphorus Additions in a Maize–Mustard Cropping System

Abstract Phosphorus (P) availability affects the accumulation and enrichment of soil nitrogen (N) forms. However, the effect of P addition on the distribution and turnover of soil N forms in the mustard–maize rotation system is unclear. A field experiment is conducted to investigate the effect of P addition on the turnover of soil N forms in a mustard–maize rotation system. The results show that after maize harvesting, the levels of ammonium N in soil with P addition are smaller compared to those without P addition. The organic N forms in soil with P addition are greater compared without P addition after mustard harvest. Moreover, the hydrolysable ammonium N and unknown hydrolysable N in soil with P addition are smaller than those without P addition after maize harvest. Structured equation model results show the intensities of hydrolysable amino acid N, hydrolysable amino sugar N, and unknown hydrolysable N transformed into ammonium N in soil with P addition are greater than those without P addition, and the intensities of these organic N forms transformed into nitrate N are weaker. The results indicate that P addition affect the accumulation and enrichment of soil N by altering the turnover of soil N forms.