Fertilizer type and organic amendments affect gross N dynamics in a Chinese Chernozem

Abstract

SummaryThe effects of partial substitution of synthetic fertilizer N (NPK) with equal quantities of maize (Zea mays L.) stover N (50 kg ha−1, NPKS) or cattle manure N (115 N kg ha−1, NPKM) were investigated after 23 years with respect to maize yield, biomass N uptake, residual soil N and gross soil N dynamics in a fertile Chernozem soil. Maize yields were not different among these three treatments: maize biomass N uptake followed the order NPKM≈NPK > NPKS, whereas total N in soil was significantly larger under NPKM. A 15N tracing method was used to explain differences in gross N dynamics of labile and recalcitrant organic N pools and total N in soil. The results showed that NPKS and NPKM compared with NPK increased gross N mineralization by 2.8 and 1.3 times, respectively. The NPKS decreased the gross rate of N nitrification by 14%, whereas NPKM increased it by 47% compared with NPK. The NPKS stimulated microbial competition for NH4+, whereas NPKM increased NO3− immobilization compared with NPK. Our results suggested that acceleration of the soil N cycle under NPKS provided the most likely reason for the small total N stock in soil. In contrast, large organic N input and considerable immobilization of NO3− to a recalcitrant pool was probably the reason for the large total N stock under NPKM.Highlights How do fertilizer regimes affect gross N dynamics and soil N stock in a Chernozem soil? Changes in NH4+, NO3− and 15N enrichment were simulated by a two‐pool model. Mineralization of recalcitrant organic N was the main source for NH4+. Large organic N input and considerable immobilization of NO3− to a recalcitrant pool probably resulted in large total N stock under NPKM.