Long-term combined application of manure and NPK fertilizers influenced nitrogen retention and stabilization of organic C in Loess soil

Abstract

Our aims were to: (1) compare the immobilization of NH 4 + -N by clay minerals and microbial biomass in soils with different fertilization history and (2) evaluate the effects of available C and N addition on the stabilization of soil organic carbon (SOC) in anthropogenic Lou soils. Here we used three soil treatments, i.e., (a) no fertilizer (NF), (b) inorganic NPK fertilizers (F), and (c) manure plus inorganic NPK fertilizers (MF) from an 18-year old field trial located in the south Loess Plateau, China. Two short-term incubation experiments were used to assess the impact of adding available nitrogen (NH 4 + -N) and C (glucose) on NH 4 + fixation by clay minerals, and the decomposition of SOC in these soils. The NH 4 + fixed by clay minerals in the MF soils (3.8% of added N) was significantly (P < 0.05) lower than that in the NF, and F soils (14.1%, and 9.5% of added N). The decomposition rate of SOC in the MF soil (3.3%) during the incubation was significantly (P < 0.05) lower than in the NF, and F soils (4.4%, and 4.2%). Addition of NH 4 + -N significantly (P < 0.05) increased the decomposition of SOC in different soil treatments, and the MF soil also had lower decomposition rate than the NF, and F soils. We concluded that long-term combined application of manure and NPK fertilizers reduces the NH 4 + fixation by clay minerals and improves the stabilization of organic C in soil.