Release of plant nutrients and changes in the copies of N-cycling genes in response to soil amendment with rice straw and waste from a food seasoning industry

Rice-derived organic matter is an important source of nitrogen for paddy soils, and this limiting nutrient is subsequently redistributed throughout the paddy and moved up the food chain. The effects were investigated of waste from a food seasoning industry (W_0;1,875 L/ha and 3, 125 L/ha) and urea fertilizer (100 kg/ha) on the decomposition of rice straw and the subsequent release of nitrogen, phosphorus, potassium and silicon by soil microbial communities. Soil amended with W₀ and urea fertilizer had a major impact on the decomposition of rice straw. However, biodegradation of rice straw did not result in large effects on the quantities of released organic matter, total nitrogen and available phosphorus, but it significantly (p < 0.05) affected the release of exchangeable potassium and available silicon. The abundance levels of 10 N-cycling genes (amoA-B, nxrA, nxrB, narG, nirS, nirK, cnorB, nosZ3, hdh and hzo) were also analyzed using quantitative polymerase chain reaction. In all treatments, the quantities of the nxrB, nirS, nirK and nosZ3 genes were greater than for the other genes over the 84d rice straw decomposition period. Moreover, the quantities of the nirS and nirK genes were greater than those of nosZ3 and nxrB. Nitrogen was estimated to be lost from the soil through nitrite reduction in the form of NO. The application of W₀ and urea fertilizer significantly (p < 0.05) increased the abundance of the nirS gene after the decomposition of rice straw over the 28d incubation period.