Effects of long term application of organic and inorganic fertilizers on the physical Properties of Reddish Paddy Soil
Fertilization is the most important measure for improving farmland soil fertility. Different fertilization patterns usually resulted in different soil physical properties. Soil physical properties and soil organic carbon content are important indicators for soil fertility evaluation. Reddish paddy soil is one of the main rice soils with lower soil fertility in the Yangtze River valley region of China.
To study the effects of long-term application of chemical fertilizers (CF) and combined application of CF (urea, superphosphate, potassium chloride) with organic fertilizers include pig manure (PM) or rice straw (RS) on the physical properties of the reddish paddy soil, under the support of IPNI China Program, the Soil and Fertilizer Institute of Hunan province conducted a research project based on a 30-year long-term field experiment, which was designed to examine long-term effects of application CF, PM and RS on soil properties and rice productivity in Wangcheng county of Hunan province. This field experiment mainly include 7 treatments: CK，NP，NK, NPK, NK+PM, NP+RS and NPK+RS. The fertilization rates in this long term field experiment is N: P: K = 150-180: 38.7: 99.6 kg/ha, and/or pig manure 30t/ha per year and/or rice straw 4.2t/ha per year for early rice and late rice. All of the P, K, PM and RS fertilizers are used as basal fertilizer before seedling transplanting, 70% of N fertilizer used for basal dressing and 30% for top dressing. In this research project, some important soil fertility properties such as soil water holding capacity (WHC), porosity, soil bulk density and soil particle density were determined.
Results showed that long-term combined application of PM or RS with chemical fertilizer significant reduced soil bulk density and soil particle density by 6.5%, and increased soil porosity 4.4%-8.7% as well. Combined application of PM and RS with chemical fertilizer were in favor of forming 5-0.5mm water stable aggregate (WSA) and increased soil aggregate stability 1.4%-8.7% compared with CK and application of chemical fertilizer treatments. Soil WHC in plow layer was 5.3%-13.6% higher in combining application of PM and RS treatments than that in chemical fertilizer treatments. Long-term combined application of PM and RS with chemical fertilizer was effective measure to improve soil physical quality and soil fertility for reddish paddy soil in Hunan province.
