Studies On The Fertility Properties Of The Paddy Soils With High Yield And Their Degradation

By field investigation and sampling, and laboratory analysis, this paper was an attempt to study the local conditions and fertility properties of paddy soils of several typical areas of rice production in Hunan Province. Two of the tested soils, alluvial sandy earth and reddish yellow clayey earth, were used to study the degradation process of the paddy soils in relation to irrational fertilization practices with pot experiment. The main results are as follows:1. The paddy soils are developed from the weathering product of limestone, the river alluvium and Quaternary Red Clay, respectively. The soil texture ranges from medium loamy to lightly clayey, and it is suitable to crop growth. The nutrient status of the soils were good on the whole, the contents of organic matter, nitrogen, phosphorus and potassium were all on the higher level, and especially the contents of organic matter and nitrogen were much higher than that of other cultivated soils. However, content of available silica was at the lower level. Among them the paddy soil developed from the weathering product of limestone has much higher nutrient contents than the paddy soils developed from river alluvium and Quaternary Red Clay does. In the profile, the content of nutrient in most soils always decreases with the increase of depth except pH.2. Fertilization is one of the efficient measures to increase the soil nutrient content, improve the soil capacity to supply nutrient. Excessive fertilization is wasteful and would do harm to rice growth and pollute the environment. The low available silica content in the soils of various treatments indicates that silica application in rice production is necessary.3. All irrational fertilization treatments facilitate leakage loss of N, P, and K nutrient. N leaching appears within 60 days after transplanting rice; P leaching appears within 15 days, and K leaching, within 30 days mostly. Application of inorganic fertilizer is one of the important factors that can lead to water eutrophication. It is noticeable that serious P vertical leaching caused by application of organic manure is threatening to water environment.4. In alluvial sandy earth, combined application of N, P and K fertilizer can increase grains per panicle and effective panicle percentage of rice; preferential application of N fertilizer can decrease grains per panicle of rice; application of P fertilizer can increase biomass production of rice; application of K fertilizer can increase plant height, panicle length, biomass production and grain yield of rice; the treatments with excessive application of chemical fertilizer or no fertilization can decrease effective panicle and tillers number; application of organic manure (straw) can increase plant height, panicle length, grains per panicle, harvest index, effective...