Evolution characteristics of soil nutrients in the main rice production regions, the middle-lower reach of Yangtze River of China

【Objectives】In China, rice accounts for more than half of total grain production, and more than 30% of the total cultivated land. However, research of paddy soil nutrient evolution with large area scale on the national level has not been carried out, the evolution dynamic and process of soil fertility need to be investigated. In this study a long-term, since 1980s multi-point monitoring experiments were set up for investigating the evolution characteristics of soil nutrients and fertility in the major rice production regions, the middle-lower reach of Yangtze River of China. 【Methods】The temporal change and principal component analysis were carried out for the soil nutrients and the rational fertilization in the paddy fields. At first, the change of paddy soil nutrients over time in the area was analyzed using temporal change descriptive statistics analysis, and summarized results of the evolution characteristics and overall trend about soil organic matter (SOM), total nitrogen (TN), alkaline-hydrolyzable N (AN), available phosphorous (AP), available potassium (AK) content and soil pH in different monitoring periods. Secondly, the fertilization amount trend in different monitoring period was analyzed using statistical analysis. Finally, the role and influence of the six fertility indicators, at the temporal trend of integrated soil fertility properties were analyzed using the principal component analysis, and the results were provided with the variation of the main contribution factor and limiting factor of soil fertility in different monitoring periods. 【Results】 1) Compared with the first monitoring stage, SOM, TN and AN slightly increased after 20-25 years, SOM significantly increased from middle monitoring stage to the later monitoring stage (P0.05), while AN also significantly increased from first monitoring stage to the middle monitoring stage (P0.05). 2) AP increased from 12.4 mg/kg to 12.9 mg/kg. Similarly, AK was increased by 13.9 mg/kg and 17.9 mg/kg respectively in the middle monitoring stage and later monitoring stage compared with the first monitoring stage. 3) In general soil pH was decreased by 0.37 units, which indicated that the famers habitual fertilization model and field management led to soil acidification in the paddy field soils. 4) Three nutrient indexes (SOM, TN, and AN) were significantly positive correlations (P0.01), with a similar temporal change trends. 5) Compared with the first monitoring stage, 20-25 years later, the main contribution factors for soil fertility in these paddy fields were changed from TN, AN and SOM to TN, AN and AK. The main restricted factors for soil fertility were changed from the deficits of AP and AK to the declined pH value.【Conclusions】In general, the soil nutrients increased under famers habitual fertilization model in the paddy fields, which indicated that soil fertility improved. However, it appeared that the soil acidification became the restrict factors for soil fertility. In addition, from the perspective of farmland nutrient balance management, soil available potassium and phosphorus are still the key influence factors of sustainable production and development of agriculture in paddy soil. Potassium and phosphorus fertilizer inputs needs to be strengthened in the fertilization process, and nitrogen fertilizer needs to be reasonable controlled.