Changes in Organic Carbon and Nutrient Contents of Highly Productive Paddy Soils in Yujiang County of Jiangxi Province, China and Their Environmental Application

Paddy field is an important land use in subtropical China. Development of high soil fertility and productivity is themanagement goal of paddy field. Fertilization and management practices have not only influenced the status of organicmatter and nutrients in the soil but also affected the environmental quality. This article investigates the contents oforganic carbon and the nutrients, and the change over the last 20 years in highly productive paddy soils and theirenvironmental application. Field soils were sampled and the analytical results were compared with the correspondingvalues in the Second Soil Survey in Yujiang County of Jiangxi Province, China. The results showed that surface soils ata depth of 0-10 cm in highly productive paddy fields in Yujiang County of Jiangxi Province had contents of organiccarbon (20.2 ± 3.88) g kg-1, total nitrogen (2.09 ± 0.55) g kg-1, and available phosphorus (42.7 ± 32.7) mg kg-1, respectively,which were all at very rich levels. Over the last 20 years, the organic carbon pool of the highly productive paddy soilsreached a steady state. Total N and available P significantly increased, whereas available K changed a little. The amountand percentage of P immobilization in the surface soil (0-10 cm) of highly productive paddy fields were (142.7 ± 41.1) mg kg-1and (36.2 ± 10.4)% of added P, and CEC (7.93 ± 1.32) cmol kg-1. These two parameters were not higher than the mean valuesof paddy soils and upland red soils in the areas. Results also showed that fertilizer P in highly productive paddy soils hada high mobility and was prone to move toward a water body, which is the main source of nutrients causing eutrophication.Because of a weak K-fixing capacity, the available K content was not high in highly productive paddy soils. This suggeststhat attention should be paid to the K balance and the increase of soil K pool.