Soil Quality Characteristics as Affected by Continuous Rice Cultivation and Changes in Cropping Systems in South China

Abstract

This study was conducted to elucidate how changes in critical soil quality characteristics relate to continuous rice cultivation and changes in cropping systems and fertilization in South China over the time span 1980 to 2017. Soil pH, soil organic matter (SOM), total nitrogen (TN), available phosphorus (AP) and potassium (AK) were determined for the samples taken in 2017 and compared to results from the paired samples collected in 1980 by grouping all samples into four cropping systems: continuous paddy fields, new paddy fields developed from uplands, continuous uplands, and new uplands developed from paddy soils. The results show a significant increase in soil pH, AP and AK in all cropping systems, which was, however, coupled with low fertilizer use efficiency. Additionally, a significant increase in SOM came with new paddy soils, whereas a little SOM accumulation and a significantly weakened correlation of TN to SOM occurred in continuous paddy soils. Both low fertilizer use efficiency and deteriorated soil C sequestration function imply a sub-health status of continuous paddy soils. The changes in cropping systems and fertilization, which essentially resulted from expeditious economic growth, should be responsible for the dynamics of C and N and the consequences to soil quality. More experimental studies on balanced fertilization vs. local commonly used fertilization are suggested to probe the mechanisms underlying the C and N dynamics in paddy soils.