A simple assessment on spatial variability of rice yield and selected soil chemical properties of paddy fields in South China

Abstract

Data related to the spatial variability of properties of paddy soil is critical for improving rice productivity and designing sustainable farming techniques. However, a systematic assessment focusing on the spatial variability of low-yield paddy soil has not been conducted in South China. In this context, 560 soil samples were collected across South China and analyzed for nine common chemical properties. Rice yield data was obtained by surveying farmers during soil sampling. Soil parameters and rice yield varied considerably throughout the study area and their coefficients of variation ranged from 17.3% to 74.2%. Experimental semivariograms were developed and a moderate spatial dependence was observed for all selected parameters. Distribution maps, derived by kriging interpolation, illustrated that these paddy fields were characterized by high concentrations of soil organic matter (SOM), total N (TN), available N (AN) and available Zn (AZn); pH values decreased widely comparing with the data reported by the National Soil Survey, especially in southeast China; the areas with low soil P concentrations (<10mgkg−1) were mainly located in southwest China; cation exchange capacity (CEC), available K (AK) and available Si (ASi) had similar trends in spatial distributions with high concentrations in southeast China and low concentrations in southwest. Notably, paddy fields in southeast China were typically deficient in AK due to their concentrations, all of which are almost less than 100mgkg−1. Correlation analysis revealed that rice yield was significantly positively correlated with pH, CEC, AK and ASi, while negatively correlated with AN and AZn. Low pH, AK, CEC and ASi levels may be the most important constraints limiting rice productivity and fertilizers with N and Zn may be over-used and must be applied appropriately. The soil quality index (SQI) was also calculated using the analyzed chemical properties and a significant correlation was observed between SQI and rice yield, supporting earlier findings that good soil chemical health is essential for optimum sustained crop production. The remarkable variations of SQI and rice yield indicated that the potential for increasing rice productivity is a real prospect. Therefore, regional planning fertilization should pay more attention to the spatial variability of soil chemical properties to avoid economic losses and environmental pollution, and especially to the limited nutrients.