Spatial Variability of Micronutrients in Rice Grain and Paddy Soil

Consumption of rice is the main source of micronutrients to human in Asia. A paddy field with unknown anthropogenic contamination in Deqing County, Zhejiang Province, China was selected to characterize the spatial variability and distribution of micronutrients in rice grain and soil. A total of 96 paired soil and rice grain samples were collected at harvest. The micronutrients in the soil samples were extracted by diethylenetriamine pentaacetic acid (DTPA). The mean micronutrient concentrations in rice grain were 3.85 μg Cu g−1, 11.6 μg Fe g−1, 39.7 μg Mn g−1, and 26.0 μg Zn g−1. The mean concentrations were 2.54 μg g−1 for DTPA-Cu, 133.5 μg g−1 for DTPA-Fe, 30.6 μg g−1 for DTPA-Mn, and 0.84 μg g−1 for DTPA-Zn. Semivariograms showed that measured micronutrients in rice grain were moderately dependent, with a range distance of about 110 m. The concentrations of the DTPA-extractable micronutrients all displayed strong spatial dependency, with a range distance of about 60 m. There was some resemblance of spatial structure between soil pH and the grain Cu, Fe, Mn, and Zn. By analogy, similar spatial variation was observed between soil organic matter (SOM) and DTPA-extractable micronutrients in the soil. Kriging estimated maps of the attributes showed the spatial distributions of the variables in the field, which is beneficial for better understanding the spatial variation of micronutrients and for potentially refining agricultural management practices at a field scale.