Spatial variability of soil chemical properties in a paddy field

To obtain basic information for site-specific soil management to improve nu trient use efficiency by plants, spatial variability of soil properties was evaluated in a. 50 m x 100 m paddy field. Ninety-one surface soil samples were collected after harvest to investigate the spatial variability of thei r chemical properties: pH, EC, total C content, total N content, C/N ratio, contents of available P, exchangeable Ca, Mg, K, and Na. Fifty samples wer e also collected after transplanting to investigate that of nitrogen-relate d properties: total C content, total N content, C/N ratio, and contents of mineralizable N and inorganic N. Geostatistical analysis was carried out to examine within-field spatial variability using semivariograms and kriged m aps as well as descriptive statistics. Descriptive statistics showed that t he coefficient of variation for the EC, total C content, total N content, c ontents of available P, exchangeable K, Na, mineralizable N, and inorganic N exceeded 10%, suggesting a relatively high variability. Geostatistical an alysis indicated a high spatial dependence for all the properties except fo r the pH and inorganic N content. The ranges of spatial dependence were abo ut 20 m for EC, total C content, total N content, C/N ratio, contents of ex changeable Ca, Mg, Na, and mineralizable N, and about 40-50 m for the conte nts of available P and exchangeable K. Based on the results of spatial depe ndence, kriged maps were prepared for the properties to analyze their spati al distribution in the field. The results reflected the history of soil man agement of the field in addition to the characteristics of the inherent soi l properties. In conclusion, rational sampling interval was evaluated at 20 -50 m depending on the soil properties, and the need for site-specific soil management and possibility of precision agriculture were demonstrated even in an almost flat paddy field.