Decadal sustainability of spatial distribution of soil properties in a paddy field as a fingerprint reflecting soil-forming factors and field management
Spatiotemporal variations of soil properties were measured in a Japanese paddy field in order to evaluate how they were created and sustained through various field managements. The field was subjected to land consolidation during 1960s, heterogeneous application of manure in the late 1970s and land leveling in 1986, 1987 and 2003. Surface soils were collected from throughout the field in 2002 and 2012, and the physicochemical properties were analyzed. Additional analyses were carried out for relative altitude in 1986, 1999 and 2012, and soil hardness in 2012. In the field examined, the distribution of field attributes reflected past field managements. The heterogeneous distribution of relative altitude was partly explained by the passage of agricultural machinery, whereas the heterogeneous distribution of soil organic matter was partly explained by both past and recent applications of animal dung manure. In general, the measured soil properties were maintained from 2002 to 2012, and the pattern of spatial distribution did not change significantly for many of the properties. The correlation coefficient of the distribution patterns between 2002 and 2012 was highest for yellowness (0.95), followed by sand (0.90), acid-oxalate extractable iron (Fe; 0.88), available phosphorus (P; 0.87), redness (0.82), lightness (0.77), sand-size organic matter (0.74) and total nitrogen (N; 0.72). Land leveling carried out in 2003 barely influenced the distribution of these properties. Among these properties, soil color parameters and sand content can be measured rapidly without reagents and will be useful for characterizing paddy fields according to the distribution of stable soil properties. The analysis of the natural abundance of 15N in soil was also effective to suggest the contribution of the application of animal dung manure to the accumulation of soil organic matter at a within-field scale. It can be concluded, as a general rule, that each paddy field has its own fingerprint which is unveiled by precise soil sampling and analyses of stable properties.
