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.

为明确日本某稻田土壤属性的时空变化规律，及其在不同田间管理措施下的形成与维持机制，本研究对该稻田开展了系统测定。该稻田曾于20世纪60年代实施土地整理，1970年代末不均匀施用畜禽粪肥，1986、1987及2003年进行土地平整。研究分别于2002年和2012年采集全田表层土壤样品，并分析其理化性质。此外，还于1986、1999和2012年测定了相对海拔，2012年补充测定了土壤硬度。研究区域内的农田属性分布特征反映了该田块过往的田间管理历史。其中，相对海拔的非均一分布可部分归因于农业机械的通行轨迹，而土壤有机质的非均一分布则可同时由过往及近期的畜禽粪肥施用行为所解释。总体而言，2002至2012年间测定的土壤属性整体保持稳定，多数属性的空间分布格局未发生显著改变。2002年与2012年的属性分布格局相关系数最高的为黄度（yellowness，0.95），其次依次为砂粒含量（0.90）、草酸浸提态铁（acid-oxalate extractable iron，Fe，0.88）、有效磷（available phosphorus，P，0.87）、红度（0.82）、亮度（0.77）、砂粒级有机质（0.74）及全氮（total nitrogen，N，0.72）。2003年实施的土地平整几乎未对上述属性的空间分布产生影响。在上述测定属性中，土壤颜色参数与砂粒含量无需化学试剂即可快速测定，可用于基于稳定土壤属性的分布特征表征稻田属性。对土壤中¹⁵N天然丰度的分析也可有效揭示畜禽粪肥施用在田块尺度内对土壤有机质积累的贡献。综上，本研究可得出一般性结论：每一块稻田均具有其独特的“指纹特征”，该特征可通过精准土壤采样与稳定土壤属性分析得以揭示。