Status and changes of cultivated soil properties in Shiga prefecture [Japan], 1: Status of physical and chemical properties of soil in the last five years

The status of and changes in cultivated soil properties in Shiga Prefecture were investigated from 1994 to 1997. The results obtained were as follows. In paddy fields, which occupy about 92% of cultivated land in Shiga, the depth of the plowed soil layer and the cation exchange capacity were lower than the soil diagnosis standards in Shiga (the depth of the plowed soil layer: 15cm, the cation exchange capacity: 20me/100g) at 71% and 85% of surveyed soils, respectively. The available phosphate content and available silicate content exceeded the upper limits of the soil diagnosis standards (available phosphate: 20mg/100g, available silicate: 30mg/100g) at 50% and 57% of surveyed soils, respectively. However, the available phosphate content was low in many Gley soils. The available silicate content tended to be low in coarse textured, medium textured and gravely soil of well drained paddy fields. Free iron oxide content in poorly drained paddy soils tended to be higher than in well drained paddy soils. In Kohoku, the northern part of Shiga, in which Gley soils are mainly distributed, the lower available phosphate content was presumably due not only to adsorption by active iron but also low application rate of soil improvement fertilizer containing phosphate. These regional changes of soil status as influenced by soil type and management suggest that deep plowing and adequate application of organic matter and soil improvement fertilizer should be practiced on the basis of soil diagnosis. In upland fields and fields under perennial crops, a large amount of organic matter was applied and a large amount of fertilizer was applied, especially in tea gardens. As a result many soils had high available phosphate content. It is also suggested that soil improvement and adequate fertilizer application based on soil diagnosis should be practiced in each crop-producing district both in terms of sustainability and from an environmental viewpoint