Changes in soil chemical properties of farmland in Kanagawa [Japan] over 30 years observed from soil diagnoses data

Kanagawa prefecture has had a long history of soil diagnosis projects. In the 1970s, the prefecture initiated the chemical analysis of exchangeable bases and fertilizer application improvement on the basis of base-saturation percentage. The prefecture introduced computers several decades ago. Further, in the 1980s, it announced a soil diagnosis system using a personal computer and spread the use of the system before the rest of the country. Later, the system was modified for Windows, and it is presently being used in the field. In this study, the data of soil diagnoses accumulated over the last 33 years using the system was analyzed and some findings were obtained. Because different regions and crops were investigated on a year-to-year basis, crop-specific changes fluctuated greatly from year to year and did not show a clear tendency. However, a comparison of 5-year average values showed distinct characteristics. The data of paddy fields did not show any significant changes from year to year, except that potassium had a tendency to accumulate in the soil to some extent. It was also revealed that the content of phosphoric acid in paddy soils differed with the drainage basins of rivers. The data of common crops fields and open air vegetables fields showed a considerable accumulation of phosphoric acid and potassium in the soils. The data of orchards also showed the accumulation of phosphoric acid and potassium. Paticularly, Asian pears fields showed a considerable accumulation of phosphoric acid and potassium in the soil. In tea fields, there was a decrease in the electric conductivity (EC) and potassium content, and an increase in phosphoric acid in the soil. The data of vegetables greenhouses showed an excess of overall nutrients accumulation, which did not fluctuate greatly from year to year. However, the EC showed a tendency to decline from 1995 onward. The data of greenhouse floriculture also showed an excess of overall nutrients accumulation, and there was a tendency of phosphoric acid and potassium to accumulate in carnation fields and rose fields, respectively.