The actual conditions of the cultivated soil properties of Chiba prefecture [Japan]

The cultivated soils of Chiba prefecture have been affected by anthropogenic impact in terms of land and subsoil improvement, plowing and harrowing, fertilizer and organic matter application, etc. Soil surveys of the cultivated soil in Chiba prefecture were started in 1979 in order to determine whether the soil properties have changed over time at certain fixed points. The changes in the cultivated soil properties of Chiba prefecture in the last thirty years have been described as follows. (1) The Soil Environment Survey, set up 500-558 fixed points in cultivated soil in Chiba prefecture, and continued monitoring from 1979 to 1997. From 1998, the Soil Monitoring Survey set up 373-380 fixed points was started. These surveys carried out in a 5 years period and tested for pedological and edaphological properties. The pedological survey was conducted to monitor the changes of the gley horizon depth of paddy fields and the content of organic matter of upland fields. The edaphological properties were studied soil fertility on soil chemical and physical aspects such as the contents of exchangeable bases (CaO, MgO, K2O extracted with 1M NH4OAc), Truog P2O5, three phases ratio and available pore ratio, etc. Local farmer's soil management methods and fertilizer applications were investigated by using a questionnaire. (2) The changes in paddy soil properties. The percentages of well, poorly drained and no-changed paddy soils at 73 points were 48%, 10% and 42%, respectively. These changes show that soil improvement related to effluent from agricultural land has affected the depth of the gley horizon considerably. Because of soil managements by farmers, the contents of exchangeable bases trended to increase, but the contents of Truog P2O5 and available SiO2 trended to decrease at the plow layer. (3) The changes in upland soil properties. The contents of exchangeable CaO and Troug P2O5 of the plow layer trended to increase. The decreasing of available pore ratio showed that this change in upland soil was caused by too much tillage in the soil management of farmers.