This study aims to clarify the removal of four soluble element concentrations (iron, manganese, calcium, potassium) in the soil solution at 20 cm using an open lysimeter at paddy fields. As a result of this study, the removal of iron and manganese elements were found to correspond to the redox potential in the plow layer. The concentration of calcium element was affected by that of iron. When the concentration of iron was high, the concentration of calcium element also became high. Potassium element concentrations were influenced by fertilization and that influence continued about 60 days after fertilization. These variations of those four element concentrations were found in the plow layer of 20 cm depth during the same stage of rice growth.
Models of stratified paddy fields of Kuroboku soil were used and composed of 3 layers. These models were planted with rice and were fertilized. The models were used to investigate the relationship between the removal of soil solution element in percolation water and percolation patterns. Concentrations of nitrate, dissolved oxygen and redox potential in the open system percolation (subsoil) increased more than those in the closed one (plow layer and plowsole). Also, electric conductivity and the concentration of iron element and manganese element tended to invert. Potassium element provided from the conventional fertilizer increased. Potassium concentrations in both plow layer and plowsole was more than that of subsoil during the 50 days from the beginning of this test. After 50 days, the concentration of soil solution in all layers became similar. Concentrations of total nitrogen in the drainage of this model were higher than that of inundation during the first 50 days from the beginning of the test. Concentrations of total phosphorus had a similar tendency. But that tendency only continued for about 30 days. After 50 days, concentrations of total nitrogen in inundation became higher than those of drainage. After 30 days, cncentrations of total phosphorus in inundation bacame higher than those of drainage.
Soil dressing with Pumice Flow Deposit (PFD) has been widely practiced in Abashiri district of Hokkaido. Soil physical properties was improved in this operation, but concentration of nutrients in soil were declined because of dilution. To solve this problem, we studied the effect of simultaneous application of organic matter with soil dressing of PFD. Application of 80 Mgha'1 barnyard manure increased CEC, available phosphorus, and exchangeable cations. The available nitrogen value also increased, but these values were still under the value recommended. a-glucosidase activities in PFD as an index of soil microbial activities was very low in PFD, therefore this activities declined in the soil dressed with PFD. However, decrease of aglucosidase activities were less than the value estimated by soil dilution ratio when the soil physical properties were well improved by dressing. a-glucosidase activities recovered to the same level of original soil with simultaneous application of barnyard manure. As a result, we can quickly recover soil chemical and biological properties in the dressed soil by simultaneous application of organic matter with PFD.
We studied the effect of soil dressing on crop productivities to establish an desirable management of organic matter in the field dressed with Pumice Flow Deposit (PFD). In the frame experiment, a decrease of crop yield may be mainly caused by dilution of soil chemical fertilities. The application of 40 Mg ha1 barnyard manure and green manure simultaneous with dressing recovered a decrease of crop yield. In the field experiment, changes of crop yield after dressing was influenced by the both of soil chemical and physical properties. The crop yield might not decrease in the field when the soil physical properties were well improved enough to compensate dilution of nutrients and in case that a-glucosidase activities did not decrease to the value estimated. In order to recover a decrease of crop yield, the application of 40 Mgha1 barnyard manure would be recommended. More significant effects were obtained in case that 80 Mgha'1 of barnyard manure was applied. Green manure should be additionally cultivated after dressing for the recovery of primary yield downfall. These effects of barnyard manure has continued at least for 3 years.
Most of irrigated water in paddy fields infiltrates underground. This process, however, has not been clarified. In the case that groundwater table is deep, the measurement of water content in unsaturated aquifer has not been reported. We measured water content in unsaturated aquifer in the Ashigara Alluvial Fan using neutron moisture meter. As a result, there was no difference in the water content between in irrigation period and in non-irrigation. It was revealed that the infiltrated water from the paddy fields goes down, not increasing water content in unsaturated aquifer in the Ashigara Alluvial Fan.
The role of soil conservation in slope land farming systems in Indonesia and the Philippines is very important. In a visit by the authors to some areas in both countries, they observed that many farmers were practicing soil conservation in their agricultural land in response to the land condition and socio-economic environments. The agricultural land was characterized by sloping farmlands and low soil fertility. Soil condition and land topography have great influence in the farmers* adoption of soil conservation practices for sustainable agricultural production.