Available database on soil physical properties in each soil classification are uniform throughout Japan. Therefore, it remains to be clarified how soil properties are spatially distributed at the prefectural scale. To quantify the soil physico-environmental properties in each prefecture, we comprehensively analyzed the saturated volumetric water content, saturated hydraulic conductivity, and soil moisture characteristics using a dataset compiled by The Basic Soil Environment Monitoring Project. Saturated volumetric water content in the fine-textured lowland soils was high in the northern part of Japan where the organic matter content is high. Andosols had less available water than the other soil types because of its lower bulk density and higher water retention. These results will be useful for fine-scale modeling calculations or agricultural management.

We performed a pot experiment to examine the effect of liming on phosphorus (P) uptake and growth of corn (Zea mays L.) in allophanic and non-allophanic Andosols using three different P sources. Both soils have similar properties: a rich humus, high phosphate retention, low pH (<4.9), and low available P status. The non-allophanic Andosols contained high exchangeable aluminium (Al), whereas Al level was low in the allophanic Andosols. The P sources included a superphosphate (SP) and two kinds of biochar, the latter derived from dairy cattle carcasses charred at different temperatures: low (450°C for 4 h) and high (1,000°C for the first 0.5 h and then 450°C for a further 3.5 h). The availability of P applied to the acid Andosols was affected by the liming, soil type, and P source, and there was a statistically significant interaction between these factors. With SP applied to the non-allophanic Andosols, liming was essential to increase plant growth and P uptake, whereas in the allophanic Andosols, the liming was not required. The high exchangeable Al content of the non-allophanic Andosols without liming caused root damage and prevented the absorption of the applied P. By contrast, the exchangeable Al content of the allophanic Andosols was insufficient for Al-toxicity, even without liming, and P availability was unaffected by liming. In the case of the biochars, liming decreased the availability of P in both Andosols, because the dissolution of P from the biochars increased by a low soil pH. Particularly for the non-allophanic Andosols without liming, with biochars applied, the plants grown did not show Al-toxicity, although the exchangeable Al content in the soil was almost the same as where Al-toxicity had occurred under SP application. The reasons for the different results between SP and the biochars treatments were unclear, and hence, further studies are needed to evaluate these differences. Based on the above results, we conclude that the ameliorative effect of liming on the availability of P applied to acid Andosols is not always reliable and varies with the soil type and P source.

We proposed a simple, inexpensive method for estimating total nitrogen (N) content in surface paddy soils by measuring their electrical conductivity after a hydrogen peroxide treatment. In this method, 5 g of air-dried, 2-mm sieved soil was extracted with 100 mL of a commercially available oxydol (approximately 3％ H₂O₂). After extraction with oxydol at 25°C for 40 h, the electrical conductivity of the soil extract [EC (H₂O₂)] was measured. For the six paddy soil samples, the coefficient of variation for the average of five repeated analyses of EC (H₂O₂) was less than approximately 2％, indicating a high reproducibility of the method. The temperature during the extraction significantly influenced EC (H₂O₂) values, and the temperature at 25°C was found more suitable than either 20°C or 30°C. Furthermore, the relationship between EC (H₂O₂) and total N content was evaluated at two sampling scales: 1) the national scale, with samples collected from paddy fields throughout Japan (n=83) and 2) the field scale, with samples collected from eight fields in Mifune town (n=39) and five fields in Takatsuki city (n=246). The coefficient of determination between EC (H₂O₂) and total N content was 0.70 for the nationwide samples, excluding 11 volcanic ash soils, whereas it was 0.68 and 0.23 for the Mifune and Takatsuki samples, respectively. The low accuracy of estimation for volcanic ash soils and some of the Takatsuki samples was mainly due to the low rate of mineralization of soil organic N by the oxydol treatment. Compared with the soil lightness (L* value), as measured by a soil color reader, EC (H₂O₂) could estimate the total N content with greater accuracy for both the nationwide and field-scale samples, provided that the volcanic ash soils were excluded.