Shimajiri mudstone is found in the southern parts of Okinawa and Miyako islands. Red-yellow soil was recently found in the Shimajiri mudstone zone on Okinawa. Previous instances of the weathering of this mudstone to red-yellow soil have not been found. We investigated the chemical and mineralogical properties of the red-yellow soil and the weathering of the mudstone. The research area in the southern part of Okinawa, managed by the University of the Ryukyus, has many trees and has never been cropped. We sampled soil at three sites from the top of a slope (site 1) to the bottom (site 3). The soil at sites 1 and 2 was red-yellow and that at site 3 was gray. The soil at site 1 was acidic and that at site 3 was alkaline. The gray soil had a lower clay fraction (smectite) than the red-yellow soil. The chemical and mineralogical properties of the gray soil suggest that it is derived from Shimajiri mudstone. The mudstone had more structural and exchangeable calcium than the red-yellow soil, possibly owing to the leaching of minerals and the weathering of smectite from the mudstone at the top of the slope. The properties of free iron oxide in the B and C horizons indicated that the activity of Fe_2O_3 (Fe_o/Fe_d) increased and the crystallization ratio ((Fe_d-Fe_o) / Fe_t) decreased toward the bottom of the slope. These results indicate that weathering of the (grey) B horizon soil at the top of the slope oxidized the iron to a red-yellow. These results suggest that the soil at the top of the slope began as Shimajiri mudstone. Long-term exposure to wind and rain leached cations out, leaving free iron oxide, which gave the soil its red-yellow coloration.

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To reduce the work involved in soil analysis used to identify fields with adequate nutrients so as to reduce fertilizer applications, I devised an easy soil extraction method to allow the analysis of multiple nutrients. When a mixture of 10 mL of 0.2 mol L^<-1> HCl and 1 g of soil was shaken for 1 h, the extracted nitrate nitrogen, ammonium nitrogen, sodium, and potassium contents almost exactly equaled the exchangeable contents. Although the extracted magnesium and calcium contents were greater than the exchangeable contents, the latter could be calculated from the former when the pH of the soil was <7. The extracted phosphorus content equaled the available phosphorus content determined by the Bray No. 2 method. The extracted carbon content had a relationship with the soil nitrogen content. This extraction method offers several advantages: The solution is easily prepared. The quantities are small, necessitating only small extraction bottles. The avoidance of non-volatile solutes avoids clogging of analytical equipment such as atomic absorption spectrophotometers. And the labor needed to estimate multiple nutrients is reduced.

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Cadmium (Cd) uptake by vegetables is sensitive to soil Cd content and soil pH. Differences among vegetable species in Cd contents of edible parts should be estimated without these influences. We evaluated three methods for estimating species differences: one based only on the Cd content of the edible parts and two based on the coefficients of regression between the Cd content of the edible parts and the soil Cd content determined by extraction in 0.1 mol L^<-1> HCl or 0.05 mol L^<-1> CaCl_2. We collected soil samples at harvest time and associated data on Cd contents in the edible parts of 17 vegetable species. We also estimated a standard of species differences from data collected in a Japanese nationwide survey of the Cd content of crops. The species differences were normalized, and the intra-class correlation coefficients (ICC) of each method, indicating degree of conformity with the standard, were calculated. The ICCs of the two regression methods were higher than those of the simple Cd content method. Thus, the species differences estimated only from the Cd content in the edible parts was strongly affected by the Cd content of the soil, but those estimated from the regression coefficients were not affected by soil Cd content or soil pH. The CaCl_2 extraction method identified a wider range of species differences than the HC1 extraction method. We propose this method for estimating the rate of decrease of Cd content in edible parts associated with species conversion. Since our data were limited, further data will be needed to estimate species differences accurately.

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We monitored emissions of nitrous oxide (N_2O) from upland soil during and after soil disinfestation treatment in the field in the summer of 2013. Plots were amended with fresh-cut sunflower (Helianthus annuus L., 6.1-7.1 kg FW m^<-2>), mustard greens (Brassica juncea L., 2.2-2.8 kg FW m^<-2>), white mustard (Sinapis alba L., 1.9-2.9 kg FW m^<-2>), or nothing. After irrigation, plots were covered with polyethylene film, virtually impermeable film, or nothing (the uncovered plots of mustard greens and white mustard were amended only with roots). The edges of the films were buried in the soil to minimize gas exchange. N_2O concentrations beneath the films were measured, and N_2O emissions from the surface of the films or soil were determined by the chamber method at the same time. The N_2O concentration inside the films increased after coverage, reaching 1.6 g-N m^<-3> in the white mustard plots and 6.8 g-N m^<-3> in the unamended plots. It then declined to nearly zero within 2 days in the amended plots, but decreased slowly in the unamended plots, remaining detectable in some plots for more than 20 days. N_2O emissions were lower in the covered plots than in the uncovered plots if plants were incorporated, but similar regardless of covering in the unamended plots. More N_2O was emitted through the polyethylene film than through the virtually impermeable film, except in the unamended plots, where a low water content might have increased the concentrations inside the virtually impermeable film.

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We applied the Comprehensive Soil Classification System of Japan First Approximation(CSCS 1st Approx.) to the existing digital soil map for cultivated fields. The records of Fundamental Soil Survey for Soil Fertility Conservation in Gunma, Tochigi, Aichi, and Mie prefectures were used to reclassify polygons of the existing map with CSCS 1st Approx. The reclassification results were used to assess the consistency of soil taxa between the original classification and the reclassification, and to assess the uniqueness of "soil series" in the existing soil maps as a reliable basis for reclassification. Comparison between the taxa on the existing map and those of the reclassification showed poor consistency within existing Wet Andosols, Brown Forest soils, Gray Upland soils, and Yellow soils, half of which were reclassified into different soil groups. The soil series in the existing soil map were not necessarily a reliable basis for reclassification by CSCS 1st Approx.; that is, several taxa in CSCS 1st Approx. could be allocated to one soil series, especially Wet Andosols, Yellow soils, and Brown Forest soils. Therefore, in updating soil maps to reclassify soil series, it may be necessary to refer to local pedon data. The application of CSCS 1st Approx. to the existing soil map saw Andosols divided into Allophanic Andosols, Regosolic Andosols, and Non-allophanic Andosols. It also changed half of the area classified as Yellow soils in Aichi and Mie prefectures to Pseudo-gley soils and Brown Forest soils.

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[in Japanese]

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