Qualities of soil organic amendments are important determinants of degradability and mineralization in soils. Recently, acid detergent analyses, which are commonly used to assess forage quality, were applied to soil organic amendments, such as composted animal manure, as an index of degradability or mineralization in soil. Concentrations of acid detergent-soluble organic nitrogen (ADSON), which is present in organic materials, were significantly and positively correlated with the quantities of inorganic nitrogen released from amended soils. In this study, we collected samples of various soil organic amendments (n=483), including composted animal manures, green manures, crop residues, and commercially available soil organic amendments (e.g., rapeseed oil cake) that are used in actual cropping systems. In subsequent assessments, ADSON contents were high in rapeseed oil cake and fish meal, and were low in some composted animal manures, some graminaceous green manure crops, leaves and stems of grain crops such as buckwheat and soybean, stubble from forage crops such as sorghum, and in rice husks. Some amendments had low ADSON contents despite the presence of low C/N ratios. Amendments with low C/N ratios typically showed high mineralization rates, likely corresponding with high ADSON contents. Relationships between ADSON contents and C/N ratios, however, were not clear in composted animal manures, but were expressed as a curve in green manure crops. For composted swine manure, ADSON contents increased with increasing ratios of animal excrement to submaterial (mainly sawdust). No other relationships were observed between ADSON contents and the duration of composting, mixing ratios of animal excrement to submaterials, or types of composting facility.

Available nitrogen, total carbon, total nitrogen, and C/N ratios in upland soil were estimated using analyses of spectra from a new fluorescence spectrometry system with an ultraviolet light-emitting diode (UV-LED). Forty six samples of andosol were collected from upland agricultural fields, and available nitrogen, total carbon, total nitrogen, and C/N ratios were estimated. Predictive abilities of partial least square models were assessed in a leave-one-out cross-validation procedure based on the entire dataset. The accuracy of calibration models was evaluated using the coefficient of determination and the root-mean-square error. Estimates of available nitrogen, total carbon, total nitrogen, and C/N ratios were highly accurate. Moreover, fluorescence spectroscopy analyses using UV-LED as a light source rapidly provided estimates of these chemical properties, suggesting utility in assessments of plant nutritional conditions and soil fertility.

We generated statistical models to estimate radiocesium (¹³⁷Cs) concentrations in rice grains according to assessments of soil chemical properties. The models were constructed by analyzing ¹³⁷Cs concentrations in soil and rice grains from paddy fields in Fukushima Prefecture collected by the Ministry of Agriculture, Forestry and Fisheries in 2012–2015 from a total of 290 fields, and data from two experimental fields with elevated risks of radiocesium transfer. A model with two explanatory variables, soil exchangeable ¹³⁷Cs and soil exchangeable potassium (K), well explained variations in ¹³⁷Cs concentrations in rice grains on log-transformed scales (R²=0.68, P<0.001, n=309). Moreover, partial regression coefficients indicated that at a constant concentration of soil exchangeable K, ¹³⁷Cs concentrations increased in rice grains with increasing soil exchangeable ¹³⁷Cs concentrations. In addition, the effects of soil exchangeable ¹³⁷Cs concentrations on rice grain ¹³⁷Cs concentrations were nearly equal to that of soil exchangeable K. The trend in the 137Cs concentration in rice grains estimated with the model for several different scenarios of soil exchangeable 137Cs concentration agreed well with observed trends. These results show that the present model can be used to manage risks of ¹³⁷Cs transfer to rice.

Following radiocesium (RCs) release due to the accident at the TEPCO Fukushima Daiichi Nuclear Power Plant in 2011, extra potassium (K) fertilizer has been applied to paddy fields to reduce uptake of RCs by rice plants. Many studies have shown that RCs uptake can be suppressed by sufficient soil concentrations of exchangeable K. However, when exchangeable K concentrations decline, RCs uptake can increase and varies widely between different soils. Therefore, risk assessments of RCs transfer to rice plants are required and need to be performed with consideration of soil properties to inform whether to continue applying K. In our previous study, we developed a statistical model for estimating ¹³⁷Cs concentrations in rice grains from concentrations of soil exchangeable ¹³⁷Cs and K. In this study, we tested the model to inform applications of K. Our model estimated upper prediction intervals for rice grain RCs concentrations under several scenarios of the concentration of soil exchangeable RCs. From the upper boundary of upper prediction intervals, we determined the concentrations of soil exchangeable K required to avoid exceedance of target rice grain RCs concentrations. The required concentrations of soil exchangeable K varied widely depending on assumed soil exchangeable RCs concetrations. This result corresponds to the finding in our previous study that the effect of soil exchangeable ¹³⁷Cs concentration on rice grain 137Cs concentration was nearly equal to that of soil exchangeable K. These results show that the model can be applied for risk management and countermeasure taking account soil properties, by elucidating spatial distributions of soil exchangeable RCs.

Lampranthus spectabilis (Aizoaceae) is a perennial plant that is common in Japanese urban settings, such as roadsides and parks. To investigate its ability to accumulate NaCl in saline soil, we grew plants in 0-, 100-, 200-, 400-, or 600-mM NaCl solutions and collected samples at 1, 2, 3, and 6 weeks. Plants grew in NaCl concentrations that were above the target electrical conductivity value for leaching in Japan. With increasing NaCl concentrations, Na⁺ contents in leaves and stems increased remarkably, and were accumulated to more than 2 fold that in roots. Under the same conditions, Cl⁻ accumulated in leaves and stems to 10 times that in roots. Furthermore, at 100- to 400-mM NaCl, plant water contents were equivalent to those in control plants. These data suggest that leaves and stems avoid the adverse effects of salt by maintaining high water contents. At 6 weeks, ion contents in leaves and stems reached 45 mg of Na⁺ g⁻¹DW and 163 mg of Cl⁻ g⁻¹DW at 400-mM NaCl, and reached 102 mg of Na⁺ g⁻¹DW and 135 mg of Cl⁻ g⁻¹DW at 600-mM NaCl. The ability of L. spectabilis to accumulate high levels of NaCl may make it suitable for phytoremediation of salinized soils.