Hidetaka Katou

Optimal Soil Eh, pH, and Water Management for Simultaneously Minimizing Arsenic and Cadmium Concentrations in Rice Grains

Arsenic (As) and cadmium (Cd) concentrations in rice grains are a human health concern. We conducted field experiments to investigate optimal conditions of Eh and pH in soil for simultaneously decreasing As and Cd accumulation in rice. Water managements in the experiments, which included continuous flooding and intermittent irrigation with different intervals after midseason drainage, exerted striking effects on the dissolved As and Cd concentrations in soil through changes in Eh, pH, and dissolved Fe(II) concentrations in the soil. Intermittent irrigation with three-day flooding and five-day drainage was found to be effective for simultaneously decreasing the accumulation of As and Cd in grain. The grain As and Cd concentrations were, respectively, linearly related to the average dissolved As and Cd concentrations during the 3 weeks after heading. We propose a new indicator for expressing the degree to which a decrease in the dissolved As or Cd concentration is compromised by the increase in the other. For minimizing the trade-off relationship between As and Cd in rice grains in the field investigated, water management strategies should target the realization of optimal soil Eh of -73 mV and pH of 6.2 during the 3 weeks after heading.

A review of rapid transport of pesticides from sloping farmland to surface waters: Processes and mitigation strategies

Pesticides applied to sloping farmland may lead to surface water contamination through rapid transport processes as influenced by the complex topography and high spatial variability of soil properties and land use in hilly or mountainous regions. However, the fate of pesticides applied to sloping farmland has not been sufficiently elucidated. This article reviews the current understanding of pesticide transport from sloping farmland to surface water. It examines overland flow and subsurface lateral flow in areas where surface soil is underlain by impervious subsoil or rocks and tile drains. It stresses the importance of quantifying and modeling the contributions of various pathways to rapid pesticide loss at catchment and regional scales. Such models could be used in scenario studies for evaluating the effectiveness of possible mitigation strategies such as constructing vegetated strips, depressions, wetlands and drainage ditches, and implementing good agricultural practices. Field monitoring studies should also be conducted to calibrate and validate the transport models as well as biophysical-economic models, to optimize mitigation measures in areas dominated by sloping farmland.

Susceptibility of undisturbed soils to compression as evaluated from the changes in the soil water characteristic curves

Undisturbed cores of fourteen soils were compressed under hydrostatic stresses, and the resultant soil water characteristic curves as well as the changes in the void ratio and water content of the soils by compression were determined. As the applied total stress increased, air-filled pores were lost first, and thereafter compression accompanied with the extrusion of excess pore water proceeded. Loss of pore volume caused by the compression was more pronounced for coarser pores with smaller drainage suctions. The ranges of the size of the pores lost or collapsed, as assessed from the changes in the soil water characteristic curves, were narrower than those expected on the assumption that the applied stress was counterbalanced exclusively by the increase in the overburden pore water pressure. Moreover, the range differed greatly among the soils used, reflecting the differences in the susceptibility of the soils to compression. From the magnitude of the applied total stress and the upper limit of the suction...

Control of soil water potential using negative pressure water circulation technique

Abstract The negative pressure water circulation technique (abbreviated as NEWCIRC) had been developed as a new technique for the control of the soil moisture conditions (Lipiec^et al. 1988: Soil Sci. Plant Nutr., 34, 417–428). In this report, the factors which influenced the hydrostatic pressure of the NEWCIRC system were examined and some guidelines were formulated to control the soil moisture conditions using this technique. Water at a negative pressure was obtained by the reduction of the air pressure in the water reservoir and the water was supplied to the soil through a ceramic tube wall. However frequently, the values of the soil water potential in the pots were not equal to those of the water in the reservoir due to the influence of water circulation which produced a pressure gradient along the water circulation system. Therefore it was considered that the hydrostatic pressure of the NEWCIRC system depended on the hydrostatic pressure of the water reservoir and the pressure difference caused by th...

Simultaneous decrease of arsenic and cadmium in rice (Oryza sativa L.) plants cultivated under submerged field conditions by the application of iron-bearing materials

ABSTRACT The Codex Alimentarius Commission has recently adopted maximum levels for inorganic arsenic (As; in 2014) and total cadmium (Cd; in 2006) in polished rice grains to maintain food safety and to decrease the risk to human health. As rice is a staple crop in Japan and monsoon Asian countries, reducing concentrations of As and Cd in rice is an urgent matter. In flooded conditions, Cd concentration in soil solution decreases whereas As concentration increases. Therefore, we aimed to evaluate the efficiency of iron-bearing materials to decrease As concentration in soil solution and rice (Oryza sativa L.) grain under submerged cultivation, while also considering Cd concentration. In experiments conducted in paddy fields in six regions, As concentrations in the soil solution during the cultivation period decreased in the following order: control (REF) > steel converter furnace slag (SCS) > non-crystalline iron hydroxide (FH) > zero-valent iron (ZVI). The concentrations of As in brown rice were in the same order, with ZVI achieving particularly strong reduction. Cadmium concentrations were low, probably owing to submerged cultivation conditions. Application of iron-bearing materials slightly and insignificantly reduced the yields of brown rice and straw. Application of these materials did not have a significant negative impact on the quality of rice. Our data indicate that the application of iron-bearing materials effectively reduces As concentrations in soil solution and rice grains without negative effects on yield and quality, with a particularly powerful effect of ZVI which is possibly explained by arsenic sulfide formation.

Effects of soil amendments on arsenic and cadmium uptake by rice plants (Oryza sativa L. cv. Koshihikari) under different water management practices

ABSTRACT Concentrations of arsenic (As) and cadmium (Cd) in rice grains are of public concern for human health. We conducted field experiments to investigate the effects of soil amendment applications, combined with different water management practices, on As and Cd uptake by rice plants (Oryza sativa L. cv. Koshihikari). Prolonged flooding, practiced for pre-heading 3 weeks and post-heading 3 weeks, led to elevated As concentrations in the soil solution and rice grain. Rainfed water management, in which no irrigation was practiced after midseason drainage until harvest, led to elevated Cd concentrations in the soil solution and rice grain. Application of short-range-order iron hydroxide (IO) reduced As uptake by rice plants, whereas Cd uptake was reduced by the application of converter furnace slag (CFS). However, it was difficult to simultaneously reduce the As and Cd uptake by a single countermeasure of the water management practice or the soil amendment application. Prolonged flooding combined with the application of IO, or rainfed water management with the application of CFS, were promising measures for the simultaneous reduction of As and Cd uptake by rice plants.

Determining competitive nitrate and chloride adsorption in an andisol by the unsaturated transient flow method

Abstract Adsorption of monovalent electrolyte anions during transport process in Andisols is largely due to the increase in the total anion adsorption rather than through anion exchange with strongly adsorbed native S04 2−. The unsaturated transient flow method has been developed for determining adsorption isotherms for weakly reactive ions without causing excessive desorption of strongly adsorbed native ions. The objective of this study was to extend the method to determine NO3 − adsorption isotherms in an Andisol in the absence or presence of Cl competing for the adsorption sites Kannondai subsoil (Hydric Hapludand), premixed with a Ca(NO3)2 or CaCl2-Ca(NO3)2 solution at different concentrations, was packed into sectionable columns, and one-dimensional water absorption experiments were conducted. Anion adsorption by soil, Q n, and the liquid-phase concentration, C n, prior to the water imbibition were obtained from the plots of the anion content vs. water content in the region beyond the ‘plane of separation,’ where the antecedent solution was accumulated. The values of Qn and C n found in a series of column experiments were then used to construct the isotherms describing the solution composition-dependent adsorption of NO3 − and Cl−. e fitted to Langmuir-type equations, the maximum adsorption for NO3 − (Qmax= 27,1-29.0 mmolc kg−1) was consistently smaller than that for Cl− (Qmax = 455 46.1 mmolc kg−1), while the empirical constant K (= 0.0238 - 0.0274 m3 molc −1) was insensitive to the anion species. The anion content profiles predicted by the inferred adsorption isotherms closely agreed with the measured content profiles.

Changes in Sediment Volume, Liquid Limit, and Plastic Limit of Alluvial Soils upon Drying

Several soils were slowly dried, and changes in sediment volume, liquid limit, and plastic limit of the soils with decreasing initial soil water content were investigated. For alluvial soils, sediment volume did not show appreciable changes unless the soils were dried to pF 4.2–4.5. Upon further drying, it decreased successively with falling initial soil water content. These results did not seem to depend on the organic matter content or drying history of the soils. Similar results were obtained for the liquid limit and plastic limit. It was considered that the significant changes in these physical properties upon drying beyond pF 4.2–4.5 were due to the decrease in the pore volume of soil-water systems through the formation of clay domains during the drying process.

Solute Dispersion during Unsteady Leaching as Affected by Aggregate Size and Soil Water Content

Abstract Solute dispersion during unsteady leaching of chloride which had been applied as a solution was investigated in soil columns differing in aggregate size (<1 and <4mm), initial soil water content, and the amount of leaching water applied. The approximate analytical solution of De Smedt and Wierenga (Soil Sci. Soc. Am. J., 42, 407-412, 1978) for solute flow during infiltration and redistribution was extended to describe solute concentration profiles in which the water content at the solute front was different from that at the front of subsequently infiltrating leaching water. The magnitude of the solute dispersion was evaluated as the dispersivity in the solution that gave the best fit of the calculated concentration profiles to those measured. The dispersivities thus determined were consistently larger for the coarse-aggregate columns than for the fine-aggregate columns irrespective of the initial soil wetness, reflecting the more efficient leaching observed in the latter columns. In the coarse-ag...

Nitrogen and oxygen isotope enrichment factors of nitrate at different denitrification rates in an agricultural soil

ABSTRACT Quantitative evaluation of denitrification by the dual isotope approach, which measures the stable isotope ratios of nitrogen (δ15N) and oxygen (δ18O) in nitrate, has been hampered by the wide range of values reported for the ratio of enrichment factors for 15N and 18O (15ε and 18ε, respectively) during denitrification. The objectives of this study were to determine 15ε and 18ε values at different denitrification rates under controlled conditions, and to infer possible mechanisms by which the 18ε/15ε ratio is influenced under different conditions. Column experiments were conducted at 25, 15, and 10°C, which enabled determination of 15ε and 18ε at different denitrification rates, in the absence of nitrate replenishment from ammonium oxidation and other sources. The values of 15ε and 18ε ranged from −11.8 to −14.9‰ and from −8.4 to −15.9‰, respectively, with 15ε less sensitive to changes in the denitrification rates. The resultant 18ε/15ε ratio, ranging from 0.70 to 1.17, was close to the values reported for sediment incubations, and larger than those for groundwater systems. These results are consistent with the explanations that 18ε/15ε value itself is close to unity during denitrification, and that at smaller denitrification rates, concurrent reactions including re-oxidation of nitrite to nitrate lead to smaller apparent fractionation of 18O and smaller 18ε/15ε ratios. This suggests that while linear relationships between δ18O and δ15N give a strong evidence of denitrification, apparent 18ε/15ε values are site specific and depend on the ambient conditions. In evaluating denitrification in such systems, we suggest the use of 15ε in preference to 18ε because 15ε is less sensitive to denitrification rates.