Japanese Journal of Soil Science and Plant Nutrition

Inorganic arsenic (As) concentration in rice grains in transplanting paddy fields has recently been suggested by investigations to be lowered by draining. The process occurred for 4 days. It was repeated six times (6-drainage) over a total of 6 weeks, 3 weeks before and after the heading. We examined the effects of 4-day drainage repeated three times (3-drainage) on inorganic As in rice grains in V-furrow direct seeding cultivation. Decrease in the volumetric soil water contents and increase in soil redox potential were found during the drainage periods in the 6-drainage and 3-drainage plots, respectively. In both the plots, total As concentrations in the soil solution were lowered relative to those in the continuously flooded plots, resulting in a decrease in grain inorganic As. However, the grain yield and quality were negatively affected in the drainage plots. The distribution of rice roots in the V-furrow paddy field was concentrated on a soil depth of 0–5 cm, shallower than that typically found in the transplanting paddy field. We conclude that inorganic As concentration of rice grains in the V-furrow paddy fields can be lowered by the 4-day drainage repeated three times without decreasing the grain yield and quality in the absence of high-temperature conditions during the draining period.

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This study was aimed to elucidate the factors of wet damage that cause low yield in barley cultivation. Therefore, the water content, oxygen concentration, and redox potential (Eh), related to moisture damage, were measured over time in the plowed soil or plowing pan in the wet field where high water retention and poor growth were observed, irrigation fields that did not stay in the water but were irrigated, and in nonirrigated fields. Although growth differences were not observed in some cases having low rainfall and others in 3 years, harvested dry weight above ground of barley tended to be lower in the wet field<irrigated fields≤nonirrigated fields. The water content of the plowing pan tended to be higher in plowed soil after rainfall, although the plowed soil was usually lower than that of the plowing pan. Oxygen concentration after rainfall tended to be lower in plowing pans than in plowed soil, sometimes reaching zero. In contrast, in the absence of rainfall, it was highest in January and lowest in May, reflecting the temperature-dependent saturated dissolved oxygen concentration. Eh was also low after rainfall, which was more likely to occur on plowing pans than on plowed soil, and lower below stock than between rows of stocks. The difference between seasons was slight in the absence of rainfall, but the decline due to rainfall was significant after March and in May, when it declined to about −0.1 V sometimes. Additionally, Eh had a significant variation by each instrument and daily variation, and sometimes dropped to −0.2 V. Consequently, the oxygen concentration and Eh in the soil decreased significantly under moist conditions, such as after rainfall in the warm season after March.

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