To clarify the influence of the extension of environment-friendly rice farming on the water environment, the effects of puddling omission and organic fertilizer application on the water pollutant loads from paddy fields during cultivation period were examined in the Hachirogata polder for 2004-2006. The soil type of the paddy fields was grey lowland soil. Controlled release nitrogen fertilizer (CRF) was applied in the nursery boxes for both puddling and no-puddling cultivations. No-puddling cultivation effectively reduced the net emission loads of suspended substance (SS), total organic carbon, total nitrogen (T-N) and total phosphorus (T-P) from paddy fields in May, since there was no turbidity in ponding water by puddling or strong wind before rice transplanting. Through the cultivation period, no-puddling cultivation reduced by 340kg ha^<-1> of SS and 1.4kg ha^<-1> of T-N as net emission loads on average. Therefore, no-puddling cultivation is an important rice farming to reduce water pollutant load from paddy. Under the same fertilizer application, it is shown that the reduction in T-N and T-P emission loads by no-puddling cultivation was smaller than the reported values when CRF was applied only for no-puddling cultivation. When the organic fertilizer with a fast degradation rate was applied at 0.67Mg ha^<-1>, an increase of net T-P emission load through the cultivation period and net T-N and T-P load in May was observed. Application of organic fertilizer raised water pollutant loads as like chemical fertilizer. The emission rate was less than 4% of the applied amount of carbon, nitrogen and phosphorus by the fertilizer. The influence on water quality by organic fertilizer application is thought to be limited if the input of the fertilizer is a similar level as this study.

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In this study, to obtain basic knowledge to develop a soybean planting system that reduced cadmium (Cd) content in seeds, using the combination of the control of soil pH, the cultivation techniques and soybean varieties which have low absorption capacity of Cd, we investigated (1) the varietals differences of the effect of soil pH correction on the inhibition of Cd absorption in pot experiment, (2) the effect of soil pH correction and tillage system on Cd content in seeds, and (3) the effect of the groundwater level on Cd content in seeds in a water table control system, "FOEAS". And the following results were obtained. In pot experiment, shoot Cd content was significantly reduced by treatment with calcium carbonate, and its treatment was particularly effective in the low Cd absorption type of soybean varieties. In field experiment, the result of application of other calcium materials such as calcium hydrated lime and gypsum indicated that the decrease of seeds Cd content was affected by soil pH rather than the differences of calcium materials. Especially, in non-tillage systems, gypsum application increased Cd content of seeds because of the reduction of soil pH. Therefore, it was suggested that the combination use of correction of soil pH with soybean varieties which was low Cd absorption type effectively decreased Cd absorption in soybean. In addition, the control of the groundwater level in "FOEAS" system decreased seed Cd content. The control of groundwater levels was suggested to be effective in lower seed Cd content.

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Adsorption and retarded transport of nitrate (NO_3^-) was studied using 9 Andisol subsoils in Japan. In all the soils investigated, NO_3^- adsorption in the NO_3^- concentration of 0-14mM was caused almost exclusively by the apparent salt sorption, the simultaneous adsorption of equivalent amounts of cations and anions, and was not accompanied by the desorption of indigenous sulfate through anion exchange. The NO_3^- adsorption was approximated by a linear adsorption isotherm with the distribution coefficient, K_d, ranging from 0.3 to 1.6L kg^<-1>, which suggests that 25 to 70% of NO_3^- in the subsoils were in the adsorbed phase. Nitrate transport in repacked soil columns showed increasing delay of NO_3^- breakthrough with the increase in K_d. Retardation factor, R, obtained by fitting the convection-dispersion model to the experimental NO_3^- breakthrough curves ranged from 1.3 to 3.2, and was in close agreement with that estimated from K_d for each soil. These results suggest that, in the absence of preferential flow, NO_3^- travel distance is 0.3 to 0.8 times that of water flow, and can be predicted using K_d obtained from batch adsorption experiments.

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We investigated an effect of planting with hairy vetch of a leguminous green manure crop on growth and yield of second crop soybean in a heavy clay soil field converted from paddy field in Hachirogata polder, Japan in 2005, 2006 and 2009. In the hairy vetch planting treatment, the soil structure was developed by hairy vetch planting, and it was thought that the drainage characteristics of the field were improved by crack generation in the soil. In the hairy vetch planting treatment, the soil water was not saturated after rainfall, and then the soil was immediately drought up if there was not rainfall. It was suggested that the water permeability of the soil was improved by the roots' elongation of the hairy vetch. The stem length and the dry weight of the soybean were promoted during the growth period, especially late growth stage. As for this, physical characteristics such as soil moisture condition of the soil were improved by the hairy vetch planting. In the hairy vetch planting treatment, the root of soybean spread in comparison with the no-planting treatment, and the roots elongated deeply into the soil along with the soil crack structure. The soybean yields in the hairy vetch planting treatment were about 30% higher than the no-planting treatment caused by increasing in the pod number in 2006 and 2009. Thus, it was suggested that the growth and yield of the soybean were promoted by the hairy vetch planting before soybean cultivation in the heavy soil field converted from paddy field.

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[in Japanese]

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