田面水の塩分濃度上昇にともなう水稲の生育と許容塩分濃度

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Author's last experiments revealed that the maximum allowable salinity concentration of irrigation water for the rice plants under permanently flooded conditions was 1800μS/cm in terms of EC (electrical conductivity). They also demonstrated that the rice plants grew healthy at any stage of their growth when the number of stems in each of the brunches was limited to 20. The present research was carried out to investigate if the above mentioned maximum allowable salinity concentration level for intermittent irrigation during the irrigation season would be suitable. Our experiments were carried out by growing rice plants in pots inside a green house from 2004 to 2005. The percolation rate for the second year was set at 5 mm/d in particular. During the period from transplanting time to the end of heading time, the average daily maximum temperatures inside the green house reached 40 degrees Celsius, with evaporation per pot at approximately 4mm/d, and the surface water salinity concentration increased on average to 1.7 times that of the supply water. Under these conditions, damage was observed only during the tilling peak stage. However, the damage was limited to brown discoloration on the first-growth blades in a very small minority. No more damage was observed on the plants at any subsequent developmental stages. Compared to the rice plants supplied with ground water (fresh water), the period required for the plants under control to tiller into 20 stems and to head fully was delayed by only one or two days. The transpiration of the rice plants under control was 4.3 mm/d, which equaled to that of the rice plants supplied with fresh water. The yield survey revealed that the percentage of the ripened grains from the rice plants supplied with fresh water fell by 3% due to the stringent growth conditions caused by the 5 mm/d percolation rate in the year 2005. No significant damage was detected on the rice plants supplied with the salt water through the entire irrigation period. Consequently, suitability of the irrigation water at 1,800μS/cm salinity concentration was verified.
日本雨水資源化システム学会の論文

田面水の塩分濃度上昇にともなう水稲の生育と許容塩分濃度

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