Effects of Irrigation Water Arsenic in the Rice-rice Cropping System
A pot culture experiment was carried out at Bangladesh Agricultural University (BAU), Mymensingh to see the effects irrigation water arsenic (As) on Boro rice (February to June) and the residual effect on T. Aman rice (August-November). There were eight treatments consisting of Control, 0.10, 0.25, 0.50, 0.75, 1.00, 1.50 and 2.00 ppm As added through irrigation water. A total of 56 L of irrigation water having different concentrations of As was needed for the Boro rice (Cv. BRRI dhan 29). After harvest of Boro rice, T. Aman rice (Cv. BRRI dhan 33) was grown in the same pots with monsoon rain. Nutrients such as N, P, K and S @ 100, 25, 40 and 25 ppm, respectively were added to sustain normal growth of both Boro and T. Aman rice. The irrigation water added As up to 0.25 ppm enhanced the plant height, panicle length, filled grains/panicle, 1000-grain weight and finally the grain yield of Boro rice and the further doses of depressed the plant growth, yield and yield components. The concentration of As in rice grain or straw of Boro rice increased significantly with increasing As concentrations in the irrigation water, the values for grain As for every As treatment were below the Maximum Permissible Level (1.0 ppm). Application of As added to the first crop (Boro rice) had significant residual effects on the second crop (T. Aman rice) in respect of plant height, panicle length, grains/panicle, grain and straw yields. Arsenic concentrations were always higher in Boro rice grain and straw compared to T. Aman rice. The grain As of Boro rice was almost double the As levels in T. Aman rice grain over the treatments. The As treatments had an adverse effect on the N, P, K and S concentration of rice grain.
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