Abstract
A study was made on the movement of arsenic in irrigated rice soil and the effects of added arsenic on Boro and T. Aman rice. This study was performed through net house and field experiment. The net house experiment with 12 (2 locations x 2 sites x 3 As treatments) undisturbed soil columns (40 cm length and 30 cm diameter) was set up at net-house of Bangladesh Agricultural University (BAU), with rice growing in Boro and T. Aman seasons of 2004 and 2005. The soil columns were collected from Faridpur (>10 mg As kg1) and Mymensingh (<3 mg As kg'). Arsenic was added through irrigation water at 0, 1 and 2 mg As L' giving the arsenic load of 102-120 mg core" for As, ppm and 204-< 240 mg core for As2 ppm treatments. Higher yield reduction coupled with higher arsenic concentration of rice grain and straw were found in Boro rice 2005. The amount of arsenic leaching was very low in all soils. Higher levels of leachate arsenic were observed during T. Aman season for the maximum soil reduction, with arsenic (III) as the predominant arsenic species in all the leachates. The amount of leached out arsenic varied with soils, Faridpur-1>BAU-1>Faridpur-2>BAU-2 soil. There was a significant positive correlation between As with Fe and P concentrations and negative correlation with Eh in the leachate. The added arsenic retention varied from 78.21- 88.14% in soil, 0.66-2.20% in rice plants, 0.58-2.13% in sand below the soil column and 0.59-2.98% in the leachate. Another set up with 12 soil columns (2 locations x 2 sites x 3 As treatments) was run without growing any crop. The concentration of arsenic in the leachates of BAU-1, BAU-2 and Faridpur-2 soils were lower in non-rice experiment while higher levels of arsenic leaching were observed in Faridpur-1 soil in both cropping and non-cropping soil columns. The accumulation of arsenic was higher in the top layers of soils compared to that in the lower layers. The field experiment was also conducted at the BAU farm during 2004 and 2005. Twenty PVC cylinders (5 treatments x 4 replication) were installed in the middle of the 1mx1m micro- plot. Boro and T.Aman rice were grown into the ring and outside the ring in sequence. Irrigation (0, 1 & 2 mg As L'') and soil (10 & 20 mg As kg') applied arsenic were added to Boro crops. The arsenic contamination of soil significantly reduced the yield and yield components of rice. Arsenic concentrations in rice grain, straw, husk and roots increased with increasing arsenic concentrations added through irrigation water or added directly to the soil. Arsenic concentration in rice plant parts followed the order: root> straw>husk grain. The arsenic concentration in the upper soil layers increased highly by irrigation or soil added arsenic compared to lower layers. Of the total arsenic added, the 0.076-0.652% was found in rice plants and the 62.22 to 69.76% retained in soil.