Effects of stress and fallow treatments on the early growth of irrigated rice in relation to soil pH and Fe (2) content
2003
Rodriguez, R.C. | Nozoe, T. | Agbisit, R. (International Rice Reseach Inst., Los Banos, Laguna (Philippines). Crop, Soil and Water Sciences Div.)
To determine the effects of water and straw management on changes in soil fertility in a continuous double-cropped rice system, a long-term experiment has been conducted at IRRI since 1972. The water treatments (main plots) are dry fallow (WO) and flood fallow (W1); and straw removal (SO) and straw incorporation (S1) are the subplots. In the 2000 wet season (WS) it was found that plant growth in an alkaline field was inhibited in the WO plots up to post-panicle initiation stage because of soil pH above 8 (pH 8 is the critical level). Furthermore, the irrigation water at the site contained high amount of Na that also contributed to high pH. Prolonged soil drying during the dry fallow (WO) caused a decrease in soil Fe (2) content and this, in turn, increased the soil pH. Plant growth was inhibited in the SO plots compared with S1 plots because of the higher soil pH in the SO plots. In addition, soil Fe (2) content was lower in the WO treatment in both SO and S1 plots. In the SO plots, soil pH was inversely related to soil Fe (2) content (r square= 0.651) and this negative correlation explains the inhibition of plant growth. In the 2001 dry season (DS), plant growth was also inhibited in the WO plots at the early growth stage. Soil pH was higher in WS than in DS and soil Fe (2) content was lower in the WO plots in WS, thereby causing greater growth inhibition in the WO plots in WS than in DS. Straw incorporation decreased soil pH, presumably because of the CO2 released during straw decomposition. Therefore, straw incorporation is an effective method to reduce soil pH in an alkaline field for improved rice growth
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