EFFECT OF FLUORINE AND PHOSPHORUS APPLIED TO A SODIC SOIL ON THEIR AVAILABILITY AND ON YIELD AND CHEMICAL COMPOSITION OF WHEAT

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Abstract
A replicated pot experiment was conducted to study the effect of 5 levels of Fl (0, 25, 50, 100 and 200 ppm F) and 4 levels of P (0, 25, 50 and 100 ppm P), applied to a rice crop grown in soils of 2 sodicities, exchangeable Na percentage (ESP) 30 and 70, on their transformations in soil and uptake by a subsequent wheat crop. Application of F resulted in increased water-extractable F in the soil, the relative increase being greater in soil of high ESP, which was associated with high pH. F uptake by plants increased linearly (r = 0.89) with increased water-extractable F in the soil, and this resulted in a significant reduction in the wheat yield. A F content of 35 ppm in mature wheat straw, which was associated with 22 ppm of water-extractable F in the soil, was the critical concentration for grain yield. Higher uptake of F by the plant resulted in increased uptake of Na although composition in respect of other constituents remained unaffected. Application of both P and F resulted in higher extractability of each other in soil, the relative increase being more at higher F levels. The effect of P on soil F was more marked at low than at high ESP. While there is a positive effect of P on soil F, it has a negative effect on its uptake by the plant. Increasing P in the soil and in the plant resulted in marked reduction in the Cl content of the plant (r = 0.79).