Abstract

Cumbu and cotton are the two important crops of the black soil region in the Southern districts of Ramanathapuram, Madurai and Tirunelveli occupying about four lakhs of acres. Both cotton and cumbu when continuously cropped deplete the soil to a great extent. An average crop of rainfed cotton in India takes away from the soil about 23 lb of nitrogen, 18 lb of phosphoric acid and 78 lb of potash (Sawhney and Sikka, (1960). Unless this annual loss is periodically replenished the yield of the crops is bound to slide down year by year. Application of adequate organic matter is useful in the rainfed areas but required quantities are not readily available. Hence there is need for use of chemical fertilizers.

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