Abstract

                                Application of phosphatic manures as superphos- phate in combination with nitrogen in the form of ammonium sulphate over a basal dressing of green leaf has been found to be essential to obtain high return in rice cultivation. Though most of the soils in Madras State are deficient in available P₂O, it has been found that the response to application of phosphates has been limited and is often erratic. This is mainly due to fixation of phosphates by the soil thereby making it unavailable to crops. With the usual method of surface application, about two thirds of the phosphates is looked up within an inch or two of the place of application depending upon the calcium content of the alkaline soils or iron or aluminium in the soils. Experiments on the placement of phosphates in the vicinity of roots have yielded useful results in certain crops. Apart from this, application of phosphates through green manure crops or through composts is also reported to make the phosphate readily available to the plant.

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