Present position of fertilizer experiments in rice in India

A large number of fertilizer experiments have been conducted in the country with an object to get a rationalised and economic programme of fertilizer for different areas. Results have shown that rice soils in India need both nitrogen and phosphate for increasing production. Response to potash application has however not been adequate enough. Nitrogenous fertilizers have been found most effective in increasing yield in almost all trials, but highly significant yield increases to phosphate application have been obtained only in a few localised areas in the country. In recent all-India trials conducted on cultivators’ fields, however, phosphate need is felt at many places. Green manuring, another rich source of nitrogen, has proved equally effective and sometimes better than inorganic fertilizers. Different nitrogenous fertilizers like ammonium sulphate, ammonium nitrate, ammonium chloride and urea have also been tested. At experimental stations, ammonium sulphate has generally proved more effective than urea and ammonium nitrate but in all-India T.C.M. trials on cultivators’ fields, results have been rather variable and not much difference between these sources of nitrogen carriers has been observed. Various phosphatic fertilizers tried are also not found different in their behaviour. Time of fertilizer application, level and type of fertilizer and magnitude of response is found to vary widely from place to place. No relationship between the soil type and any of these factors has as yet been established. Available soil analytical data have also not thrown light on this aspect. In the absence of this, it becomes difficult to formulate fertilizer schedules and advisory standards for different areas. Apart from soil type, soil texture, drainage and soil water status in rice soils during the growth period may be considered responsible for such wide variation in fertilizer response. Great losses of nitrogen by leaching and denitrification occur when a rice soil profile left in aerated condition for a few days is submerged. Subsurface placement of ammoniacal fertilizer has been suggested as a rational method to reduce such fertilizer losses and increase fertilizer efficiency. Other examples of influence of soil water on fertilizer response by ammonium sulphate and urea are given and urea is considered more profitable, when used mixed with dry soil and flooded about 48 hours after application. Physiological acid action of ammonium sulphate is not likely to play any important part in deterioration of soil fertility in water-logged soils, except under highly acid soil conditions. This is because of acid tolerance of rice crop and increase in pH of rice soil on flooding. Danger from ammonium sulphate may however arise due to sulphide injury in soils lacking in active iron and manganese. Importance of soil-water relationship in fertilizer application in manurial trials is stressed and collection of data on soil water condition before and after fertilizer application and during critical growth condition of the crop up to flowering is suggested so that experiments under similar soil water patterns can be pooled for interpretation of fertilizer response. Separate investigations to study interaction of different soil water patterns with fertilizer response are also suggested. This may give useful information on which fertilizer schedules and advisory standards for different areas may latter be based.