A Study of Fertilizer Application and Irrigation Effects on Nitrate-N Leaching in Paddy Crop Fields near Cauvery River Basin - A Case Study

Fertilizer leaching affects farm profitability and contributes to nonpoint source pollution of receiving waters. The objective of the study was to evaluate nitrate leaching, i.e., nitrogen export for six application rates of inorganic fertilizer and two applications of cattle manure (A-50, B-75, C-150 D- 200, E-225 and F-350 G_CM 150 and H_CM 200 Mg/ha) from the irrigated lands in Mandya district near Cauvery basin (65.51%ha). Nitrogen (N) fertilization/application in the district was determined through interviews with local farmers for the years 2006, and NO₃-N load in the plots was monitored during the irrigation period and non irrigation period. The most fertilized crop in the region was paddy. The moderate nitrogen fertilizer rates in fields A, B and C were able to completely cover the N needs of irrigated paddy. Low nitrogen fertilizer rate in field A with sufficient side dressing was best as it did not pollute the surroundings with nitrogen leachate and the crop yield was also good. In case of fields D and E, nitrogen fertilization was higher than N uptake for irrigated crops and indiscriminate use of fertilizer did not increase the paddy yield, in contrast the high fertilizer rate above the nitrogen crop need, produced highest risk of pollution to water resources due to higher nitrate concentrations in drainage. In the field F, the crop yield was not quite good as there was no side dressing which also produced risk to environment. In fields G and H, crop yield was good and also negligible pollution since only cattle manure was applied with sufficient side dressing.