Influence of nitrification inhibitor on hydrolyzed products of urea in Munnar soils

An incubation study on urea hydrolysis revealed that the conversion of ammonia to nitrate is much faster in Munnar soils than in the soils of other regions. The higher rate of nitrification in Munnar soil is an unwanted phenomenon as far as the tea crop is concerned. Tea soils are known to prefer ammoniacal nitrogen than nitrate nitrogen. Most of the studies indicate that nitrification inhibitors, when supplied to soil in conjunction with N-fertilisers or animal wastes, reduce nitrate leaching and nitrous oxide emission, leading to increased plant growth. However, this always is not the case. There are reports on variable effects of nitrification inhibitors on N loss and plant yields. Hence, effectiveness of nitrification inhibitor should be tested locally. The present trial dicyandiamide (DCD), a nitrification inhibitor was used to control nitrification process of soils collected from Munnar. To determine the effect of nitrification inhibitor on urea hydrolysis, two separate test portions were prepared with 10 g of soil. To the first set of soils, 0.1 g of urea and 0.005 g of dicyandiamide were added and to the second set of soils, 0.1 g of urea was added all the samples are incubated simultaneously at 25°C. The amount of ammoniacal nitrogen and nitrate nitrogen formed were estimated at 5 days interval.





On 0th day, even though fertilisers were not applied, the nitrate nitrogen concentration was four times higher than that of ammonium nitrogen (data available on request). Application of urea had brought down the concentration of NO3--N by about 50 % on the third day, while ammonium nitrogen content increased drastically. When DCD was not added along with urea, there was a sharp fall in the content of ammonium nitrogen in course of the time, while nitrate nitrogen content increased. Application of DCD along with urea prevented the formation of nitrate ions, which resulted in the accumulation of ammonium ions. Therefore, it is concluded that the application of DCD blended urea could result in higher agronomic efficiency of urea nitrogen in the tea soils of Munnar.

Authors -S. Venkatesan and V. Sudhahar