Evaluation of methods to improve the nitrogen use efficiency of urea in rice

Abstract

An investigation was carried out to evaluate the various methods recommended by different agencies to increase the N use efficiency of urea in rice. The study consisted of an incubation study and a field experiment during two crop seasons, first and second crop seasons in 1991 using rice variety jyothi. The incubation study was conducted at College of Horticulture, Vellanikkara, Trichur. There were five treatments for the incubation study which were control and recommended dose of N as prilled urea, meemcake – coated urea, neemcake-mixed urea and Nimin – coated urea. The experiment was laid out in Completely Randomised Design. The 13 treatments for field experiments consisted of control, recommended dose of N in two types of splits (50 :50 and 75:25) as prilled urea, neemcake – coated urea, neemcake – mixed urea and Nimin – coated urea and 75 per cent of the recommended dose of N in 50:50 split as prilled urea, neemcake – coated urea, neemcake – mixed urea and Nimin – coated urea. The field experiment was conducted at Agricultural Research Station, Mannuthy under Kerala Agricultural University. The soil for the incubation study was collected from the location where field experiment was carried out. The soil was sandy clay loam in texture, acidic and non saline. Ammoniacal nitrogen content of the soil in incubation study, increased upto a period of 20 days in all the treatments. The treatments showed significant difference in the NH4 –N content at most of the later intervals. In the initial period no definite trend due to treatments was observed but from 15th day onwards Nimin – coated urea recorded highest value at all the intervals. Neemcake – coated urea and neemcake – mixed urea have also recorded higher content of NH4-N than prilled urea but the difference was statistically not significant. At all the intervals control recorded lowest value. The proportion of NO3-N formed compared to total nitrogen was quite low. Significant difference in the NO3-N content of soil due to treatment application was noticed from 8th day of incubation. Significant difference due to different treatment application was not obtained for total N content of the soil and pH of soil and soil solution at different periods of incubation. Ammoniacal nitrogen content of the soil solution was high during the initial periods of incubation both for control and treatments, and gradually decreased and reached minimum value by the end of the period of incubation. The control recorded lowest value throughout the period of incubation and there was not much variation between the other treatments. The NO3-N content of the soil solution was found to be high than that of the soil. The control recorded lowest value at most of the intervals and among the four treatments with N application, the lowest value was recorded by Nimin – coated urea at most of the intervals. In the field experiment significant difference was noticed in the NH4-N content of the soil throughout the period of study in first crop season. At all the intervals control recorded lowest value. Nimin – coated urea recorded highest value at most of the intervals for both full and 75 per cent of the recommended dose of N. Neemcake – coated and neemcake – mixed urea were also found to be better than prilled when full dose of N was applied. But such difference was not noticed when 75 per cent of the recommended dose of N was applied. In the second crop season, variation due to treatments was not significant in the initial periods. Nimin – coated urea recorded higher NH4 – N content than prilled urea at most of the intervals from 15th day after transplanting both for full and 75 per cent of the recommended dose of N. Neemcake – coated urea and neemcake-mixed urea were alsostages this treatment recorded comparatively higher values, both for treatments with full and 75 per cent of recommended dose of N. As in the case of Incubation study proportion of NO3-N formed was quite low. Similar trend was obtained during second crop season also. No uniform trend was obtained in the total N content of soil at different intervals due to treatments in both the seasons. Significant difference in soil pH was also not noticed. The difference due to treatment application was not high enough to attain the level of statistical significance for the major biometric characters of the plant during both the crop seasons. Though the difference due to treatments was not significant on grain yield, Nimin – coated urea recorded maximum grain yield both for full and 75 per cent of the recommended dose of N during both the crop seasons. Nitrogen content in plant was increased by N application. Nimin – coated urea showed a favourable influence in increasing the N content of grain during both the crop seasons. In general application of Nimin enhanced the uptake of N by grain and straw during both the seasons. Significant variation was obtained in the content and uptake of P, K, Ca and Mg at various stages of crop growth during both the seasons.