Comparative Effect of Prilled Urea and Neem-coated Urea on Plant-available Forms of Nitrogen in Rice (Oryza sativa L.)

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Date
2017-07
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Department of Soil Science & Agricultural Chemistry, BAU, Sabour
Abstract
Rice (Oryza sativa L.) is one of important cereal crop grown in India. Our country has the largest area under rice cultivation. Rice is the basic food crop and being a tropical plant, it flourishes in humid climate. Among 17 nutrients which are essentially required by crop plants for their normal growth and reproduction, nitrogen (N) is generally required by them in the largest amount. Urea is one of the most widely used source of N fertilizer in the world. It also has a high nitrogen content (46%), in comparison to other popular nitrogen sources. When applied to soil, urea is first transformed into ammonical (NH4+) form after its hydrolysis and then to nitrite (NO2-), followed by to nitrate (NO3-) forms by the process of nitrification. Addition of urea in soil, by virtue of its hydrolysis, increases soil pH thereby causes tremendous ammonia volatilization losses. Use of slow-release fertilizers and nitrification inhibitors and puddling of the rice fields are also ways of reducing leaching losses. The present investigation on “Comparative effect of prilled urea and neem-coated urea on plant available forms of nitrogen in rice (Oryza sativa L.) was undertaken to elucidate the relative influence of nitrogen dose, nitrogen source and nitrogen split on rice crop. Soil analysed for basic characteristics of experimental site was alkaline in reaction, deficient in available nitrogen, medium in organic carbon content and sandy loam in texture. Long duration rice cv. Rajendra Mahsuri was taken as a test crop. Graded doses of nitrogen i.e 100 kg, 120 kg and 140 kg nitrogen ha-1 were applied through prilled and neem-coated urea in splitting manner. The balance sheet of nitrogen in post harvest soil checked and results indicate that the maximum available-N, ammonical-N and nitrate-N were 207.8 kg ha-1, 97.7 kg ha-1 and 52.3 kg ha-1 respectively at 140 kg ha-1. In case of nitrogen sources neem-coated urea build up more nitrogen in soil by 8.12 % and 4.42 % for available-N and ammonical-N respectively over prilled urea. No conclusive impact of nitrogen split was found. Highest grain yield (66.9 q ha-1) of rice was found at 140 kg ha-1 nitrogen applied through neem-coated urea and statistically significant over the yields 60.2 q ha -1 and 66.7 obtained respectively at 100 and 120 kg ha-1 nitrogen. No significant effect of source and split of nitrogen was found on grain yield. Maximum 1.47 % nitrogen content in rice grain and 0.64% in straw was noticed at 140 kg N ha-1 respectively that was significantly superior over the content obtained at 100 kg ha-1 and 120 kg ha-1 nitrogen level. Neem coated urea registered significant difference in nitrogen content in rice grain and straw over prilled urea. Total nitrogen uptake (152.8 kg ha-1) as biological yield of rice crop was estimated at 140 kg ha-1 applied nitrogen dose and was statistically superior over both level of nitrogen. Neem coated urea responded more uptake of nitrogen than prilled urea. To assess the release pattern of nitrogen, soil treated with neem-coated urea and prilled urea adding 50 mg N kg-1, 60 mg N kg-1 and 70 mg N kg-1 of soil had been taken for incubation study upto 90 days. In initial soil available-N, ammonical-N and nitrate-N were 70 mg kg-1, 28 mg kg-1 and 7 mg kg-1 respectively. The results of incubation study showed that neem-coated urea registered 11.94 %, 12.38 % and 13.32 % slow release of nitrogen over prilled urea at 15 days after incubation (D.A.I) for available-N at 50 mg kg-1, 60 mg kg-1 and 70 mg kg-1 nitrogen doses respectively. Almost similar trend was observed in case of ammonical-N. At 45 D.A.I, nitrogen release pattern of both neem-coated and prilled urea have showed less changing in nitrogen mineralization. Onward 60 to 90 D.A.I, nitrogen mineralization pattern had been changed and neem-coated urea released about 10 % more nitrogen over prilled urea as available-N at 50 mg kg-1 nitrogen dose. It might be due to slow and steady release nature of neem-coated urea. Almost similar trend was observed for ammonical-N forms of nitrogen and the trend of nitrogen mineralization for nitrate-N at all D.A.I at different nitrogen doses and nitrogen sources was observed in indiscriminate manner.
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