Author(s): S. K. RAJ, J. S. Bindhu And L. Girija Devi

Abstract: Nitrogen uptake and N availability at different phenological stages of semi-dry rice was studied in a field experiment with time of N application as main plot treatment and sources of N as subplot treatments for two consecutive rabi seasons of 2009-10 and 2010-11 respectively in sub-split plot design. Results revealed that time of N application and sources of N had profound influence on the soil available N status and N uptake at different stages of crop growth. Available N in the soil increased up-to panicle initiation stage and then started declining as the growth advanced. The available N status was the highest with application of N in 4 equal splits at 5-10 days after emergence (DAE), 20-25 DAE, 40-45 DAE and 60-65 DAE. Among the sources, neem cake blended urea maintained high available N status in the soil at all phenological stages compared to other slow release forms of urea. Prilled urea maintained lower N status in the soil during both the years of study. Time of N application greatly influence the N uptake in semi dry rice. On an average, the N uptake was 28.3, 40.6, 55.3 and 81.7 kg ha-1 at 60, 75, 90 DAE and at harvest respectively. The treatment received half the portion of N at 20-25 DAE recorded the lowest uptake. With regard to different N source, neem cake blended urea recorded the highest uptake and prilled urea recorded the lowest uptake at all the phenological stages. The better uptake of N with minimum N losses and optimum N supply throughout the crop stage resulted in better growth and yield attributes. The highest grain yield was recorded in neem cake blended urea applied in four equal splits (3752 and 3872 kg ha-1) during first and second year respectively. The study conclusively proved that physical blending of urea in four equal splits from 5-10 DAE to 60-65 DAE enhanced the N availability, N uptake and productivity in semi dry rice....

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