Relative performance of neem (Azadirachta indica) coated urea vis-à-vis ordinary urea applied to rice on the basis of soil test or following need based nitrogen management using leaf colour chart

Neem coated urea (NCU) applied to rice can result in high N use efficiency as it contains nitrification inhibition properties. Field experiments were conducted for three years (2005-2007) at Ludhiana (sandy loam soil) and Gurdaspur (clay loam soil) for evaluating the relative performance of NCU vis-à-vis ordinary urea as a source of N for transplanted wetland rice. Along with a no-N control, the two N sources were tried at three N levels--40, 80 and 100% of the recommended level of 120 kg N ha⁻¹. Different doses of N were applied in three equal split doses at transplanting, 21 and 42 days after transplanting (DAT). For need based site specific N management for improved N use efficiency, the two sources of N were applied using leaf colour chart (LCC). In this treatment a basal dose of N at the rate of 20 kg N ha⁻¹ was applied after 7 DAT and LCC readings were recorded at weekly intervals starting 14 DAT. Whenever the intensity of green colour of the first fully opened leaf from the top was less than shade 4 of the LCC, N was applied at the rate of 30 kg N ha⁻¹. The application of N through NCU and ordinary urea increased the rice grain yield significantly with increasing levels of N at both the locations. The application of NCU at recommended rate (120 kg N ha⁻¹) produced significantly higher rice grain yield than the yield obtained with ordinary urea at Ludhiana. The differences were not significant at Gurdaspur. Need based N management using LCC revealed that rice required only 110 kg N ha⁻¹ at Ludhiana and 80 kg N ha⁻¹ at Gurdaspur, irrespective of the N sources. The application of NCU using LCC produced significantly higher (8.6%) rice grain yield than ordinary urea at Ludhiana but increase was not significant at Gurdaspur. The superiority of NCU over ordinary urea at Ludhiana was accompanied by spectacular increase in N uptake and nitrogen use efficiencies when applied on soil test basis or using of LCC.