TRACER STUDIES ON THE BALANCE AND CHEMICAL DISTRIBUTION OF APPLIED NITROGEN UNDER DIFFERENT MOISTURE REGIMES USING LYSIMETER

Tracer studies were made on balance and chemical distribution of added fertilizer under field conditions using a modified type of lysimeter at different moisture regimes. A modified chemical method was also used for the determination of different forms of organic N. An average of 25 per cent of the isotope enriched nitrogen applied to soil could not be accounted for at the end of the 3 years of experiment. The amount of residual added N in soil was around 33 per cent of which 27 per cent was in 0-20 cm layers and only 6 per cent was found in 20-50 cm layers. The average crop recoveries were around 43 per cent. Only 0.18 per cent of NO₃-N was leached from the irrigated plots. The alkali-stable N (amino acid-N) fraction was higher for irrigated (19 per cent) than non-irrigated plots (15 per cent). There were no difference in the amounts of fixed NH₄, non-hydrolyzed and alkali-labile N fractions for irrigated and non-irrigated plots. Only an average of 1.5 per cent of total fertilizer N was found as fixed NH₄-N form but the total fixed NH₄-N was higher (10-13 per cent) than that reported by other workers for surface soil layers. The sum of different soil-nitrogen fractions were always higher than the total nitrogen in soil.