Effects of urea rates, farmyard manure, CaCO₃, salinity and alkalinity levels on urea hydrolysis and nitrification in soils

Abstract

The effects of urea concentration, farmyard manure, CaCo3, pH and EC levels on urea and nitrification rates in different Indian soils at constant temperature (25 ± 1°C) and moisture (50% WHC) were studied. The hydrolysis rate of urea was not proportional to the amount of urea added. In all cases, hydrolysis was completed within 6 days, except with 16.64 dS m-1 EC and 4% and 8% CaCO3 treatments. An increase in CaCO3, pH and EC levels inhibited urea hydrolysis. The NH4+ concentration increased up to 6 days and then decreased up to 24 days, with a corresponding increase in the NO3- concentration. The maximum NO2- concentration was observed at 12 and 18 days and decreased at 24 days. However, accumulation of NO2- continued up to 24 days at higher CaCO3, EC and pH levels. An increase in urea levels decreased the rate of nitrification. The nitrification rate was fast in the presence of farmyard manure and slow at the higher CaCO3, pH and EC levels.