Laboratory incubation experiments were conducted to study the comparative volatilization loss of NH3 in a calcareous soil from sulfur-coated urea (SCU) with fast (F), medium (M), and slow (S) dissolution rates, ammonium sulfate (AS) and urea, at two temperatures 22 and 32C, and at three soil moisture levels 25, 50, and 80% of the water-holding capacity of the soil. The effect of the addition of organic amendment (filter press mud) to soil on NH3 loss from these N-sources was also studied. Losses were studied up to 21 days. At both temperatures increasing soil moisture levels led to reduction of NH3 loss regardless of the N-source, despite the fact that the soil analysis showed higher dissolution of N from SCU at high soil moisture.
Higher temperature increased the NH3 losses from all N-sources. Losses usually followed the order of Urea > AS > SCU(F) > SCU(M) > SCU(S). At 32C losses from uncoated urea and AS at low, medium, and high moisture were 20.6 and 16.7%; 14.5 and 13.1%, and 8.4 and 6.6% of the N application rate, respectively. Losses from SCU(F) and SCU(M) as percentage loss of uncoated urea varied from 34% and 26% at low moisture, 29% and 23% at medium moisture, and 28% and 23% at high moisture, respectively. At 22C losses from uncoated urea and AS at low, medium, and high moisture were 11.1 and 10.2%; 7.7 and 8.8%, and 4.2 and 3.5% of the N application rate, respectively. Losses from SCU(F) and SCU(M) at three moisture levels were 26 and 17%, 18 and 10%, and 24 and 16%, respectively.
Incorporation of filter press mud to the soil resulted in reduction of volatilization loss of NH3 from all N-sources which was partly due to exchange reaction and biological immobilization of NH4-N and partly due to reduction of urease activity.