Effects of Urea, Humic Acid and Phosphate Interactions in Fertilizer Microsites on Ammonia Volatilization and Soil Ammonium and Nitrate Contents*

Abstract

The objectives of this study were to compare the effect of four different types of urea-TSP-humic acid mixtures on NH3 loss, soil NH4 and NO3 contents with surface-applied urea (urea alone). surface soil samples from Typic Kandiudutls (Bungor seies) were used. four different types of urea-TSP-humic acid mixtures and surface-applied urea were compared. All the mixtures significantly reduced ammonia loss ranging between 35 and 50% compared with urea alone. The mixtures with the highest amount (1 g) of humic acid showed a pronounced ammonia loss reduction. All the mixtures of acidic P fertilizer and humic acid with urea significantly increased soil NH4 content but no such observation was made for NO3. The nitrate contents for all of the five treatments were similar. The mixtures of acidic P fertilizer and humic acid with also significantly increased soil exchangeable Ca, K and Mg compared with urea alone. The effect of acidic phosphate and humic acid in the mixtures on NH3 loss was related to their effect in benefiting formation of NH4 over NH3, increaase in exchangeable cations and reduction in pH (that may have retarded urea hydrolysis in the fertilizer microsite). Surface-applied urea fertiliser efficiency could be increased if applied together with TSP and humic acid.