Reducing ammonia loss from urea and improving soil-exchangeable ammonium retention through mixing triple superphosphate, humic acid and zeolite

Ammonia losses from soil following fertilization with urea may be large. This laboratory study compared the effect of four different, urea-triple superphosphate (TSP)-humic acid-zeolite, mixtures on NH3 loss, and soil ammonium and nitrate contents, with loss from surface-applied urea without additives. The soil was a sandy clay loam Typic Kandiudult (Bungor Series). The mixtures significantly reduced NH3 loss by between 32 and 61% compared with straight urea (46% N) with larger reductions with higher rates of humic acid (0.75 and 1 g kg(-1) of soil) and zeolite (0.75 and 1 g kg(-1) of soil). All the mixtures of acidic P fertilizer, humic acid and zeolite with urea significantly increased soil NH4 and NO3 contents, increased soil-exchangeable Ca, K and Mg, and benefited the formation of NH4 over NH3 compared with urea without additives. The increase in soil-exchangeable cations, and temporary reduction of soil pH may have retarded urea hydrolysis in the microsite immediately around the fertilizer. It may be possible to improve the efficiency of urea surface-applied to high value crops by the addition of TSP, humic acid and zeolite.