Interactive effects of synthetic nitrogen fertilizer and composted manure on ammonia volatilization from soils

When synthetic fertilizer is co-applied with composted manure (compost), the high urease activity of compost may stimulate urea hydrolysis, thus increasing NH₃ volatilization when urea is co-applied as a synthetic fertilizer. In this study, the interactive effects of compost type (low vs. high urease activity, referred to as CL and CH, respectively) and synthetic fertilizer form (urea vs. ammonium sulfate) were assessed in a 60-day greenhouse study. The compost was applied as a basal fertilization only at the initiation of the experiment, and the fertilizers (¹⁵N labeled or not) were split into basal and additional fertilization. During the 10 days after the basal fertilization, co-application of CL with urea did not increase NH₃ volatilization as compared with urea alone treatment. However, co-application of CH with urea resulted in a significant increase in NH₃ volatilization by more than 3-fold, not only from applied fertilizer-¹⁵N but also from compost and/or soil over the other two (urea alone and urea with CL) treatments. Meanwhile, when ammonium sulfate was co-applied with CH, NH₃ volatilization from fertilizer became 3-fold lower than that when urea was co-applied. During the second 10 days after the application of urea as an additional fertilizer, the amount of NH₃ volatilization from CH-treated soil did not differ from that observed with CL, and this is probably attributable to a reduction in urease activity in soils over time. These results indicate that not only the combination of compost and synthetic fertilizer, but also the time difference between the application of compost and synthetic fertilizer, are crucial to reducing NH₃ volatilization.