Effects of Biochar Based N Fertilizer Application on Ammonia Volatilization from a Rice Growing Soil: A Laboratory Scale Closed Chamber Study

Ammonia Volatilization (AV) in rice growing soils is one of the major pathways to lower the use efficiency of added nitrogen (N) fertilizers. Direct broadcasting of urea facilitates AV by increasing the substrate availability. Urea intercalated biochar (BC_U) can be a novel approach that could improve N use efficiency and reduce AV in paddy cultivation. Therefore, a laboratory experiment was conducted to quantify the effect of BC_U pellets on AV losses and N dynamics in a rice growing Entisol. We determined the changes in soil urease activity (UA) and pH buffer capacity (pHBC) after application of BC_U to soil under flooded or saturated conditions. Treatments were zero application of N (control), urea (U) and BC_U pellets added at a rate of 23 mg N kg soil-1. Under saturated conditions, significantly higher NH4+ concentration in soil solution was observed in urea added soils and the highest NO3- was observed in U. Under flooded conditions, a significantly higher NH4+ was in U and NO3- was not affected by urea application. In general, AV losses were very small under the investigated experimental conditions and it varied from 0 to 2.72 % of added urea. Under saturated conditions, AV was significantly (p<0.05) higher in U (2.72 %) and BC_U (1.21 %) than in the Control (0 %). Under flooded conditions, only U showed a significant AV (2.42 %; p<0.05). The pH buffer capacity (11-12 mmols kg-1 pH-1) and urease activity (6.3 - 8.5 μg NH4+-N g-1 hr-1) did not significantly changed (p>0.05) by N treatments. Although there was a small AV loss (<3 %) after N application, it could be further reduced by application of urea as BC_U and/or maintaining a flood water layer for few days after N application.