Effects of rice husk biochar in minimizing ammonia volatilization from urea fertilizer applied under waterlogged condition

Abstract

Rapid ammonia volatilization from surface applied urea in waterlogged condition is one of the drawbacks as it leads to poor nitrogen use efficiency by plants. Thus, a laboratory scale closed dynamic air flow system was carried out in this study to assess the effect of rice husk biochar on ammonia volatilization, soil exchangeable ammonium and available nitrate in comparison to the urea without additives under waterlogged conditions. The study conducted consists of 6 treatments, soil alone (T0), soil + 175 kg ha-1 urea (T1), soil + 175 kg ha-1 urea + 5 t ha-1 rice husk biochar (T2), soil + 175 kg ha-1 urea + 10 t ha-1 rice husk biochar (T3), soil + 175 kg ha-1 urea + 15 t ha-1 rice husk biochar (T4) and soil + 175 kg ha-1 urea + 20 t ha-1 rice husk biochar (T5). T2, T3, T4, and T5 significantly minimized ammonia volatilization by 23.8%–34.5% compared to T1. However, only T2, T3, and T4 had significantly retained more soil exchangeable ammonium by 14%–43% compared to urea without biochar (T1). Additionally, soil available nitrate was lower in all treatments except T1. This clearly gives an idea that rice husk biochar minimize ammonia volatilization, retaining more ammonium and slowing down the conversion of ammonium to nitrate under waterlogged environment. Mixing urea with rice husk biochar at rate of 5 t ha-1 and 10 t ha-1 offers a significant advantage over urea alone. The mixture successfully increased formation of ammonium ions in soil over ammonia. Additionally, it has retained more ammonium and nitrate ions in the soil. Hence, biochar amended soil with urea is a promising approach to minimize ammonia loss and increase plant N use efficiency and uptakes.