Co-application of biochar and compost with decreased N fertilizer reduced annual ammonia emissions in wetland rice
Jannatul Ferdous, Nusrat Jahan Mumu, M. Belal Hossain, Md. Anamul Hoque, Mohammad Zaman, Christoph Müller, M. Jahiruddin, R.W. Bell, M. M. R. Jahangir
Abstract
Ammonia (NH 3 ) emission from rice fields is a dominant nitrogen (N) loss pathway causing negative impacts on farm profitability and the environment. Reducing N fertilizer application to compensate for N inputs in organic amendments was evaluated for effects on N loss via volatilization, rice yields and post-harvest soil properties in an annual irrigated rice (Boro) – pre-monsoon rice (Aus) – monsoon (Aman) rice sequence. That experiment was conducted using the integrated plant nutrition system (IPNS; nutrient contents in organic amendments were subtracted from the full recommended fertilizer dose i.e., RD of chemical fertilizers) where six treatments with four replications were applied in each season: (T 1 ) no fertilizer (control), (T 2 ) RD, (T 3 ) poultry manure biochar (3 t ha −1 ; pyrolyzed at 450°C) + decreased dose of recommended fertilizer (DRD), (T 4 ) rice husk ash (3 t ha −1 ) + DRD, (T 5 ) compost (3 t ha −1 ) + DRD, and (T 6 ) compost (1.5 t ha −1 )+ biochar (1.5 t ha −1 ) + DRD. The N loss via volatilization varied twofold among seasons being 16% in irrigated rice and 29% in the pre-monsoon rice crop. In irrigated rice, T 6 had significantly lower NH 3 emissions than all other treatments, except the control while in pre-monsoon and monsoon seasons, T 6 and T 3 were alike. Pooling the three seasons together, biochar (T 3 ) or biochar plus compost (T 6 ) reduced NH 3 loss via volatilization by 36-37% while compost alone (T 5 ) reduced NH 3 loss by 23% relative to RD. Biochar (T 3 ) and biochar plus compost mixture (T 6 ) reduced yield-scaled NH 3 emissions by 40 and 47% relative to the RD of chemical fertilizer (T 2 ). The organic amendments with IPNS reduced the quantity of N fertilizer application by 65, 7, 24, and 45% in T 3 , T 4 , T 5 , and T 6 treatments, respectively, while rice yields and soil chemical properties in all seasons were similar to the RD. This study suggests that incorporation of biochar alone or co-applied with compost and decrease of N fertilizer on an IPNS basis in rice-based cropping systems can reduce N application rates and NH 3 emissions without harming yield or soil quality.