Field Balance Estimation of Rice Straw Generation, Biomass Partitioning and Greenhouse Gas Emissions from In-field Burning of Rice Straw in Enugu State, Nigeria

Abstract

Data on empirical, field-based rice straw biomass generation, partitioning and global warming potentials under Nigerian smallholder rice farming conditions are extremely limited. This research estimated the quantity of harvestable and recoverable rice straw based on Enugu State farmer’s harvesting practice and the potential greenhouse gas emissions from burning them in- field, using wind tunnel chamber.  The state average straw yield was 7.53 t ha^-1, and rough and milled grain yield of 8.09 and 4.58 t ha^-1, respectively Total biomass varied significantly among the five prominent rice growing areas in the state. The fertilizing value (N, P₂O₅, K₂O) content of fresh straw was 0.96%, 0.26 and 2.09 gKg^-1 respectively. That of the ash was 0%, 1.36 and 10.45 gKg^-1. They did not differ significantly among the locations. Farmers in the area burn their rice straw at a moisture content range of 16.5% at Adani to 29.8 at Amaechi Idodo, with state average of 22.5%. In Enugu state, the methane (CH₄, g/kg) and nitrous oxide (N₂O, g/kg) emission factors (EF) and global warming potential GWP₁₀₀ (CO₂-eq/kg) from in- field burning of rice straw were 5.096, 0.142 and 0.2, respectively. By straw burning, for every one kilogram of milled rice produced in the state, there is a potential to warm the globe by 0.2 (CO₂-eq/kg). Therefore, the environmental footprint of burning rice straw in the state should be a source of concern as the farmers usually burn the straw immediately after harvest to plant their late season cucumber, okra and vegetables.