Estimating Cultivar Effects on Water Usage and Greenhouse Gas Emissions in Rice Production

Abstract

Previous research has demonstrated that rice (Oryza sativa L.) production poses two large, global environmental concerns: rice uses 25% of the global freshwater supply and generates considerable greenhouse gas (GHG) emissions. The shorter vegetative stage of hybrids compared with conventional (inbred) cultivars may provide two environmental improvements: reduced water consumption and decreased CH4 emissions. This study evaluated the effect of cultivar type on water‐use efficiency and net GHG emissions. Water usage and GHG emissions on a per‐hectare and per‐kilogram‐of‐grain basis were estimated for hybrid and conventional rice cultivars with a new methodology using seven consecutive years of cultivar‐trial data. Because GHG emissions have not been observed directly in cultivar trial experiments, a method of synthesizing GHG emission levels was designed. This method utilizes results from in‐field chamber experiments from flooding to after harvest plus emergence and 50% heading dates. Hybrid rice cultivars were estimated to be 23.22% more efficient than conventional cultivars in reducing GHG emissions and 33.47% more efficient in reducing water required per unit grain yield produced. Unlike other approaches to lowering GHG emissions and water usage, substituting hybrids for conventional cultivars appears to be a viable option with low producer transaction costs as opposed to such alternatives as alternate wet–dry flooding, building on‐farm reservoirs, etc.. The methodology used produced results that are consistent with the present knowledge of the physiological and cultural practice differences between conventional and hybrid rice production. The GHG synthesizing methodology could be directly applied to other states’ historic cultivar trial data.