Greenhouse gas emissions and grain arsenic and cadmium concentrations as affected by a weed control drainage in organic rice systems

Abstract

Abstract Rice (Oryza sativa L.) is the primary staple food for more people than any other crop, but it is also a significant source of methane (CH4) emissions and arsenic (As) in the human diet. For organic rice, these factors pose a greater challenge due to the use of organic fertilizers and that organic rice consumers often prefer brown rice. A major management challenge for organic rice producers is weed control. In California, organic producers have developed a practice to control weeds that involves a severe dry‐down (DD) about 30 days after planting. Our objective was to determine the impact of a DD on greenhouse gas emissions and grain As and cadmium (Cd) concentrations compared to a continuously flooded (CF) control. The DD treatment reduced seasonal CH4 emissions by 50% (from 359 to 181 kg CH4 ha−1). Only during the DD period were nitrous oxide (N2O) emissions detected, but cumulative emissions were low (0.35 kg N2O ha−1). The global warming potential (GWP) was reduced by 49% in the DD treatment relative to the CF. Grain As and Cd concentrations were not at levels deemed a health concern in any treatment. However, grain As concentrations in the DD treatment were reduced by 30% and 37% in brown and white rice, respectively. Under the DD treatment, Cd concentrations increased but remained low. This study confirms that the weed management DD practice has a positive effect on GWP and grain As concentrations. In Cd contaminated soils, this practice may not be advisable.