Integrating tactics for weed seed management provides sustainable weed control in organic rice production

Abstract

Overdependence on manual weeding has limited the expansion of organic rice systems. Although various weed control methods are available for organic rice, they tend to be labor-intensive, costly, and time-consuming. This underscores the importance of identifying cost-effective, labor-saving, and sustainable weed control strategies for organic rice farming systems. Accordingly, a comparative study spanning 10 years was carried out, investigating five weed control treatments in a field trial. These treatments included irrigation water filtration and the removal of floating seeds using a net during irrigation (IR), combined with vinegar sludge (IRV), or a bioherbicide (Sclerotium rolfsii) (IRF), or both V and F (IRVF), as well as conventional triple chemical control (H3) before and after rice transplanting (IRH3). For comparison, H3 alone was used as a control. Compared to H3, the IR-based treatments achieved an average reduction of 90.32%, 91.63%, and 72.32% in seedling weed density, mature weed density, and seedbank density, respectively, over the 10-year study period. Excluding IRH3, the organic weed control treatments (IRV, IRF, and IRVF) reduced seedling weeds, mature weeds, and seedbank density by an average of 91.22%, 93.97%, and 71.96%, respectively, while increasing rice yields by 16.59% compared to H3. During the initial 4 years, the high weed density rendered the three organic treatments ineffective, necessitating an average of 39 h of manual weeding per hectare per year to ensure economic viability. Using exponential model fittings, weed densities of 30 plants·m⁻² and seedbank densities of 65,000 seeds·m⁻² were established as theoretical intervention thresholds for additional manual weeding, below which all the aforementioned organic methods could effectively control weeds without further manual weeding. Therefore, we propose that these IR-based treatments can be integrated as primary methods into weed control programs for organic rice production, while complementing other weed control approaches.