Preliminary trial of cover cropping and weed control for organic rice

Authors: MAHATO, GENA - University Of Arkansas At Pine Bluff; McClung, Anna; NTAMATUNGIRO, SIXTE - Texas A&M Agrilife; SURENDRA, SINGH - University Of Tennessee; POKHAREL, MEGHNATH - Kansas State University; WILEY, VINCE - University Of Arkansas At Pine Bluff; HUANG, BIHU - University Of Arkansas At Pine Bluff

Submitted to: American Journal of Plant Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2017
Publication Date: 10/23/2017
Citation: Mahato, G.R., McClung, A.M., Ntamatungiro, S., Surendra, S., Pokharel, M., Wiley, V., Huang, B. 2017. Preliminary trial of cover cropping and weed control for organic rice. American Journal of Plant Sciences, 8, 2758-2768. https://doi.org/10.4236/ajps.2017.811186.
DOI: https://doi.org/10.4236/ajps.2017.811186

Interpretive Summary: Although there is a high demand for organically produced rice, there has been limited objective research to identify optimize production methods for rice grown in the southern US. One of the biggest constraints is weed management, as synthetic herbicides are prohibited from use in certified organic crop production systems. Although many cultural management methods used in organic production of other crops are not useful in rice production, use of season long flooding and water seeding in rice paddies are practices that are helpful for weed control in organic rice. This study explored the use of these methods in conjunction with winter cover crops and different rice varieties, to identify improved cultural practices for organic rice production. Two winter cropping systems were compared, cover cropped land (CCL) using a mixture of crimson clover and winter wheat and fallow land (FL) which had naturally occurring white and crimson clovers. In the spring, biomass samples were harvested from the two systems, and the CCL had 46.78% more above ground biomass and 33.36% less weed biomass than FL. These results demonstrate the additional benefit of planting a winter cover crop for producing greater "green manure" for incorporation into the soil and reducing the weed seed population. For the summer season, 15 diverse rice cultivars were water seeded to evaluate plant stands and weed density. Weed pressure was very high in all plots, although significant differences were identified among the varieties for stand establishment and competitiveness with the weeds. The varieties Rondo and Jasmine 85, both high tillering indica germplasms, had the highest plant stands and the lowest weed densities in comparison to Sierra, Cocodrie, and Ark 061, which were all low tillering tropical japonica cultivars. These results demonstrate the importance of year around field management methods that include the use of cover cropping that will reduce weed populations and enhance soil fertility along with choosing the best adapted cultivar that grows rapidly and competes with indigenous weeds in an organic management system.

Technical Abstract: The experiment site at UAPB agronomy farm was left undisturbed for several years for organic rice experiment. Soil samples taken in September 2015 showed that the experiment site was deficient in plant nutrients (NPK) and an organic fertilizer (8-5-5) was applied before planting a mixture of crimson clover and winter wheat as cover crop in the fall 2015. Prior to spring planting, biomass samples taken from the cover cropped land (CCL) and fallow land (FL) demonstrated a decrease in weed biomass by 33.36% and increase in total biomass by 46.78% in CCL versus FL. Cover crops were incorporated one month before the rice sowing in June 2016. Fifteen rice cultivars were evaluated for weed competition under water seeding cultivation method. However, the water seeding method was not effective in controlling the weeds which dominated most of the rice plots from the onset of seedling emergence. However, two rice cultivars, Jasmine 85 and Rondo, showed strong weed competition due to higher plant stand and better seedling establishment. These results show the value of winter cover cropping in reducing weed pressure and improving soil health for summer planted crops. In addition, using water seeding of rice for additional weed control must be managed carefully to sustain a deep enough to reduce weed growth. Rice varieties differ in their ability to compete with weeds and establish a dense crop stand and the best adapted variety needs to be selected to optimize productivity under organic cropping systems.