|Koger iii, Clifford|
Submitted to: American Journal of Plant Sciences
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/1/2013
Publication Date: 7/15/2013
Citation: Koger III, C.H., Zablotowicz, R.M., Patterson, M.R., Walker, T.W., Weaver, M.A., Street, J.E. 2013. Effect of Winter Flooding on Weeds, Soybean Yield, Straw Degradation, and Soil Microbiol Activity. American Journal of Plant Sciences. 4:10-18. Interpretive Summary: Winter flooding of harvested rice fields in the midsouth USA attracts migratory waterfowl, helps in degrading rice straw residue, and may help in reducing winter weed populations. However, there is concern that winter flooding may also reduce yield of the soybean crop planted the following spring. Winter flooding reduced winter weed populations and weed biomass up to 99% when compared to no flooding. Winter flooding of harvested rice plots reduced soybean yields by as much as 25% compared to soybean yields in no winter flood plots. The practice of winter flooding should be reconsidered when planting soybean the next spring, as reduced crop yields can significantly reduce net economic returns.
Technical Abstract: Winter flooding of harvested rice fields attracts migratory waterfowl and may assist in degrading rice straw residue. A field study was conducted twice between 2003 and 2005 in Stoneville, MS to evaluate impacts of winter flooding of harvested rice fields on rice straw degradation, winter weeds, soybean yield, and soil microbial activity and nutrients. The experimental area each year consisted of a harvested rice field that remained no-till after harvest and that was dissected into 7.6-by 15-m bays with constructed levees to accommodate winter flooding treatments. Flooding treatments each year consisted of 1) flooded mid-October thru early March, 2) flooded mid-October thru early January, 3) flooded mid-December thru early March, 4) flooded mid-December thru mid-January, and 5) no flood. Flood depth was maintained at 10 cm and treatments were replicated four to six times. Winter weeds were counted and existing rice straw and winter weed biomass was harvested from a 1-m2 quadrat per plot before flooding and in early April of each year. Existing weeds were controlled with 0.86 kg ae ha-1 glyphosate 2 weeks prior to planting glyphosate-resistant soybean in mid-April of each year. Winter flooding reduced rice straw biomass 32 to 60% compared to 21 to 31% reduction for no winter flood. Winter flooding treatments reduced weed populations and weed biomass from 43 to 99% when compared to no flood. The longest flood duration resulted in the greatest loss of carbon and nitrogen from straw residues in both years. Soybean yields ranged from 3295 kg ha-1 with winter flooding from mid-October thru early March to 4295 kg ha-1 with no flooding. Significant reductions in soil nitrate levels were most consistent in the upper 0 to 2.5 cm of soil. Soil enzymatic activity (dehydrogenase and fluoresacein diacetate hydrolysis) was increased by flooding in 2003 thru 2004, while minimal effects were observed in 2004 thru 2005 due to inconsistent anaerobic conditions attained in 2004 thru 2005 experiment.