|Wells, M - North Carolina State University|
|Reberg-horton, S - North Carolina State University|
Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2014
Publication Date: 6/1/2014
Citation: Wells, M.S., Reberg-Horton, S.C., Mirsky, S.B. 2014. Cultural strategies for managing weeds and soil moisture in cover crop based no-till soybean production. Weed Science. 62:501-511.
Interpretive Summary: A cover crop-based organic rotational no-till soybean production system combines the soil conservation practices associated with conventional no-till with the soil building practices associated with organic crop production. This crop production system relies on growing high levels of cover crop biomass for weed suppression. However, weed control can still be inconsistent and high levels of cover crop biomass can reduce soil water needed for soybean production. Therefore, we tested how crop row spacing and timing of planting affect weed suppression and soil water availability, respectively, in cover crop-based organic rotational no-till soybean production. The high levels of cover crop biomass provided excellent weed control, however, narrowing row spacing did increase overall weed control. Furthermore, 38 cm row spacing had the highest yields compared to 17 cm and 76 cm. The presence of a cover crop can greatly increase soil water content throughout the growing season when there is adequate rainfall after cover crop termination. However, delaying soybean planting after cover crop termination will only influence subsequent crop performance on dry production years where killing the cover crop is synchronized with a rain event. This work will be included in organic production guides and used by farmers as a decision tool for how and when to plant soybean in high biomass cover crops.
Technical Abstract: A four site-year study was conducted in North Carolina to evaluate the effects of soybean planting timing and row spacing on soil moisture, weed density, soybean lodging, and yield in a cover crop-based no-till organic soybean production system. Soybean planting timing included roll-kill/planting and roll-kill/delayed planting where soybean planting occurred either on the same day or approximately 2 weeks later, respectively. Soybean row spacing included 19, 38, and 76 cm, and all treatments included a weedy check and weed-free treatment. Rye biomass production averaged above 10,000 kg ha-1 dry matter, which resulted in good weed control across all sites. Despite having good weed control throughout all treatments, weed coverage was highest in the 76-cm row-space treatment when compared to both the 19-cm and 38-cm row spacing in two of the four site-years. Soybean lodging is a potential consequence of no-till planting of soybeans in high residue mulches, and of the three row spacings, the 19-cm spacing exhibited the greatest incidence of lodging. Row spacing also influenced soybean yield; the 19- and 38-cm row spacing out yielded the 76-cm spacing by 10%. Soil volumetric water content (VWC) was higher in the cereal rye mulch treatments compared to the no rye checks. Furthermore, delaying soybean planting lowered soil water evaporation. However, the increased soil VWC in the rolled-rye treatment did not translate into increased soybean yield. The rolled-rye treatment exhibited significant (P'<'0.01) increases in soil VWC when compared to the no-rye treatment at three of the four site-years. These results highlight planting date flexibility and potential risk to lodging that producers face when no-till planting organic soybeans.