|WELLS, SCOTT - North Carolina State University|
|REBERG-HORTON, CHRIS - North Carolina State University|
Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2014
Publication Date: 2/1/2014
Citation: Wells, S., Reberg-Horton, C., Mirsky, S.B. 2014. Cultural strategies for managing weeds and soil moisture in cover crop-based no-till soybean production. Weed Science. 62(3):501-511. DOI: 10.1614/WS-D-13-00142.1.
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 pressure, soybean lodging and yield in a cover crop-based soybean production system. Soybean planting timing included roll-kill and soybean planting occurring on the same day, and roll-kill with approximately a two-week delay prior to planting. Soybean row spacings included 76, 38, and 17 cm and all treatments included a weedy check and weed-free treatment. Rye biomass production was excellent across all four site-years, averaging above 10,000 kg ha-1 dry matter. The high rye biomass production resulted in excellent weed control. Despite the great weed control, weed coverage was higher in the 76 cm row-space treatment when compared to both the 17 cm and 38 cm row spacing in two of the four site-years. Row spacing also influenced soybean yield; the 38 cm spacing out-yielded the 17 cm and the 76 cm spacing by 3.2% and 12.7% respectively. 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. Soybean lodging is a potential consequence of no-till planting of soybeans in high residue mulches, and of the 3 row spacings, the 17 cm spacing exhibited the greatest incidence of lodging. These results demonstrate the flexibility and potential risk organic no-till soybean producers face when planting organic soybeans post roll-kill. Furthermore, the rolled-rye treatment exhibited significant (p < 0.01) increases in soil VWC when compared to the no-rye treatment at Goldsboro, Kinston, and Salisbury (2012) with 27.4%, 13.4%, and 29.7%, respectively.