Project Overview
Weed and fertilizer management are among the greatest challenges associated with organic corn production. Without the use of synthetic herbicides, organic corn production often relies upon intensive primary and frequent secondary tillage to manage for weeds; however, such intensive tillage practices can disrupt soil microbial communities, reduce soil aggregate stability, and increase erosion. As such, there is a need for effective no/low-till weed management practices in organic corn.
Cover crop mulching, where cover crops are terminated and left in the field as ground cover into which a subsequent cash crop is seeded, is one such approach to no-till weed/nutrient management in organic corn production systems. However, there are a number of challenges associated with cover crop mulching. Mulches must have a sufficiently high biomass in order to prevent weed growth, and they must be able to provide at least some nutrients (especially N) to the subsequent cash crop. For these reasons, it is important to consider which cover crop species/mixtures to use. Furthermore, terminating the cover crop at the correct time (during critical growth stages) is important to ensure that soil moisture reserves are preserved for the subsequent cash crop. Some producers have experimented with delaying planting of the cash crop after cover crop termination, in order to allow soil moisture to recharge.
This study, conducted at several agricultural research stations across North Carolina, examined the impacts of cover crop mixture and delayed planting on weed management and corn performance in a no-till, mulched system.
Farmer Takeaways
- Delaying planting corn after terminating a cover crop did not significantly recharge soil moisture, nor did it impact corn yield.
- Both hairy vetch/rye and winter pea/rye cover crop mixtures performed well as mulches, with average biomass production in the suggested range for optimal weed suppression.
- Cover crop mulches may be an effective weed management strategy for organic corn production in North Carolina, offering weed biomass reductions similar to or greater than conventional herbicides and limiting weed biomass levels to below 500 kg/ha.
- Certain cover crop mixtures (i.e., hairy vetch/rye) may allow for greater soil water retention due to differences in growth form.
Project Objectives and Approach
To determine the impacts of cover crop mixture and delayed planting of corn after cover crop termination on soil moisture, weed control, and subsequent corn performance
- Field experiments were conducted over four site-years at the Center for Environmental Farming Systems (Goldsboro, NC; 1 year), Caswell Research Farm (Kinston, NC; 2 years), and the Piedmont Research Station (Salisbury, NC; 1 year) to represent a range of climate conditions and soil types experienced by North Carolina corn producers.
- Treatments included: (a) corn planting date after cover crop termination via roller-crimper (same day vs. ~2 weeks after termination) and (b) cover crop treatment (no till/no cover crop, winter pea + cereal rye, and hairy vetch + cereal rye).
-
- **Note: Supplemental N fertilizer was provided to minimize potential N limitations from the cover crops, and herbicides were used in a no-mulch control plot.
-
- Cover crops were planted in early fall (mid-September) and terminated via roller-crimper in early May, when cereal rye was at the soft-dough stage and legumes were at early pod set.
- Corn plots in the ‘Early Planting Date’ treatment were planted immediately after roller-crimping, and corn plots in the ‘Late Planting Date’ treatment were planted approximately 2 weeks after using a no-till planter with certified organic corn seed.
- Plant and soil measurements collected throughout the season included cover crop biomass production, percent soil volumetric water content, corn yield, percent weed coverage, and total weed biomass.
Key Findings
Cover Crop Performance
- High levels of cover crop biomass were achieved for both cover crop mixtures, with no significant differences between treatments except at the Goldsboro site, where the winter pea + cereal rye treatment performed better than the hairy vetch + cereal rye treatment (8876 and 7781 kg/ha dry matter, respectively).
-
- Average biomass production for both cover crop treatments (across all sites) were in the suggested range for optimal weed suppression (8000 kg/ha).
-
Weed Control
- Corn planting date did not tend to impact weed biomass or % coverage, which was surprising to the researchers, as they expected the ‘Late Planting Date’ treatment to have greater weed incidence, given the 2-week period between cover crop termination and corn planting during which weeds could obtain a head-start on the corn crop. However, weed coverage was roughly the same for the ‘Early’ and ‘Late’ planting date treatments.
- In general, cover crop treatment did not impact % weed coverage, except at the Goldsboro site, where a smaller % weed coverage was observed under the hairy vetch + cereal rye treatment.
- Weed biomass was significantly lower for both cover crop treatments than for the no cover crop control (w/ herbicides) for both years at the Kinston site; however, at the other two sites, there was no significant difference in weed biomass between treatments. It should be noted that, for three of the four site-years, weed biomass for all cover crop treatments was very low (<500 kg/ha).
-
- These findings suggest that using cover crop mulches may be an effective weed management strategy for organic corn production in North Carolina, reducing weed biomass by an equal or greater amount than conventional herbicides.
-
Soil Moisture
- Corn planting date after cover crop termination did not significantly impact soil volumetric water content (VWC).
- Cover crop treatments, however, did impact soil water content, although this impact varied by site. At the Kinston site, VWC was greater under the hairy vetch + cereal rye treatment than for the winter pea + cereal rye and no-till/no cover crop treatment. At the Salisbury site, greater VWC was observed under the hairy vetch + cereal rye treatment than the no-till/no cover crop treatment.
-
- The researchers postulate that these findings could be due to differences in growth form between the two mixtures, as they observed increased lodging/intertwining and fewer gaps in soil cover after rolling for the hairy vetch + cereal rye treatment than for the winter pea + cereal rye treatment. This suggests that a hairy vetch + cereal rye cover crop mulch may allow for greater soil water retention prior to a corn crop.
-
Corn Yield
- Cover crop treatment did not tend to impact corn yield.
- In general, corn planting date did not significantly impact corn yield, except during one of the years at the Kinston site, where corn yields were higher in the ‘Late Planting Date’ treatment.
Resources
Wells, M. S., Reberg-Horton, S. C., & Mirsky, S. B. (2016). Planting Date Impacts on Soil Water Management, Plant Growth, and Weeds in Cover-Crop-Based No-Till Corn Production. Agronomy Journal, 108(1), 162–170.
Read MoreLocation
North CarolinaCollaborators
Scott Wells, University of Minnesota
Chris Reberg-Horton, North Carolina State University
Region
Southeast
Topic
Crop Nutrient Management, Weed Management, Cropping Systems
Category
Grain and Field Crops
Year Published
2016
