Why is interseeding important?
Interseeding cover crops increases the time they offer their environmental and soil health benefits by planting them in between still-growing rows of corn or soybeans. Especially when farmers are transitioning to organic production, the more cover cropping that can be implemented, the better.
But how do the corn plants influence the interseeded cover crops? The aim of this experiment was to determine the effect of corn planting density on interseeded cover crop performance, weed suppression, and corn grain yield during the transition to certified organic production. We planted a study at two different locations, one at the Musgrave Research Farm in NY, and the other at the Penn State University research farm in PA, to explore the relationship between corn and interseeded cover crops.
We hypothesized that 1) corn planting density, yield, and cover crop and weed biomass would be the same between experimental sites; 2) light transmission, and cover crop and weed biomass would decrease as corn planting density increased; 3) corn grain yield would increase as corn planting density increased; 4) the effect of corn planting density on cover crop biomass would be mediated by light transmission and weed biomass; 5) weed biomass would decrease as cover crop biomass increased.
We planted the following five different treatments in the study:
- No corn crop + interseeded cover crop
- Low corn density (15K seeds/acre) + interseeded cover crop
- Medium corn density (30K seeds/acre) + interseeded cover crop
- High corn density (45K seeds/acre) + interseeded cover crop
- Medium corn density (30K seeds/acre) + no interseeded cover crop
A cereal rye-ryegrass-legume cover crop mixture was interseeded in between the corn and soybean rows in mid-summer. We measured light transmittance through the cash crop canopy and measured fall biomass of cover crops and weeds.
How did corn influence interseeded cover crops?
We observed a tradeoff between corn density and cover crop biomass. The effect of corn planting density on interseeded cover crop biomass was significant and also connected to corn canopy light transmission and the amount of weeds present. The interseeded cover crop biomass in the Medium planting density ranged approximately from 1.6 to 54.0 g m-2 dry weight across all sites and sample dates.
Weed biomass in treatments with- and without interseeded cover crops was significantly lower in plots with cover crops when we sampled in October. No difference in corn grain yield was observed between treatments with and without cover crops. Results from this experiment should be interpreted cautiously because the experiment used one corn hybrid and was conducted during a dry year (2016).
Overall our results suggest that farmers can increase the performance of interseeded cover crops, without reducing corn grain yield, by using flex ear varieties and corn planting rates that are slightly lower than what is typically used. It is likely that acceptable corn yields can be achieved from this flex ear corn planted at approximately 75,000 plants ha-1.