Performance of Interseeded Cover Crop Mixtures in Mid-Atlantic Organic Corn Production.

Reducing tillage in organic grain systems has the potential to combine the soil-conserving and labor-saving benefits of no-till practices with the soil health-building benefits of organic practices, which includes diverse crop rotations and incorporation of cover crops. Relay planting cover crops into standing corn using a high-clearance no-till drill is a reduced-tillage strategy with the potential to lengthen cover crop and cash crop growing season windows. On-farm trials were conducted in 2015-2016 to determine the performance and management constraints of interseeding strategies at three organic farms: New Holland PA, Mifflintown PA and Hartleton PA. Treatments included 1) interseeding cover crops with an Interseeder® no-till drill, 2) broadcasting cover crops with a rotary spreader, and 3) a control in which standard practices in the corn to soybean transition were maintained by cooperating growers. For each cover crop treatment, a mixture of annual ryegrass (11.2 kg ha^-1) + orchardgrass (11.2 kg ha^-1) + forage radish (3.3 kg ha^-1) was established after last cultivation at the V5-V6 corn growth stage. Cover crops established across treatments and locations. Timely precipitation events likely contributed to high levels of establishment. Late-fall cover crop biomass did not differ among broadcast and interseeding treatments, ranging from 145 to 1230 kg ha^-1 dry matter biomass across locations. Results showed that the establishment strategy influenced the composition of the cover crop mixture. Forage radish represented a greater proportion of total biomass in interseeded treatments compared to broadcasting, whereas orchardgrass represented a greater proportion of total biomass in broadcasted treatments compared to interseeding.  At two of three locations, no differences in corn grain yields were observed among treatments.  At Hartleton PA, interseeding and broadcasting resulted in significantly lower yields than the control. Regression analysis indicated that corn populations mediated the effect of cover crops on grain yields. Cover crop biomass, particularly forage radish, increased where corn populations declined below 55,000 plt ha^-1 and corn grain yields declined with increasing cover crop biomass. The results of this study demonstrate the potential for interseeding cover crops in organic grain systems, though further agronomic studies are needed to optimize this reduced-tillage strategy.