Time interseeding for cover crop success

In South Dakota, cover crops frequently produce limited biomass when they are planted following soybean harvest.

Cereal rye, due to its superior winter hardiness, is frequently planted following harvest of corn or soybeans in a corn-soybean rotation and is terminated prior to planting the following year.

This has led to a study to test the feasibility of interseeding cover crops into soybean.

Biomass production

A recent review article published in the “Agronomy” journal identified several studies that have inter-seeded various individual species and mixtures of cover crops into soybean.

Diverse mixtures — that have four or more species — and the individual species of peas, radish, oats and cereal rye produced the most fall biomass when they were interseeded into soybean.

Clover generally produced the least fall biomass.

Spring biomass production was highest for cereal rye and hairy vetch, both as individual species and cover crop mixtures. All the cover crop mixtures that overwintered contained either cereal rye or hairy vetch.

The studies included in this review ranged from plant hardiness Zone 3 (North Dakota) to Zone 7 (Maryland).

Most of the study sites did not receive enough heat units to produce significant cover crop biomass following soybean harvest.

Harvesting soybeans may require extra carefulness, as some of the top cover crop biomass may get cut or, at times, even killed while combining.

Soybean impacts

Soybean growth stage at the time of interseeding cover crops can be a critical decision.

Planting cover crops before the canopy closes during early vegetative stages or during later reproductive stages (R4 or later) when leaves begin to fall off will allow for more light to penetrate through the crop canopy to help the cover crop establishment.