Courtesy Agricultural Research ServiceAgricultural Research Service horticulturist Eric Brennan compared different crop crops for organic matter, weed suppression and cost.Fine-tuning cover crop mixes to the weather may help organic vegetable growers maximize yields and reduce costs, according to a long-term study in the Salinas, Calif., area.
Overall input costs for organic broccoli or organic lettuce can run as high as $7,000 per-acre, so growers may be tempted to cut costs, according to a news release.
Agricultural Research Service horticulturalist Eric Brennan led the study that looked at rye, mustard and a legume-rye mix as winter covers for subsequent lettuce and broccoli crops.
The study also compared typical seeding rates to one that was three times higher.
Heavier seeding rates help the cover crop out-compete weeds.
During lettuce and broccoli production, all plots received the same inputs.
Harvest was done commercially.
All three cover crops yielded more than 2 tons of crop residue per acre, which is the often-recommended amount for maintaining soil organic matter.
The legume-rye and plain rye covers produced about 25 percent more dry matter than the mustard covers.
The legume-rye blend required a seeding rate three times greater than the typical rate to suppress weeds, while the rye and mustard crops were able to keep weeds in check with typical seeding rates.
The study also shed light on why legume populations within the blends varied from year to year.
Brennan said he thinks cooler early-season weather helps legumes compete with the rye.
So if growers expect a hot, dry fall, they may want to use a rye cover crop and not spend the additional money on the legume component, since legumes make up most of the seed costs in the blends.