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Cover Cropping & Green Manures

After 22 years of farming, my farm’s soil is markedly more fertile and productive. It has been a wonderful journey learning what works and how to continue to improve long-term productivity while harvesting bountiful crops.

Flail mowing summer Sudangrass/cowpea green manure at Potomac Vegetable Farms – West in Virginia.

There are several methods that deserve credit for this increase in soil quality: the use of compost, the use of a balanced mineral fertilizer and a serious commitment to cover cropping.

For this article I want to focus on the growing of cover crops and green manures. When I became the farm manager at Potomac Vegetable Farms – West in 1992, I sought advice on how to transition the farm into organic production.

The land had been growing mostly sweet corn, pumpkins and green beans with commercial chemical fertilizers and herbicides. The soil was biologically inactive and nutrients were missing. I can clearly remember the words from a fertility consultant, “I can sell you something in a bag, and I can sell you something in a bucket, but what you really need to do is to make compost and grow cover crops.” And thus began my journey into both compost-making and cover cropping.

Why take on both of those jobs rather than just one? Well, they go hand in hand, each leveraging the benefits of the other to move a soil more quickly toward health and resilience.

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Vetch Cover Crop Recommended for Organic Zucchini

Illustration_Vicia_sativa0In a new study, the popular cover crop vetch (Vicia sativa L.) was used in a two-year field experiment designed to determine the effects on organic zucchini yield and quality of vetch residue management strategies incorporating green manure using a roller-crimper (RC) and organic fertilizers.

To allow for timely crop rotation in organic farming, the growing cycle of cover crops is often terminated before natural maturity using mechanical chopping and/or plowing, field disking, mowing or crushing with a roller-crimper. Innovative conservation tillage production systems using RC technology to end cover crops are gaining popularity. The technique uses one or two passes of the RC to flatten the cover crops, leaving a thick mulch layer into which the next crop is sown or transplanted. The thick mulch hinders the development of weeds during the critical growing period, contributes to reduced soil erosion and increases soil moisture and fertility.

Researchers used municipal solid waste compost, anaerobic digestate and a commercial organic fertilizer in the field experiments designed to determine yield, yield components, crop quality, and soil nutritional status in organic zucchini fields in southern Italy.

“Our results showed that zucchini yield was influenced positively by the vetch residue management strategy, although the response was significantly different between years,” the scientists said. “The vetch cover crop increased marketable zucchini yield in the first year by 46.6 percent compared with the fallow treatment, indicating that this fertility-building crop could reduce off-farm nitrogen (N) fertilizer input for subsequent crops. Averaging over two years of the experiment, marketable zucchini yield increased by 15.2 and 38 percent with the roller-crimper mulch and green manure plow-down, respectively, compared with the fallow treatment, although differences were significant only in the first year.”

The application of organic fertilizers in vetch management plots increased marketable zucchini yield by 21.8 percent in the first year compared with the unfertilized control.

This article appears in the December 2013 issue of Acres U.S.A.