Cover Crop Grazing on a Vegetable Farm


Wayne Brown and his family graze cattle and breeding ewes all over the San Luis Valley’s high desert. Over the past three decades in Mosca, Colorado, the family has increased their herd numbers and found economic stability through long-term grazing agreements with farmers.

“We don’t have a ranch with enough acreage to do the ranch thing,” Brown said. “We are buying feed wherever I can find it throughout the year. Knowing you have a place you can go back to is big. It is a relief.”

Three years ago, Brown heard that Brendon Rockey, 42, a specialty potato farmer in Center, Colorado, had cover crops that he was turning into the soil at the end of the growing season. At the time, Rockey was terminating the crop as green manure because a previous grazing arrangement fell apart. Cattle broke through an electric fence, resulting in calls to the sheriff, angry neighbors and a threat to the cash crops. The deal was off.

“Planting a cover crop does not automatically mean you improve your soil health,” Rockey said. “You can actually send it the other direction. Same thing with cattle. Managing the cattle correctly improves your soil health.”

Finding a responsible rancher to graze cover crops in the middle of potato country was seemingly impossible. Rockey needed someone willing to take full responsibility for the labor, someone who could respond to an emergency within the day and respect government livestock and vegetable production regulations. There was interest from a certified organic rancher in the area, but Rockey is not certified organic. Despite his intensive biological practices, the absence of this label prevented that potential partnership.

When Brown heard about Rockey’s cover crops, he presented him with a plan that posed minimal risk — a plan that, if executed, would meet all his conditions and Brown’s, too. The first season, they agreed on grazing calf-cow pairs on an annual cover crop mix from July through the late fall using an electric fence around the perimeter of a 120-acre circle and a 60-acre half circle under center-pivot irrigation. under center-pivot irrigation.

Colorado rancher Wayne Brown and his sheep in the Rio Grande National Forest.


The keys to successful cover crop grazing on a vegetable farm are tonnage, time, water and fencing.

“Is there enough?” Brown said he asks himself when considering entering into an agreement with a farmer. “If it takes me three days to get ready, I want more than a week — the longer, the better. You don’t want to drive all day for one cow.”

During the winter months, Brown’s goal is to maintain his 60 head of Angus crossbred cows and 800 head of Merino breeding ewes. He grazes his livestock all year except for during spring calving and lambing when the animals are bale-fed at his ranch.

“Those are the most expensive months when you are feeding hay,” he said.

When he is grazing cattle in a circle with center-pivot irrigation, Brown uses a two-strand electric fence around the outer perimeter and runs one strand of fencing from the center pivot to the perimeter to create a pie slice in the circle. Every forth post on the perimeter is a t-post. He runs a second strand from the center pivot to this post to create a second pie slice. This design, he said, makes it easier to control the cattle when they open up the subsequent paddock. It creates a “leap frog” situation.

“It is a portable fence you can move everyday,” he said. “You decide on how big of a piece you want grazed depending on what the farmer wants. You want to clean it up and figure how long it will last.”

Brown’s cows spend 8 to 10 months out of the year behind a hot wire, and understand that they must eat everything — including, most importantly to the farmer, weeds.

Nutritional value is a crucial factor. Based on the number of cattle Brown turns out in the field and the forecasted time it will take to graze each pie slice, Rockey choses to plant his cover crops in phases to accommodate the cattle’s diet. This timing also ensures the cover crop won’t go to seed too early and reestablish on the farm the following year.

“You assume the nutritional value will be there and for the most part it is,” Brown said. “You have to go off of the body condition of the cow. You have to visually be watching and that is tough because it can change quick.”

Brown’s bulls have foundered on Rockey Farms because the feed is too rich, resulting in sore feet. One remedy, he said, is bringing in roughage. However, convincing the cattle to eat it is not easy. He’s found giving the animals time to adapt is the best first reaction.

Brown turns out his cattle on to five to six farms throughout the year. Some of the fields, especially those that are only one or two cover crop species, are also very rich. It seems that the more diverse the mix, the healthier the animal.

Last fall, Brown found fresh feed for 1,400 breeding ewes on a 60-acre mature cover crop half circle that rotates with Rockey Farm’s specialty seed potato lots. The 17-day graze was completed without a hitch, and the expected carbon cycle and weed control benefits are highly down into the pit on a regular basis.

Cows graze a Rockey Farm’s cover crop in mid-July. Water tanks are placed at the center pivot for easy access.


For Rockey Farms, the economics of grazing Brown’s livestock is the foundation of the relationship. The pasture rent, calculated per head, balances out the seed costs, reduces the farmer’s labor and complements the carbon cycle.

“I don’t have to go out and mow anymore,” Rockey said, emphasizing that the livestock are controlling unwanted pigweed without compacting the soil. “This is another huge advantage. Then there is the nutrient cycling — the stimulation of microbial activity.”

The stimulation improves the health of the cash crop, specialty potatoes, which is planted the following year.

“When we had barley stubble instead of the cover crop, we had a huge nutrient tie up,” Rockey said. “Now, when the nutrients goes through the cow, produces that manure, the nutrients are ready to go and we have a better cash crop.”

Before bringing livestock into his fields, Rockey would mechanically incorporate the green manure, never terminating with chemicals. He’s found that the livestock’s grabbing and pulling of the plants releases root exudates and feed the soil’s biology in ways mowing does not.

“When you are just using green manure, it is a closed loop,” Rockey said. “There is nothing in that biomass that didn’t come from the soil. Having the cattle out there is still a closed loop, but you are adding one more component to it.”

When you incorporate the green manure, it is broken down biologically. “The fungi and bacteria are doing the job for you,” Rockey explained. “But now you are more dependent on soil temperature. If that residue is out there the next spring, you have to give it enough time to warm up so that biology can break it down so that the nutrient becomes available. The cows have a huge jump start on that process.”

That rumen stimulation, along with compost and biological fertilizer applications, he added, are crucial to efficient nutrient cycling. The compost is taking an outside source and bringing it in, similar to a situation where you would supplement feed with hay bales.

“I struggle with a lot of people because they see the cattle out there and they see the manure out there and they think I just added nutrient to my soil,” Rockey said. “No, I didn’t. I just cycled what is already out there.”

Timing is a crucial factor for successful cover crop grazing for Rockey, too, particularly because the San Luis Valley’s growing season is no more than 100 days.

“We are planting potatoes as soon as we can and we are still pushing going into cold soils,” Rockey said. “There is a lot of opportunity for disaster. In some other areas, where me. You have to be very careful. You have to pay attention.”

The sprinkler stays ahead of the cattle, keeping the cover crop growing throughout the season. Rockey and Brown communicate regularly about the water and field management.

There is also no guarantee the cattle won’t escape, which Rockey has experienced first hand.

“There is potential for a wreck,” Brown confirmed. “We deal with that year round. Getting to know each other and what you are comfortable with is part of all this. We work with people all year. You have to learn to read people.”


Brown and Rockey are committed to their grazing relationship as long as they can meet everyone’s, and every animal’s, needs.

“The most beneficial is running your own cows,” Brown said, having worked with farmers that ended up buying their own cattle or sheep. “That is one of the problems I run into now. There is not enough money for both of us. You have to decide what is best for you.”

Rockey has no interest in getting into the livestock business. He will graze both Brown’s cattle and sheep on his cover crops this season, and hopefully for many seasons to come.

“The way I look at economics is a lot different,” Rockey said. “Most farmers are really set on short-term economics. Having Wayne on our place benefits our economics long term. There is a longer pay back on it, but it is definitely there.”

He added, “Most farmers are only going to be interested in bringing you out if you are going to increase tonnage on the potato crop next year. To me, I am content with my tonnage, but I am looking to reduce my inputs to maintain that tonnage. That is a different mindset.”

Lauren Krizansky and her husband Brendan Rockey run Rockey Farms in Colorado’s San Luis Valley.

Companion Planting: The Magic of Corn, Beans and Squash

By Jeff Poppen

Companion planting is an important part of any gardener or farmer’s planning.

Recent discoveries in quantum physics, microbiology and ecology verify something gardeners have long known. Everything in nature is related. There are no solid lines between the plants’ roots, the soil and the bacteria and fungi tying it all together. To help understand why garden crops do or do not thrive, we are led into the enigmatic field of companion planting.

Just as we work and feel best around our friends, plants will grow better in their preferred company. Although the reasons may be obscure, a lot of observation and a little intuition can reveal mutual attractions and aversions. The garden teaches us the value of old-time practices, fresh experiments and keeping our eyes open.

Companion planting
In the spring garden lettuce, carrots, peas, beets and radishes all grow well together.

Following the advice of Steiner, Albrecht, Howard, Rodale, and others, we build up a live soil humus with an inherent microbial intelligence. Native Americans did not have to do all that reading; they simply did not plow, compact, or put chemicals on their soils in the first place. Right off the bat, they taught us companion planting with the “three sisters” — corn, beans and squash.

Corn belongs to the grass family. Its shallow, fibrous root system requires extra nitrogen. Beans, on the other hand, have a deep taproot and a symbiotic relationship with soil bacteria that accumulate nitrogen. Squash grow well in the shade of the beans, which climb up the corn stalks. The big squash leaves provide shade that keeps the soil moist and the weeds from sprouting. An Iroquois corn patch produced three times as much grain per acre as European wheat farmers were getting, along with extra vegetables to boot.

In the spring garden lettuce, carrots, peas, beets and radishes all grow well together. Although carrots are companion plants with peas as well as onions, peas do not grow well next to onions. The pea and bean families do not like the onion family, which includes garlic, leeks and shallots. Radishes repel cucumber beetles and are harvested quickly.

Cabbage grows well with beets and potatoes; they can be planted together in early spring. We grow kale and Chinese cabbages in the fall for several reasons: they like cooler weather, and are not bothered by bugs as much then.

In our crop rotation, potatoes follow a grass or clover sod because untilled land has more fungal activity underground. Plenty of compost and loose soil keep the potatoes from attracting beetles. After a season of cultivating, the microbial domination has shifted in favor of bacteria. This is well suited for the cabbage family. Companion planting is related to crop rotation, since certain crops prepare the soil for the next one.

Potatoes and beans planted together help to repel each others’ pesky beetles. However, they are planted in different seasons, so we do not use this particular combination. We plant alternate rows of bush beans and cucumbers. Along with their mutual attraction, the timing works well. The quick-maturing beans yield a few pickings before the cucumber vines invade their rows and hide the future pickles in their shade.

Cucumbers also like dill in the garden and in the jar. Similarly, basil and tomatoes grow and taste good together. Herbs add a whole new dimension, aroma and beauty to the garden. They have also long been observed to be good companion plants. Parsley and her sisters in the Umbelliferae family have blooms that supply nectar to beneficial insects. Fennel and wormwood are the herbal exceptions, as other plants generally do not like them. When folks see flowers in the garden, they often think we are trying to keep bugs away. Nothing could be further from the truth. We love flowers because they attract insects, most of which are beneficial. Marigolds excrete a toxin for certain nematodes, but flowers are grown for the birds and the bees.

Companion Planting, by Helen Phibrick and Richard Gregg, was published in 1966. It became a source of conversation and experimentation in my parents’ organic gardens. It makes sense that plant species will show signs of sympathy and antipathy with each other. The garden combinations of flowers, herbs and vegetables are endless. Therefore, we must consider this a recent science wide open for exploration. Every garden and every year is a new opportunity to marvel at and unearth nature’s mysteries, wisdom and interconnectedness.

By Jeff Poppen. Biodynamic farmer Jeff Poppen lives, works and writes at Long Hungry Creek Farm in Red Boiling Springs, Tennessee. For more information visit

This article appeared in the March 2014 issue of Acres U.S.A.

Vetch Cover Crop Recommended for Organic Zucchini

In 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.

Grasping the True Value of Cover Cropping

Planting cover crops in rotation between cash crops is even more valuable than previously thought, according to a team of agronomists, entomologists, agroecologists, horticulturists and biogeochemists from Penn State’s College of Agricultural Sciences. Research, published in Agricultural Systems, quantified the benefits offered by cover crops across more than 10 ecosystem services.

man in field
Photo by USDA NRCS

Benefits included increased carbon and nitrogen in soils, erosion prevention, more mycorrhizal colonization and weed suppression. Researchers simulated a three-year, soybean-wheat-corn rotation with and without cover crops in central Pennsylvania, which presented agroecological conditions broadly representative of the Northeast and mid- Atlantic regions. The cover crop rotation included red clover, frost-seeded into winter wheat in March, and winter rye, planted after corn was harvested in the fall. The research, funded by the U.S. Department of Agriculture, used simulated management practices, including tillage, synthetic fertilizer use and mechanical weed control.

This report appears in the May 2014 issue of Acres U.S.A.

Cover Crops for Pest Management

Two small farmers in Florida are partnering with University of Florida Extension to determine how cover crops can be used to manage insect pests. In a newly funded Southern Sustainable Agriculture Research & Education On-Farm Research Grant, “Establishing and Evaluating Selected Cover Crops on Small Farms to Increase the Impact of Beneficial Arthropods on Crop Pests,” strips of sunflower and buckwheat are being incorporated into crop fields to act as trap crops for pests and as attractants for beneficial predatory insects and pollinators.

Bradley Hoover, of Hoover Farms, owns 20 acres of about 50 different types of vegetables, all certified organically grown and sold in the wholesale market. In his field of tomatoes and peppers, Hoover, with the help of University of Florida Extension agents, has planted rows of sunflowers and buckwheat along the field perimeters, as well as additional rows of buckwheat in the center. The study compares the cover crops to the control (no cover crop plantings) to see where they fit into Integrated Pest Management practices.

The sunflowers attract stinkbugs, specifically the leaf-footed bug, which aggressively attacks tomatoes and peppers. The sunflower is acting as a trap crop, keeping the pest away from the farm’s cash crop. In addition, buckwheat attracts a wide array of beneficial insects, including native pollinators.


Scott and Billie Rooney, with Rooney’s Front Porch Farm, are looking at the same two cover crops, but evaluating their effectiveness in fruit production. Stinkbugs easily make a meal of their U-pick blackberry and blueberry plants.

“We are only in our first year of the study, but we are not seeing as many stinkbugs in the berries as we’ve had in the past,” said Billie Rooney.

Billie and her husband have already made some keen observations participating in the project. For example, she said that the sunflowers bordering the woodland contain more leaf-footed bugs than the sunflowers bordering their hair sheep grazing pasture.

The Rooneys are also interested in planting the winter small grain triticale in their grazing pastures. Triticale, it turns out, also acts as a trap crop for stinkbugs and will attract the early flights of stinkbugs before the sunflower crop is planted and ready.

This article appears in the September 2014 issue of Acres U.S.A.

Cover Crops on the Farm

By Tara Maxwell

Cover crops are increasingly being used by farmers across the country to suppress weeds, conserve soil, protect water quality and control pests and diseases.

The fourth annual SARE/CTIC Cover Crop Survey collected data from more than 2,000 growers from 48 states and the District of Columbia. The survey provides insight into cover crop usage and benefits and explores what motivates farmers to include cover crops in their farm management and soil health plans.

Respondents reported a steady increase in the number of acres they have cover cropped over the past five years. They said the most important benefits of cover crops include improved soil health, reduced erosion and compaction, and increased soil organic matter. Other reported key benefits of using covers are weed and insect control, nitrogen fixation, attracting pollinators and providing deep taproots.

flowering cover crops
A cover crop mix of rye, clover and vetch.

North Central SARE (Sustainable Agriculture Research and Education) and CTIC (Conservation Technology Information Center) sought data on how farmers use cover crops to manage their fertilizer inputs. Growers were asked to indicate their level of agreement with a series of fertilizer-related statements using a scale ranging from 1 (strongly agree) to 5 (strongly disagree). The statement that got the highest level of agreement was “Using cover crops has enabled me to reduce application of nitrogen on my cash crop,” with 134 of 1,012 respondents strongly agreeing and 244 checking “agree.” The statement that had the highest level of disagreement was “Using cover crops has required me to use additional crop fertility inputs over time to meet the needs of my cash crop.”

Cover Crops & Yields

For the fourth year in a row, the survey found yield increases in both corn and soybeans after cover crops (1.9 percent in corn and 2.8 percent in soybeans). According to the survey analysts,

cereal rye growing in a field
various objects of the summer season in the best of this wonderful period

“Those are modest bumps, but they are statistically significant. A new angle of exploration — on the effects of a cereal rye cover on a subsequent crop of soybeans — revealed that a majority (52 percent) responded that their soybeans often or always rise after a cover crop of cereal rye. Notably, 82 percent said cereal rye cover crops helped with weed control. In all, the popular practice of planting cereal rye cover crops before soybeans was validated in this year’s survey.”

While a majority of those surveyed saw no loss in profit, or lacked the data to tell, about one-third found a profit increase from cover crops, and two-thirds of the respondents said cover crops helped yields remain steady during extreme weather events.

Cover Crop Mixes & Timing

Cereal rye was the most popular cover species in the survey, followed by radish. However, cover crop mixes were planted on nearly as many acres as cereal rye. More than half of the participants in the survey reported that they started with a single species and “graduated” to mixes, while another 17 percent started with mixes and increased their use of blends. 61 percent of the respondents said they designed their own blends and 22 percent relied on their crop consultant or cover crop seed dealer to help them develop a mix.

Legumes are popular among many cover crop users because they fix nitrogen in the soil, in addition to all the other benefits of covers. Crimson clover led the legume category in average acreage per user, followed by winter pea, hairy vetch, other clovers, cowpea, red clover, other vetches and sunn hemp.

Covers have traditionally been planted after harvesting cash crops. However, many farmers have found that seeding cover crops into growing cash crops can provide a vital head start in cover crop establishment.

Tara Maxwell served as managing editor of Acres U.S.A. magazine for 8 years. She is a graduate of Virginia Tech with a background in journalism and animal science, and has a passion for sustainable farming.

Cover Cropping & Green Manures

By Ellen Polishuk

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.

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.

The consultant warned me that just growing huge biomass cover crops might overwhelm this inactive soil — without a good population of microbes present it would be difficult for the soil to digest so much raw organic material. That’s where the addition of compost helps — by inoculating the soil with a diverse mix of microbes.

flail mower
Flail mowing summer Sudangrass/cowpea green manure at Potomac Vegetable Farms – West.

The addition of a well-developed compost is always good, but it’s expensive and isn’t much of an organic matter addition at the rate of 5 tons per acre. Compost alone is too costly and at high rates will create nutrient imbalances, but putting both practices together is a winning combination.

I think it’s important to make a distinction between the term “cover crop” and the term “green manure.” What these practices have in common is that a crop is grown that will not be harvested — everything is given back to the soil. The difference between the two practices is when this gift crop is grown. A cover crop is grown between cash crops — for those of us in Zones 3-7 that means over the winter. A green manure crop is grown instead of a cash crop — during the main growing season. The soil benefits of each practice are virtually the same, but the erosion prevention aspect of a cover crop is more relevant and important as it is grown in the winter when many farmers don’t plant anything at all.

In case you have forgotten the myriad benefits of a green manure/cover crop, here’s a reminder:

  • Organic matter extraordinaire – both roots and tops of plants can add up to 9 tons per acre of dry matter.
  • Biological stimulant – the growing plants’ exudates feed the soil microbes.
  • Erosion control – there is nothing better than a healthy crop to keep the soil in place.
  • Biodiversity – many cover crop families are different than those typically grown on a mixed vegetable farm and provide a habitat for different insects, some of which will be beneficial. Also these different plant families will feed the soil microbes a different ration of exudates.
  • Soil aggregation – always having plant roots growing helps to form and maintain soil aggregates, which leave the soil more aerated.
  • Weed management – healthy timely cover crops reduce weed pressure in future years.

While many growers commit to growing cover crops over the winter, few practice green manuring on a regular basis. Why? Most perceive it as too costly in terms of time, effort, seed money and losses from forgoing the opportunity to grow a cash crop.

By growing a green manure crop in the main season, there is usually little time left to grow most cash crops.

There are a few exceptions to this rule — either with very short season cash crops, like salad mix species or radishes, or with very short season green manure crops like buckwheat. I have found that the benefits gained through a well thought out and executed green manure program outweigh the costs. How did I come to this conclusion?

I used to believe I could not afford to implement a green manure system. What was missing for me was an aggressive and exacting rotation plan and the determination to follow through on actually planting the green manure crops. I heard the Nordells of Beech Grove Farm in Trout Run, Pennsylvania, give a talk about crop rotation at a conference. Finally it all came together for me and I understood how to approach the management of the land via a rotation that includes green manure crops.

The Nordells created their rotation with weed management as one of the primary goals. In its simplest definition, my farm is neatly divided in half; at any given time at least half of the acreage is “on vacation,” growing cover crops or green manure crops. The other half is “working,” growing cash crops. Another way to say it is that half of the farm is making money and the other half is getting ready to make money next season. The cash crop years alternate between early and late crops. This system mixes up the times of year that tillage takes place, thus helping to combat weeds that result from always tilling in April/May and September/October.

My farm has been on this vacation rotation plan for several years and the results are gratifying. The soil continues to improve and the crops are more vigorous and productive.

We are also making a dent in the weed pressure on the farm. There is nothing that makes me smile more than driving by a gorgeous field of Sudangrass and cowpeas in the middle of summer, knowing that all those soil benefits will make the following season easier and more lucrative.

Cover Cropping: What do you need to do to get started?

First, I would recommend reading SARE’s Managing Cover Crops Profitably. This manual tells you all you need to know about which species to choose, when to plant, seeding rates and the attributes of each species.

Second, get serious about your rotation. Figure out how to set aside up to 50 percent of your acreage each season for soil improvement. If that sounds outrageous, start small with 15-25 percent. Get organized and make a plan that you can enact.

Third, make sure you have the implements you need to make the rotation work. How will you plant the cover crop/green manure? Spin seeder or drill? How will you manage the top growth? Bushhog or flail mower? How will you work that dry matter into the soil? Plow/disk or rotovator or spading machine? Fourth, get your seeds before you get too busy with your cash crops. Have everything ready to go so that when the time is right you can get those cover crops/green manures planted.

I encourage you to make any form of progress possible in incorporating cover crops and green manures into your regular farm schedule. Once you begin to see the benefits on your land, you’ll be convinced to improve and increase their use. Don’t worry too much about the fine points of the perfect polyculture right off the bat — just get started with planting one or two species at a time. I promise you will love watching those “gift” crops grow.

This article appeared in the December 2014 issue of Acres U.S.A.

Cover Crops Don’t Deplete Moisture

Among the myriad of benefits cover crops provide to a row crop or vegetable operation, Clemson University researchers have found another one: Cover crops do not deplete water stored in the soil profile, thus preserving the precious resource for the cash crop — an all important function, specifically in times of drought.

USDA photo showing a cover crop mixture that includes oat, proso millet, canola, sunflower, dry pea, soybean and pasja turnip.

In the Southern Sustainable Agriculture Research & Education (SSARE) On-Farm Research Grant-funded study (OS16-096), “Cover Crop Influence on Stored Water Availability to Subsequent Crops,” researchers evaluated common fall cover crops grown in the state for water use efficiency and biomass production.

“We need to bring biodiversity to our farming systems to alleviate drought stress, and cover crops are one practice that provides the benefits to achieve that,” said Ricardo St. Aime, a Master’s student and Fulbright Scholar from Haiti who worked on the project. “But many farmers are hesitant to adopt cover crops. One reason is that they fear cover crops might bring water resource competition for the following cash crop. We conducted this study to determine whether or not this is true.”

Cover Crops Comparison

In the two-year study, St. Aime, along with principal investigator Sruthi Narayanan, compared seven cover crop treatments to two controls (a weedy fallow field and a weed-managed fallow field). The cover crop treatments covered the three major categories: grasses, legumes and brassicas.

They included:

  • Single species of rye;
  • Single species of crimson clover;
  • Mixture of crimson clover and turnip;
  • Mixture of oat and radish;
  • Mixture of crimson clover and rye;
  • Mixture of oats, wheat, crimson clover, radish and turnip;
  • Mixture of Austrian winter pea, rye, crimson clover, hairy vetch and oats.

Soil water content was evaluated starting from 74 days after cover crops planting and measured at various depths, ranging from 4 inches to 39 inches. Biomass was hand harvested at 83, 111 and 137 days after planting to determine dry weight.

“Cover crop water use efficiency was estimated as the amount of dry biomass produced per unit of water used during the growing period,” said Narayanan, an agronomist with the Department of Plant and Environmental Sciences. “Identification of high water use efficient cover crops, as a single species or in a mix, helps identify cover crops that produce large amounts of biomass, use less water, or a combination of both.”

Researchers found that all cover crop treatments, both in the vegetative stage and the flowering stage, retained more or equal amounts of soil moisture compared to the controls. Even after one month after cover crop termination, results showed that soil moisture was still available for use by the cash crop.

“This does not support the perception that cover crops will deplete soil moisture, which would lead to water stress for the following cash crop,” said St. Aime.

Cover Crop Mixes

In terms of the performance of the cover crop treatments, researchers found that the best ground covers were the single treatment of cereal rye and the cover crop mix of Austrian winter pea, rye, wheat, crimson clover, hairy vetch and oats. The worst ground cover was the single treatment of crimson clover, the two-mix treatment of oat and radish, and the two-mix treatment of turnip and clover.

The five cover crop mix (Austrian winter pea, rye, wheat, crimson clover, hairy vetch and oats) and cereal rye were also two of the best cover crops for biomass production. The single crimson clover treatment produced the least amount of biomass.

“The findings emphasize that it’s important to incorporate a grass, legume and brassica for the best cover crop mixture,” said St. Aime. “Grasses produce high biomass and catch nutrients, legumes fix nitrogen, and brassicas are good for biofumigation and alleviating compaction. For more residue, grow either cereal rye or a mix of all three functional groups. Although turnips and crimson clover didn’t use much water, they are poor biomass and ground cover producers.”

Of the two five-combination cover crop mixtures, the Austrian winter pea-rye-wheat-crimson clover-hairy vetch-oats mix outperformed the oats-wheat-crimson clover-radish-turnip mix in terms of biomass production, said St. Aime. Researchers suspect rye in the mix made the difference.

Researchers hope that the results will help farmers develop a cover crops package that will optimize biomass while conserving moisture for subsequent crops.

Continuing Research

Narayanan has received a second SSARE On-Farm Research Grant (OS18-118), “Cover Cropping to Increase the Sustainability of Cropping Systems by Developing Soil Organic Matter, Improving Soil Health, and Suppressing Weed Growth,” to study the effect of cover crops on soil health and soil compaction. Researchers are taking the best soil water conservation cover crops and determining how well they conserve soil nutrients, increase organic matter, improve soil health and suppress weed growth for the subsequent cash crop.