CROP ROTATIONS AND COVER CROPS FOR STRAWBERRIES
by Vern Grubinger
Vegetable and Berry Specialist
University of Vermont Extension

When I started in Extension, a local fruit grower gave me a tour of his farm and some sage advice. “Anyone can grow strawberries for 10 years” he said. “Then comes the real challenge: getting good yields after all your best land has been planted to berries at least once.” Since that time I’ve heard many growers fondly recall the high production they had on ‘virgin’ fields. Clearly, bad things happen when land is planted too often to strawberries. Soil-borne diseases, insect pests, and weed populations tend to increase. Soil fertility may also suffer due to compaction and a decline in organic matter quantity and quality.

Crop rotation is essential if one wants to remain a strawberry grower. The rotation design depends on how much land a grower has to work with, how much strawberry acreage is needed to meet market demand, and what the farm’s overall crop mix is. If land on the farm is limited, a grower should consider renting or acquiring additional land, or temporarily trading land with nearby farmers that grow other crops suitable for strawberry rotation, such as forages.

Exactly what makes a good rotation for strawberries, or any small fruit, is not entirely clear, but several suggestions can be made with confidence based on research results and grower experience: 1) rotate out of berries for as long as possible between plantings, 2) avoid rotating with crops that host strawberry pests, and 3) include cover crops in the rotation.

By adding organic matter to the soil, cover crops can improve soil structure, enhance nutrient reserves, and promote the biological activity that is associated with ‘healthy’ soil. Leguminous cover crops like clovers, hairy vetch and field pea add nitrogen to the soil. Fast-growing cover crops like buckwheat, sorghum-Sudangrass and Japanese millet can suppress weeds. Growers need to select cover crops that best address their production priorities. The book Managing Cover Crops Profitably (1) describes the attributes and management of many cover crop species.

Marvin Pritts of Cornell, writing in the Strawberry Production Guide (2) advises: “Do not grow strawberries for 5 or more consecutive years on the same site without some type of crop rotation. Plan to reserve at least 30% of your land (preferably 50 to 70%) for rotation in future years, because a minimum of 3 years should elapse between plantings on the same site. Land not planted in strawberries should be planted in soil improving cover crops or cash crops that allow for easy weed management.”

Bill Lord of the University of New Hampshire suggests a 5-year rotation at a minimum (3). For example, set the plants in year 1, fruit them in years 2 and 3, then turn the crop and weeds into the soil and start cover cropping immediately after harvest with the sowing of Sudangrass, or Japanese millet in short-season areas. Either cover crop will winter kill in northern climates, and after incorporation of residues in the spring of year 4, sow oats, followed by Sudangrass in summer. In year 5 repeat the cover crop cycle or plant sweet corn to provide income. Corn also adds a significant amount of organic matter to the soil if the stalks are chopped or flail-mowed, incorporated, and followed by fall oats once more before strawberries are planted again.

Strawberry growers are using many different rotations. Below are descriptions of the strategies employed by several growers in New England.

Grower 1 has been growing half an acre of organic strawberries in southern Vermont for over 20 years, rotating on 2 acres. He has never had a serious root disease problem, or a decline in yield (other than normal fluctuations). He uses the matted row system, fruits the berries for just one year, then goes out of berries for 4 or 5 years after that. His rotation has varied over time depending on which pieces of land dry out and what his crop mix is. He likes to use long term cover crops like medium red clover for 2 years as a soil builder, and has had very good berry yields after that. He has also used hairy vetch mixed with rye. One limitation is that he cannot easily follow the vetch with berries because he plants berries in the spring before it’s time for the  vetch plow down. He finds that legume cover crops do not suppress quack grass, which is becoming a problem on his farm. Recently he has been growing annual crops like sweet corn or cut flowers immediately before and after the berries in order to get better perennial weed control. “If you’re looking for a firm rotation plan, I don’t have it. But I do follow some principles, like staying out of berries for several years, and preceding the berries with a crop that I can get good weed control in, so that basically the soil is bare of perennial weeds at the end of the growing season before berries. Then I go in with rye or oats as a winter cover prior to planting berries. Hopefully in 10 more years I’ll have the perfect rotation down.”

Grower 2 has been growing strawberries conventionally for 50 years in southern Vermont. He has  5 acres bearing fruit each year on 30 acres of tillable land. He plants an acre or an acre and a half of new strawberries each year. His crop mix includes about 5 acres of raspberries, too, which complicates rotation. “What I’ve concluded is: if you don’t have to, don’t plant where you’ve had strawberries before! Of course, you have to use the land you’ve got. Seventy-five years ago my uncle used to prepare a strawberry field with buckwheat, and I’m still a buckwheat believer - it does something good to the soil for berries. I pick a berry field for 2 years, so they are in for 3 years including the planting year. Then I idle the field for 3 or 4 years, and there are lots of things one can do during that time, including a legume plow down. We’re also grown raspberries to utilize the land economically, although they don’t improve the soil. There are a couple of other ingredients besides the crops themselves in a rotation; where I’ve  used Sinbar several times, that stuff is murder on a re-planting of strawberries, so I try to get by with other herbicides.”

Grower 3 is a conventional grower in New Hampshire that grows 10 acres of strawberries along with about 50 acres of vegetables and cover crops. “We always seem to tie up a high percentage of our tillable acreage with annual crops, as a result we have less acreage committed to  permanent sod or green manures than I would like. Over the years we have accumulated enough land so that we can rotate out of berries for 3 to 4 years, but unfortunately we have to include solanaceous crops in the rotation, which we usually try to do in the first year after berries. In the second year we grow cucurbits or what we call ‘the small stuff’ - carrots, radishes, lettuce, etc. These first 2 years of the rotation contribute to the weed seed bank of the soil so I like to plant sweet corn the next year or two, prior to planting strawberries, because the cultivations and herbicides for corn help reduce some of that weed pressure. We winter cover crop everything and sow cover crops in the summer on land that is open. We use buckwheat as a quick weed suppression crop in the summer. Our spring cover crops include field peas plus tritcale. In the fall we find that inexpensive horse oats work just fine, and you can glom them on the field at high rates in fields where small seeded or very early crops are going to go in the following spring. Hairy vetch plus winter rye are used in areas where sweet corn or crops on black plastic are going. We’ve also had success establishing Dutch white clover as a strip crop between rows of black plastic and plowing it down the following spring. We like the using clover rather than a less expensive intercrop like ryegrass because of our crabgrass problem. We are able to establish a solid mat of clover by mowing off the broadleaves and then we suppress the crabgrass by spraying a post-emergent grass herbicide  over the crabgrass.

Grower 4 is located in northwest Vermont. “For years and years, my bread and butter rotation has been this: Year 1: July after berry harvest, quick tillage and sow sorghum-Sudangrass; September 1, flail the cover crop, till lightly, sow winter rye. Year 2: late May flail the winter rye, light tillage, sow sorghum-Sudangrass, September 1, flail, till lightly, sow winter rye. Year 3: same as year 2, then late October moldboard plow the rye. Year 4: plant strawberries. Years 5 to 7 crop the strawberries. Year 7 is the last crop, same as year 1, above. This rotation kept the organic matter up around 5 percent. With only one moldboard plowing per six years, the soil structure stayed pretty good. I stuck with grass/grain crops on the theory that they'd be more likely to break the disease/nematode cycle than legumes. This rotation kept production pretty good for 3 cycles (18 years) or so, but lately production has fallen off. I know this is pretty common experience. I have heard that applying compost and switching to a soil spader for tillage solved it for one grower. I certainly never wanted to start down the fumigation road. I'm fooling around with some currants and grapes. I'd like to plant something permanent out there -- I've done the rock picking thing for too many years. It seems odd that I'm sitting on 11 acres of fertile, tile-drained, irrigated land, with good tilth, have 20 years of farming experience, but don’t know what to plant.

References:

(1) Bowman, G., C. Shirley and C. Cramer. 1998. Managing Cover Crops Profitably. 2nd edition. Sustainable Agriculture Network, Hills Building, University of Vermont, Burlington VT 05405. nesare@zoo.uvm.edu

(2) Pritts, M. and D. Handley (eds.) 1998. Strawberry Production Guide for the Northeast, Midwest and Eastern Canada. NRAES, 152 Riley Robb Hall, Ithaca NY 14853.
www.nraes.org

(3) Lord, William.1995. Strawberry crop rotation strategies. Proceedings, New England Vegetable and Berry Conference.  http://ceinfo.unh.edu/agbiowl1.htm

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