Question of the Week
Answer: I am pleased to provide you with information regarding soil management strategies for your new farm. This letter is outlined to provide you with more details regarding amending a heavy clay soil with compost and green manures (i.e. cover crops). Heavy clay soil responds best to organic matter.
Composting is certainly a way to reduce off farm inputs on your farm as well as increase the organic matter and the workability of a heavy clay soil. Listed below is an introductory publication on composting manure. It will provide you with some basic tips on how to get started on this process for your farm, including carbon to nitrogen ratios, materials that compost well, placement, etc. I have also referenced the Rodale Institute’s “Making and using compost at The Rodale Institute Farm,” from their web site New Farm. They provide a good on-farm example and recommendations for developing a compost system on your farm, including methods of turning and sources of materials.
Some other useful resources to consider are “The On-Farm Composting Handbook” and the “Field Guide to On-Farm Composting.” These are practical handbooks which present a thorough overview of farm-scale composting and explain how to produce and use it. The information on where and how to obtain these books is listed below under “Further Resources.”
Cover cropping is another way to loosen your heavy clay soil and provide organic matter. Cover crops are soil-building crops that are not harvested, but are composted or tilled back into the soil. They can be part of a crop rotation, or can be used to prevent soil erosion and improve fertility. When choosing a cover crop you need to make several considerations. There are many ways to use cover crops in a production cycle:
• as a main crop during the primary growing season. Used as a rotational crop, the cover will exclude production of a cash crop.
• as a companion crop, or living mulch, the cover is planted between the rows of the cash crop—for example pumpkins interplanted with white clover.
• as a 'catch' crop for nutrients, planted after harvest of the main crop or between the rows of the cash crop to reduce leaching of nutrients.
• as an off-season crop grown to protect the soil, usually during the winter when there is no main crop—this is not the case in your farm, of course. This is the most common practice in temperate areas.
Pleas refer to the ATTRA Publication “Overview of Cover Crops and Green Manures.” This publication will help outline some of the cover crops used for the specific purposes that I outline above. The ATTRA publication Sustainable Soil Management will be a helpful resource as well.
A rotation plan used in conjunction with cover cropping and compost is an ideal way for a vegetable farmer to increase fertility and organic matter, while minimizing off farm inputs.
In general, many farmers use the season in which the cash crop is produced as a rotation tool. E.g Spring/ fall crops, winter crops, short season cucurbits, solanaceous crops, etc. Farmers will often plant these “types” of crops in blocks and rotate the entire block each year. E.g. The winter crops of radishes, arugula, lettuce, and beets are planted in block one and rotated to block two next year. This “block” system meshes well with cover cropping, as you can simply have one block in cover crops at any one time. The best way to illustrate this is with some examples. Referenced below is a “real farm” sample of crop rotation sequences for a diversified vegetable farm titled “CEFS Student Farm Upper Field Crop Rotation” from the Center for Environmental Farming Systems at North Carolina State University. They grow several acres of vegetables year-round on their student farm.
I encourage farmers, if they have enough space, to plant one block/ section in cover depending on the season—winter annuals such as oats and peas or rye and vetch, or in the summer, buckwheat, cowpeas, or sudan grass.
Cover crops in annual rotations
In annual cropping systems, cover crops are often chosen to maximize benefits such as biomass and nitrogen production. However, other factors must also be considered. For example, fitting a cover crop into the sequence of a crop rotation can be difficult. Therefore, fast-growing, drought-tolerant cover crops that require minimal management are preferred. Cover crops with fast germination and good seedling vigor are usually chosen because of their ability to compete with weeds. Also, species with the potential to reduce pest populations should be chosen, while those that harbor diseases or arthropod pests of the cash crops should be avoided.
Common cool-season legumes used as cover crops in annual rotations include vetches, winter pea and bell bean. Because clovers and medics grow slower and compete poorly with weeds and require more management (e.g., mowing), they are used less commonly in annual rotations. For similar reasons, cereal grains are usually preferred over other grass species, such as bromes, in annual rotations. Sometimes, however, the annual cereal grains can be used as a “nurse crop” for clovers and medics. They are seeded at the same time and the cereal grains are mowed once or twice. This system gives some shelter to the clovers and helps distribute the seed evenly.
In choosing warm- season cover crops, the ability to perform well with minimal irrigation is often of primary consideration. Legume species in this category include cowpea, hyacinth bean and sunnhemp. Typical grass cover crops for warm conditions include sudangrass and sorghum (1).
Managing Cover Crops Profitably, by Greg Bowman, Christopher Shirley and Craig Cramer describes several rotation and cover crop scenarios for vegetable farms. The Nordell Farm profile is particularly inspiring for many farmers.
It is important to have a sprinkler irrigation system to establish cover crops. If you tend to have droughty summers, establish a drought resistant cover crop such as cowpeas with the spring rains.
(1) Ingels, et al. 1993. Selecting the Right Cover Crop Gives Multiple Benefits. California Agriculture 43 (5):43-48.
Sayre, Laura. 2004. Making and Using Compost at The Rodale Institute Farm. Rodale Institute. The New Farm.
Hopkinson, Tim. 2005. Composting Livestock Manure. Klickitat County Solid Waste Department.
Grover, Joel. 2005. CEFS Student Farm Upper Field Crop Rotation. Center for Ecological Farming Systems. North Carolina State University.
On-farm Composting Resources:
Rynk, Robert, ed. 1992. On-Farm Composting Handbook, NRAES-54, is available for $25.00 per copy (plus shipping and handling) from NRAES, Cooperative Extension, PO Box 4557, Ithaca, New York 14852-4557 or
Mark Dougherty, ed. 1999. Field Guide to On-Farm Composting. NRAES Publishing. Ithaca, NY.
Greg Bowman, Christopher Shirley, Craig Cramer. 1998. Managing Cover Crops Profitably. Sustainable Agriculture Network.
This book distills findings from published studies and on-farm experience into a user-friendly reference tool for farmers and agricultural educators. You will find detailed information on how to select cover crops to fit your farm, and how to manage them to reap multiple benefits.
Magdoff and van Es. 2000. Building Soils for Better Crops. Second ed. Sustainable Agriculture Network. Handbook Series 4.
Sustainable Agriculture Publications
Hills Building, room 10
University of Vermont
Burlington, VT 05405
Call to order: 802-656-0484
Cover Crop Seed Suppliers:
Try a local feed or field crop seed supplier! They often carry many different cover crops.
Organic Growers Supply
PO Box 520, Waterville, ME 04903
Call to get a catalog
Johnny's Selected Seeds
955 Benton Avenue
Winslow, Maine 04901
Toll Free: 877-Johnnys (877-564-6697)
Peaceful Valley Farm Supply
P.O. Box 2209
Grass Valley, CA 95945
To place an order, call toll free at 1-888-784-1722.
Turner Seed Co.
Source of cowpea cover crop seed.
211 County Road 151
Breckenridge, TX 76424-8165
Toll-Free Tel 800.722.8616
Fax Line (254) 559-5024
General Farming info:
Grubinger, Vern. 1999. Sustainable Vegetable Production from Start-Up to Market
Publication number: NRAES-104
Length: 280 pages
Date of Publication: August 1999
Available from: NRAES Cooperative Extension
Phone: (607) 255-7654
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