Appendix A

Testing Cover Crops on Your Farm

by Marianne Sarrantonio

To find your best cover crops, you needn’t become Dr. Science or devote your life to research. It’s not hard to set up valid, on-farm tests and make observations. Follow these steps:

A. Narrow your options. Aim for a limited-scale trial of just two to five species or mixtures. You can test the best one or two in a larger trial the next year. Unsure of the best place and time in your rotation? Start with small plots separated from cropped fields and plant over a range of dates, under optimal soil and weather conditions. If you’re sure where and when to plant and have just two or three covers to try, put the trial right in your cropped fields, using your normal seedbed preparation. This method provides rapid feedback on how the cover crops fit into your cropping system. Keep in mind management may need some tweaking (such as seeding rate or date) to get the best results.

B. Order small seed amounts. Many companies provide 1- to 10-pound bags if you give them advance notice. If 50-pound bags are the only option, arrange to share it with other growers. Don’t eliminate a species just because seed price seems high. If it works well, it could trim other costs. You could consider growing your own seed eventually, and perhaps even selling it locally. Be sure to obtain appropriate inoculants if you’ll be testing legumes, which require species-specific rhizobial bacteria so the cover can capture and “fix” N efficiently. See Nodulation: Match Inoculant to Maximize N.

C. Determine plot sizes. Keep them small enough to manage, yet large enough to yield adequate and reliable data. Plots two to four rows wide by 50 to 100 feet could suffice if you grow vegetables for market. If you have 10 or more acres, quarter- or half-acre plots may be feasible. If you use field-scale machinery, establish field length plots. For row crops, use plots at least four rows wide, or strips based on your equipment width. Keep in mind the subsequent crop’s management needs.

D. Design an objective trial. Plots need to be as uniform as possible, randomly selected for each option you’re testing, and preferably replicated (at least two or three plots for each option). If parts of the field have major differences (such as poorer drainage or weedy spots), put blocks or groups of plots together so each treatment has equal representation in each field part, or avoid those areas for your trial entirely. Label each plot and make a map of the trial area.

E. Be timely. Regard the trial as highly as any other crop. Do as much or as little field preparation as you would for whole fields, and at an appropriate time. If possible, plant on two or more dates at least two weeks apart. In general, seed winter annuals at least six weeks before a killing frost. Wheat and rye can be planted later, although that will reduce the N-scavenging significantly.

F. Plant carefully. If seeding large plots with tractor-mounted equipment, calibrate your seeding equipment for each cover crop. This can prevent failures or performance differences due to incorrect seeding rates. Keep a permanent record of drill settings for future reference. A hand-crank or rotary spin seeder works well for small plots getting less than five pounds of seed. Weigh seed for each plot into a separate container. To calculate seeding rates for small plots, use this formula : 1 lb. /Acre = 0.35 oz (10 grams)/ 1000 ft2 area seeded. If your cover crop seeding rate calls for 30 lb/acre, multiply 0.35 oz by 30. You will need 10.5 oz (300 grams) of seed for each 1000 ft2 you seed. Put half the seed in the seeder and seed smoothly as you walk the length of the field and back, with a little overlap in the spread pattern. Then seed the remainder while walking in perpendicular directions so you crisscross the plot in a gridlike pattern. If broadcasting by hand, use a similar distribution pattern. With small seed, mix in sand or fresh cat litter to avoid seeding too much at a time.

G. Collect data. Start a trial notebook or binder for data and observations. Management information could include:

  • field location 
  • field history (crops, herbicides, amendments, unusual circumstances, etc.)
  • plot dimensions
  • field preparation and seeding method
  • planting date and weather conditions
  • rainfall after planting
  • timing and method of killing the cover crop
  • general comments

Growth data for each plot might include:

  • germination rating (excellent, OK, poor, etc.), seven to 14 days after seeding 
  • early growth or vigor rating, a month after establishment
  • periodic height and ground cover estimates, before killing or mowing
  • periodic weed assessments
  • a biomass or yield rating

Also rate residue before planting the next crop. Rate survival of winter annuals in early spring as they break dormancy and begin to grow. If you plan to mow-kill an annual, log an approximate flowering date. Regrowth could occur if most of the crop is still vegetative. Rate overall weather and record dates such as first frost. Note anything you think has a bearing on the outcome, such as weed infestations. If time allows, try killing the cover crops and continuing your expected rotation, at least on a small scale. You might need hand tools or a lawn mower. Use field markers to identify plots.

H. Choose the best species for the whole farm system. Not sure which covers did best? Whatever you found, don’t be satisfied with only a single year’s results. Weather and management will vary over time.

Assess performance by asking some of the questions you answered about the cover niche (see Selecting the Best Cover Crops for your Farm). Also ask if a cover:

  • was easy to establish and manage 
  • performed its primary function well
  • avoided competing excessively with the primary crop
  • seemed versatile
  • is likely to do well under different conditions
  • fits your equipment and labor constraints
  • provides options that could make it even more affordable

In year two, expand the scale. Test your best-performing cover as well as a runner-up. With field crops, try one-acre plots; stick with smaller plots for high-value crops. Also try any options that might improve the cover stand or its benefits. Entries for the major cover crops in this book include some management tips that can help. Record your observations faithfully.

I. Fine-tune and be creative. Odds are, you won’t be completely satisfied with one or more details of your “best” cover. You might need to sacrifice some potential benefits to make a cover work better in your farm system. For example, killing a cover earlier than you’d like will reduce the amount of biomass or N it provides, but could ensure that you plant summer crops on time. In most cases, fine-tuning your management also makes it more affordable. Lowering a seeding rate or shifting the seeding date also could reduce the tillage needed. Narrower rows in your cash crop might hinder establishment of an overseeded legume but reduce weeds and bump up the cash crop yield. Don’t expect all of a cover’s benefits to show up in yearly economic analyses. Some benefits are hard to assess in dollars.

Your best covers may seem well-suited to your farm, but there could be an up-and-coming species or management technique you haven’t thought of testing. See Up-and-Coming Cover Crops for a few examples. Overwhelmed? You needn’t be. Initiative and common sense— traits you already rely on—are fundamental to any on-farm testing program. As a grower, you already test varieties, planting dates and other management practices every year. This section offers enough tips to start testing cover crops. You also can collaborate with others in your region to pool resources and share findings. There’s a good chance others in your area could benefit from your cover cropping wisdom!

[Adapted and updated in 2006 from Northeast Cover Crop Handbook by Marianne Sarrantonio, Rodale Institute, 1994.]