Cover crops offer benefits from fertility to
weed management
Penn State’s “cover crop summit” lays out species options and soil health tests for hands-on farmer learning.

By Ed Bialon

Posted July 13, 2007: As a new farmer—new to both rural living and Pennsylvania—I was glad to attend Pennsylvania’s Cover Crop Research and Management Summit last month. I found a tremendous amount of information about cover crops in sustainable and organic farming systems.

My wife, Joan, and I purchased our 91-acre farm near Huntingdon, Pennsylvania, in January 2005. We spent the next two years moving from St. Louis, Missouri, upgrading some of the farm’s infrastructure, and obtaining an organic crop certification. At this point we are most interested in producing organic vegetables and hay, and at some future date having an on-farm produce market. I have also given some thought to growing organic grain and forages to sell to the increasing number of organic dairy farms in the area.

We want our farm to be both sustainable and organic. We are engaged in constant discussion and debate on where we want to go with this farm in terms of our mission and goals. We also lack basic farming skills and experience, a situation which puts our farm at risk. I’m looking for wisdom in others’ experiences. To learn a bit about our challenges this spring, see the sidebar “Our farm year so far.”

This planting season I moved in the direction of solving a soil-fertility issue of low nitrogen in my commercial vegetable garden. In reviewing seed catalogs, we saw cover-crop seed mixes were being marketed as green manure to enrich the soil with nitrogen and organic matter. My wife and I were drawn to a spring-planted, green-manure mix of 60 percent field peas, 25 percent oats and 15 percent hairy vetch.

We decided to create our own green-manure mix using chickling vetch, forage peas and soybeans based on information from a seed salesman from the Midwest. However, as we explored this alternative and prepared to execute it, we realized how little we knew about managing cover crops to assure us of a successful outcome. We decided not to sow the early-season mix until we understood things better. The summit looked like a great way to learn about improving soil nitrogen with cover crops.

Cover crop selection

Held at the Penn State University agronomy farm at Rock Springs, the event turned out to be a great day for those of us who wanted to use cover crops in sustainable farming systems. Penn State and Rodale Institute staff paired up to give four presentations.

Dave Wilson, agronomist at Rodale, and Ron Hoover of Penn State discussed cover-crop species attributes and selection. Cover crops serve multiple purposes, and their incorporation into your crop rotation provides multiple benefits in a comprehensive approach to soil fertility and quality issues. Dave Wilson’s handout titled “Cover Crops for the Northeast” is a must-read resource on this topic. [ Can we link to this? ]

Cover crops discussed or displayed in research plots included rye grass, winter rye, sweetclover, sorghum-sudan grass hybrids, red clover, hairy vetch, alfalfa, berseem clover, crimson clover, white clover, peas, forage radish, oilseed radish, daikon radish, oats, buckwheat, bahiagrass, sun hemp, mucuna, teff, wheat, fava and bell beans, rapeseed, canola, millets and lab lab. What I heard and saw made me aware of the many cover crop options and their contribution to improving soil quality, combatting weeds, managing pests and fighting crop diseases.

The summit presentation by Wilson and Hoover gave me, a new organic planter, an understanding of the why, what and when of cover crops I should implement in my crop rotation in order to improve my soil. I’m planning to use a cover crop in my commercial garden after the snow peas and English shell peas finish in mid-July, which will probably be a non-legume such as rye. In my sweet corn plots, as the harvests are completed sequentially between late July September, I plan to use hairy vetch to rebuild my nitrogen for the next season.

Monitoring soil change

Professor Mary Barbercheck prepares to place a drop of soil solution (made mixing water and soil) onto a test paper to determine the soil’s pH level.

Mary Barbercheck, a Penn State professor of entomology, demonstrated four low-tech ways to monitor changes in soil quality:

Use test meters and test strips to monitor soil pH. The optimum range for most crops is between 6 and 7.5.

Use test strips to monitor soil nitrate which will show the amount of nitrogen in nitrate form that is available for use by plants.

Use a plastic barrier, water, a watch and a form that holds at least an inch of water to monitor the soil’s ability to take in water through the surface over time (infiltration). One inch of water soaking in per 30 minutes is considered to be moderately rapid.

Assess how easily an object can be pushed into the soil to monitor soil compaction. A penetrometer will actually measure the force being applied.

Also key to success is keeping records of these soil tests to have them for comparison later. In her presentation, Barbercheck introduced a soil-quality health card which I plan to use in my record keeping. This card lists items that can be assessed without the aid of technical or laboratory equipment, including soil tilth, compaction, water infiltration and generation, erosion, subsurface cover, soil life, soil organic matter, plant growth and plant roots.

There are three assessment description ranges (good, medium and poor). Within the ranges a numbered rating can be applied for more detail. Using a comparative approach, I can learn a lot about my soil. You can easily compare fields on your own farm or compare your fields with other farms' fields. For example, I could observe and assess that the Penn State fields would have a “good” rating compared to the same indicators in my farm fields—which I would place in the “poor” range.

Keeping natural N where it belongs

Robert Gallagher, an associate professor of cropping systems at Penn State, along with his students Justine Cook and Anna Starovoytov, presented management alternatives to improve nitrogen utilization from hairy vetch. They explained the need to manage excessive nitrogen from hairy vetch to prevent nitrogen leaching and environmental damage. This was surprising to me, because I wasn’t aware that N leaching was possible from a cover crop. I realized I needed to know: How much N does the vetch produce? What makes it leach away? How can you have a great crop of vetch, and keep it from becoming a pollutant?

Under good growing conditions and proper management, hairy vetch can supply enough N to even heavy nitrogen feeders. As a legume, it’s able to fix nitrogen from the atmosphere and convert it into a form that’s available to other plants. Vetch is managed to grow long enough to produce a huge amount of biomass, since the residue of the above-ground plant contributes significant nitrogen, in addition to what’s in the nodules on the roots.

Having a good crop of vetch depends on timely planting within the late summer to early fall sowing window, the weather in winter and spring, and the sowing date of the cash crops that follows. Heavy rains in the fall and spring can cause soil nitrogen to leach. Rye or other grains planted with the vetch can act as a “catch crop” for the nutrient nitrogen. These non-legumes take up nutrient N and prevent it from moving downward to below the root zone where it can become a pollutant.

Got your weed management covered?

Entomologist Tim Leslie, PhD., of Penn State, displays carabid beetles, some of which are granivores, or insects that eat only weed seeds. He described cover crops and weed management.

Timothy Leslie briefed us on beneficial macro-organisms relative to soil quality and weed suppression. He explained that some beetle species, known as granivores, feed exclusively on weed seeds, and demonstrated a low-tech insect trap he uses to assess and identify insect populations in the field.

Bill Curran, a professor of weed science, with team members Ruth Mick, Steven Mirsky and Matt Ryan, discussed cover crops in weed management. The highlights of their presentation were the mechanical tactics of mowing and the use of roller/crimper technology to create a barrier of mulch and residue for weed suppression.

I gained much insight about how cover crops will help us achieve our productivity goals in the coming years by improving soil quality and helping us manage weeds.

Ed Bialon farms 34 tillable acres 3.4 miles from Huntingdon, Pennsylvania. His cash crops are sweet corn, snow peas, English shell peas and mixed grass hay.