Maximizing crop production is a multifaceted endeavor that includes careful management of the soil. In the past, adding fertilizer was considered soil management. Now, however, universities and extension educators are encouraging growers to take a more holistic approach.
Comprehensive soil programs have been established at numerous universities throughout North America and at some private companies. The goal of these programs is to help growers maximize soil health on their farms and thus optimize crop productivity.
Even on a specific farm, no two fields will be the same, so it's likely that multiple management approaches will be needed. The issues involved will determine the necessary strategy.
Soil management is an ongoing process, but for those involved in fruit production and other perennial plantings (e.g., asparagus) the preparation of the soil prior to planting is critical, as major modifications and improvements after planting will be challenging. For these long-term crops, the soil may need to be worked for a couple of seasons prior to planting.
Visual assessments and data from laboratory soil tests are both important to understanding the health status of the soil. For example, if the ground crusts or water ponds or runs off after heavy rain, these are signs of compaction and poor soil health. Soil color can give an indication of organic matter status, with darker soils generally having higher levels of organic matter. Soil friability and the presence of earthworms are indications of healthy soil. The biological activity, chemical composition and structure of the soil are all important.
A mixed-species seeding that included Tillage Radish, which has a large root mass and great ability for breaking up compacted soils.
Photo court esy of Cover Crop Solutions.
To test or not to test
In their book, "Building Soils for Better Crops," Fred Magdoff, University of Vermont professor emeritus of plant and soil science, and Harold van Es, a professor in the department of crop and soil sciences at Cornell University, say that soil tests are a key nutrient management tool.
Many laboratories perform soil testing, but for reliable year-to-year comparisons, soil samples should be taken at the same time each year and sent to the same laboratory every time. "Springtime soil testing is actually very good for the more comprehensive Cornell soil health test, which is recommended for growers who want to gain a more holistic perspective on soil health," said van Es.
Testing soils every few years is usually adequate, but consistent and thorough record-keeping is invaluable, as it allows you to follow the nutrient changes and to know when the optimum levels are reached. Recording crop yields for the fields is also important, as this allows you to see how they correlate with changes in soil health status. For growers who rent land, van Es suggests that those who plan to use the fields for several years perform a soil health analysis like the Cornell soil health test, which will provide a good assessment of the overall health of the land, along with recommendations on how to address specific soil constraints.
Soil erosion and compaction
Soil erosion and compaction are major issues for vegetable growers worldwide.
Soil erosion, as Magdoff and van Es explain in their book, "is the result of the combination of an erosive force (water, wind or gravity), a susceptible soil, and several other management or landscape-related factors."
Soil texture, aggregation and water content all affect erodibility. There are different types of erosion, with the results of wind erosion seen during the Dust Bowl era coming most readily to mind. However, other types of erosion occur on a much more frequent basis. For example, when tillage is performed on a sloping field with a moldboard plow, erosion is occurring with every tillage operation, as the soil is typically thrown down the slope with every pass. This type of erosion is unrelated to weather extremes.
Deep soils with good levels of organic matter can best tolerate erosion. For those who are working with soils that are more susceptible to erosion, there are several management practices you can use to alleviate the problem. The approach you choose will depend on several factors, including the type of erosion you're trying to control.
For many plants, soil compaction will result in poor growth, as the roots are unable to penetrate the soil and form the dense structure necessary for optimal yields. Some crops are more affected than others. For example, Magdoff and van Es report that an experiment performed in New York state showed that direct-seeded cabbage and snap beans were more affected by compaction than cucumbers, table beets, sweet corn and transplanted cabbage.
Following rain events, prolonged soil saturation may lead to an increase in certain soilborne pathogen populations, which can cause disease issues. In addition, there may be a reduction in beneficial soil microbial activity.
Susceptibility to compaction varies with soil type. Sandy soil, because of its ability to drain quickly, is less prone to compaction than fine-textured loams and clays.
Well-aggregated soil from an organically managed field that had been under cover crop management.
Photo by Harold van Es.
What can a grower do?
Management practices for alleviating soil compaction and most types of erosion will usually include the reduction of tillage, using cover crops and crop rotation.
Vegetable producers often have constraints on harvesting and have to work the land under less-than-ideal conditions. When possible, it's important to limit the use of heavy equipment on wet ground.
"In my view, the best approach is to start using permanent traffic lanes and beds in between," van Es says. "This way the compaction damage is limited to those lanes, and the rest of the soil does not get subjected to compactive forces."
He realizes this may be difficult to implement, so a second option would be to plant cover crops and till the soil to break up the compaction layers. He says the tillage tools should be shank-type, like Unverferth's Ripper-Stripper or Zone-Builder, if possible.
As always, soils with higher levels of organic matter will have fewer problems with compaction, as they drain more readily and provide better air circulation. Improving organic matter levels is an important component of soil health, whether achieved by the addition of manure or compost, or by the planting of cover crops.
There are many cover crops to choose from, so before making a decision, consider your climate, cropping system and the management goal. Thomas Bj<0x00F6>rkman, associate professor of vegetable crop physiology at Cornell University, has an excellent cover crop website that includes a cover crop decision tool, which growers in New York and neighboring states can use to identify the cover crops that best fit their management goal, planting time and growing time available before planting the next cash crop.
For example, if a producer wants to reduce soil surface hardness and is able to seed in the winter and commit the field for four to 10 months, the decision tool suggests planting white clover. For a winter erosion protection crop for vegetable growers who have to plant late, rye is the suggested crop, with oats, wheat, spelt or triticale as options if seeding occurs in the early fall.
Research continues on cover crops, with crop mixtures, as opposed to single-species stands, receiving attention.
A number of growers working in collaboration with university staff have identified excellent cropping systems that work well to alleviate specific soil health issues.
Wheat straw/mustard can stabilize soil when wind erosion is an issue. Serious wind erosion of the soil is evident in the top image, which shows a field with corn residue, whereas the field in the bottom image, in which wheat straw and mustard were sown, shows less erosion.
Photo by Dale Gies, Moses Lake, Wash.
Steve Groff is one of those growers. He produces pumpkins, tomatoes, sweet corn and other vegetable crops at Cedar Meadow Farm in Holtwood, Pa. Groff developed a cropping system that helped him to establish a no-till operation, resulting in virtually no soil erosion on the farm's 3 to 17 percent slopes.
"You could not pay me to till my land anymore," Groff says. "Soil erosion has gone from 15 tons per acre per year to almost nothing." He says that over a 15-year period, the soil's organic matter has increased from 2.7 to 4.8 percent, along with corresponding yield improvements of 10 percent. Groff started practicing no-till in the early 1980s and later began using cover crops as another soil conservation measure.
Groff is also co-owner of Cover Crop Solutions LLC (http://www.tillageradish.com), a seed company specializing in Tillage Radish and Tillage Radish seed mixes. Groff says, "I liked Tillage Radish for its compaction-busting ability and the way it made the soil noticeably mellow."
Using some brassicas as a cover can result in an increased likelihood of clubroot in brassica cash crops, but Groff says that no such issues have been observed with the Tillage Radish. "No piece of steel can benefit the soil like the roots of a good cover crop," says Groff.
Organic growers use cover cropping fairly extensively, but using no-till is difficult due to weed control. The majority of growers who practice no-till use some herbicides. Some growers, including Groff, use them at low rates. However, organic growers have few herbicide-type products in their toolboxes.
Rodale Institute has done work integrating no-till systems with cover crops specifically focusing on the needs of organic growers. A detailed technical bulletin (see sidebar), produced by Rodale Institute, can help organic growers who are considering incorporating no-till/cover cropping into their management practices.
Healthy soil is central to successful crop production, and planting cover crops and no-till are two practices that can help boost soil health. If you're interested in pursuing either or a combination of these systems, do your research first, starting with your local extension office.
The author is an agricultural freelance writer and plant pathologist who lives in the Finger Lakes region of New York.