by Mark Dempsey, CFSA Farm Services Manager | Monday, Jun. 22, 2020 —

A field in dense cover crop

The idea that farmers should manage their land and crops for soil health is not a new one but has been gaining popularity and permeated into mainstream farming over the last decade. There are advocates all across the board: from small-scale, organic vegetable farmers, large-scale conventional grain producers, livestock farmers, to permaculturists, and so on.

While the messaging on how to prioritize soil health is more or less consistent, the details often depend on the farming system, climate, and soil type. Farming organically in the Southeast has its own set of soil management of challenges—owing to the highly weathered clays of the Piedmont, and the droughty, low fertility soils of the Coast Plain—which shifts the way we prioritize management strategies for soil health.

Below are five management priorities for improving soil health, tailored to our Southeastern soils.

 

1. Focus on building organic matter

While there is no special sauce in soil health, soil organic matter is the closest thing. It is both a bank of soil nutrients (released upon decomposition) and a parking lot for plant-available nutrients adhered by ionic charges (i.e., exchangeable cations), and building soil organic matter is the most important way to improve your soil’s ability to retain and supply plant-available nutrients. This is particularly relevant in soils with a limited ability to hold onto nutrients—i.e., those with low cation exchange capacity (7 or less)—which is common among our old clays and sandy soils in the Southeast.

Soil organic matter also makes up the glues that hold soil particles together to give soil its structure. Because good soil structure is critical for water infiltration and flow in soil, air exchange with the atmosphere, and resistance to compaction and erosion, any attempt to preserve or build organic matter can help preserve soil function and protect it from erosion. Soil organic matter can also improve the tilth of heavy clay soils and water retention in sandy soils.

Soil organic matter both drives soil health and is a product of a healthy soil ecosystem, and in the end, your aim should be to strike a balance between decomposition of organic matter (i.e., nutrient supply to crops) and building soil organic matter.

Organic matter in soil can be increased in three basic ways:

  • Direct applications of manure, compost, and other plant- or animal-based material
  • By reducing soil disturbance (see priority #2 below)
  • By maximizing crop biomass and time in the ground (see priorities #3 and #4 below).

 

2. Minimize soil disturbance (e.g., plowing, tilling, cultivating)

Soil disturbance—referred to here broadly as “tillage”—can increase the decomposition of organic matter, which has a cascade of negative effects including the rapid release of nutrients at a time when few if any crops are planted, or are capable of using these nutrients (e.g., seedbed/bed prep and early-season cultivation), as well as those addressed in priority #1 above. Tillage can also negatively affect crop symbionts such as mycorrhizal fungi and many root-dwelling bacteria. Perhaps most importantly, however, tillage leaves soil much more vulnerable to erosion.

Because today’s agricultural soils formed over the course of millennia, the soil should be thought of as a non-renewable resource and protected as such. In fact, if using the USDA’s rate of sustainable soil loss (3 tons/acre/year), that translates to 1/100th of an inch (clay soils) to 1/64th of an inch (sandy soils) per year.

Soil should be thought of as a non-renewable resource and protected as such.

All that said, tillage is not uniformly detrimental to soil health and it can be an effective tool for weed control and incorporating manure and other fertility sources into the soil. The important part is thinking of it as a tool used when necessary instead of as a requirement for successful crop production. The effect of tillage on soil health depends on soil type (coarse-textured soils are less affected), tillage conditions (dry conditions limit compaction), slope (the flatter the better), and organic matter additions (which can make up for losses due to tillage).

Because the two primary uses of tillage are weed control and cutting in fertility, ways to reduce tillage focus on alternative strategies for both.

  • Using cover crops or mulches to suppress weeds enables at least one no-till crop in the spring or summer and can be used creatively later in the season for a second no-till crop. For more information on how cover crops are used in organic low/no-till management, see Reduce Tillage and Increase Cover Crops for Soil Conservation on Your Farm.
  • No-till approaches to fertility management involve fertigation (i.e., fertilizer in irrigation water) and injection technology (specialized tech to place fertilizer underground, near the root zone, in row crops). Otherwise, fertility is typically applied and incorporated in the fall prior to winter cover crop establishment.

Roller-crimped cover crop mulches like this enable no-till crop establishment – an important way to reduce soil disturbance – and suppress weeds for much of the season. Credit: Claire Keene

Roller-crimped cover crop mulches like this enable no-till crop establishment—an important way to reduce soil disturbance—and suppress weeds for much of the season. Credit: Claire Keene

 

3. Aim for live plants in the ground 24/7/365

Live plants in the ground mean the soil is covered, protecting it from rainfall and slowing water flow across the soil surface, thereby reducing erosion. When compared to, say, only having the previous crop’s residue covering soil over winter, a well-established winter cover crop can reduce erosion and nutrient loss substantially.

Additionally, an ever-clearer picture is emerging that points to soil fertility being driven by soil life—both decomposers and plant symbionts—which is driven by the carbohydrates that plants feed to those microorganisms, and which is ultimately driven by the capture of sunshine by those plants. Specifically, the carbon that is fixed by plants through photosynthesis eventually makes its way underground to soil microorganisms through plant roots or the decomposition of aboveground plant biomass. That carbon-based food source feeds symbiotic relationships between plants and many types of microorganisms—including those that mine nutrients from soil minerals, dramatically improve access to soil water, and help the plant’s ability to resist disease and insect pressure, and it also feeds the soil foodweb that releases plant nutrients by decomposing organic matter from dead plants and soil organisms. In contrast, by leaving the ground bare and unplanted, the soil foodweb is on a leaner diet and soil symbionts aren’t well-fed by their host plants, leading to a subtle decline in myriad beneficial soil microorganisms. Thus, it is important that growers prioritize having live plants in the ground as often as possible, covering as much ground as possible with foliage, to minimize soil erosion and maximize the capture of sunshine across time and space.

While it may not be technically feasible to always have live plants in the ground (“24/7/365”), think of it as a goal. Growing a vigorous cover crop in your off-season is the first step toward that, and once you’re familiar with cover crop management, you can try relay cropping or intercropping with annual or perennial cover crops between crop rows for more consistent cover throughout the year. Research on cover crops interseeded into corn point to there being a sweet spot for cover crop establishment—where the corn doesn’t take a yield hit and the cover crop is well established going into winter—that can likely be adapted to other crops with some careful management and some trial and error. All that said, the important part about aiming for the 24/7/365 goal is having a well-established cover crop going into winter so that it can better reduce soil erosion and nutrient leaching over the winter.

Cover crops inter-seeded into corn when the corn was still young means there is no time after corn establishment when the ground isn’t covered, and ensures that the cover crop is well-established going into winter. If weeds are kept under control, a cover crop such as this could be roll-killed and planted to the next crop without tillage. Credit: John Wallace. Cover crops inter-seeded into corn when the corn was still young means there’s no time after corn establishment when the ground isn’t covered and ensures that the cover crop is well-established going into winter. If weeds are kept under control, a cover crop like this could be roll-killed and planted to the next crop without tillage.
Credit: John Wallace

 

4. Manage for high plant diversity and biomass

Diverse crop rotations, especially those that include a diversity of cover crops grown before or after cash crops, are optimal for improving or maintaining soil and crop health. Plant diversity leads to many different types of organic compounds being produced, which eventually feed the soil food web a diverse diet. The resulting nutrients released from diverse organic matter sources can increase a crop’s ability to grow in weedy conditions.

Plant diversity also maintains a diversity of symbiotic relationships between plants and microorganisms, many of which are yet unknown. Diverse crop rotations increase the disease suppressive capacity of soil, and cover crops can “mine” nutrients from deep in the soil profile (especially potassium) that are made available to subsequent crops.

High biomass crops have more leaf area and more extensive root systems, allowing more soil coverage by foliage and more stable soil aggregates, thus better protecting the soil against erosion. High biomass crops also increase organic inputs to soil, and, simply because they’re in the ground longer, are better able to mine nutrients from deep and foster relationships with symbionts.

Finally, when considering nitrogen management, legume crops should be used to increase soil nitrogen.

When considering ways to achieve this management priority, the easiest strategy is to incorporate a diversity of cover crops into your system if you haven’t already. If this isn’t as simple as filling a gap or making a basic substitution (low-value cash crop for a cover crop), then it may be worth taking a step back to evaluate your crop rotation and rework it so that there are cover cropping opportunities. If you can’t find or create a cover cropping window between crops, perhaps due to timing, then your next best strategy is to interplant between or within crop rows.

This diverse mix consists of four crop species (rye, hairy vetch, crimson clover, and radish) and is allowed to grow six feet tall before being terminated with a roller-crimper or flail mower. Credit: John Wallace.
This diverse mix consists of four crop species (rye, hairy vetch, crimson clover, and radish) and is allowed to grow six feet tall before being terminated with a roller-crimper or flail mower.
Credit: John Wallace

 

5. Apply nutrients sufficiently but judiciously

Apply nutrients sufficiently by replacing the nutrients that were removed by the last harvest and by applying additional nutrients for any subsequent crops with higher nutrient demands.

Be sure to test soil annually for:

  • macronutrients (P, K, Ca, Mg, S)
  • pH
  • cation exchange capacity, and
  • organic matter;

Testing for micronutrients (B, Cl, Cu, Fe, Mn, Mo, Zn) is advised for crops that are sensitive to specific deficiencies (e.g., boron in brassicas), although most standard soil testing methods test for both macro- and micronutrients. If deficiencies are observed in-crop (chlorosis, stunted growth, etc.), get the leaf tissue tested to help identify which nutrient(s) are deficient.

Be careful to not overapply phosphorus when using manure or manure-based compost, as the use of these materials often leads to a buildup of soil phosphorus, threatening water quality downstream as well as mycorrhizal symbionts. Because a well-established crop-mycorrhizae relationship can improve resistance to drought and pest pressure, special care should be taken to avoid the buildup of soil phosphorus.

Healthy, biologically active soil should be able to supply nutrients from organic matter and from soil minerals to meet a portion of the crop’s needs. The key to good nutrient management is to, first, follow sound fertilizer recommendations, and then, once you are familiar with your soil’s ability to supply nutrients, you may be able to apply fertilizer at rates lower than the replacement/sufficiency rate. While it’s not always necessary or possible to cut back on fertilizer rates, it has the potential to save you money and protect waterways.

With these five management priorities in mind hopefully can turn them into practices on your farm if you haven’t already.

 


Questions?

If you have any questions about translating these management priorities into practices please contact Mark Dempsey at [email protected].