Great Bend Tribune
Published June 5, 2016
Part I
Since wheat harvest is a little ways off, let’s take some time to consider one of the next big things in crop production – Cover Crops. This has become much more than the interest of a “fringe” of crop production (organic farming and sustainable agriculture) and has entered the mainstream with Research and Extension along with the NRCS conducting research and promoting adoption by producers. The actual movement for cover crops really started around forty years ago with the organic/sustainable agriculture movement and has slowly gained acceptance in many quarters. This week, we briefly examine what a cover crop is. Next week examines what the potential benefits are and finally the objective reality of cover crops.
A cover crop may be generally defined as a crop planted primarily to manage soil erosion, soil fertility, soil quality, water, weeds, pests, diseases, biodiversity and wildlife in crop production systems. Some definitions are more precise, more along this line: a crop, usually a legume, planted to keep nutrients from leaching, soil from eroding, and land from weeding over, as during the winter. Finally, the NRCS uses this definition: “A cover crop is grasses, legumes, forbs or other herbaceous plants that are established for seasonal cover and conservation purposes.” In English, a cover crop is a planted when the soil would normally be bare or idle. It may consist of a typical crop plant or something less traditional like tillage radishes, vetches, pea species, sunn hemp, and many others. The cover crop may be terminated chemically, mechanically, or by frost/winter depending on what you planted.
They are generally planted in the fall for summer row crops and in early summer for winter crops such as wheat. The idea is they will trap nutrients, or even add nitrogen for legumes, and when terminated provided organic matter for the soil. They must be terminated early enough to facilitate adequate soil moisture for the crop to be harvested and to allow for timely planting. Cover crops differ from green manures, which may be considered a type of cover crop, in that a green manure is turned into the soil while actively growing. Typically, a legume is part of the plant mix. The idea is to provide nutrients and organic matter more rapidly than with a traditional cover crop. The difference is that often cover crops are left on the soil surface as part of a conservation tillage program.
What plants can make up cover crops? The list is pretty substantial and numbers over 100 entries by the USDA. A sampling includes winter and spring cereal crops such as wheat, oats, barley, rye, triticale; legumes such as clovers and annual Medicago species (like alfalfa), peas like cowpea and Austrian winter pea, and hairy vetch; grasses like sorghum-sudangrass hybrids or even just sudan grass; and species like turnips, radishes, amaranth species, canola, millets, and even buckwheat. This is just a partial list but you get the idea. What makes a suitable cover crop varies by region, climate, soil type and soil chemical environment.
Next week, how do cover crops accomplish all the benefits associated with them.
Part II
Published June 12, 2016
First, combines are rolling in Kansas and early reports are promising with good yields, test weights and protein levels. The rains and relatively mild weather allowed wheat to maximize filling and mature instead of dying, provided diseases didn’t interfere. The forecasted rains could slow down progress and lower test weights. Now back to cover crops.
Last week’s column provided an overview of what cover crops are. This week, let’s focus on their potential benefits. We will stay away from the exaggerated claims and focus on the agreed upon potential benefits (i.e. what mainstream institutions such as K-State have stated).
- Decreased fertilizer costs – This can be achieved in two ways. First, by planting legumes that fix nitrogen, a producer can capture nitrogen from the atmosphere for use by subsequent crops. The amount varies based on a number of factors. Second, some studies have shown producers can “mine” nutrients from deeper in the soil profile when deeper rooted taproot plants are used. These nutrients are then released as the cover crop is decomposed.
- Pest control – It is possible for a heavy cover crop to outcompete weeds for resources (water, nutrients, space, light). If the cover crop is markedly different from the harvested crops, it can interrupt disease and insect life cycles.
- Erosion control – A covered soil is more stable and better able to withstand wind and water erosion. Cover crops can “break” the force of the wind, absorb the energy of falling raindrops, and provide structural stability to keep soil in place.
- Improved soil physical and chemical environment – As the cover crops decompose they provide a food source for soil microorganisms and as they become humus release plant nutrients like any crop residue. For all soils, but especially the sandier ones, this provides a reservoir to hold plant nutrients, increase the water holding capacity of the soil, and provide for better soil structure which improves porosity, infiltration and aeration. For heavier soils, as the organic matter content in the surface horizon increases, the bulk density decreases and porosity increases. For compacted soils, cover crops like tillage radishes can help reduce compaction and break up hard pans. These benefits are most evident under strip and no-tillage.
- Improved soil moisture – For the reasons previously listed, the soil holds more moisture. Proponents also point to studies in places like Eastern Colorado and Western Kansas showing the cover crop making better use of available moisture than fallow systems, especially those using tillage for fallow. You are using the moisture to grow organic matter which benefits the soil in a variety of ways, including better water holding capacity instead of allowing over half of it to evaporate.
- Increased yields – Whether or not the cover includes legumes, there are yield benefits due to the previously listed reasons. When the cover crop is dissimilar (say a legume between grass crops) there is a yield benefit to the rotation apart from the nitrogen added by the legume.
These are the main benefits but there are other potential positives. Next week finishes the series with the potential downsides of cover crops and their potential fit in our area.