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.