Editor’s note: The following was written by Anthony Bly, Jennifer Mueller, Troy White, Sandeep Kumar, and Tong Wang with South Dakota State University.
Planting cover crops and returning crop residues (stover) to the soil both add nutrients and improve overall soil quality. These practices are common with producers across the Midwest and have been recently studied by researchers to identify how they impact the release of greenhouse gases into the atmosphere.
Cover crops and crop residues can improve soil by impacting soil properties. Researchers have found that these management practices increased carbon in the soil, improved water infiltration and lowered bulk density.
These combined improvements mean healthier soil and improved yields for producers.
The plant residue left on the soil surface from cover crops or residues also leads to increased activity of the microorganisms in soil. Increased amounts of carbon and less standing water enhances microbial activity leading to even healthier soil.
Impact on greenhouse gases
Greenhouse gases, climate change and global warming are buzz words we now hear constantly. It is easy to get lost in all the information that is available, especially when it comes to agriculture. So, how do these things impact producers, our soil, and our management decisions?
Healthier soil from cover crops and returning residues leads to healthier microbe populations in soil. Microorganisms that are present on the soil surface release greenhouse gases as they undergo their natural processes. Therefore, crop management practices can directly impact the amount of these gases released by impacting the activity of the organisms present on the soil surface. This activity results in the release of greenhouse gases which contributes to changing air temperatures and rainfall totals.
Impact on soil carbon
Implementing diverse crop rotations and no-till practices are also common suggestions to reduce erosion, control pests and improve yields. These practices can also improve soil health through an increase in soil carbon levels.
Research has been done on both management practices, but researchers wanted to dive deeper and see how exactly they impact the soil.
There are two different types of soil organic carbon. The first is called the light fraction of carbon (LFOC). This is the most sensitive and responds to changes on the surface such as no till or crop rotations. This carbon influences nutrient cycling which keeps soil healthy and microorganisms active. This type of carbon is the free organic matter in the soil.
The second type of soil carbon is the passive pool, which is carbon that has combined with other minerals. This carbon can only be slowly altered by microbial activity, which means it can take years to impact this carbon pool. Both types are key pieces to healthy, stable soil.
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Common examples of crop rotations include a two-year corn/soybean rotation, a three-year corn/soybean/wheat rotation, or a four-year corn/soybean/wheat/oat rotation. These rotations lead to better nutrient availability and can also improve soil carbon.
No-till practices have also become more commonplace. This practice leaves crop residue on the surface which leads to healthier, more productive soil.
Both practices provide benefits, so combining these practices can be even more beneficial to producers. Researchers in South Dakota have found that implementing crop rotations (especially a four-year rotation) with no-till practices increases both types of soil carbon and leads to improved bulk density and soil structure. These soil improvements will be best seen when this combination is used over a long period of time.
Soil and switchgrass
Switchgrass (Panicum virgatum) is a tall, native prairie grass often seeded on marginal lands in South Dakota. It has gained popularity over the past decade not only as a source of biofuel and feed, but also as a method to improve soil properties.
With this growing popularity, researchers have taken a deeper look at how switchgrass improves soil’s physical, chemical and biological properties. Researchers also have identified the best application rates to fertilize switchgrass fields. This wealth of information can help producers make more informed decisions when considering seeding switchgrass on their own lands.
Over time, switchgrass improves soil properties in two ways. First, it increases organic matter in the soil through the decomposition of the plant structure and roots. Second, switchgrass has a deep root system that penetrates deep into the soil horizon. These two work together to improve soil’s physical and chemical properties, as well as microbe and biological health.
Research has shown that over a 10-year period, marginal lands seeded with switchgrass showed significant improvement in soil organic carbon levels, infiltration rates, saturated hydraulic conductivity, soil water retention and pore size distribution. Research also showed a significant reduction in soil bulk density and soil penetration resistance.
Overall it is clear that, over time, switchgrass significantly improves the physical and chemical properties of the soil.
Another key aspect of healthy soil is microbial communities. These consist of both microbes and enzymes in the soil and are crucial in soil health and nutrient cycles. These microbes decompose organic matter and release nutrients back into the soil. Researchers have found that switchgrass fields have improved microbe and enzymatic populations in soil. This increases soil organic carbon levels and leads to healthier soil.
Researchers have also taken a deeper look at the proper nitrogen application rates for switchgrass seeded lands. As with any crop, proper nitrogen application helps to increase yields and can lead to even further improvements in soil health.
Through analyzing varying application rates over time, researchers have found the “sweet spot” of N application to be around 123 lbs. ha-1. While adjustments may need to be made based on soil type and environmental factors, this amount provides a good baseline for producers in South Dakota.
As with any new management practice, implementing switchgrass on marginal lands can come with challenges for producers. Often producers are more comfortable with the methods they are already using. Producers may also have a general lack of knowledge about the benefits of seeding switchgrass or about the management strategies needed to be successful.
To combat this, often initial investments of time and resources are needed. However, over time, even the most compacted soils and marginal lands can be improved with the implementation of switchgrass, making it a useful tool to producers.