Saturday, April 20, 2024

Cover Crop Basics

Are They Right For You And Your Operation?

Editor’s Note — Hunter Frame, Virginia cotton specialist and Tidewater Agricultural Research and Extension Center field crop agronomist, recently sat down with associate editor Cassidy Nemec to discuss the benefits, challenges and basic components of cover crops. Read the following Q&A to find out whether cover cropping might be worth exploring for your operation.

Q. How do I know if the ground in my area is suitable for cover crops?

A cover crop plot containing cereal rye, crimson clover, hairy vetch and wheat.

A. All soil/ground is suitable for cover crops. The ground that is historically more weathered, eroded and/or tilled may often have the greatest returns in the short term from cover crops. Ground that has lower productivity (yields) is going to produce lower biomass levels than more productive ground, which also means less nutrient cycling. An important point to remember is that if you are looking to improve less-productive ground with cover crops, it will be a long-term commitment. Current results from a long-term experiment in Virginia shows that cover crops coupled with conservation tillage systems increased soil carbon 50% over the conventional control in just six years.

Q. What are some initial considerations I should have when just starting to think about implementing cover crops into my operation?

A. The primary consideration is “what are your operation’s goals?” Do you want to improve soil chemical and physical properties? Nutrient cycling? Weed control? Take advantage of cover crop cost share programs? Each objective will result in different species selection, biomass goals and management of cover crops.

Q. Based on research up to this point, what type(s) of cover crops have shown the most benefit? For yield? For weed control? For plant health?

A. So overall, if you want to manage cover crops for the short-term, you are looking at nutrient cycling from green manure crops. To achieve this, managing legumes for high biomass will give you the most bang for your buck. Species such as hairy vetch, crimson clover and Austrian winter peas are the safest options for winter annual covers throughout the cotton belt. These have shown to have high nitrogen and potassium cycling (>200 pounds of N or K2O per acre), which are the most advantageous to cotton production. We have shown in Virginia that we can grow cotton without additional fertilizers following a crimson clover/hairy vetch cover and maintain lint yields 1,100 pounds to 1,500 pounds per acre.

If weed control or building soils is your primary goal, having a small grain (cereal rye, triticale, oats, wheat or barley) in the mix is a necessity. These high carbon-to-nitrogen (C:N) ratio covers with small grains provide a great mulch to limit weed emergence. However, to increase the benefit, you will need to maximize biomass for greater effect.

These covers all provide carbon to the soil and have the potential to increase soil carbon and organic matter, which will aid in improving soil structure, water holding capacity and nutrient-holding capacity.

Q. How do I go about getting started with cover crops? NRCS? Extension office?

A. The first thing to do is define your goals and be realistic in what you want to achieve. Then plan out what species you may want to plant to achieve these goals. Then you can research and look into programs through NRCS and state agencies that have cost share programs. There are good resources across the cotton belt on characteristics of different cover crops and what their greatest benefits might be.

Q. What if I tried cover crops last year, but they didn’t really add any benefit? How long might it typically take to see an added benefit?

A. Again, it depends on the goals. If you are looking to reduce your fertilizer bill, then biomass is king, and you need to have a legume in that mix or just use a single legume species. You should be able to see the impact of a legume cover in the first year as that nitrogen will be released to the cotton following the cover crop. Again, if you have biomass levels of 4,000 pounds to 8,000 pounds of dry biomass per acre, there should be enough nitrogen and potassium to supply the cotton for high yields.

To improve soil quality or productivity is the long-term objective. It will take multiple years to see the benefits of cover crops when coupled with other conservation practices. You should start to see some measurable benefits in three to five years.

“Current results from a long-term experiment in Virginia shows that cover crops coupled with conservation tillage systems increased soil carbon 50% over the conventional control in just six years,” Frame said. Pictured here are cereal rye, crimson clover and hairy vetch cover crops in a field.

Q.

How do I manage the cover crop?

A. This is where growing high biomass cover crops can become difficult in a cotton production system. When you have 5,000 to 8,000 pounds of dry biomass per acre, there is a substantial residue mat to plant through. Seeding depth is critical for cotton and ensuring that 0.5-inch to 0.75-inch planting depth is essential for having cotton emerge. This is going to take changes to planters and attention to detail when operating the planter. To maximize nitrogen cycling, legume covers need to be allowed to get to 50% bloom in order to maximize nitrogen accumulation for the legume. Doing this can sometimes delay cotton planting as the cover is easier to plant through when it is completely dead. In Virginia, we are nearly all strip tillage, so ensuring a good kill aids in preparing a seed bed for cotton planting.

For small grains, you will need to allow that plant to get to a minimum of the heading stage. This will allow for greater biomass production and a high C:N ratio to allow for the residue mat to persist throughout the growing season to control weeds. Again, these can be tricky to plant through, and some of our producers have found that rolling small grain the same direction of planting is beneficial. We have experimented with leaving non-planted strips where strip tillage will be done the following spring, and this has resulted in better stand establishment. Another drawback to small grain cover crops is that nitrogen can be immobilized from the high C:N ratio, so cutting back a soil fertility program is not recommended, and your nitrogen fertilization rates may need to be increased slightly.   

Q. When do I terminate the cover crop? How long after planting?

A. For the Southeast U.S., cover crop termination is going to take place most likely in late March through early May depending on your latitude.  Again, you want to terminate at 50% flowering or heading depending on legumes and small grains. Cover crop variety selection is important to select species and/or varieties to synchronize flowering for optimum termination to achieve goals.

Cereal rye, crimson clover and hairy vetch cover crops.

If chemically terminating, it will take approximately two to four weeks for a complete kill of cover so that you can plant into it successfully. A complete kill is when all of the biomass is brown and desiccated to make it easier to cut through with coulters and double disc openers on the planter. You can also plant without terminating (planting “green”), and it would be beneficial to roll the cover in the same direction as planting, especially if you have strip tilling. These decisions largely depend on equipment available and how comfortable you are that you can successfully produce cotton stands for optimum yields.

Q. What about drier areas that lack excess moisture for another crop (ex. The cover crop is taking up the moisture I need to grow my cotton, etc.)? What would you recommend?

A. In areas where moisture can be limiting, cover crops can be detrimental to cotton establishment and early season growth. I would recommend consulting your state’s Extension specialist on best management practices for cover crops. This goes along with what information may be needed to ensure cover crops can work on your farming operation. Even in Virginia, we had a situation where late-planted cover crops delayed maturity until late May. As a result, soil moisture was depleted at the site and cotton establishment was poor. Situations can arise, even in humid regions, where soil moisture depletion can come into play using cover crops.

Q. How would fertilizer recommendations change with cover crops?

A. The one area where cover crops can have an immediate impact on economic returns to producers is reducing fertilizer costs, especially nitrogen costs in cotton. First, you have to select the appropriate legume species to maximize nitrogen uptake and potential release upon decomposition. For us in Virginia, this has been hairy vetch, crimson clover and Austrian winter peas. These species routinely can achieve biomass between 4,000 pounds to 8,000 pounds of dry biomass and can accumulate nitrogen in the aboveground biomass from 140 pounds to 210 pounds of nitrogen per acre.

Studies have shown that nitrogen application following legume cover crops can be reduced 50% to 100% while maintaining cotton lint yields of two to three and a half bales per acre. An additional benefit is the legume cover crops also uptaking 180 pounds to 250 pounds of potassium oxide per acre. This would be highly significant to cotton that suffers from potassium deficiencies. Research is ongoing to determine whether this potassium is plant available following termination.

“The one area where cover crops can have an immediate impact on economic returns to producers is reducing fertilizer costs, especially nitrogen costs in cotton,” Frame said. Pictured here is a cotton crop planted into cereal rye, crimson clover and hairy vetch.

If using small grains as cover crops, the opposite may be true regarding nitrogen fertilizer management. As the small grain cover crop elongates and approaches heading stages, a carbon penalty is incurred each day, meaning that the C:N ratio increases. As a result, upon decomposition, soil microbial communities will scavenge free nitrogen in order to metabolize the small grain biomass. Thus, they are competing with (also known as immobilization) the crop plant for applied nitrogen in the form of fertilizers. If the C:N is greater than 25, it may take more nitrogen fertilizer to produce the same lint yields due to immobilization.

There are trade offs depending on what system or objectives you may have for cover crops. Understanding these will help you plan a sound fertilizer management strategy prior to implementing cover crops on your operation.

Q. How do I go about getting started with cover crops? NRCS? Extension office?

A. The first thing to do is define your goals and be realistic in what you want to achieve. Then plan out what species you may want to plant to achieve these goals. Then you can research and look into programs through NRCS and state agencies that have cost share programs. There are good resources across the cotton belt on characteristics of different cover crops and what their greatest benefits might be.

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