Soil Building Using Annual Forages
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Lots of farmers incorporate annuals into their forage mix at some point but it is usually from a cover crop standpoint; something to hold the soil and possibly be grazed or made into hay until their perennial grass comes back into season. However, with the ever-increasing selection of annuals available, you might want to consider adding annuals into your regular forage rotation from the aspect of soil building.
Soil building is all about increasing the overall health and growth capacity of your soil. Soil is a complex system of minerals, microorganisms and organic matter. Every soil type has a different composition of these “ingredients” but the “recipe” is basically the same. However, the amount of each does greatly affect how well plants are able to exchange nutrients, therefore grow, and the more organic matter and microorganisms, the more readily that nutrient exchange occurs. There are multiple aspects to soil building; we will cover increasing organic matter and decreasing compaction, both of which can be accomplished with annual forages.
Increasing organic matter: Depending on where you are located in the state, increasing your organic matter may be the most important thing you can do to amend your soil. Organic matter consists of living organisms (soil microbes) and partially decomposed plant tissue and animal waste, which can be broken down further into humic matter and non-humic matter (but we won’t go into that). Organic matter is important to plant growth and soil health for several reasons, not the least of which is the humic matter allows for greater moisture retention in the soil, which obviously is key for plant water and nutrient absorption, but also decreases the amount of erosion because instead of running right through or off the top of the soil, it allows for heavy rainfall to be absorbed like a sponge. The other important aspect of organic matter is the microorganisms. The organisms are composed of bacteria and mycorrhizae both of which help to decompose plant matter and animal waste into items usable by plants. You can add organic matter by incorporating compost, which is a great practice, but if you have more than a few acres to manage, this can get expensive very quickly. Annual forages give you the benefit of increasing your soils organic matter, while still giving your livestock something to munch, at a much cheaper price. Annuals increase your organic matter by incorporating trampled leaf matter and animal waste into the top couple of inches of soil. As the soil microbes break down the products they not only increase their own population because of the increase in availability of food but they also move the broken down material several inches further into the soil profile. It is an amazing positive feedback system!
As for which annuals do the best job of increasing organic matter, the answer is: They all do! Especially when planted as a mix of grasses or small grains, legumes and brassicas. Grasses such as millet, sorghum-sudan or crabgrass gives you tons of biomass. Legumes such as cowpea, vetch or clover will give a good bit of biomass as well with the added bonus of nitrogen fixation. Brassicas such as daikon radish, purple top turnip or tillage radishes provide a lots of biomass above the ground to be grazed, a tasty tuber treat under the ground if the animals happed to pull it up but also lots and lots of biomaterial that will breakdown if the tubers are left in the ground to decompose.
Decreasing compaction: Soil compaction is an issue in almost all soil types in traditionally farmed systems. Years of tillage, heavy equipment usage or minimally maintained perennial grasses all can contribute to compacted soil. Compaction restricts the amount of root growth in a plant which will in-turn reduce forage yields and can slow forage establishment. Since forage establishment is stunted compaction can also open the door for pasture weeds to take hold. Most annual mixes can be planted with a no-till drill which itself will help reduce compaction but the plants themselves are really what does the brunt of the work. As previously mentioned, brassicas added to a forage mix give a delicious and nutritious grazing option above the ground but under the ground these terrific tubers are pushing their way through the most compact of soils, allowing for water and subsequently nutrients and microbes to go where they could not have otherwise gone. Forage radishes have a taproot (the tuber portion of the plant) that can reach 8-14” in length!
Soil building is like making a long term investment in your soil health. If you would like to implement some soil building practices into your grazing systems contact your local extension agent to find out what options will work best for your farm.