August 2020 Articles

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Soil Health in Forage Systems

Soil Health in Forage Systems E.K. Twidwell, M.W. Alison – LSU AgCenter In the past several years there has been a great deal of interest in the topic of soil health. While this term is somewhat difficult to define, the Natural Resource Conservation Service (NRCS) defines soil health as “the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals and humans.” For many decades, soil health was determined by measuring the physical and chemical properties of soil. These measurements included such items as soil drainage, infiltration rate, fertility, and many others. However, one aspect of soil that has been neglected for many decades is the biologic factor. Soil can no longer be viewed as an inert growing medium, but rather as a living ecosystem comprised of billions of bacteria, fungi, and other microbes. This shift in thinking reflects the desire of producers, agricultural researchers, and other agricultural professionals to protect the long-term sustainability of soil, water, and cropping systems. The NRCS has outlined four basic soil health principles. These include: 1) minimize soil disturbance; 2) keep soil covered; 3) maximize plant diversity; and 4) maximize the period of living root growth. Presently there are many different public and private entities throughout the United States working to develop different cropping systems to optimize these four principles and strengthen long-term environmental sustainability. One major issue that remains is how to quantify soil health. Scientists are currently working to develop a broadly applicable, relatively inexpensive, yet scientifically robust soil health test kit for producers to use. There are many research studies currently being conducted across the United States that are dealing with various aspects of soil health. Perennial grass pastures, which are typical across the southeast US, are rarely extensively disturbed and maintain soil cover and live roots even when dormant. With Louisiana forage systems, the emphasis has been on evaluating different cool-season grasses, legumes, and brassica species for their impact on the soil health of pastures. The emphasis has been on seeding these cool-season forages into existing perennial warm-season grass pastures and measuring the effect on soil chemical, physical and biological parameters. Soil biological activity is primarily controlled by the availability of soil organic matter or organic exudates from the plant roots. The inclusion of cool-season annual forages provides actively growing roots during a period when root growth is minimal from warmseason grasses. It has been shown that the cool-season forages can increase soil carbon (C) and nitrogen (N) and enhance microbial activity and aggregate stability. Death and degradation of the annual forage roots leaves macropores in the soil which along with improved aggregate stability can lead to improved water infiltration rates. The various functional groups (grasses, legumes, and brassicas) were included in studies because they present different potential benefits. Grasses offer greater forage production as well as extensive root growth potential while legumes could enhance N input into the system and brassicas could reduce soil compaction because of larger taproots. Results indicate brassicas are not well suited for planting in warm-season perennial grass sods in the fall as slow development in this situation and winterkill minimize the effect of brassicas.