Soils in the Southern United States are notoriously low in fertility and organic matter. Methods for maximizing cover crop value need to be identified and adopted by Southern farmers. Winter annuals are by far the most commonly planted cover crops because they can be grown without interrupting the production of most agronomic and horticultural crops. However, summer annuals can produce significantly more biomass than winter annuals, thus providing additional benefits of cover crops. Summer annuals have the added benefit of disrupting insect pest, disease, and weed life cycles when those problems are at their peak in the South. A summer annual cover crop will change the typical crop rotation employed by most farmers, but will produce more biomass than the winter annual and thus have a greater impact on soil productivity. Cover crops are an important part of sustainable agriculture in their own right, but research has shown that incorporating livestock into cover crop rotations can magnify the impact of this practice. Livestock have been shown to increase biodiversity (especially in microorganisms), improve nutrient cycling, and speed the breakdown and incorporation of organic matter. This is a major benefit to agronomic and horticultural crop farmers, but there are also benefits for livestock farmers. In addition to poor soils, farmers also face the challenge of limited access to farmland, especially land suitable for livestock. If crop land were made available for livestock grazing for periods of the year, it would increase land access for livestock farmers. This would be particularly valuable to beginning or limited resource farmers who could begin without purchasing additional land. Economic benefits for crop farmers may come from the addition of livestock to an existing operation or by renting grazing land to nearby livestock farmers.
To create a model for the use of summer annual cover crops, a livestock farmer will partner with an agronomic crop farmer to develop a system that achieves both of their goals: forage for the livestock farmer and improved soil health for the crop farmer. The perspective of both farmers will be used to measure the value and weakness of the model and build on it in the future. Economic feasibility will be measured by keeping a detailed enterprise budget for the livestock operation based on enterprise budgets from Virginia Tech. This budget will provide the basis for the benefit to the livestock farmer as well as potential rental rates for the crop farmer. To measure changes in soil health, Sunn hemp (Crotolaria juncea) and Sorghum-sudangrass (Sorghum bicolor x S. bicolor var. sudanese) will be planted in separate treatments as cover crops. These crops were chosen based on their success growing in the area and their suitability for grazing. Using two crops will account for potential crop failure, and will also provide a useful comparison and demonstration. Treatments will include Sunn hemp (grazed and ungrazed) and Sorghum-sudangrass (grazed and ungrazed) across three replications, for a total of 12 randomly assigned plots. Each plot will be one acre in size. To measure changes in soil properties with respect to soil health, the Alabama Soil Quality Index test through the Auburn University Soil Testing Lab will be conducted. This test covers a variety of routine and non-routine soil health measures, including pH, extractable P, K Ca, Mg, soil organic matter, and soil respiration to estimate mineralizable N (http://www.aces.edu/anr/soillab/soilquality.php). Compaction, a concern with the use of grazing animals and a potential negative outcome of this system, will be measured using a soil penetrometer already owned by the farmer. These measurements will be taken before the experiment begins to establish baseline soil health. Data will be taken again at the end of each cover crop cycle, before the land is planted in a winter small grain. This experiment will include two cover crop cycles and two small grain crops over the course of two years.
Before planting the experiment began, a field was divided into 12 plots. A soil test was taken from each plot to get a baseline measurement of soil fertility, and soil compaction was measured using a penetrometer.
In May, the farmer drilled 12 plots – 6 of Sunn Hemp and 6 of Sorghum Sudan.Mature ewes grazed three plots of Sorghum Sudan and three of Sunn Hemp, leaving the rest ungrazed to determine the interactions of livestock with soil health.
Sheep were introduced on June 22, 2017, when the Sunn Hemp had reached a height of about 24 inches and the Sorghum Sudan had reached about 36 inches.
Sorghum Sudan was less resilient to grazing than Sunn Hemp, which branched prolifically after being grazed. Finding the proper grazing interval for Sunn Hemp was one of the major challenges to maximize harvest before plants reached above the grazing height of sheep. Also, once the Sunn Hemp set seed, the farmer noticed negative impacts from the sheep grazing the seed heads. It’s unclear if the effects were directly caused by the consumption of Sunn Hemp seed, which are toxic when consumed in a great enough quantity.
In the fall of 2017, all plots were bush hogged to terminate the crop and oats were drilled. Oats were fertilized according to recommendations from soil tests. Visual inspection showed a much more vigorous oat crop on the former Sunn Hemp plots than the Sorghum Sudan plots, which is likely due to Sunn Hemp being a legume.
Educational & Outreach Activities
The farmer and several farmers in the community have learned about grazing interval on cover crops, weed competition with cover crops, and are considering the potential of summer annual cover crops pared with winter annual cash crops.