Livestock producers are always looking for ways to make their forage-based systems more economically and environmentally sustainable. One potential strategy is incorporation of a diverse mixture of annual grasses, legumes, and crucifer species over-seeded into a long-term commercial grazing operation. The grasses provide biomass both above ground for forage and below ground for soil microbial communities. The legumes fix nitrogen and incorporate it into the system. Crucifer species provide considerable root biomass and potentially retain soil moisture. The site is a bahiagrass (Paspalum notatum) perennial pasture located in southern Mississippi. The soil is a Loring Silt Loam, and area precipitation is approximately 150 cm annually. Soil samples will be collected and analyzed for physical, chemical, and biological properties. Bulk density and particle size analysis are the soil physical properties. Soil chemical assessments will include macronutrients, pH, soil organic matter (SOM), soil organic C (SOC), inorganic nitrogen and total nitrogen (TN) to 30 cm. The biological soil properties to be analyzed include fatty acid methyl ester biomarkers and the enzyme assays β-glucosidase and N-acetyl-β-glucosaminidase. The objective of this research is to determine the effect that cool-season annuals may have on soil quality in a warm-season perennial pasture over time and to determine the rate of change in soil health using this management strategy. This research may influence future decisions of livestock producers in how they manage their grazing operations.
- Compare soil health under earlier stages of similar management strategies
- Determine how long term inclusion of winter annuals in a perennial pasture affect soil health
Soil samples are collected twice per year: spring and fall. The soil samples are collected using a soil corer of 10.16 cm diameter to a depth of 30 cm which are sectioned into four 7.5 cm layers. Three samples are collected at three areas of each site for pseudoreplication at each depth for a total of twelve samples per site. The 0-7.5 cm and 7.5-15 cm depths are analyzed for biological properties and are transported in coolers and stored at -20°C. Analysis of total carbon and nitrogen; the nutrients phosphorus, potassium, calcium, magnesium, copper, sodium, sulfur, and zinc; and soil pH are carried out by the LSU AgCenter Soil Testing and Plant Analysis Laboratory on the LSU campus. Ester Linked-Fatty Acid Methyl Ester (EL-FAME) analysis identifies phospholipids in the soil belonging to specific microbial groups which provides information about the presence and abundance of the microbial groups such as Gram(-) bacteria, Gram (+) bacteria, actinomycetes, saprophytic fungi, and arbuscular mycorrhizal fungi. Gas chromatography is used in this procedure. To determine the nutrient cycling activity of these soil organisms, two enzyme analyses are conducted. The first is the β-glucosidase analysis which provides information about the carbon cycling activity of the soil organisms. The second is the N-acetyl-β-glucosaminidase analysis which provides information about the nitrogen cycling activity. The methods used in these analyses are following those of Tabatabai (1994). Soil nitrate and ammonium, the inorganic and plant available forms of nitrogen, are determined through potassium chloride extraction and filtration. For nitrate, a vanadium chloride reagent is added and the solution incubated for one hour in the dark at 37°C before being analyzed by spectrophotometry. For ammonium, a salicylate solution and a bleach/hydroxide solution are used as reagents and the mixture is only incubated for 50 minutes at room temperature in the dark before being analyzed by spectrophotometry. Particle size analysis is used to determine the soil texture or proportions of sand, silt, and clay of the soil. This is done using a hydrometer and a sodium hexametaphosphate solution. Soil organic matter is determined using the Loss-on-Ignition method. First the soil is oven dried at 105°C over-night and then placed in a muffle furnace at 400°C for at least 8 hours. The weights of the sample after drying and after ignition are used to determine soil organic matter content. Bulk density of the soil is determined for each location.
To address the first objective, the methods and analyses described above will be carried out on one farm that has three separate pastures: one that has been rotationally grazed for ten years, one that has been grazed for four years, and one that has just been converted from fallow ground to pasture. The ten year and four year pastures have been planted to a winter annual mixture for the past four years. Comparisons of data across these sites will address objective one. To address the second objective, these methods and analyses will be carried out each year until the project’s end in 2018. Year will be the replication.
To date, the soils under this management type (rotational grazing and overseeding of a diverse mix of winter annuals) have been found to have lower bulk density in pastures managed for 10 years (1.27 g/cm3) compared to the 0 years and 4 years (1.38 g/cm3). While organic matter (0 year: 2.8%, 4 year: 2.8%, 10 year: 2.9%), total nitrogen (.12%, .13%, and.14%), and pH (5.3, 5.4, and 5.9) were found to be higher under increasing years of management. There has been no effect of years of management on the soil microbial community structure or abundance. However, the enzyme activity has increased with increasing years of management. β-glucosidase has increased from 28 in 0 years to 33 in 4 years to 42 mg p-nitrophenol/kg soil/h under 10 years of management and N-acetyl-β-glucosaminidase did the same increasing from 25 to 34 to 42 mg p-nitrophenol/kg soil/h.
These trends of higher measurements under the 10 year treatment may be due to site characteristics, but gradual increases from 0 to 4 year treatments support an effect of years of management. As the enzymes utilize C and N, it may be that as these substrates increase so does the enzyme activity. pH may have also had an effect on enzyme activity. Grazing and winter annual management may increase soil health over time by increasing SOM, TN, and possibly TC as well as soil microbial enzyme activity. It can be concluded that these management techniques are not negatively impacting soil health.
Educational & Outreach Activities
- 2 oral presentations for LSU AgCenter Extension: 2018 Soil Health and Cover Crop Conference
- 25 participants in special session (total 180 participants over 2 days)
- Participants included crop and cattle producers, faculty, extension professionals, and NRCS agents
- 1 oral presentation for 2018 Acadiana Beef Cattle Field Day
- 100 participants
- Participants were cattle producers and extension professionals
- 1 upcoming poster presentation at the 2018 SARE Our Farms, Our Future Conference
- 1 upcoming oral presentation at the 2018 ASA & CSSA Annual Meeting
Despite no differences in the microbial community and soil organic matter, there has been a positive relationship between bulk density, soil pH, and microbial activity. Improvements in overall soil health in these low disturbance, high input systems may require longer time periods (>10 yrs), but improvements in some sensitive indicators suggesting that the combination of winter annuals and intense grazing may be a viable conservation management practice for pasture ecosystems.
As a graduate student, my knowledge of sustainable agriculture has expanded, and I believe that this project has demonstrated the ability of sustainable agriculture to improve soil health. Katy continues to exceed expectations in progressing towards her doctorate with her management of course loads and research requirements. She has stepped into the role of project manager for this research successfully and continues to meet the goals she has set.
Through the work done here Dr. Fultz and Katy have been invited to attend and meet with various producer groups to discuss the importance of soil health outside the existing AgCenter’s scheduled field days and workshops. There appears to be a growing interest in the potential use of and benefits associated with winter annuals in both pasture and row crop management.