Donna S. Morgan, Gentry, Glen T., Gurie, Jeffrey A.
Donna Morgan, Jeff Gurie and Glen T. Gentry
Best management practices in agriculture help reduce the amount of nonpoint-source pollution, such as sediment, nutrients and pathogens, from entering surface water and groundwater. These practices can be a voluntary means for agricultural producers to make their operation more sustainable and at the same time improve water quality. Studies conducted at the LSU AgCenter Dean Lee Research and Extension Center in Alexandria evaluated a number of practices used in livestock and forage production, specifically nutrient management and conservation tillage. Nutrient management is managing the amount, source, form, placement and timing of fertilizers and other plant nutrients while protecting the environment. Conservation tillage conserves soil, water and other resources by reducing tillage intensity. Altering any of these variables can affect not only forage production but the potential for pollutant runoff.
Conservation Tillage Study
In 2013, a two-year study was begun to evaluate how traditional and conservation tillage planting methods for winter forages affected forage growth and nutrient runoff in a cow-calf grazing system. Water quality data collected throughout the growing season resulted in higher concentrations of total phosphorus and phosphates in runoff from sod-seeded plots compared with prepared seedbed, drill seeded, and an unplanted or untreated plot.
In sod-seeded plots, the soil is not disturbed before planting, and seed is broadcast across the top of the sod. In a prepared seedbed, the land is cultivated, typically to a depth of 4 to 6 inches, before seed is planted. In drill-seeded plots, cultivation is kept to a minimum, and the seed is planted into narrow trenches cut into the sod.
Higher nutrient concentrations from the sod-seeded plots may have been due to fertilizer being applied to undisturbed, compacted soils, and nutrients were more vulnerable to heavy rainfall. However, the prepared seedbed offered more grazing opportunities compared with all other treatments.
Sources of Nitrogen Study
A second study conducted in 2015 included a winter ryegrass (Lolium) and a summer hayfield component, specifically Alicia bermudagrass (Cynadon dactylon). Fertilizer treatments included urea ($380 per ton), urea treated with the nitrogen stabilizer Agrotain ($443 per ton), and the controlled-released, polymer-coated urea Environmentally Smart Nitrogen ($480 per ton). For the winter season, ryegrass was planted into prepared seedbeds and received a total of 150 pounds of nitrogen per acre. Mature cows grazed the plots at recommended forage heights (8-10 inches) throughout the season. The Environmentally Smart Nitrogen plots received half the required total nitrogen at planting and the balance applied during the first week of January. The urea and urea + Agrotain plots received 30 pounds of nitrogen per acre after ryegrass reached 3-4 inches in height, with subsequent 30-pound-per-acre applications after each grazing session. Results showed no difference in runoff concentrations of nitrates across treatments.
Although the trials produced no differences in forage quality or average dry matter, the Environmentally Smart Nitrogen plots reached initial grazing height 10 days sooner than other treatments and recovered within 21 days after the first grazing. Because of this, those plots were grazed a total of six times by April 30, compared with five times on all other treatments.
The summer component included the same nitrogen sources, with the recommended 200 pounds per acre of total nitrogen applied for the growing season. Similar to the winter applications, the Environmentally Smart Nitrogen plots received half the recommended nitrogen in the initial application and the balance after the second hay cutting. To initiate growth in these coated-urea plots, a blend of 60 percent coated-urea and 40 percent urea comprised the first application. Urea or urea + Agrotain was applied to other plots at 67 pounds of nitrogen per acre initially and subsequently after the second and third hay cuttings. Data collected showed no differences in forage dry matter, quality or yield across treatments.
In summary, multiple variables can affect the amount of nutrients leaving a field or pasture as well as forage production and quality. Rainfall intensity, in relation to fertilizer applications, may be one of the greatest contributors of nutrient loss. Soil type and texture as well as vegetative cover at the time of rainfall also have a significant impact on nutrient concentrations and volume. Based on these results, growers should use this information and other relevant research to determine which management practices are beneficial to their unique production systems.
Donna Morgan is a conservation agronomist; Jeff Gurie is a research associate and livestock farm manager for the Dean Lee Research Station in Alexandria; Glen T. Gentry is an associate professor and research coordinator at the Bob R. Jones-Idlewild Research Station in Clinton.
(This article appears in the fall 2017 issue of Louisiana Agriculture.)
related article is in the summer 2015 issue of Louisiana Agriculture: Environmental
Impact and Forage Production of Various Ryegrass Planting Methods.
Water quality data collected throughout the growing season resulted in higher concentrations of total phosphorus and phosphates in runoff from sod-seeded plots compared with prepared seedbed, drill seeded, and an unplanted or untreated plot. Photo by Jeff Gurie