Feed costs are typically one of the largest costs of dairy and beef cattle production. Grazing is an option that can greatly reduce the need for, and cost of, hay production. The addition of legumes into the pasture can reduce the need for additional fertilizer.Unfortunately, grazing can also accelerate nutrient cycling and increase nitrogen (N) leaching. This study examines the effect of adding birdsfoot trefoil (Lotus corniculatus L.), a legume with condensed tannins (CT), to the grazing system. Condensed tannins are noted for their ability to improve nutrient utilization and shift N excretion from the urine to the feces. Nutrient cycling under the grass-legume mixtures and grass monocultures were evaluated. The nitrogen content in urine and feces of cattle grazing forages with, and without CT, was also examined and compared to a traditional total mixed ration (TMR) diet.
What Did We Do?
Four grasses, tall fescue (Schedonorus arundinaceus Schreb.), meadow bromegrass (Bromus biebersteinii Roem. & Schult.), orchardgrass (Dactylis glomerata L.), and perennial ryegrass (Lolium perenne L.) in monocultures, and in binary mixtures with birdsfoot trefoil (Lotus corniculatus L.) were evaluated. The study was conducted at the Utah State University Intermountain Irrigated Pasture facility in Lewiston, Utah. Jersey dairy heifers (~450 lbs) were used to rotationally graze the paddocks with heifers being moved to a new paddock every seven days for a 35-day rotation cycle. Pastures were irrigated every two weeks. All pastures were fertilized with Chilean nitrate (25 lbs N/acre) in April. Grass monocultures also received Feathermeal (31 lbs N/acre) in the late spring/early summer, and an additional dose of Chilean nitrate (25 lbs N/acre) in July. Body weight, and urine and fecal (grab) samples were collected before each grazing event, and at the end of the grazing season. Urine samples were analyzed for urea-N on a Lachat FIA analyzer. Fecal samples were analyzed for total N and total carbon by combustion analysis using an Elementar varioMAX CN elemental analyzer, and ammonia-N on a FIAlab 2500 instrument. Soil samples were collected at the beginning and end of each grazing season, and analyzed for available N (nitrate and ammonia) on a Lachat FIA analyzer. Soil water (leachate) N was monitored by means of zero-tension lysimeters bi-weekly during the growing season, and as much as possible in the spring and fall. Leachate samples were analyzed for nitrate-nitrite concentration on a Lachat FIA analyzer. The amount of leachate produced from each lysimeter was measured, and total Leachate N determined. Forage protein levels were determined using NIR. Nutrient cycling in the urine and feces were analyzed and compared to the overall protein levels in the forage.
What Have We Learned?
Average daily gains were greater with the grass-legume mixtures than the monocultures (Figure 1). This is most likely due to the higher protein content of the grass-legume mixtures versus the grass monocultures (data not shown).
Both the urea-N concentration in the urine (Figure 2), and the fecal N content (Figure 3) were higher in the grass-legume mixtures than the grass monocultures. This is most likely the result of being fed a higher protein content diet in the grass-legume mixtures.
Although the grass monocultures were not heavily fertilized, and the protein content of the monocultures was lower than that of the grass-legume mixtures, nitrogen leaching observed in the leachate was generally higher under the grass monocultures.
Grass-legume mixtures may be able to more effectively capture nitrogen due to the differences in the rooting structure and the microbial populations. The grass-legume mixtures were also better economically.
The forage type explains approximately 40% of the variability. We plan to examine the impact of breed on the rates of gain and nutrient cycling next.
Rhonda Miller, Ph.D., Agricultural Environmental Quality Extension Specialist, Utah State University
Corresponding author email address
Blair Waldron, ARS Forage & Range Research Lab; Clay Isom, Utah State University; Kara Thornton – Kurth, Utah State University; Kerry Rood, Utah State University; Earl Creech, Utah State University; Mike Peel, ARS Forage & Range Research Lab; Jacob Hadfield, Utah State University; Ryan Larson, Utah State University, and Marcus Rose, Bureau Land Management
Hadfield, J., B. Waldron, S. Isom, R. Feuz, R. Larsen, J. Creech, M. Rose, J. Long, M. Peel, R. Miller, K. Rood, A. Young, R. Stott, A. Sweat, and K. Thornton. 2021. The effects of organic grass and grass-birdsfoot trefoil pastures on Jersey heifer development: Heifer growth, performance, and economic impact. J. Dairy Sci. 104(10): 10863-10878. DOI: 10.3168/jds.2020-19524.
Rose, M., B. Waldron, S. Isom, M. Peel, K. Thornton, R. Miller, K. Rood, J. Hadfield, J. Long, B. Henderson, and J. Creech. 2021. The effects of organic grass and grass-birdsfoot trefoil pastures on Jersey heifer development: Herbage characteristics affecting intake. J. Dairy Sci. 104(10): 10879-10895. DOI: 10.3168/jds.2020-19563.
Funding for this project was provided by OREI, Western SARE, and Utah State University Experiment Station.
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