ARS | Publication request: SOIL RESISTANCE UNDER GRAZED INTERMEDIATE WHEATGRASS

Submitted to: Canadian Journal of Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 10, 2008
Publication Date: N/A

Interpretive Summary: Seeded perennial forages can be used to meet nutritional demands of livestock in the northern Great Plains. Among the forages available, intermediate wheatgrass has been found to be a high-yielding cool-season grass with excellent quality. Furthermore, intermediate wheatgrass has proven to be an adaptable forage, with applications for use as pasture or hay, as well as in soil restoration and conservation efforts. Despite its adaptability, use of intermediate wheatgrass has been limited because of its inadequate stand longevity under grazing stress. An evaluation was conducted near Mandan, ND to determine if the stand longevity of intermediate wheatgrass was affected by changes in soil properties due to grazing. Soil samples were collected from two intermediate wheatgrass entries grazed at three growth stages (early, mid, and late) after four years of grazing. Samples were analyzed for basic soil physical and chemical properties to a depth of approximately 16 inches. Infiltration rate was measured in each of the grazing regimes after sampling. Overall, grazing effects on soil properties were modest. Available soil NO3-N was over two-fold greater for intermediate wheatgrass grazed during the early stage relative to the mid- and late stages. Among the three grazing regimes, infiltration rates were lowest when grazing occurred in the early stage. Trends in available soil N and infiltration rates among grazing regimes may have contributed to greater regrowth of intermediate wheatgrass during the early stage. Collectively, results from this evaluation indicate grazing effects on soil properties would not be expected to negatively affect plant persistence of intermediate wheatgrass.

Technical Abstract: Intermediate wheatgrass [Thinopyrum intermedium (Host) Barkw. & D.R. Dewey subsp. intermedium] is a productive, high quality perennial forage that lacks persistence under grazing. Grazing effects on soil condition may contribute to this lack of persistence. An evaluation was undertaken to better understand the effects of grazing on soil properties within an intermediate wheatgrass pasture. The evaluation was conducted near Mandan, ND on a Wilton silt loam (FAO: Calcic Siltic Chernozem; USDA: fine-silty, mixed, superactive frigid Pachic Haplustoll). Soil samples were collected from two intermediate wheatgrass entries (Oahe and Reliant) grazed at three morphological stages (early vegetative, mid-culm, late boot) following four years of grazing. Samples were analyzed for basic soil physical and chemical properties to a depth of 40-cm. Infiltration rate was measured in each of the grazing regimes after sampling. Available soil NO3-N was over two-fold greater for intermediate wheatgrass grazed during the early vegetative stage relative to the mid-culm and late boot stages. Among the three grazing regimes, infiltration rates were lowest when grazing occurred in the early vegetative stage. Trends in available soil N and infiltration rates among grazing regimes may have contributed to higher tiller recruitment and replacement ratios during the early vegetative stage. Differences in root biomass contributed to the presence of over 30% more particulate organic matter C under Reliant than Oahe at 5 to 10 cm. Overall, grazing effects on soil properties would not be expected to negatively affect plant persistence.