Measuring soil nitrogen and moisture depletion at a distance gradient from perennial bunchgrasses

Authors: Harmon, Daniel - Dan; Clements, Darin - Charlie; Blank, Robert - Bob

Submitted to: Society for Range Management
Publication Type: Abstract Only
Publication Acceptance Date: 12/21/2020
Publication Date: 2/16/2020
Citation: Harmon, D. N., C. D. Clements and R. R. Blank. 2021. Measuring soil nitrogen and moisture depletion at a distance gradient from perennial bunchgrasses. Society for Range Management Virtual Annual Meeting, February 15-18,2021. 74:64. #379814

Interpretive Summary:

Technical Abstract: Perennial grasses are the most effective tool for biological suppression and long-term control of the invasive grass, cheatgrass. While the concept of an established perennial grass outcompeting an annual for resources is well known, the mechanisms by which the suppression of cheatgrass occurs involves complex plant-soil interactions. We theorize that perennial grass is depleting the available soil nutrients and moisture to the detriment of cheatgrass, which requires adequate soil moisture to germinate and available nitrogen to support high seedling vigor.The effect is seen on the landscape by the bare soil “suppression” rings that exist around perennial bunchgrasses. The size of the suppression ring can vary based on the species and vigor of the bunchgrass, and the annual weather conditions. Studies by Dr. Robert Blank USDA-ARS and others have measured the decrease in available soil nitrogen within the rootzone of perennial grasses. The most recent greenhouse study conducted by Dr. Blank determined a gradient of soil nitrogen depletion extending from the perennial grass rootzone. We designed a field experiment to examine this gradient. To conduct the field study, we located three stands of perennial bunchgrasses that exhibited cheatgrass suppression. We created a defined edge from the bunchgrass stand by using herbicides to create bare ground. Bare ground was maintained for 2 years prior to sampling to avoid measuring any immediate nitrogen root leaching. Because the sampling area was free of any plants the only moisture or nitrogen uptake that could occur was from the perennial grass. We collected soil at distances of 10cm, 30cm and 80cm from the bunchgrass and measured moisture and available nitrogen. Our results indicated a strong gradient of resource depletion was occurring. The degree of depletion has important management implications for determining desired perennial grass densities on the landscape that would enable long-term cheatgrass control.