Grazing management, season, and drought contributions to near-surface soil property dynamics and greenhouse gas flux in semiarid rangeland

Authors: Liebig, Mark; Kronberg, Scott; Hendrickson, John; GROSS, JASON - Us Forest Service (FS)

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2014
Publication Date: 5/14/2014
Publication URL: https://handle.nal.usda.gov/10113/59049
Citation: Liebig, M.A., Kronberg, S.L., Hendrickson, J.R., Gross, J.R. 2014. Grazing management, season, and drought contributions to near-surface soil property dynamics and greenhouse gas flux in semiarid rangeland. Rangeland Ecology and Management. 67:266-274.

Interpretive Summary: Rangeland soils are looked upon to serve as a foundation for ecosystem resilience under increasingly dynamic weather and market conditions. Studies evaluating management influences on soil properties within growing seasons and across consecutive years in semiarid rangelands are limited, yet such studies may provide insight into ecosystem resilience, particularly if the study period encompasses extreme weather conditions (e.g., drought). Given this context, we sought to evaluate near-surface soil property dynamics in three long-term grazing management systems in central North Dakota: two native vegetation pastures differing in stocking rate (moderately and heavily grazed) and a fertilized, heavily grazed crested wheatgrass pasture. Evaluations were conducted three times during the growing season (spring, summer, fall) over three consecutive years (2004-2006). High stocking rate and fertilizer N application within the crested wheatgrass pasture contributed to increased soil bulk density and extractable N, and decreased soil pH and microbial biomass compared to native vegetation pastures. Soil nitrate-N tended to be greatest at peak aboveground biomass, whereas soil ammonium-N was greatest in early spring. Drought conditions during the third year of the study contributed to nearly twice the amount of extractable N under the crested wheatgrass pasture and heavily grazed pasture, but not moderately grazed pasture. Regression analyses found significant relationships between greenhouse gas emissions and soil electrical conductivity, implying that the latter may serve as a useful screening property for identifying greenhouse gas ‘hotspots’ in grazing land. Overall, soil properties measured in this study suggest high stocking rate combined with fertilizer N application may compromise soil functions necessary to support and regulate key ecosystem services in semiarid rangeland.

Technical Abstract: Semiarid rangelands provide an array of ecosystem services, yet the role of grazing management and environmental conditions to affect rangeland soil function is poorly understood. A study was conducted to assess effects of grazing management, season, and drought on soil property dynamics and greenhouse gas (GHG) flux within semiarid rangeland. Grazing management treatments evaluated in the study included two native vegetation pastures differing in stocking rate [moderately and heavily grazed pastures (MGP and HGP, respectively)] and a fertilized, heavily grazed crested wheatgrass [Agropyron desertorum (Fisch. ex. Link) Schult.] pasture (CWP) near Mandan, ND, USA. Over a period of three years, soil properties were measured in the spring, summer, and fall at 0-5 and 5-10 cm, while soil-atmosphere fluxes of carbon dioxide, methane, and nitrous oxide were measured annually on one to two week intervals. High stocking rate and fertilizer N application within CWP contributed to increased soil bulk density and extractable N, and decreased soil pH and microbial biomass compared to native vegetation pastures. Soil nitrate-N tended to be greatest at peak aboveground biomass, whereas soil ammonium-N was greatest in early spring. Drought conditions during the third year of the study contributed to nearly two-fold increases in extractable N under CWP and HGP, but not MGP. Stepwise regression found select soil properties to be moderately-related to soil-atmosphere GHG fluxes, with model r-square ranging from 0.09 to 0.76. Among soil properties, electrical conductivity was included most frequently in stepwise regressions. Soil attributes measured in this study suggest high stocking rate combined with long-term fertilizer N application may compromise soil functions necessary to support and regulate key ecosystem services in semiarid rangeland.