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Research Project: Bridging Project: Integrated Forage Systems for Food and Energy Production in the Southern Great Plains

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Title: Climate effects on tallgrass prairie responses to continuous and rotational grazing

item ZHOU, YUTING - Oklahoma State University
item Gowda, Prasanna
item Wagle, Pradeep
item MA, SHENGFANG - Chinese Academy Of Sciences
item Neel, James
item KAKANI, VIJAYA - Oklahoma State University
item STEINER, JEAN - Retired ARS Employee

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2019
Publication Date: 4/30/2019
Citation: Zhou, Y., Gowda, P.H., Wagle, P., Ma, S., Neel, J.P., Kakani, V., Steiner, J.L. 2019. Climate effects on tallgrass prairie responses to continuous and rotational grazing. Agronomy.

Interpretive Summary: Tallgrass prairie systems are important forage sources for beef cattle in the Great Plains of the United States where cattle production is a major revenue for farmers in the region. Cattle grazing also acts as an effective way to maintain the prairie landscape. In contrast to yearlong (or growing season) continuous grazing, rotational grazing has been recommended as an effective tool to maximize livestock production and maintain sustainability of the operations since the mid-20th century. However, there has been a long history of debate over continuous versus rotational grazing by both rangeland managers and research scientists across the world that is yet not resolved. The interaction of climate and different grazing management strategies make it even more complex. To study the impacts of different grazing management under variable climate conditions, this study examined the vegetation phenology (reflected by Enhanced Vegetation Index, EVI) and productivity (reflected by Gross Primary Productivity, GPP) of tallgrass prairie in two pairs of continuous (C) and rotational (R) grazing systems during a span of ten years (2008-2017). Results showed that vegetation growth (EVI and GPP) in tallgrass prairie was mainly controlled by the seasonality of precipitation and temperature. The average EVI values only converged in very dry year in inter- and intra-treatments comparisons. The vegetation growth was also highly related to the original pasture conditions. The intra-treatment analysis showed that paddocks in rotational grazing systems had relatively small variations in different years, indicating that the rotational grazing created an even grazing pressure on grassland. Rotational grazing increased grassland productivity and thus had higher stocking capacity than continuous grazing systems under variable climate conditions.

Technical Abstract: Cattle grazing is an important economic activity in the tallgrass prairie systems in the Great Plains of the United States. Tallgrass prairie may respond differently to grazing management (e.g., high and low grazing intensity) under variable climate conditions. This study investigated the responses of two replicated (rep a and rep b) tallgrass prairie systems to continuous (C) and rotational (R) grazing under different climate conditions over a decade (2008-2017). The Enhanced Vegetation Index (EVI) and Gross Primary Productivity (GPP) were compared between grazing systems (C vs. R), while EVI was compared among paddocks under rotational grazing. The average EVI in rep a was usually higher than that in rep b which could be explained by different land characteristics (e.g., soil types) associated with different landscape positions. Similar to EVI, GPP was usually higher in rep a than rep b. The average growing season EVI and GPP were higher in rotational grazing than continuous grazing in rep b but not in rep a. The average EVI of paddocks in rotational grazing systems only converged in the growing season-long drought year (2011). In other years, EVI values varied from year to year and no paddock consistently outperformed others. The variations in EVI among rotational grazing paddocks in both reps were relatively small, indicating that rotational grazing generated an even grazing pressure on vegetation at annual scale. Overall, climate and inherent pasture conditions are the major drivers of plant productivity. However, the stocking rate in continuous grazing systems were reduced over years because of deteriorating pasture conditions. Thus, the results indirectly indicate that rotational grazing improved grassland productivity and had higher stocking capacity than continuous grazing systems under variable climate conditions. Adaptive grazing management instead of a fixed management system might be better for profitable and sustainable usage of the pastures.