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Title: Spatial distribution of soil phosphorus and herbage mass in beef cattle pastures: Effects of slope aspect and slope position

Author
item Sigua, Gilbert
item Coleman, Samuel
item Albano, Joseph
item WILLIAMS, MARY - Natural Resources Conservation Service (NRCS, USDA)

Submitted to: Nutrient Cycling in Agroecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/22/2010
Publication Date: 6/10/2010
Citation: Sigua, G.C., Coleman, S.W., Albano, J.P., Williams, M.J. 2010. Spatial distribution of soil phosphorus and herbage mass in beef cattle pastures: Effects of slope aspect and slope position. Nutrient Cycling in Agroecosystems. 89:59-70.

Interpretive Summary: Lack of a clear relationship between grazing practices and soil nutrients has been attributed to inherent landscape and soil variations, depth of soil sampling, and insufficient evaluation of nutrient distributions within pasture system. Characterizing and assessing spatial distribution of soil phosphorus and herbage mass in relation to landscape properties, land use or landscape positions is important for understanding how pasture sustainability can be managed and improved properly. Our reason for conducting this study was to determine the effects of different slope aspects and slope positions on spatial distribution of soil phosphorus and herbage mass in subtropical pastures. Soil and forage samples were collected from contiguous south-, north-, east-, and west-facing slopes across different landscape positions (top slope, middle slope, and bottom slope) in 100 ha of bahiagrass (Paspalum notatum)-based pastures from 2003 to 2006 in subtropical region of southeastern U.S.A. The results showed that north slopes had higher P concentration. Also we found that both forage mass and total soil P declined from the top to the bottom of all slopes. This means that both slope aspect and location on the slope are important for assessing nutrient concentration and forage production in cattle operations.

Technical Abstract: Characterizing and assessing spatial distribution of soil phosphorus and herbage mass in relation to landscape properties, land use, or landscape positions is important for understanding how pasture sustainability can be managed and improved properly. Our reason for conducting this study was to determine the effects of different slope aspects and slope positions on spatial distribution of soil phosphorus and herbage mass in subtropical pastures. Soil and forage samples were collected from contiguous south-, north-, east-, and west-facing slopes across different landscape positions (top slope, middle slope, and bottom slope) in 100 ha of bahiagrass (Paspalum notatum)-based pastures from 2003 to 2006 in subtropical region of southeastern U.S.A. Averaged across years, soils on the north-facing slope contained the greatest amount of soil P (12.4 mg kg-1) when compared with other slope aspects. The greatest herbage mass (averaged across year) of 2,967 kg ha-1 and the highest phosphorus accumulation of 7.7 kg ha-1 for bahiagrass were from the top slope position. There was a significant (p=0.05) decrease in the average herbage mass and phosphorus accumulation with decreasing slope (top to middle slope). Between the top slope and the bottom slope, herbage mass declined from 2,967 to 1,805 kg ha-1 while phosphorus accumulation was reduced by approximately 40% (7.7 to 4.6 kg ha-1). Results of our study may increase awareness on how the arrangement of food, water, and shelter and their interactions with topographic and landscape features can significantly influence distribution of animals and utilization of different pastures’ resources. Our study supports our hypothesis that slope aspect and slope position could be of relative importance in controlling spatial distribution of soil phosphorus and herbage mass.