Submitted to: Environmental Science and Pollution Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2013
Publication Date: 8/22/2013
Citation: Sigua, G.C., Chase, C.C., Albano, J.P. 2013. Soil-extractable phosphorus and phosphorus saturation threshold in beef cattle pastures as affected by grazing management and forage type. Environmental Science and Pollution Research. 21(3):1691-1700. Interpretive Summary: The effects of grazing management and/or forage type that control phosphorus (P) cycling and distribution of pasture’s resources have not been sufficiently evaluated. Characterizing how nutrients vary across pastures is important for understanding how soil nutrients availability is controlling net primary productivity. Therefore, assessing spatial variability and distribution of P in relation to animal grazing with different types of forages is critical for predicting rates of ecosystem processes and environmental stability. The objective of this study was to evaluate the effect of grazing management (zero grazing versus rotational grazing) on the levels of Mehlich-1 extractable soil P and degree of P saturation in beef cattle pastures with bahiagrass and rhizoma peanuts. Overall, there was no net gain of soil P due to the presence of animals in pastures with rotational grazing. Averaged across years, soil P in pastures with rotational grazing and with “zero” grazing was less than the threshold above which a crop production and environmental caution. There had been no movement of soil P into the soil pedon since average degrees of P saturation in the upper soil depth while the average degree of P saturation in soils at bottom horizon. Our study revealed that rhizoma peanuts and bahiagrass differ both in their capacity to acquire nutrients from the soil and in the amount of nutrients they need per unit growth. Rhizoma peanuts which are leguminous forage would require higher amount of P compared with bahiagrass. The difference in the amount of P needed by these forages could have a profound effect on their P uptake that can be translated to the remaining amount of P in the soils. Periodic applications of additional P may be necessary especially for pastures with rhizoma peanuts to sustain their agronomic needs and to potentially offset the export of P due to animal production. Addition of organic amendments could represent an important strategy to protect pasture lands from excessive soil resources exploitation.
Technical Abstract: Grazing can accelerate and alter the timing of nutrient transfer and could increase the amount of phosphorus (P) cycle from soils to plants. The effects of grazing management and/or forage type that control P cycling and distribution of pasture’s resources have not been sufficiently evaluated. The objective of this study was to evaluate the effect of grazing management (GM) and forage types (FT; bahiagrass, Paspalum notatum, Flugge versus rhizoma peanuts, Arachis glabrata, Benth) on the levels of extractable soil P and degree of P saturation in beef cattle pastures. The GM treatments were “zero” grazing, where animal grazing was excluded using 10-meter x 10-meter metal fence exclosures and rotational grazing. The experiment was maintained on the same pastures for four years (2004-2007). The levels of soil P and degree of P saturation (averaged across FT and soil depth) of 22.1 milligrams per kilogram and 11.6% in pastures with “zero” grazing were not significantly (P = 0.05) different from the levels of soil P and degree of P saturation of 22.8 milligrams per kilogram and 12.9% in pastures with rotational grazing, respectively. On the effect of FT, levels of soil P and degree of P saturation were significantly higher in pastures with rhizoma peanuts than in pastures with bahiagrass. Average soil P and degree of soil P saturation at all pastures with “zero” and/or rotational grazing did not exceed the crop requirement threshold and dissolved reactive P, suggesting that pasture grazing by beef cattle appeared to have minimal (if any) effect on soil extractable P and degree of P saturation.