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Title: Phosphorus Uptake During Four Years by Different Vegetative Cover Types in a Riparian Buffer

item Kovar, John
item Moorman, Thomas

Submitted to: Nutrient Cycling in Agroecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2007
Publication Date: 2/7/2007
Citation: Kelly, J.M., Kovar, J.L., Sokolowsky, R., Moorman, T.B. 2007. Phosphorus Uptake During Four Years by Different Vegetative Cover Types in a Riparian Buffer. Nutrient Cycling in Agroecosystems. 78:239-251.

Interpretive Summary: Planting grass and tree buffers to filter nutrients and sediment from runoff water and near-surface groundwater is being promoted by conservationists to prevent streams and lakes from being polluted. However, the role of plant uptake in controlling phosphorus (P) losses in buffers is limited by our incomplete understanding of P cycling. This study showed that after four years the potential P removal by a mixed species buffer was 63% greater than from a bromegrass (Bromis inermis Leyss) buffer, primarily because of fast-growing cottonwood (Populus deltoids Bartr., clone 42-7) trees. Periodic harvesting of the mixed species buffer has the potential to reduce P losses to surface waters. The results will provide useful information to commercial growers, local environmental groups, Cooperative Extension and NRCS personnel interested in promoting buffers to help reduce negative agricultural effects on water quality.

Technical Abstract: Vegetative buffers have been shown to reduce nutrient loss associated with the transport of detached soil particles and may through plant uptake offer a means to capture dissolved nutrients moving to surface waters through the soil solution. The objective of this 4-year study was to evaluate changes in the biomass and phorphorus (P) content of the roots and shoots of plants growing in a multi-species vs. a single species riparian buffer as an index of P capture potential. Periodic harvests of above ground vegetation were combined with root cores to estimate the total standing biomass and the pool of P in plant tissue in three vegetative cover types. The mixed-buffer species included switchgrass (Panicum virgatum L.), an alfalfa (Medicago sativa L.)-smooth bromegrass (Bromis inermis Leyss) mixture, and a fast growing superior cottonwood (Populus deltoids Bartr., clone 42-7). An existing smooth bromegrass served as the single species control. Standing biomass increased in all three cover types during the 4-year study, with the greatest increases in the cottonwood (2345 g m-2) and switchgrass (1818 g m-2). Biomass production in the smooth brome control did not change during the study period. Based on the fourth year samples, standing pools of P closely paralleled total plant biomass and root surface area with cottonwood accumulating the greatest amount of P at 19.4 g m-2 compared to 4.3 g m-2 for the smooth brome control. Estimates of potential P removal via biomass harvest from a mixed buffer over a 4-year interval were 101 kg ha-1 compared to 62 kg ha-1 for the smooth brome control; a 63% increase in export capacity due largely to the inclusion of cottonwood. Addition of a fast growing woody species combined with periodic biomass harvests has the potential to reduce P movement to surface waters.