Phosphorus uptake during four years by different vegetative cover types in a riparian buffer

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 P content of the roots and shoots of plants growing in a multi-species versus 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 dominated by either switchgrass (Panicum virgatum L.), an alfalfa (Medicago sativa L.)-smooth bromegrass (Bromis inermis Leyss) mix, or a fast growing superior cottonwood (Populus deltoids Bartr., clone 42-7). An existing stand of smooth brome served as the single species control. Standing biomass increased in all three cover types during the 4 years of study, with the greatest increases observed 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 4th-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 export 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.