Agroforestry on runoff nitrogen and phosphorus losses from three paired watersheds after 25 years of implementation

Non-point source pollution and agriculture have been correlated in a negative context. Conservation practices such as upland agroforestry buffers can help reduce the adverse impact of agriculture on water quality by reducing erosion and retaining nutrients in the fields. This study used a paired watershed approach to determine the effect of agroforestry buffers on runoff flow, total suspended solids (TSS), nitrate–nitrite (NN), total nitrogen (TN), and total phosphorus (TP) after 25 years of establishment and management. Linear models were developed for each parameter of interest during the treatment period and compared to previous models during the calibration period. Three paired watersheds were the subject of this study with a control watershed (no treatment), an agroforestry buffer (AB) watershed (trees + grasses), and a grass buffer (GB) watershed. The agroforestry watershed had 4.5 m wide buffers with [Pin Oak (Quercus palustris Muenchh.), Swamp White Oak (Q. bicolor Willd.), and Bur oak (Q. macrocarpa Michx.) with Redtop (Agrostis gigantea Roth), brome grass (Bromus inermys Leyss.) and birdsfoot trefoil (Lotus corniculatus L.)]. The grass buffer watershed had 4.5 m wide buffers with the same grasses planted in the agroforestry buffer watershed. The AB watershed had 62