Influence of Fertilization On Nitrogen and Phosphorus Runoff Losses During Roadside Establishment.

               Mississippi Department of Transportation (MDOT) roadside establishment practices specify 13-13-13 fertilizer be applied at rates from 561 to 1122 kg ha^-1. Thus, there are concerns over the impact of nitrogen (N) and phosphorus (P) runoff losses on surface water quality. A study was designed to evaluate the influence of N and P sources, rates, and application timings on nutrient loss and vegetative establishment. In July 2011 and June 2012, stainless steel runoff frames (0.75 x 2.0 m) were installed on a roadside near Starkville, MS. A bahiagrass (Paspalum notatum Flugge), tall fescue (Festuca arundinacea Shreb), sericea lespedeza [Lespedeza cuneata (Dum. Cours.) G. Don] and common bermudagrass [Cynodon dactylon (L.) Pers.] mixture was seeded within each frame. Eight fertilizer treatments consisting of 73.5 or 147 kg N and P₂O₅ ha^-1 as 13-13-13, poultry litter, ammonium nitrate, stabilized urea, polymer coated urea, or diammonium phosphate were applied immediately after seeding. Treatments were arranged as a randomized complete block with four replications. Runoff from natural and simulated (30 minute duration, 66 mm hr^-1 intensity) rainfall was collected and analyzed for PO₄^3--P, total P, NO₃^--N, and NO₂^--N. Preliminary results indicate differences in PO₄^3--P loss during natural and simulated rainfall occurred between P sources in both years. Total P, NO₃^--N, NO₂^--N, and PO₄^3--P losses were correlated with runoff volume from natural rainfall. Therefore, rainfall intensity rather than fertilizer source may have the largest influence on nutrient loss. However, NH₄⁺-N, total N, and sediment data are needed to better quantify total nutrient loss as a result of each fertilizer program.