Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/18/2005
Publication Date: 1/1/2006
Citation: Pote, D.H., Kingery, W.L., Aiken, G.E., Han, F.X., Moore Jr, P.A. 2006. Incorporating granular inorganic fertilizer into perennial grassland soils to improve water quality. Journal of Soil and Water Conservation. 61(1):1-7. Interpretive Summary: Every year commercial fertilizer granules are spread on the surface of many permanent pastures and hay fields to increase forage yields, but this method allows valuable nutrients to be lost and water quality compromised when runoff from heavy rainfall carries the exposed fertilizer into streams and lakes. Research was conducted to evaluate a knifing method that incorporates fertilizer granules into the soil below the surface of permanent pastures. This study showed that the fertilizer incorporation method decreased nutrient losses in runoff water by more than 90%, while increasing hay production. These results are of interest to scientists, watershed managers, extension personnel, and agricultural producers because this method of incorporating fertilizer into permanent pastures could potentially lead to better water quality and higher forage yields on millions of acres.
Technical Abstract: Commercially-available inorganic fertilizers are often used by beef and dairy producers to increase forage growth on perennial pastures and hay fields, but the usual practice of spreading fertilizer granules on the surface of these grasslands leaves the nutrients exposed for transport in runoff, and for rapid N loss to the atmosphere as ammonia. We hypothesized that such problems could be minimized by using a knifing technique to move the fertilizer granules into the subsurface root zone of perennial forages, and conducted a study to determine the effect on runoff water quality. Plots were constructed on a hillside (8-10% slope) field with a silt loam soil covered by well-established bermudagrass [Cynodon dactylon (L.) Pers.] and mixed grass forage. Each plot had borders to isolate runoff and a downslope trough with sampling pit for collection. Inorganic 13-13-13 fertilizer granules were applied (1.34 Mg ha-1) by one of three methods: surface spreading, incorporation, or surface spreading on soil cuts. Each treatment had six replications and there were three control plots that were not fertilized. Runoff samples from natural and simulated (50 mm h-1) rainfall events showed that nutrient losses in runoff from incorporated fertilizer were statistically no higher than from control plots, but were usually at least 90% less than those from surface-applied fertilizer. Soil cuts slightly decreased nutrient losses from surface-applied fertilizer, but this effect was rarely significant. When compared to surface-applied fertilizer, the incorporated fertilizer not only improved water quality, but also showed a strong tendency to increase forage yield.