Surface application of phosphorus (P) and potassium (K) fertilizers to alfalfa (Medicago sativa L.) is necessary, but may result in nutrient stratification that could impact P and K uptake. Our objectives were to: 1) determine the effects of long-term P and K fertilization on soil P and K levels by sampling depth; 2) determine how P and K distribution influences fine root density and vertical distribution of alfalfa; and 3) the impact of P and K on taproot physiology. A factorial arrangement of P (0 and 75 kg/ha) and K (0 and 400 kg/ha) treatments was replicated in the field four times in September 2001. In June 2004, September 2004 and May 2005, root and soil cores were taken to depths of 60 to 100 cm. The root cores were divided into the following depth increments: 0 to 5 cm, 5 to 10 cm, 10 to 15 cm, 15 to 20 cm, 20 to 30 cm, 30 to 40 cm, 40 to 60 cm, and greater than 60 cm. Fine roots were gently washed free of soil, and quantified using WinRHIZO to determine root length density. Soil cores were analyzed for P and K concentrations at these corresponding depths. Taproot samples were taken in September 2003 and June 2004, September 2004, and May 2005. The roots were analyzed for volume, density, and organic reserves. Significant P x K interactions were observed, in the fine root analysis, for root length density at specific depths. Taproot volume nearly doubled for plants provided P and K when compared to plants receiving neither P nor K.