Proper phosphorus (P) and potassium (K) fertilization is a key management component for maximizing alfalfa productivity. We have summarized the results of a six-year study where we determined the impacts of fertilizer P and K additions on alfalfa yield, stand persistence and nutrient use on a field in West-central Indiana with initially low soil test P and K levels (Bray P1 < 10 ppm and exchangeable K < 100 ppm). A factorial combination of four P rates (0, 50, 100, 150 lbs P2O5/acre) and five K rates (0, 100, 200, 300, 400 lbs K2O/acre) (twenty treatments) were arranged in a complete randomized block design with four replications of each treatment. Forage harvests occurred four times annually and yield, mass per shoot, shoots per area, and herbage nutrient concentrations were determined. Roots were dug in May and December each year to determine plant populations and find out whether plants were dying during the summer (May to December) or the winter (December to May). Total annual yield increased with P and K fertilization, but K fertilization did not increase first harvest yield. Yield increases were due to greater mass per shoot, not more shoots per plant. While K fertilization did not influence plant populations, P fertilization actually decreased plant populations. Plant K removal rates exceeded K fertilizer application each year even at the highest (400 lbs K2O/acre/yr) rate as long as some P was applied.