Rechel, E., Novotny, T. and Ott, R. 2012. Lower levels of harvest traffic on alfalfa (Medicago sativa L.) have minimal impact on long-term yields. Can. J. Plant Sci. 92: 1253-1258. Studies quantifying the effect of harvest traffic on alfalfa yield often only analyze data from treatments where either 0% or 100% of the surface area of the field is trafficked. These do not represent traffic patterns in commercial alfalfa production operations. To further understand the impact of field traffic on alfalfa yield, different percentages of traffic at harvest were analyzed. Our objectives were to quantify the yield produced from different intensities of harvest traffic throughout a 4-yr production cycle. The experimental units were furrow-irrigated raised bed systems with four harvests per year on a Youngston clay loam. A John Deere 2955, weighing 4004 kg, trafficked 0, 21, 42, or 83% of the area of alfalfa plots 7 d after swathing. The 0, 21, and 42 % trafficked treatments did not reduce yield in any year. The 83% trafficked alfalfa had 7 and 10% lower yields in the second and third years of production but had no effect the first and fourth years. The cumulative 4-yr yield from the 83% trafficked alfalfa was 7% lower than the 0% trafficked alfalfa. Single passes of a tractor impacting a high percentage of the field (83%) decreased yearly yield but was not detectable until the second year. Yield was the same whether the experimental units received 0 or 42% traffic.