Effect of Potassium and Harvest Time on Forage Accumulation and Potassium Uptake of Alfalfa.

Fertilizing alfalfa (Medicago sativa L.) with potassium (K) along with harvesting at the right time could be a viable option to offset the current trend of plateauing alfalfa production. Unfortunately, limited information is available of K and its interaction with harvest time on growth and productivity of alfalfa. A field study was conducted at the University of Wyoming James C. Hageman Sustainable Agriculture Research and Extension Center at Lingle to determine effect of K on forage accumulation and K uptake on alfalfa under two harvest schedules. Treatments included two cultivars (“Hi-Gest 360”; “AFX 457”), four K rates (0, 56, 112, and 168 kg K₂O ha^-1), and two harvest times (early harvest, late bud to early (10%) bloom; late harvest, 7 days after early harvest). The study was initiated in 2016 with four replications in a randomized complete block design. There were four harvests in 2017 at each harvest time. Differences were observed among K rates and cultivars (P < 0.05) for forage accumulation and K uptake. Hi Gest 360 (8372 kg ha^-1) and AFX 457 (8283 kg ha^-1) had the highest total forage accumulation at 168 and 112 kg K₂O ha^-1, respectively. This indicates that Hi-Gest 360 requires high levels of K and AFX 457 requires moderate levels of K for increased yields. Both Hi-Gest 360 and AFX 457 had the highest total K uptake of 360 kg ha^-1 at 168 and 112 kg K₂O ha^-1, respectively. Harvest time did not affect (P > 0.05) forage accumulation and K uptake. However, on average, late harvest had high forage accumulation (2260 kg ha^-1) and K uptake (87 kg ha^-1) compared to forage accumulation (2055 kg ha^-1) and K uptake (81 kg ha^-1) in early harvest. First year’s results indicate that K application can influence sustainable alfalfa production in longer term.