Alfalfa Planting Date Effects.

Delivery of surface water for irrigation is frequently delayed in the Southwest for optimum spring plantings, but the availability of Roundup Ready® varieties enhances summer weed control options during establishment. Alfalfa was planted into plots (5 ft x 25 ft) on June 5 & 26, July 17, August 7 & 28, and September 18, 2013, in a Randomized Complete Block design with 3 replications. After the first planting, irrigations with Class 1B treated municipal wastewater were applied approximately twice weekly to the test area. Plots were harvested for yield using a self-propelled forage plot harvester as soon as possible after 80 days after planting and approximately 35 days after that, unless that interfered with a 42 day rest period between planting and the anticipated first hard freeze (about November 5). The last two planting dates were not harvested at all, consequently, zero yields were entered. Yield data were subjected to SAS Mixed procedures for tests of significance and means separation. First harvest yields of the earliest four planting dates were not significantly different despite differences in harvest date over shortening daylength and cooling temperatures. Only the first two planting dates were harvested twice and yields were significantly different leading to a difference in total yield, such that, planting on June 5^th produced significantly higher total yield than all other planting dates in the seeding year. Additionally, both harvests for that planting date yielded >1 ton/acre making them more economically feasible than individual harvests for the later planting dates, which averaged 0.57 tons/acre.