Alfalfa Planting Date Effects on Nutritive Value during Early Stand Life.

The crop production and protection climate has evolved over the past several decades due to the development new pesticide products and improved genetics. Now, producers desire to know if they can use the new herbicide technologiesto plant alfalfa in the spring rather than late summer and begin recovering some of the establishment costs by harvesting hay in the seeding year. At NMSU's Tucumcari Agricultural Science Center, WL 424HQ.RR (FD 7) was sown every three weeks (6/5, 6/26, 7/17, 8/7, 8/28, and 9/18) in 2013 and 2014 and sprinkler-irrigated with treated municipal wastewater. Seeding year harvests were taken about 80 dap and again 28-35 days later, if possible, to allow for >42 d before hard freeze anticipated on about 10/31. Harvests in subsequent years were taken 6 times at 1-10% bloom (28-35 day interval) with at least a 42-day interval between the last two harvests. Subsamples were dried at 60°C for 48-h to determine dry matter concentration and to estimate nutritive value by NIRS using the universal alfalfa equation. Later planting may actually lead to reduced yields in the first year of an established stand compared to spring-seeded alfalfa. Although differences in crude protein and in vitro total digestible dry matter concentrations were observed due to planting date, crude protein and digestible dry matter production (Mg ha^-1) were nearly doubled by earlier planting simply due to greater yields (3.38 vs 1.81 Mg crude protein ha^-1, for alfalfa planted 6/5 and 7/28, respectively, and 11.28 vs. 5.90 Mg in vitro total digestible dry matter ha^-1, for alfalfa planted 6/5 and 7/28, respectively). Changes in the crop protection climate have led to a discovery with the potential to enhance dry matter and nutritive value production of alfalfa, at least in areas where semi-dormant (FD 6-7) varieties are grown.