Strategies for N Transfer From Alfalfa to Wheat.

Terminated alfalfa (Medicago sativa L.) can provide nitrogen to the next crop, but it is unknown whether using glyphosate and/or tillage for stand termination would transfer the most nitrogen to the next crop. Studies were initiated at NMSU’s Agricultural Science Center at Tucumcari in 2006 and 2007 to evaluate the effects of a 2.5% glyphosate application and/or tillage on alfalfa stand termination and relative leaf chlorophyll the succeeding wheat forage crop using a factorial treatment arrangement with four replicates each year. Data were analyzed using SAS Proc MIXED procedures. The treatment effect was significant (P < 0.02) for % alfalfa in the harvested forage, but the year x treatment interaction also was (P < 0.02) because of a difference in herbicide efficacy between studies, possibly due to environmental conditions (0a, 0a, and 0a % alfalfa in the harvested forage for the sprayed only, tilled only, and sprayed/tilled treatments in the first study, respectively, and 20b, 0a, and 0a% alfalfa in the harvested forage for the sprayed only, tilled only, and sprayed/tilled treatments in the second study, respectively). The treatment effect was significant (P < 0.04) for relative leaf chlorophyll content (41b, 45a, and 46a SPAD readings for the sprayed only, tilled only, and sprayed/tilled treatments, respectively). Consequently, herbicide efficacy may not be reliable as a sole means of alfalfa stand termination and glyphosate application alone is not the most effective means of maximizing nitrogen release to the next crop. Additionally, both glyphosate and tillage are not necessary for those purposes.