Opportunities Exist to Improve Alfalfa and Manure Nitrogen Crediting in Corn Following Alfalfa.

A survey of Minnesota growers was conducted to determine adoption of extension N rate guidelines for fertilizer and manure for first- and second-year corn (Zea mays L.) following alfalfa (Medicago sativa L.) (AC and ACC, respectively) during 2009 to 2011. There were 421 and 273 valid responses for AC and ACC, respectively. Adoption rates were higher without manure; almost one-half of respondents adopted N rate guidelines for AC and about one-third adopted for ACC. With manure, adoption decreased to only 29% for AC and 25% for ACC. In all cases, the odds of adoption decreased when corn followed good or fair alfalfa stands relative to poor stands. In most cases, the odds of adoption also decreased when corn yield goal was used as a factor for determining fertilizer N rates for AC and ACC. Growers who did not adopt N rate guidelines in AC were less likely than others to follow guidelines in ACC, whether manure was applied or not. Respondents’ past experience and soil testing lab recommendations were rated as the most reliable information sources for N management, followed by fertilizer dealers and independent crop consultants. Additional information sources used for N management decisions included extension, family members, other producers, and public agencies. The high frequency and rate of excess N application in this rotation highlights a need for enhanced research and stakeholder engagement to increase adoption of alfalfa and manure N credits. In particular, there is a need to discourage manure applications to AC and ACC, which often require little or no applied N beyond alfalfa N credits. Efforts should involve multiple stakeholders and may require improved, more site-specific, N rate guidelines for AC and ACC.