Opportunities exist to improve alfalfa and manure nitrogen crediting in corn following alfalfa

We conducted a survey of Minnesota growers to determine the 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). There were 421 and 273 valid responses for AC and ACC, respectively. Adoption rates during 2009 to 2011 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 nonadoption increased when corn followed fair or good alfalfa stands relative to poor stands. In most cases, the odds of nonadoption also increased when corn yield goal was used as a factor for determining fertilizer N rates for AC and ACC. Nonadoption of N rate guidelines in AC increased the odds of nonadoption 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. The high frequency and rate of excess N application in this rotation highlights a pressing 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.