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ARS Home » Midwest Area » St. Paul, Minnesota » Plant Science Research » Research » Publications at this Location » Publication #304588
Title: Opportunities exist to improve alfalfa and manure nitrogen crediting in corn following alfalfa

Author
item YOST, MATT - University Of Minnesota
item COULTER, JEFFREY - University Of Minnesota
item Russelle, Michael
item DAVENPORT, MAE - University Of Minnesota

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/24/2014
Publication Date: 8/1/2014
Citation: Yost, M.A., Coulter, J.A., Russelle, M.P., Davenport, M.A. 2014. Opportunities exist to improve alfalfa and manure nitrogen crediting in corn following alfalfa. Agronomy Journal. 106(6):2098-2106.

Interpretive Summary: Nitrogen fertilizer is one of the most expensive inputs in contemporary crop farming, but many farmers have alternative and lower cost nitrogen sources, namely legumes and livestock manure. The increased nitrogen supply is called the legume or manure nitrogen credit, which can offset the need for fertilizer nitrogen. Ignoring these nitrogen credits decreases profit and increases the risk of water and air pollution. In this research, we learned how much nitrogen Minnesota farmers apply to the first and second crop of corn grown after the legume, alfalfa. About one-half adopted the University guidelines for the alfalfa nitrogen credit to the first corn crop, but only one-third adopted the credit in the second year corn crop. For those who also applied manure in the rotation, adoption of the legume and manure nitrogen credits dropped to 30% for first corn crop and 25% for the second. Some of the nonadoption of nitrogen guidelines may be related to the lack of an improved nitrogen recommendation system that is more reliable. But there also is a need to develop better understanding of the current nitrogen guidelines, since the vast majority of farmers appear to be using outdated guidelines. We learned that these farmers relied on several sources of information to make their fertilizer decisions, and this will help target future educational efforts.

Technical Abstract: A survey was conducted in 2012 to evaluate the acceptance of fertilizer and manure N extension N rate guidelines for corn (Zea mays L.) grown as the first (AC) and second (ACC) crop following alfalfa (Medicago sativa L.) during 2009 to 2011 in Minnesota. There were 421 valid responses for AC and 273 valid responses for ACC. Adoption rates were higher when manure was not applied; almost one-half of growers adopted 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. In most cases, the odds of nonadoption also increased when corn yield goal was used by growers as a factor for determining fertilizer N rates for AC and ACC. Nonadoption of N guidelines in AC increased the odds of nonadoption in ACC, whether manure was applied or not. Growers’ past experience and soil testing lab recommendations were rated as the most reliable information sources for N management. Several opportunities remain for improved N management in AC and ACC. Further research and education are needed to increase adoption of alfalfa and manure N credits and especially to reduce manure N applications to AC and ACC, which often require little or no additional N beyond alfalfa N credits. Efforts should involve multiple stakeholders and may require improved, more field- or site-specific, N guidelines for AC and ACC.