Title: Nitrogen fertilizer applications to corn after alfalfa? Author
Submitted to: Extension Publications
Publication Type: Other
Publication Acceptance Date: June 10, 2013
Publication Date: June 17, 2013
Citation: Riedell, W.E. 2013. Nitrogen fertilizer applications to corn after alfalfa? South Dakota State University Extension iGrow Publications. Available: http://igrow.org/agronomy/corn/nitrogen-fertilizer-applications-to-corn-after-alfalfa/. Technical Abstract: Alfalfa is a deep-rooted plant that fixes nitrogen (N) and takes N from deep in the soil profile and brings it close to the soil surface. Alfalfa helps build soil health by giving N-rich leaves, stems, roots and root exudates to the soil. Through the action of soil microbes, the N in this organic matter becomes available for other crops for a least two growing seasons after the alfalfa is killed. Farmers often wonder if it makes good sense to apply N fertilizer to corn after alfalfa. The effect of N fertilizer applications on the yield of first year corn after alfalfa has been extensively studied. These studies showed that N fertilizer was often applied to corn after alfalfa at rates greater than needed to attain maximum yields. These studies did not explore other potential benefits of N fertilizer applications to corn after alfalfa, such as increased kernel protein or mineral concentrations. Fertilizer N applications affect corn root growth, which in turn may alter the uptake of other minerals from the soil. It is possible that fertilizer N applied to corn after alfalfa at rates greater than those needed to increase yield may affect other essential mineral nutrients in grain. Because N fertilizer is expensive, we conducted further studies of crop and yield responses to N fertilizer on corn after alfalfa. This two-year field experiment looked at the effects of N fertilizer treatments (no N fertilizer, 65 pounds per acre, or 120 pounds per acre) on corn stalk dry weight and N mineral concentration at the tassel stage, as well as on grain yield and kernel components (protein, oil, starch, P, and K) in corn after alfalfa at the Eastern South Dakota Soil and Water Research Farm near Brookings, SD. Fertilizer N increased stalk N concentration but did not increase stalk dry weight. These results showed that increasing N fertilizer rates to corn after alfalfa resulted in the luxury consumption of N in corn stalks. Grain yields were not affected by N fertilizer treatments. Thus, luxury consumption of N by stalks at the tassel stage did not result in grain yield benefits. Yields of protein, oil, starch, P, and K kernel components, expressed as a pounds per acre, were also unaffected by increasing N fertilizer rates. We conclude that there was no advantage in applying N fertilizer to corn after alfalfa under the environment experienced during this experiment. Farmers who want to reduce the potential over-fertilization of corn after alfalfa should use a 2-foot soil nitrate test, applicable legume N credits, and realistic yield goals to support their N fertilizer application decisions.