No-tillage corn following alfalfa has become a viable option for alfalfa-corn growers seeking to reduce input costs, conserve soil moisture, and even improve corn yield in some cases.

To reap these benefits, however, growers must apply the correct alfalfa nitrogen (N) credit for corn following alfalfa, because too little fertilizer N reduces yield and net returns, whereas excessive N fertilization is wasteful and potentially damaging to the environment, and likewise reduces net returns.

Yet, while the fertilizer N response of first-year corn following alfalfa has been reported for more than 350 site-years of research, N responses under no-tillage have been reported for only 17 site-years. Moreover, university fertilizer guidelines differ on whether alfalfa N credit estimates should be adjusted for tillage intensity.

Specifically, when no-tillage rather than full-width tillage is used to terminate alfalfa, university guidelines from some Corn Belt states recommend that growers reduce the alfalfa N credit to first-year corn by one-half, and supplement with fertilizer N. But the majority of university guidelines for other states make no adjustment to alfalfa N credits for tillage systems.

To better understand whether the alfalfa N credit provides enough N for first-year, no-tillage corn, a team of researchers from the University of Minnesota and USDA-ARS evaluated the response of first-year corn grain and silage yield to fertilizer N rate and timing in a no-tillage system. The full report appears in the January-February 2013 issue of Agronomy Journal.

The research was conducted on seven farms in southern and central Minnesota and western Wisconsin, with soils ranging from loam to clay loam. The scientists applied five fertilizer N rates (0-160 lb N/ac) to corn at planting and a sixth rate of 40 lb N/ac as a sidedress application. They then measured corn yield at one farm in 2010 and six farms in 2011.

Their results demonstrated that moderate- to high-yielding, no-tillage corn (222 to 244 bu/ac) planted after a good stand of alfalfa did not respond to fertilizer N in either grain or silage yield. This confirms that alfalfa N credits can supply the entire N requirement of no-tillage corn following alfalfa and supports the guidelines of most Corn Belt states.

In other words, growers shouldn’t anticipate a yield response to fertilizer N in no-tillage corn following good stands of alfalfa in most cases. Instead, if they apply similar alfalfa N credits to first-year corn across tillage systems, they will likely maximize net returns and reduce excessive, residual soil nitrate-N, which is susceptible to loss by leaching and denitrification.

The presidedress soil nitrate test and the basal stalk nitrate test also were evaluated, but both tests had limited success at identifying the lack of response to supplement fertilizer N across farms. These results indicate that improved methods or tests are needed to accurately predict when fertilizer N is needed in corn following alfalfa under no-till conditions.

Material summarized from:

Yost, M.A., J.A. Coulter, and M.P. Russelle. 2013. First-year corn after alfalfa showed no response to fertilizer nitrogen under no-tillage. Agron. J. 105:208-214. View the abstract