First-year corn after alfalfa showed no response to fertilizer nitrogen under no-tillage

Published in Agron. J. 105:208–214 (2013) doi:10.2134/agronj2012.0334 Copyright © 2013 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. T majority of current university N fertilizer guidelines in the midwestern United States advise growers to use an alfalfa N credit (fertilizer N replacement value) of 112 to 168 kg ha–1 for fi rst-year corn regardless of tillage management, when ≥43 or 53 alfalfa plants m–2 are present at the time of alfalfa termination (Michigan, Ohio, Indiana, Vitosh et al., 1995; Wisconsin, Laboski et al., 2006; Nebraska, Shapiro et al., 2008; Illinois, Fernandez et al., 2009; Minnesota, Kaiser et al., 2011). Additionally, Missouri and Iowa N fertilizer guidelines for fi rst-year corn do not change for tillage (Killpack and Buchholz, 1993; Blackmer et al., 1997). Th e basis for tillage considerations in some of these state N credit recommendations was research conducted nearly two decades ago. Direct comparisons between moldboard plow and no-tillage systems on mediumtextured (silt loam and loam) soils in Ohio, Ontario, and Pennsylvania resulted in similar alfalfa N credits for fi rst-year corn grain yield (Triplett et al., 1979; Levin et al., 1987; Afl akpui et al., 1993). Wolkowski (1992) also found similar alfalfa N credits to fi rst-year corn grain yield with moldboard-, chisel-, and no-tillage systems on two silt loam soils in Wisconsin. In all four studies, the alfalfa N credit was the same across tillage systems, regardless of whether N fertilizer was required to maximize corn grain yield. In contrast, current university guidelines from Kansas and South Dakota advise growers to reduce the alfalfa N credit to fi rst-year corn by one-half when no-tillage rather than a full-width tillage system is used to terminate alfalfa (Leikam et al., 2003; Gerwing and Gelderman, 2005). It is reasonable to expect that the N credit would be lower under no-tillage because mineralization of organic matter can be delayed compared to tilled systems (Phillips et al., 1980; Kitur et al., 1984). Th e disparate recommendations among neighboring states indicate that questions about tillage eff ects on alfalfa N credits are still relevant. Current recommendations in midwestern U.S. states also advise growers to apply the same N credit whether fi rst-year corn is harvested as grain or silage. However, recent research on tilled soils in Minnesota suggests that fi rst-year silage corn can respond to higher rates of fertilizer N than corn harvested as grain (Yost et al., 2012). In no-tillage systems, few studies have evaluated the response of fi rst-year corn grain yield to fertilizer N (only 17 [Table 1] of more than 350 site-years of research on fi rst-year N credits [Yost et al., unpublished data, 2012]). Even fewer (only 3 site-years) have measured silage yield and they (Rasse and Smucker, 1999; Meek et al., 1994) found no diff erence in the response of fi rst-year silage corn to fertilizer N between moldboard plow and no-tillage systems on a loam soil in Michigan and an irrigated silt loam soil in Idaho, respectively. Neither article reported grain yield. Additional research is needed to determine whether N fertilizer requirements for fi rst-year corn are diff erent for grain and silage yield in a no-tillage system. More research also is needed to determine the validity of using the PSNT and BSNT for no-tillage corn following ABSTRACT Although fertilizer N response of fi rst-year corn (Zea mays L.) following alfalfa (Medicago sativa L.) has been reported for more than 350 site-years of research, N responses under no-tillage have been reported for only 17 site-years. To determine the rate of N fertilizer required for fi rst-year corn aft er alfalfa in no-tillage systems, on-farm experiments were conducted at seven locations in southern Minnesota and southwestern Wisconsin. Th e accuracy of the presidedress soil nitrate test (PSNT) and basal stalk nitrate test (BSNT) to identify the need for supplemental N in fi rst-year, no-tillage corn also was evaluated. Across seven site-years, no yield response to fertilizer N was observed for corn grain, cob, stover, or silage yield, confi rming that alfalfa N credits can supply the entire N requirement of no-tillage corn following alfalfa. Critical levels of PSNT used in other U.S. Corn Belt states, incorrectly predicted responses to supplemental N at all six locations where PSNT was measured (soil NO3–N concentrations were ≤18 mg kg–1), suggesting that critical levels may need to be reduced in no-tillage corn following alfalfa. In this fi rst report under no-tillage conditions, the BSNT concentrations in nonfertilized corn aft er alfalfa were in the marginal range at two locations (between 250 and 700 mg NO3–N kg –1) and optimum or above at the other fi ve locations, indicating that the BSNT incorrectly characterized N supply in two of seven cases.