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Fluid Journal : Winter 2015
13 The Fluid Journal Winter 2015 concentration is illustrated in Figures 4 and 5. Data from Iowa are used to illustrate these relationships. While the slope of the relationships is between ear-leaf N concentration, and that of the various nutrient concentrations was unique for each element, the two hybrids performed similarly. The relationships for Iowa were linear in all cases, and generally similar for Illinois. Relationships between ear-leaf N versus P, K, and S were insignificant. The above relationships in Figures 4 and 5 for Iowa compliment the data from the Illinois and Nebraska locations. In general, nutrient concentrations increased as ear- leaf N concentration increased up to the point of N adequacy (i.e., 2.75% N). Figure 6 illustrates that nutrient concentrations tended to reach a plateau when ear-leaf N concentrations exceeded 2.75 percent N. Perhaps these plateau concentrations could serve as reference values when using the DRIS approach for assessing nutrient adequacy. Be Careful One might be tempted to conclude that increasing fertilizer N rates should increase yields because it increases the concentrations of other nutrients. In fact, one might also conclude that a little N fertilizer (approaching the 130 percent N rate) might even compensate for small deficiencies in other nutrients. This conclusion is probably erroneous because when N ions (nitrate or ammonium) are taken up, plants must also take up a companion ion with the opposite net charge. Summing up The second year of this study, funded by the Fluid Fertilizer Foundation, confirmed preliminary observations made in 2012. The take-home lesson might be that when evaluating tissue testing data, make sure the ear-leaf N concentrations are adequate before drawing conclusions about the adequacy of other nutrients. 0.0 0.1 0.2 0.3 0.4 0.5 0.6 1.0 1.5 2.0 2.5 3.0 Ear-Leaf (%) Ear-Leaf N (%) Iowa - 2013 Mg - P33D53 Mg - P1498 Ca - P33D53 Ca - P1498 Ca Mg Figure 4. Effect of ear-leaf N concentration on Mg and Ca concentrations at silking for two Pioneer brand hybrids in Iowa in 2013. 0 5 10 15 20 25 1.0 1.5 2.0 2.5 3.0 Ear-Leaf (ppm) Ear-Leaf N (%) Iowa - 2013 Zn - P33D53 Zn - P1498 Cu - P33D53 Cu - P1498 Zn Cu Figure 5. Effect of ear-leaf N concentration on zn and Cu concentrations at silking for two Pioneer brand hybrids in Iowa in 2013. 0 20 40 60 80 100 120 140 1.0 1.5 2.0 2.5 3.0 Ear-Leaf Fe (ppm @ silking) Ear-Leaf N (% @ silking) P1498 - 2013 Nebraska Iowa Illinois Figure 6. Effect of ear-leaf N concentration on Fe concentration at silking for P1498 at three sites in 2013. Dr. James Schepers is soil scientist emeritus at the University of Nebraska.