Wheat Nutrition – Adding an Extra Touch

Richard Taylor, Extension Agronomist; rtaylor@udel.edu

With the current wheat price, many producers may be thinking of adding extra nitrogen (N) to push yield potential to the maximum. The high cost of N actually could limit any gain from this approach since we know that in most cases what limits yield are the environmental (water-primarily-and temperature) conditions during grain fill and not N availability. Wheat yield, like corn, responds to additional N in a way that for each additional pound of N applied the incremental increase in yield becomes smaller and smaller until the point of maximum economic yield (MEY). After the MEY point, although more N may increase yields slightly, the extra N actually reduces net profit per acre.

So, what extra touch can be used to increase yield. In a four year study, Bob Uniatowski and the author found that a split application of N could on average add an extra five or more bushels to yield even at the highest N rate applied in the study (160 lb N/acre). Although the actual proportion of N applied at each split wasn’t as important as using a split application, the rate of N for the first split (mid-February to green-up in March) should be larger than the second split (growth stage Feekes 5, first node evident above the soil surface) if the plants are not yet at full tiller, were planted late, or did not have enough available N last fall to fully establish. If the first application is at a higher rate, the extra N helps the crop complete the tillering process; encourages top growth and root formation resulting in a reduced impact from late-season stresses; and, most importantly, helps insure against the possibility that weather conditions will prevent the application of the second split.

The longer the time from N application to stem elongation, the greater the risk of N loss from volatilization, leaching, or denitrification. Thus, very early applications of N (mid-January to mid-February) potentially can reduce yield if only a single application is made. Where adequate fall N is available from the soil or applied at planting, late winter/early spring crop N needs will be low, so a later first application is preferred. Many growers apply N early in the spring to stimulate tiller production. The majority of yield comes from the primary tillers laid down last fall and an early spring N application or split N application will not alter this. However, the small but significant (especially at today’s wheat price) increase we observed can be partially explained by an increase in the number of secondary, smaller heads. Another likely factor is that some of the yield increase from splitting the N into two applications comes from the conservation of fertilizer N (providing late-season N if significant leaching, volatilization, or denitrification occurs). In our study, we observed a split effect even at very high N rates so both factors likely came into play during the study.

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