Wheat: To Split or Not to Split—That Is the Question

Richard Taylor, Extension Agronomy Specialist; rtaylor@udel.edu

I’ve seen several small grain fields that had so much growth on them last fall that they look rather bad this spring because of winter injury on the lush fall growth (Photo 1). In many cases, you will be seeing new green growth starting up as we have more and more days with warming temperatures. In these cases, the plants are fully tillered but lack leaf area to get off to a fast start this spring. Nitrogen application will be essential to help the crop recover from the damage caused over the winter months when we did experience some very cold temperatures.

Winter injured wheat

Photo 1. Winter injury to wheat showing severe leaf symptoms from which the wheat was able to recover.

One of the most difficult decisions growers have to make is whether to apply in one single application all the nitrogen (N) the crop will need to obtain maximum yield. This decision is complicated by the fact that some fields tend to remain wet for long periods of time in the usually rainy spring or the worry that a wet spring will lead to the loss of a substantial portion of the applied N either through denitrification or leaching. If the small grain crop did not fully tiller last fall, it will require at least some N as soon after green-up occurs as possible. It will take some scouting to determine if there are adequate tillers present this spring to maximize crop yield. In research on intensively managed wheat in Virginia, the researchers determined that if more than 100 tillers are present per square foot of soil, additional N is not needed until the crop reaches the Feeke’s Stage 5 growth stage (the first node is visible or can be felt above the soil surface). Below 60 tillers per square foot, at least half the total amount of N should be applied now to encourage tillering. I generally count a side shoot as a tiller if I can see three leaves on the shoot. The leaves do not need to be fully developed leaves where the collar is visible on each leaf.

In research Bob Uniatowski and I conducted at the University of Delaware and research from other locations, we have seen some responses to split N applications ranging from about a 5 to a 10% yield increase for winter wheat. If your operation is set up to allow multiple or split N applications and if the fields in question usually dry out quickly enough to allow the needed equipment on the fields both now and around the time the crop begins to joint (Feeke’s growth stage 5), then a split of 50% of the total N at green-up and 50% around Feeke’s Stage 5 can increase your yield potential. If the field does not typically lend itself to more than one application timing, then a single N application can be effective. The single N application is most effective if it is applied shortly before or at crop green-up, unless the tiller count is above 100 tillers per square foot. The initial N is used by the crop to finish tillering and produce a vigorous root system. Late-season N applications at Feeke’s growth stage 5 will promote higher yield per kernel and increase the crude protein content of the grain but the N will have less effect on tiller number or ultimate plant height.

To distinguish between growth stage 3, when tillering is nearly complete and sheath elongation begins, and growth stage 5, when jointing begins, you should carefully dig or pull several plants from the soil in a number of locations across the field. Carefully clean away excess soil from around the roots and plant base and remove any loose leaves and leaf sheaths from the base. A sharp knife can then be used to split the central stem down the center to look for the growing point. The growing point will be a conically shaped object about 1/8 inch or less in length that will be located near where the roots emerge from the stem base. If the crop is still at Feeke’s growth stage 3, the growing point will still be below the ground right against the stem base where the roots emerge. At Feeke’s growth stage 5, the stem internodes (the stem portion between stem nodes which are felt or seen as slight swellings in the stem) elongate moving the growing point upwards about a half inch to an inch above the stem base and at or just above the soil surface. As the first joint elongates enough to move the growing point above the soil surface and additional internodes begin to elongate the crop will be at the beginning of growth stage 6.