This past winter, intensive wheat management has received a lot of attention. In particular, Concord Environmental Equipment has been promoting a complete Intensive Wheat Management System. Some key elements of the system have been adopted from practices in Europe. The management decisions that are being discussed are to increase your seeding rates, to use tramlines, and to use fungicides to increase grain yield. One component of the intensive wheat management that is discussed as well is to split your total nitrogen requirement into two applications; one at planting and one at the 5 to 6 leaf stage. Many of the elements of the intensive wheat management system are very valid and good agronomic practices that are applicable for spring wheat production in the Northern Plains. However, we would like to provide some background to the split application of nitrogen as discussed by Concord Environmental Equipment. One of the premises used to promote the split application of nitrogen is that tillers waste valuable nitrogen and are not needed. The recommendation is to ‘starve’ the crop for nitrogen and limit the number of tillers and then provide adequate nitrogen for the main stem and first tiller. If the standard University of Minnesota recommendations for seeding rates are used, the population itself, not nitrogen, because of interplant competition rather than nitrogen is the limiting factor in the formation of the number of tillers. In addition, the wheat plant recycles the nutrients in aborted tillers.

The idea of splitting the total nitrogen requirement of the crop over multiple applications was first discussed in the early nineties. These discussions were the result of the work that had been done in Europe at the time. The applicability of that work to our region was questioned and Drs. John Lamb and George Rehm, Extension soil scientists with the University of Minnesota, and their co-workers conducted research throughout western and northwestern Minnesota, which compared a single pre-plant application to split (pre-plant + top dressed) applications of N fertilizer to hard red spring wheat. The trials were conducted at twenty-one sites in farmer’s fields over three years. Three levels of pre-plant soil N plus fertilizer N were developed (50, 100, and 150 lbs N A^-1) by soil testing to a depth of 2 feet and broadcasting urea in appropriate amounts prior to planting to obtain the desired N levels (soil test nitrate-N + fertilizer N). Five rates of top-dressed N fertilizer (0, 15, 30, 45, and 60 lbs N A^-1) were applied to the wheat at the 4 to 5 leaf stage within each level of pre-plant soil N using ammonium nitrate (dry). Grain yield (Figure 1) and grain protein (Figure 2) were used to evaluate the effects of the various N management strategies.

Applying N fertilizer as a top dress to the hard red spring wheat increased grain yields and grain protein only when there was not sufficient pre-plant N available (Figure 1). Top dressing 45 lbs N per acre increased grain yields by 6 bushel per acre when the pre-plant N level was 50 lbs per acre. When 100 lb N per acre was available prior to planting, 15 to 30 lbs top dressed N resulted in a 2 bushel per acre yield increase. In both cases grain protein increased by about a half to one percent. When the pre-plant soil N level was 150 lbs per acre there was no grain yield or grain protein increase with applications of top dressed N. Interestingly, maximum grain yields when pre-plant soil N was limited to 50 lbs per acre never equaled those produced by greater pre-plant soil N levels regardless of how much additional N was applied as a top dress.

The data strongly suggest that a split application N management strategy is not necessary to obtain optimum grain yields and grain protein in the Northern Plains. The data further suggests that a strategy where pre-plant soil N is maintained at low levels with subsequent applications of top dress N may result in lower grain yields than a strategy where adequate amounts of N are applied prior to planting.

An obvious difference between the work done by John Lamb and George Rehm and the approach taken by the Intensive Wheat Management System as promoted by Concord Environmental Equipment is that the later uses a liquid fertilizer rather than dry fertilizer as a source of nitrogen. No direct comparisons are available. The nitrogen has to move from the soil surface into the root zone to be effective. Adequate precipitation, even with the use of a liquid source of nitrogen, is essential in that regard. In sandy soils, where leaching is a problem, a split application of nitrogen at the 5 to 6 leaf stage may be very valid strategy to increase the efficiency of nitrogen use by the plant. In all other cases a single application of nitrogen prior to planting appears to be most economical.