As spring wheat planting gets underway, a soil scientist reminds farmers not to cut back on an important nutrient….phosphorus. "The yield of wheat, even at very high yield levels, comes almost entirely from three types of stems, the main stem, the T1 tiller, and the T2 tiller," says R. Jay Goos, Professor of Soil Science at NDSU. Goos explains, "The T1 tiller begins to grow when the main stem is between the 2 and 3 leaf stage, and the T2 tiller begins to grow about a week later. If plants are short of phosphorus at these early stages, the T1 and T2 tiller may not be formed, and significant yield potential will be lost very early in the growing season."
Although farmers have been applying phosphorus for decades, Goos is still concerned for several reasons. "There has been a trend for declining soil test levels for phosphorus in the region, largely due to the expansion of soybean acres," Goos says, "Soybeans are not as responsive to phosphorus fertilization as wheat, and farmers often do not apply as much phosphorus as the soybean seed is removing from the field. This ultimately leads to declining soil test values for phosphorus."
The other reason why Goos is concerned about phosphorus fertilization of wheat, is that spring wheat varieties can differ significantly in how much phosphorus is required. A study conducted by Goos and his graduate student Jessica Paler (née Christianson) showed large differences in the amount of phosphorus needed for normal T1 and T2 tillering. "The amount of P needed for normal tillering can differ dramatically from variety to variety. In general, the fastest-developing varieties, the ones that require the fewest growing degree days to produce a leaf on the main stem, tend to be the varieties that require the most P for normal development." Examples of varieties Goos and Paler identified as having higher than average P requirements are: LCS-Breakaway, Bolles, TCG-Wildfire, HRS-3530, Barlow, ND VitPro, Steele-ND, ND901CL, Prosper, Faller, and Brick.
Because wheat begins tillering very early in the growing season, Goos is a strong proponent of starter fertilization. "I've concluded, after 40 years of studying wheat fertilization, that the old practice of putting a starter fertilizer of P with the seed of wheat is still the best practice. Application of the projected crop removal as a low-toxicity material like monoammonium phosphate will assure that there is adequate phosphorus for normal tillering. A 60 bu/A wheat crop removes about 30 pounds of phosphate per acre, and a starter fertilizer at about that rate will be very helpful in providing the phosphate the young plants need," Goos says. The research performed by Goos and Paler was funded by the North Dakota Wheat Commission.