From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335

Fall 1998, No. 5


Most growers are aware of the importance of nitrogen in producing high yielding wheat—but few recognize the crucial role phosphorus plays in increasing yields and in improving efficiency of other nutrients like nitrogen and potassium.

Phosphorus has many vital functions in wheat in addition to the unseen roles it plays in photosynthesis, energy storage and transfer, respiration, cell division and other plant processes.

Wheat lacking phosphorus is stunted, has poor root growth, and has few tillers. Montana researchers found phosphorus responsible for about 75 percent of adventitious root development. Adventitious roots grow from the crown as a complement to each new tiller added and dominate the root mass of mature wheat plants. Phosphorus is critical to the development of the first two tillers, and they are critical to the wheat’s yield potential.

Wheat has a high demand for phosphorus. An average crop removes about 0.5 pounds of P2O5 per bushel. But when yields are pushed to high levels, phosphate removal can exceed 0.6 pounds P2O5 per bushel. About 60 to 70 percent of the phosphorus uptake by wheat occurs prior to flowering, so it’s important to have a good supply available early in the growing season.

Because phosphorus is so important to root growth and early plant development and because it’s immobile in the soil, wheat is very responsive to starter phosphorus. Long-term research in Saskatchewan shows how starter phosphorus consistently increases spring wheat yields. During a 28-year period, seed-placed phosphorus increased stubble wheat yields an average of 2 bushels per acre and fallow yields an average of 4 bushels per acre. Yield increases frequently exceeded 10 bushels per acre in years when growing conditions were ideal and occurred although soil test phosphorus was gradually building up. After 28 years of regular starter phosphorus, soil test levels doubled from about 17 to more than 40 pounds per acre.

Phosphorus can increase wheat yields by 50 percent on low testing soils and frequently increases yields on high testing soils. Response to applied phosphorus depends on year-to-year soil and climatic conditions. To take advantage of ideal growing conditions, the soil must be well supplied with available phosphorus.

If you want to maximize your wheat yields, build soil test phosphorus into the medium-high range and always apply starter phosphorus. You never know when Mother Nature will provide the ingredients for a bumper crop.

— TLR —

For more information, contact Dr. Terry L. Roberts, Western Canada Director, PPI, Suite 704, CN Tower, Midtown Plaza, Saskatoon, Saskatchewan, Canada S7K 1J5. Phone (306) 652-3535. E-mail:
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