AGRI-BRIEFS   AGRONOMIC NEWS ITEMS

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

Fall 2002, No. 3

Wheat produces two kinds of stems: 1) the main stem, and 2) a variable number of tillers. The kinds and numbers of tillers developed by the wheat crop are determined early in the growing season. Factors such as phosphorus or nitrogen deficiency, hard soil, or planting too deep can create stresses that reduce the initiation of tillers.

Of all the tillers formed, grain from the T1 and T2 tillers (originating from the bases of the first and second leaves, respectively) accounts for about half of the final yield. The other half comes from grain from the main stem.

On deficient soils, phosphorus fertilization increases phosphorus uptake. Early in the season, when the number of tillers initiated–and thus potential yield–is being determined, phosphorus from fertilizer may account for more than 50 percent of the total phosphorus in the plant. If phosphorus supplies in the plant become deficient, the initiation of T1 and T2 tillers can be significantly inhibited, cutting into sources of approximately half of the final yield.

Wheat takes up phosphorus throughout the growing season. Total uptake by wheat is about 0.68 pounds of P₂O₅ per bushel. Harvesting grain removes phosphorus from the field at a rate of about 0.50 pounds P₂O₅ per bushel. Banding phosphorus near the seed provides ready access to phosphorus supplies during early season growth. Maintaining adequate phosphorus supplies throughout the soil ensures phosphorus will be adequate to meet plant needs during the remainder of the season.

For more information, visit the website at www.ppi-ppic.org/fallfertilization.