AGRONOMIC NEWS ITEMS
From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335
Winter 2002, No. 7
Wheat takes up about 2.0 to 2.5 pounds of nitrogen per bushel produced. Wheat forage will take up about 40 pounds per ton, assuming 2% nitrogen in the tissue. Where wheat is grazed, it takes about 1 pound of nitrogen for each 3 pounds of animal gain per acre. Adequate nitrogen must be available to the plant at all phases of development. Shortages of nitrogen will ultimately result in reduced tillering, reduction in head size, poor grain fill, reduced yields, and low protein content. Splitting nitrogen applications generally improves use efficiency, minimizes risk, and safeguards the environment. This is especially true in medium to light textured soils and in higher rainfall regions where the risk of nitrogen leaching is increased. Topdress applications should be made early, prior to jointing, to maximize production efficiency. Timing and nitrogen source should be managed to fit climatic conditions, soil type, and tillage system.
Another nutrient that should be considered in topdressing winter wheat is chloride. There have been many studies across North America over the past several years that have evaluated wheat response to chloride. Chloride is essential for photosynthesis, it is important in controlling the opening and closing of leaf stomata (pores), it influences the nitrogen nutrition of plants, and also advances plant maturity and improves overall disease resistance. Wheat response to chloride is usually expressed in improved color, suppression of fungal diseases, and increased yield. The average yield increase due to chloride is usually about 5 bushels per acre in responsive conditions, although yield increases as high as 23 bushels have been observed.
Chloride is highly mobile in soils, so split or topdress application may be beneficial. Several factors and tools can be used to determine whether a specific situation is likely to be responsive to chloride fertilization.
• Tissue testing may also be useful—chloride level below 0.1% at the boot stage is considered very low.
• Wheat variety is an important factor—some varieties are more responsive that others. Contact the appropriate university extension specialist to determine which varieties are likely to be responsive in a specific area.
Providing winter wheat with adequate fertility is important in producing optimum yield and maximum profit. Surface or topdress application in the spring with certain nutrients is agronomically sound because of the tendency of these nutrients to leach from the root zone. So, look beyond nitrogen this topdress season and consider the need for nutrients such as chloride in wheat production.