Yellow wheat may or may not be N deficient
click image to zoom Farmers normally associate iron (Fe) deficiency with soybeans, but wheat can occasionally develop iron deficiency as well. Level soils, lower on the landscape, are often poorly drained, with a high water table in the spring. Such soils will commonly have lime in the topsoil, and the topsoil will "fizz" when treated with acid. It would be rare for a sulfur deficiency to occur on such soils, but iron deficiency is possible. Iron deficiency in wheat is not as common as iron deficiency in soybeans, but I have observed it in North Dakota. Elevated salinity can also aggravate the problem. Iron is even less mobile in the plant than sulfur, and the deficiency symptoms appear first on the younger leaves. Figure 3 shows an iron-deficient wheat leaf from a field near Leonard, ND. Notice the stripes, as the veins remain green, and the tissue between the veins turns yellow. If this happens on the youngest leaves of wheat, grown on a poorly-drained soil with lime in the topsoil, it is possibly an iron deficiency.
Tissue analysis is usually not reliable for diagnosis of an iron deficiency in wheat. Plant tissues can contain inactive forms of iron, and dust contamination can raise apparent iron levels dramatically.
Differentiating the visual symptoms of nitrogen, sulfur, and iron is best done when the deficiency begins to develop, when the yellowing begins. A rescue treatment is usually indicated when nutrient deficiencies are properly identified in a young wheat crop. Farmers should consult with their local agronomist or to select proper fertilizer rates, sources, and methods of application.
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