May 21, 2010

Cool temperatures, rain, and snow early last fall in central and eastern Nebraska have contributed to an increase in nitrogen deficiency problems in winter wheat this spring.

Last October North Platte set a new record for snowfall with 32 inches (more than tripling the previous record of 10.5 inches). Average October snowfall for North Platte is 0.9 inches.

With the early winter conditions, wheat seeded late and even some seeded on time had limited growth last fall. This year early planted wheat may result in higher yields, but this is not typical and planting before the recommended time is not recommended due to potential losses.

With the snow, rain, and excellent crop yields last year (resulting in lower nitrogen residuals in the soil), any nitrogen was likely leached out of the root zone. Also, there was less mineralization with the cooler soil temperatures. All of these factors led to the increase in nitrogen deficiencies being observed this spring.

Figure 1a. Nitrogen deficiencies are visible between areas where nitrogen was knifed in. The wheat between these bands had less nitrogen due to two factors: 1) wet weather that caused nitrogen leaching and 2) the previous year’s high yields which left little residual nitrogen.	Figure 1b. No wheat growth is visible on previous corn rows due to high yields last summer and excessive moisture last fall.  Wheat growth is visible between corn rows where nitrogen was applied.

The fields shown in Figures 1 and 2 were fertilized with 60 lbs N and 30 lbs P₂O₅ knifed in on a 15-inch spacing in fall before seeding winter wheat. Notice the deficiencies or lack of growth between where the nitrogen was knifed in. This is most likely due to the wet weather conditions. Nitrogen has been leached below the root zone, moving deeper before the wheat could find and use it. This has resulted in nutrient deficiencies and poor growth. Unfortunately the wet spring has made it difficult to get into the field to amend these deficiencies.

Generally, deficiencies can be addressed with a urea nitrogen fertilizer applied before the “boot stage,” which is rapidly approaching or even has passed in some areas. This assumes that some precipitation will follow the urea application. Otherwise, the nitrogen in the material can volatilize or just sit on the soil and not be used until a rain comes, which may be too late.

Figure 2a and 2b. Wheat stands are good in areas of high residue cover where nitrogen mineralization and water capture and retention occurred. Wheat stands are poor on the bare areas that had no residue cover. This is due to poor residue distribution at harvest (right) when the combine created bands of cover and no-cover.

These pictures show winter wheat planted into a field where the residue was poorly distributed at harvest. (These are not terraces.) Note how the wheat grew poorly where there was no residue. Also note on the outer edges, the winter wheat is better than in the middle, apparently because the spreader placed more crop residue on the edges. This demonstrates the value of crop residue for the next year’s crop. Areas that had residue had a source of nitrogen through residue mineralization. Areas without any residue did not have a source of nitrogen and had poor growth.

The residue also created an environment where water capture and storage was optimized. Bare soil areas experienced more evaporation and water runoff than areas with residue cover. This created optimum growth conditions for the wheat in the residue and poor growing conditions in bare soil areas. The resulting differences in wheat growth are easy to see.

Robert Klein
Extension Western Nebraska Crops Specialist
Tim Shaver
Extension Nutrient Management Specialist
Both at the West Central REC, North Platte