Cooperative Extension Fertilizing Small Grains in Arizona Nitrogen Content of Crop

Nitrogen is the primary fertilizer nutrient required by wheat and barley. A wheat crop contains 33 to 37 pounds of nitrogen per 1000 pounds of grain in a range of grain protein from 12 to 14%. A barley crop will contain about 20 % less nitrogen than wheat at similar yield levels due to lower grain nitrogen concentration. The actual total amount of nitrogen contained in the crop will vary greatly depending on yield level and protein content of the grain (Table 1). If high yields are expected or high protein content is desired, the grower needs to increase nitrogen fertilizer rate accordingly. The expected crop nitrogen content and optimum nitro-gen fertilizer rate are not identical due to nitrogen that may be available in the soil and water or losses of nitrogen fertilizer that may occur throughout the season. Sources of Nitrogen Small grains obtain nitrogen not only from fertilizer, but also from the soil and irrigation water. In a study con-ducted at the Maricopa Agricultural Center with durum, about half of the nitrogen taken up by the crop was from fertilizer and the remainder was from soil and water (Ottman and Pope, 2000). Pounds of nitrogen per acre in the irrigation water can be calculated by multiplying the parts per million of nitrate-N in the water by 0.226 and by the number of acre-inches per acre of water to be applied. Pounds of nitrate-N per acre in the soil potentially avail