It’s the time of year when small grains producers are currently top-dressing their crops or trying to decide whether it is time to top-dress. Deciding when or if to apply nitrogen, like with so much in the agriculture industry, has a complicated answer of “it depends.” Here in Bosque County with primarily dryland production the weather will play a huge role in the timing. Nitrogen applications do not become effective until the nitrogen has moved into the root zone by rain or snowmelt. In order to have full benefit, nitrogen must be in the rooting zone by the time wheat is jointing. So now is the time you should be checking your wheat for jointing and considering your options for top-dressing your small grains.
As to the amount of nitrogen to apply, there are a few things to consider: the general nitrogen requirement for wheat grain production, if there is no soil test, is 1.2 lbs. of nitrogen per bushel of yield goal. With a soil test, use 1.5 lbs. nitrogen per bushel of yield goal, then adjust fertilizer N down for the level of nitrate-nitrogen reported in the soil test (usually a 6” test, but down to 24” if you have deeper soil sample info.) The second version incorporates those producers who also graze their small grains prior to going to grain. These producers should fertilize up to 2 lbs. of N per bushel of yield goal at planting, then when the cattle come off (by first jointing), fertilize again with another 0.75 lbs. N per bushel of yield goal. Also, keep in mind that about 1.25 lbs. of nitrogen per bushel is removed from the field. In contrast the same bushel of wheat grain removes about 0.45-0.50 lbs. of P per bushel.