Tapping into deep nitrogen and phosphorus reserves, applying fertilizers in a timely manner, and using the appropriate fertility rate based on soil tests and a realistic yield goal, will help grain farmers maintain yields and improve nutrient use efficiency.
Soil testing, as basic a principle as exists in crop management, remains the crucial factor in production efficiency. Yet many farmers have ignored the practice in the past and can no longer afford to with fertilizer prices at record levels.
Texas AgriLife Extension Agronomist Brent Bean says fertility requirements differ between grain crops but the basics are the same. Bean addressed corn, wheat and grain sorghum fertility during the recent West Texas Agricultural Chemical Association annual conference in Lubbock.
He said growers should fertilize for realistic yield goals. In wheat, they should apply 1.5 pounds of nitrogen for each bushel of yield target. “They may need about 0.5 lbs more if they graze wheat,” he said. Often grazed wheat will need to be topdressed with 0.5 to 0.75 pounds of nitrogen for each bushel after cattle have been removed.
Grain sorghum requirements are 2 pounds of nitrogen for each 100 pounds of grain yield goal. For corn, historically farmers should count on 1.2 pounds of nitrogen for each bushel of grain expected. The amount of nitrogen needed may be less if fertilizer is applied in a timely manner and banded.
Farmers may not need to apply that much each crop year, but they have to know what’s in the soil, Bean said. “Soil test,” he said. “And the results are only as good as the sample.”
He said growers should consider collecting soil samples from deeper in the soil profile than they may be accustomed to. A recent study showed as much as 25 pounds of nitrogen at 24 inches deep and 28 pounds at 36 inches. “Crops will use this nitrogen,” he said. “We often have residual nitrogen available we don’t know about if we don’t test. We’re beginning to push for deep sampling with high fertilizer prices. Farmers could save a significant amount of money on fertilizer if they have nitrogen or even phosphorus deeper in the soil profile that could be used by the corn plant.”
Bean recommended farmers soil test for crop fertility needs “as close to the expected application date as possible.”
He also recommended adding about 20 percent to the wheat nitrogen rate if growers apply in heavy residue. Heavier nitrogen rates are also necessary with grazed wheat. “We need 15 pounds of dry forage per day for 400 to 500 pound stockers. That’s 15 pounds of nitrogen per acre per month. Most people will use a stocking rate of one steer per acre on dryland wheat and plan to get four months of grazing.”
Timing is also important. “Some nitrogen should be applied in the fall if the soil tests indicate nitrogen is needed, especially if the wheat is going to be grazed, but apply no more than one-third of the total nitrogen needed in the fall.”
Most nitrogen for wheat should go on as a topdressing, he said. “Yield is not hurt by late application, but it should be made before jointing. Farmers have an advantage with topdressing nitrogen because they know better what the yield potential will be and can schedule nitrogen rate accordingly.”
Bean said phosphorus fertilization in the fall is important for wheat, especially if it will be grazed. “Phosphorus helps get the crop up quickly. Farmers can improve grazing by injecting phosphorus. If phosphorus is applied with the seed in the seed furrow, make sure that the sum of the nitrogen and potassium rates does not exceed 20 pounds per acre, otherwise damage to the germinating wheat can occur due to a salt effect.”
Bean recommends farmers get nitrogen on grain sorghum before panicle initiation, around 32 to 35 days after planting. “Some growers may see some iron or phosphorus deficiency, but it usually grows out of it.”
He said during the reproductive phase, farmers “want to have most of their fertilizer out. Sorghum following wheat may have as much as much as 30 to 40 pounds of residual nitrogen.”
Bean said it is important to get corn “up and growing quickly. We’re planting a little later in warmer soils but in some cases, no-till or strip till planting keeps soils cool. A starter fertilizer can be important, especially the phosphorus.”
Research data show a 2-by-2 fertilizer placement gives the best result for corn. “Dribble application 2 inches beside the corn row comes close,” Bean said.
Nitrogen use efficiency is generally improved with multiple applications. To get the most out of your nitrogen fertilizer, consider applying 25 percent preplant in a band, apply 6 pounds or so with your phosphorus as starter, apply 30 percent as a sidedress application prior to the 8-lf stage, and apply the remainder through the sprinkler system during the growing season.