Continued worldwide demand for fertilizer could result in limited supplies for the 2005 growing season, according to Bob Hoeft, soil fertility specialist with University of Illinois Extension. "With potentially short supplies, it is important
for producers to make the best use of available fertilizer to ensure maximum production on their fields," Hoeft said. "Growers who have not had a recent soil test should consider having a sample from each two and half acres of their fields analyzed for pH, phosphorus, and potassium."
He suggests applying lime, which will not be in short supply, to any field with less than 6.0 soil pH. Growers should also consider adding phosphorus and potassium to low-testing fields first.
"The allocation should be made to fields that have phosphorus test-levels less than 40 pounds per acre or potassium levels less than 260 pounds per acre," Hoeft said. "Research has shown that application of an amount equal to about one and a half times crop removal will often optimize yields, even on low-testing soils. If supplies are limited, growers should think about delaying the build-up portion until the quantities are more plentiful."
Hoeft points out that various crops can differ considerably in their ability to extract nutrients from the soil.
"Corn and soybeans yields will be at near maximum at phosphorus test levels greater than 25 pounds per acre with supplemental applications," he said. "Failure to add phosphorus to wheat will result in yield losses when test levels are below 50 to 70 pounds per acre. At the same time, wheat has a low demand for potassium compared to corn and soybeans."
Hoeft advises growers to spread limited supplies of fertilizer over all the acres, rather than adding full rates to some fields and none to others. The exception would be only when phosphorus test are greater than 70 pounds per acre and potassium levels are greater than 400 pounds per acre.
"When test levels are low and soil pH is high, limited supplies of phosphorus can be applied in a band two inches below and two inches to side of the seed," Hoeft said. "It is, however, important to remember that the high yields in 2004 will remove more phosphorus and potassium from the soil than during an average year."
Hoeft notes that nitrogen will likely not be in short supply, although prices could be higher than normal.
