Advice to growers
Gelderman says if growers suspect significant N loss they should soil sample at least a few fields to determine loss trends.
He directs growers to probe down 3 ft., taking samples in 1-ft. increments to be analyzed for nitrate-N.
"This will give some indication of total available nitrate-N in this depth and also an idea about N movement. This information can then be extrapolated to other fields with similar conditions," Gelderman says.
He warns growers to avoid applying N after heavy rains based on plant color.
"Plant roots growing in a saturated soil under low oxygen conditions cannot effectively take up nutrients. Therefore, a plant can exhibit N-deficiency symptoms, even though the soil can have adequate nitrate-N," he says. "Once root zone aeration is established, these plants will often green up – although yield potential may have been reduced."
Many growers ask Gelderman if applying foliar N will help green up the plants? If leaching is the problem, and soils are not saturated, a foliar application will not help.
"It's too small an amount to meet the plant's needs – even assuming that the plant takes up this N foliarly, which is unlikely," he says. "In this case the producer would be better advised to apply more N as a broadcast or injected application"
Gelderman adds that if the plant is a yellow color, and it is due to possible denitrification losses, a grower would need to wait until the soil is firm enough to hold a sprayer.
"By that time, the plant will probably green up on its own, or roots will be so damaged that the N will make little difference in yield potential," Gelderman says.