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Where are your soil nutrients?

Jeff Caldwell 04/30/2012 @ 8:26am Multimedia Editor for Agriculture.com and Successful Farming magazine.

Most all fall-applied anhydrous was still in the soil when winter broke. But, that happened earlier than normal, and some nitrification happened throughout the month of March, when temperatures were warmer than normal.

Any nitrogen losses since then depend on how much rain you've had this spring. But, even if you haven't had a gully-washing rain every other day this spring, you still may be losing some nitrogen, according to University of Illinois Extension crop scientist Fabian Fernandez.

"It is important to remember that between rain events, nitrate will likely start to move back up," he says. "Between rain events, water evaporation from the soil surface creates an upward suction that moves water and nitrate closer to the surface. Similarly, if crops are already actively growing, evapotranspiration results in a similar suction force, in addition to some nitrate uptake by the crop."

But, if you've been planting into the dust this spring so far, your chances of losing fall-applied nutrients are lower than if your soils are a little wetter, Fernandez says. That's because typical Corn Belt-type clay, loam or silt-loam soils, it takes quite a bit of rain on top of a fully-recharged soil profile in order to put nitrates on the move.

"Because soils are dry, it would take a large amount of water to recharge the soil profile first," Fernandez says. "Once the soil is recharged, one can expect nitrate to move approximately 5 to 6 inches for each inch of rain in a clay loam or silt loam soil. In sandy soils or heavily tile-drained soils, it is possible to move nitrate as much as 12 inches for each inch of rain."

If your soils are low on nutrients, you'll know whether it's nitrogen, phosphorous, potassium or another nutrient in short supply based on the color of young corn plants.

"The pale green is most likely due to N deficiency. Nitrogen is important in chlorophyll, which gives leaves their typical dark-green color. The purple coloration is due to lack of phosphorus in the plant. These symptoms are the result of cool and dry soils that reduce nutrient availability. Also, the crop is not yet actively growing, which also reduces the capacity of roots to take up nutrients," Fernandez says.

"Another common symptom that is often observed early in the season when soils are dry is potassium deficiency," he adds. "I have not seen or heard reports of this symptom so far this year. Whatever the nutrient deficiency symptom may be, remember that if soil has adequate nutrient levels or has been adequately fertilized, these symptoms are temporary and have no negative impact on yield. Once the crop starts to actively grow, the symptoms will quickly disappear."

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