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Soil sampling saves money in dry years

Row crop producers can chalk up some serious savings by soil testing for nitrogen before applying fertilizer for their next crop.

South Dakota State University Extension soil fertility specialist Jim Gerwing said just as in the drought year of 2002, dry conditions in 2006 prevented crops in many areas of the state from using much of the fertilizer that had been applied to fields.

"Really, this is a year when a person could make some serious money by soil-sampling for nitrate," Gerwing said. "The fertilizer that wasn't used by the crop this year is still there as nitrate. In years now when we have so little rainfall, we know we didn't lose it by leaching or denitrification."

Nitrogen fertilizer rate recommendations are based partly on the nitrate nitrogen that is found in the soil. For every pound that a two-foot-deep nitrate nitrogen soil test finds, the producer can lower the amount of nitrogen he or she will apply by that same amount.

"With fertilizer prices, especially nitrogen, the way they are now, a soil test to confirm how many pounds are out there would really, really pay high dividends," Gerwing said. "It's obvious that the corn failed in a lot of places and the wheat was pretty low-yielding. We are getting some soil samples into the soil-testing lab. The samples are showing extremely elevated nitrate levels.

"When I say elevated, much, much higher than after a normal year. In fact, there are some areas coming back that are over 100, 150 pounds of nitrate carryover."

Gerwing said there will probably be at least as much nitrate carryover as in 2002, when the average nitrate carryover after corn was about 107 pounds an acre -- up from more usual soil test nitrate levels of near 55 pounds an acre after corn.

Gerwing said some producers have been inquiring about the fertilizer value of nitrogen that is tied up in crop residue such as corn stalks. Gerwing cautioned that it is not the same as readily available nitrate nitrogen and won't immediately lower your fertilizer rate recommendation for the next crop year.

He added that for other nutrients -- phosphorus, potassium, and micronutrients -- soil tests are indexes of availability and those levels don’t change rapidly. Consequently, rate recommendations for those nutrients for the next crop year will probably be very close to this year.

"For those nutrients, the drought has very little impact. The big one, again, is nitrate. We would expect that the average nitrogen rate recommendations could be 50 to 75 pounds less next year than it was for the current year or the previous couple of years."

Row crop producers can chalk up some serious savings by soil testing for nitrogen before applying fertilizer for their next crop.

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