Model Takes the Guesswork Out of
Soil scientist Alan Olness and chemist Jana Rinke inspect corn plants in a
tillage/nitrate study that helped show the accuracy of the Pre-Plant Soil
A new Agricultural Research Service
computer model could save farmers millions of dollars worldwide in soil test
costs and wasted nitrogen.
Before year's end, the ARS Nitrogen Fertilizer Decision Aid will be posted
on the World Wide Web for farmers, consultants, and anyone else who wants to
Tested for 9 years with Minnesota corn farmers, the model helps eliminate
uncertainties that lead many farmers to overapply nitrogen in the spring. They
add so-called "insurance fertilizer" to the amount called for by a
fall soil sample, to compensate for possible nitrogen losses over the winter.
Alan E. Olness, a soil scientist, says the new model requires very little
information from farmers planning to use it.
"Mostly the farmer needs to know only the clay and organic matter
content of the top 6 inches of soil, as well as the soil pH and data from a
field weather station," he says. "Then the farmer sends in soil
samples to the usual state university or private lab for a Pre-Plant Soil
Nitrate Test. This test is gradually gaining popularity because it's so
accurate and useful."
Olness serves on the North Central Regional Committee that evaluated
pre-plant and pre-sidedress tests on 307 sites in the north-central Corn Belt.
One of the committee's goals is to facilitate more accurate nitrogen
recommendations, to avoid waste, and to minimize possible nitrate pollution of
The Pre-Plant Soil Nitrate Test solves the problem of estimating nitrogen
losses over winter by sampling for nitrogen just before planting. The idea
behind the test is this: Farmers can trust the test's analysis and apply only
the amount of nitrogen the soil is lackingif anybecause they then
follow up later with another soil test, in time to add more nitrogen if needed.
Olness says his model eliminates the need for the second soil nitrate test
by predicting nitrogen content for up to 90 days after planting.
The model uses soil and weather information to predict how much nitrogen
will be producedafter spring plantingby microbes. The microbes feed
on soil organic matter and decaying plants, stalks, and leaves from the
previous year's crop. In many soils, the microbes will naturally produce
between 50 and 100 pounds of nitrogen per acre.
By adding this natural production to the amount measured at planting, the
model tells farmers exactly how much nitrogen will be available to plants
during the critical 60-day uptake period. The model subtracts this sum from the
corn's total fertilizer need to recommend how much, if any, nitrogen fertilizer
should be added for the best economic yield.
Olness says his model can also help farmers time the microbial production of
nitrogen to meet plant needs at various growth stages.
"They can slow down the rate by leaving crop residue on the surface and
planting without tillage," says Olness. "Or they can till the soil
first, to bury the residue and speed up the nitrogen production."By
Don Comis, Agricultural Research
Service Information Staff.
This research is part of Integrated Crop Production and Protection
Systems, an ARS National Program (#305) described on the World Wide Web at
Alan E. Olness is at
the USDA-ARS North Central Soil
Conservation Research Laboratory, 803 Iowa Ave., Morris, MN 56267; phone
(320) 589-3411, ext. 131, fax (320) 589-3787.
"Model Takes the Guesswork Out of Fertilizing" was
published in the October 1999
issue of Agricultural Research magazine.