Soil Samples Are Key to Precision
Farming, NDSU Ag Engineer Says
By Vern Hofman, Power
and Machinery Specialist
NDSU Extension Service
Accurate soil sampling is an important
first step in precision farming systems, according to a North Dakota
State University agricultural
engineer.
NDSU research shows that zone soil
sampling based on topography and soil type is an excellent and accurate
way of determining residual soil nutrient amounts. "It will cost more than
a composite sample for a field, but will give a much better prediction of
the field’s fertility level at a much cheaper cost than grid soil
sampling," says Vern Hofman of the NDSU
Extension Service.
Hofman and other researchers used precision
agriculture methods at Mandan in cooperation with the
USDA-Agriculture Research Service on the Area IV Soil Conservation
District. Fifty acres have been divided into three fields with a crop
rotation of spring wheat, winter wheat and
sunflower.
They found that soil fertility zones
followed the topography and soil types of fields. As a result they were
able to develop soil sampling strategies that were as accurate as grid
sampling, but less costly – an important factor for applying precision
agriculture technology to the lower value crops grown on the Upper Great
Plains.
Initially, intensive soil sampling
found considerable variation in soil nutrients. Under those conditions,
variable rate application of fertilizer showed a positive return, Hofman says. With variable applications tailored to
soil fertility and crop needs, the nutrient variability decreased.
Consequently, the economic benefit of variable rate applications
decreased.
However, in years when crop production
was reduced because of dry conditions or winter kill, variable rate
application showed a positive return, Hofman
says. That’s because soil testing revealed variable amounts of nitrogen
left in the soil by stressed crops. Based on soil test results,
researchers were able to fertilize fields taking into account the residual
nitrogen. "The variability disappeared, but less fertilizer was used,
which showed a positive return for variable application," Hofman explains.
During wet years, the researchers
found that nitrogen in the soil may move to lower soil profiles 2 to 4
feet below the soil surface. "Small grain rooting systems are unable to
retrieve this nitrogen," Hofman says. "However,
sunflower has been found to be excellent in retrieving deeper soil
nitrogen with its tap root system that will reach down 4 to 5 feet into
the soil."
Retrieving deep soil nitrogen helps
reduce the amount of applied fertilizer and helps reduce the potential or
nitrogen pollution of underground water supplies.
"It is accurate soil sampling that
will help producers make the best use of precision farming technology to
tailor applications of inputs to crop needs," Hofman says.
|