Growing Magazine - December, 2012

FEATURES

Site-Specific Farming

Reduce inputs without reducing yield
By Janet Aird

"Farmers deal with a lot of variability in their land," says Dr. Stephen Machado, associate professor of agronomy, Oregon State University (OSU), Columbia Basin Agricultural Research Center (CBARC), "and most apply the same amount of inputs on all parts of their fields. My job is to make them aware that that isn't efficient. They need to farm according to the land's potential."


Agricultural engineer Dean Evans inspects young peanut plants. In the background, water is being applied automatically on an as-needed basis (note that some sprinklers are on, some off) to specific plots using site-specific irrigation.
Photo by Peggy Greb, courtesy of USDA-ARS.

Machado leads OSU's long-term cropping systems research activities at CBARC Pendleton, CBARC Moro, and in Heppner in eastern Oregon. He's also working on a project to connect African professionals living in the U.S. with universities in Africa. His goal is to have them volunteer to teach courses a semester at a time, either in Africa or online, to help develop agriculture in Africa.

"My work at OSU involves coming up with sustainable cropping systems, including tillage, rotation and intercropping," he says. "I am for sustainability, whether organic or traditional."

This includes site-specific farming (SSF), or precision agriculture, which increases efficiency because growers apply inputs based on the yield potential of specific areas within a field, not evenly on the entire field. While Machado's research has been with wheat, SSF is very effective with vegetables and fruit as well.

SSF reduces the cost of inputs and the amount of time and energy needed to apply them, with no or little change in yield. It makes decision-making easier. And when growers apply less water and fewer chemicals to their crops, they reduce the possibility of having polluted runoff leaving the farm and having to pay for remediation. SSF may also help reduce insecticide and herbicide resistance, because fewer chemicals are sprayed.

"SSF used to be expensive, but now it's very inexpensive," Machado says. "Farmers are high-tech." Instead of costly sampling, SSF now combines technology such as GPS and GIS with yield monitor sensors, electrical conductivity (EC) or electromagnetic sensors, and remote imagery, including satellite images and aerial photography.

These tools identify the factors that affect crop productivity in specific areas of a field. Factors include soil depth, texture and fertility; slope and aspect; and pests and diseases. Growers can choose the number of factors to map. The findings determine the amount of yield the field is able to produce. For each factor, growers apply the inputs required to reach the potential yield in specific areas.

For example, because north-facing slopes are cooler and wetter than south-facing ones, they produce more yield. This is where growers should apply more seed and fertilizer.

When a certain factor varies in different areas within a field, the inputs must account for that. For instance, if there are pockets of deep and shallow soil, growers should apply less seed and fertilizer to the shallow soil. If they're applied at the same rate throughout the field, the crops in the shallow soil (which holds less moisture) compete for water, especially in dryland farming and in drought years. In spite of the inputs, the yield will be lower in shallow soil than in deep soil.

"Save your inputs for specific areas in the xzfield that have high yield potential," he says.

Another example is differences in soil texture, whether clay, loam or sandy. "There's no point putting too much fertilizer on sandy soils," Machado says. "It will get washed away."

It's the same with insects and diseases. Growers' profit margins increase when they spot-apply insecticides and herbicides to affected areas only.

One of the most accurate methods of gathering information about a field's characteristics is still soil sampling. GPS systems can be foiled by atmospheric conditions, although differential GPS (DGPS) systems are more accurate. Yield monitors and soil EC measurements can also generate errors. It's a good idea for growers to confirm the results (depth, soil texture, etc.) on the ground, Machado says.

Mapping with yield monitors and EC is the least expensive way to obtain information about the yield potential of different areas in a field.


Stephen Machado, Ph.D., associate professor, crop physiology/agronomy, Oregon State University, Columbia Basin Agricultural Research Center, Pendleton, Ore.
Photo courtesy of Stephen Mac hado.

"A yield monitor is a gadget growers put on their combine," Machado says. "It weighs the yield on the go with GPS. At the end of the harvest, growers will have a map of the field that shows the low and high yield points in the field."

A single-year yield map shows how management and climate affected the current growing season. Multiyear (or yield frequency) maps are more useful in determining how much yield growers can expect to get over the long term.

Yield maps are valuable in other ways too. Growers can use them to secure loans and show them to future renters or buyers of the land. They can also pass them down to the next generation so the knowledge they've gained about their fields isn't lost.


Two commercial soil electrical conductivity (EC) sensors map soil variability. One is mounted on the back of a tractor and uses disc coulters contacting the soil to measure EC at two depths. The other, attached to the small vehicle behind the tractor, does not require soil contact and measures EC at only one depth.
Photo by Newell Kitc hen, courtesy of USDA-ARS.

EC measurements are used mostly by researchers and private consulting companies, Machado says. They provide the same information on soil texture, soil depth and soil water as yield monitors do, in more detail. They only need to be used one time to map the field.

"Growers can start with a yield monitor, and if they're more inquisitive, go to EC to find out what soil characteristics correlate well with yield," he explains, "but they'd still need to go and verify the findings in the field."

Because of the expense, consultants are the most frequent users of remote imagery.


Field management zones

Of all the factors within a field - soil depth, texture and fertility; slope and aspect; and pests and diseases - growers can choose how many or how few to map. If they choose multiple factors, they overlay the maps. This determines which inputs to apply through variable rate.


Researchers use remote sensing from satellite images to determine the efficient use of land and inputs such as water, nutrients and pesticides.
Photo courtesy of USDA-ARS.

From there, growers decide how many management zones they want to create within the field. This typically depends on the field's variability, but zones that are smaller than a few acres are usually not efficient.

"It becomes complicated," Machado says, "but some things are more important to start with. Look at the factors that have the most direct impact on yield."

The most important input is almost always nitrogen fertilizer. Growers should always fertilize for the target yield. The second most important is usually herbicide.


Growers can add sensors and computers for site-specific farming to their existing farm machinery.
Photo by Bob Nichols, courtesy of USDA-ARS.


Dean Evans downloads control algorithms to the site-specific irrigation system controller.
Photo by Peggy Greb, courtesy of USDA-ARS.
"You might have good fertilization, but if weeds are growing, they compete for nutrients and water," he says. Soil depth (especially in dryland areas) and soil type are also important.

Growers can apply varying amounts of virtually any input - fertilizers, manure, pesticides, seed - with any number of pieces of equipment.

They can calibrate their existing applicator to apply the predetermined amount of inputs within a field by programming it and using the yield or EC map and GPS points.

They can also invest in a variable-rate applicator that automatically calibrates to the maps. These are becoming more affordable, and they save growers time on the calibrations.

Variable-rate application equipment can be as large as a commercial fertilizer applicator or as small as a variable-rate seeder. "The technology has advanced so much that growers can use the same unit for all the applications," Machado says. "They just apply the map information to the applicator. It's pretty neat."

SSF is crucial for the future of agriculture, he says. "We can minimize the effect of chemicals and sprays if we use them more efficiently. It benefits farmers financially and environmentally. It's one good step we can take to improve sustainability."

The author is a freelance writer based in Altadena, Calif.

Resources

NDSU Extension: www.ag.ndsu.edu/pubs/plantsci/soilfert/sf1176-1.htm

University of Nebraska-Lincoln: http://cropwatch.unl.edu/web/ssm/home

Alabama Cooperative Extension System: www.aces.edu/anr/precisionag

Virginia Cooperative Extension: http://pubs.ext.vt.edu/442/442-503/442-503.html

International Society of Precision Agriculture: www.ispag.org