Precision ag pays off big in reduced fertilizer costs

When fertilizer prices were doubling and tripling last year, Kings County, Calif., producer Ted Sheely left $350,000 in his farm’s bank account that he would have otherwise spent for fertilizer.

Sheely did not quit farming. He just quit spending money on nitrogen and phosphate fertilizer and went to his soil bank account for a withdrawal.

Sheely’s farm near Stratford, Calif., has for eight years been the guinea pig for developing and commercializing precision agriculture technology. However, when Sheely started his precision ag adventure, he had a rule for everyone who used his farm as a research plot — costs must be cut significantly without sacrificing yield.

Most have paid off, one handsomely last season.

Consulting agronomist Brock Taylor told the Central Coast Cotton Conference (CCCC) he used aerial mapping and grid soil sampling to generate a 560 percent return on investment for Sheely’s AzCal Farm Management operation.

Taylor was part of a three-man precision agriculture panel at CCCC that also included Tim Sherrill, agronomist for J.G. Boswell, Corcoran, Calif., and Lowell Zelinski, conference director and consultant with his own company, Precision Ag, Inc., Templeton, Calif.

This year’s conference attracted more than 150, a significant increase over last year’s 113.

Over the years, fertilizer costs have been a relatively inexpensive part of farming. In addition, farmers know skimping on nutrients can cost yield and quality.

Over the past three years Sheely and his peers have seen fertilizer costs soar to stratospheric heights, giving agronomist Taylor a dream scenario to use precision agriculture technology to write precise fertilizer prescriptions to save big dollars.

Sheely’s budget for 1,650 acres of wheat last year called for a blanket 100 pounds of nitrogen and 50 pounds of phosphate at a cost of $130 per acre.

Using soil sampling, lab analysis to determine the amount of residual fertilizer in the soil, and four variable rate maps developed from aerial imagery costing just $1.10 per acre, Taylor was able to reduce fertilizer use to an average of 60 pounds of N per acre and just 6 pounds of phosphate. This represents a reduction in budgeted costs of almost $71 per acre, a savings of 54 percent.

He used the same strategy on 18 cotton fields totaling 2,700 acres that were budgeted for 12 gallons per acre of 10-34-0 or 50 pounds of phosphate per acre at a cost of $84.50.

After sampling, getting lab analyses and creating two variable rate maps at a cost of less than $1 per acre, he determined none of the fields required phosphate, since all fields had phosphate levels of 12 ppm or higher. Only two fields needed chelated zinc for a total of 150 pounds of zinc.

Taylor estimated he saved more than $83 per acre on 2,700 acres of cotton for a savings over budget of more than $225,000 or 98 percent.

“It does not cost a lot of money to find out what your residual nitrogen and phosphate levels are,” Taylor says. This could be particularly important in a drought year like this when growers may wait until the last minute to plant based on water availability, he noted.

Water was a major topic at the conference and one of the tidbits Zelinski offered was that in a drought situation, added nitrogen may pay off. When plants are given adequate water, root systems are larger than when plants are under water stress.

Where 175 pounds of available N per acre may be a good number for optimum irrigation; where there is water stress 250 pounds may be better because the plant’s root system is not as expansive to forage for nutrients, Zelinski explained.

Precision agriculture’s genesis is satellite mapping and tractor auto guidance systems that allow for precise passes through fields.

Taylor said it is critical that the Global Positioning System (GPS)/Geographic Information System (GIS) is used in all field operations from disking to planting to harvesting. Some growers are using GPS for only a portion of the operations.

Taylor works with tomato growers and others who use permanent beds. “I had three fields where the rows were 6 or 7 inches off the GPS map. GPS guidance and maps should be used in all field operations for maximum uniformity and efficiency,” he added.

GPS/GIS is automated, no hands steering of tractors. Tractors are guided by satellites. One of the fears when the technology came in was that drivers would be less attentive and might even fall asleep in a moving tractor.

Sherrill discovered that drivers are actually more alert, monitoring the other operations like cultivating or planting rather than worrying about driving a straight line.

Variable rate planting based largely on salinity of the soil has not proven successful in traditional 30 to 40-inch row cotton for either yield enhancement or cost savings, according to Sherrill. However, he saw increased yields using it in ultra narrow-row 15-inch cotton.

However, he believes variable rate seeding in wheat and alfalfa may offer a cost savings.

At AzCal, Taylor says increasing seeding rates by as much as a 2x factor due to soil salinity (ECs of 10-13) has actually increased seeding rates in those areas, but resulted in stands where there would not be otherwise.

“We are talking about seeding rates of 100,000 to 110,000 seeds per acre. We are using 90 percent plus germ seed and getting only about a 60 percent germination, but we get a stand where we would not otherwise,” Taylor notes.

Variable rate nitrogen has resulted in yields of up to 6 bales per acre in spots using 240 to 270 pounds of nitrogen in cotton fields averaging 3.25 to 3.5 bales per acre fields, says Taylor. This, he added, offers incentive to continue to fine-tune N levels with yield monitors and N rates.

Sherrill believes there is no cost savings or yield enhancement increasing N rates on low vigor areas, where he says yield limiting factors are often soil texture or other factors. He has seen a cost savings in reduced N rates using precision ag technology.

Sherrill uses aerial maps in pest control decisions. “When there is a potential lygus issue, I know it usually starts in high vigor areas and those are where I want sampling done first,” he says. He uses the aerial maps to identify those areas.

Those same types of maps identifying low vigor areas lead Sherrill to investigate why. It can be late season grasses in the cotton. “We have applied Poast to some of those areas and that has helped in getting the weed population to a manageable level,” he says. He also uses these vigor identifying maps in seed alfalfa to manage irrigation water.

Defoliation/desiccation of both cotton and seed alfalfa is another area where vigor maps help in decision-making. However, Taylor and Sherrill noted that they have discovered it is the low vigor areas in both crops that require added defoliation/desiccation material. Low vigor plants often harden off more than higher vigor plants, requiring added material to drop leaves.

“As margins in farming become thinner, precision farming makes more and more sense,” said Taylor.

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