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Precision ag research becomes commercial practices

Kings County, Calif., producer Ted Sheely planted 30 percent of his cotton crop this year using variable rate nitrogen and planting technologies developed on his farm on the West Side of the San Joaquin Valley. Next year he plans to utilize the two precision ag techniques to plant 60 percent of his planned 4,000 acres of cotton on his farm near Lemoore, Calif.

And what he has learned from prescription farming cotton is being transferred to his three other major crops, processing tomatoes, garlic and pistachios.

Two years ago Sheely turned over large blocks of his farming operation to a gaggle of researchers from the University of California, USDA, California State University Fresno, NASA and others as part of an Ag 20/20 project to see if precision farming could either increased yields or reduce costs by 20 percent on a commercial farm.

Sheely is convinced prescription farming using aerial imagery and field mapping to break down fields into decision-making grids is a better way to farm. The technology gives him better tools for making site-specific decisions, specifically in applying gypsum for managing saline soil conditions, nitrogen management and planting cotton.

Cultivation first

However, this spring Sheely took the space-age technology to where even he nor anyone else expected it to go; he saved a cotton field by cultivating it before seedlings ever emerged.

His stealth cotton cultivation story captured the attention as much as anything for the more than 200 farmers, consultants and others who attended the second annual precision ag field day on his farm sponsored by Kings County and Tulare County UC Cooperative Extension farm advisors Bruce Roberts and Steve Wright and USDA-ARS.

The field day featured several research updates on the work at Sheely’s farm, but it was the cultivation tale that captivated everyone.

Early season planting weather was miserable this year for San Joaquin Valley producers. Sheely did not escape problems. Not long after Sheely seeded a quarter section of cotton, a thunderstorm dumped more than two inches of rain on it.

The downpour imprisoned the seed under an impenetrable crust. To save it without replanting, Sheely had to break up the crust.

"Normally what we would do would be to go through with a rotary hoe. However, when you do that you throw more dirt atop the seed row, making it hard for the seed to get through," he said. "You hate to do it but you don’t have a choice when rain crusts over a field and you want to try to save a field without replanting."

Sheely’s fields are listed with auto-steering Global Positioning System (GPS)-equipped tractors. Part of that includes stored computerized field maps, basically showing tractor drivers exactly where seed rows are.

Rolling cultivator

"What we decided to do was go in with a rolling cultivator rather than the rotary hoe and get as close to the seed line as we could and gently break up the crust," said Sheely.

That would have been almost impossible without GPS technology. Computerized auto-steering allowed the tractor to get within an inch and a half of the seed line, close enough to lightly shatter the crusted cap atop the seed to give seedlings openings to emerge.

"We saved the field and have a nice stand of cotton," said Sheely. "I certainly don’t want to cultivate cotton before it emerges every year, but you can with the precision ag tools available to farmers today."

Precision ag involves identifying variability within fields using either aerial or ground sensing techniques. This information is then often field-truthed with soil or tissue sampling.

This technology can be used to identify differences within a field in plant vigor or residual nitrogen to vary nutrient rates, salinity to vary planting rates and plant vigor to vary plant growth regulator rates or defoliants.

Soil salinity is a growing problem in the West with a third of the state’s cotton crop affected, according to consultant Brock Taylor of Fresno, Calif. Salts are built up in the soils with imported irrigation water. Salinity can be mitigated by applying gypsum to loosen salts so they can be flushed out with rain or irrigation water. However, saline conditions can vary within fields.

Gypsum savings

Many of Sheely’s fields have been mapped for saline using ground electrical conductivity measuring instruments developed at California State University, Fresno. This information is used to vary gypsum rates and has reduced overall gyp costs for Sheely.

It can take several seasons for saline conditions to improve using gyp. A more immediate remedy developed at Sheely’s farm is variable rate seeding.

Historically, Sheely seeds at 15 pounds per acre. The past two season using computers and salinity maps, he has varied the seeding rate in many fields between 10, 15 and 18 pounds per acre across fields, the higher rate for higher saline areas.

"The bottom line is I did not save seed costs, but I gained an average yield increase of 90 pounds of lint per acre," he said.

Variable rate nitrogen also was used, but that was more difficult for Sheely to embrace "particularly when the mapping and other information said I did not need any nitrogen in some areas because of residual nitrogen.

"As a cotton farmer, zero N is hard to accept," he said.

Sheely has not been a big nitrogen user, averaging 140 to 165 pounds of N per acre overall. However, Taylor said using variable rate reduced Sheely’s average nitrogen use by 20 pounds and gave him a return of 15 to 20 pounds more cotton per acre after one year’s work.

Last season Sheely reduced his Pix use by 51 percent on the Ag 20/20 trial field using variable rates of the plant growth regulator based on aerial imagery to identify plant vigor. According to NASA researcher Matt Bethel, there was a 19 percent increase in net profit using variable rate Pix on Acala cotton.

Grids enlarged

This season Bethel is testing the concept on Pima cotton and for the first time used variable rate PGR aerially. Most Pix is put on by air in the San Joaquin Valley. With ground rigs, Bethel was able to use grids as small as 45 by 30 feet to vary rates. With an airplane traveling at 140 miles per hours, the smallest grid had to be extended to 70 by 200 feet. That is as quick as the aircraft’s on board computer could turn nozzles off and on.

"For years we have tried to use what we now call variable rate Pix. We’d tell the pilots to turn of the nozzles when they see dirt between the rows and turn them back on when the rows are closed over," said Sheely. "That is not very scientific, but that’s all we could do because we have long known that not every area in a field needs the same Pix rate. Now we can identify aerially those areas needing less or more Pix."

The concept of variable rate Pix was first tried in Mississippi. It works there, but it works better in California, said Bethel. "It is basically cloud free in the summer in California. That is not the case in Mississippi. "Scheduling for aerial imagery is difficult in Mississippi. It is much simpler in California and that is a "big plus" in getting the information needed for variable Pix," said Bethel.

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