When it comes to applying crop nutrients, most growers agree there is merit to tailoring the rates to specific parts of a field. The real debate centers on how to determine the customized rates.

Two new variable rate systems for fertilizer application illustrate the different approaches being taken in the still-evolving science of precision farming. NTech Industries has developed its system around optical sensors that measure the amount of accumulated nitrogen in plants, then feed the information to a microprocessor-driven spray system, which makes the customized application.

Cargill Crop Nutrition has developed a new software system designed to use most any type of soil maps, as well as other cropping information and GPS technologies, to develop a variable rate fertilizer prescription for each field.

Real-time nitrogen readings

NTech developed its system, called GreenSeeker, in a joint venture with researchers at Oklahoma State University (OSU). Its patented optical sensors use both red and near-infrared light to measure the volume of plant matter above the ground and the amount of nitrogen in the plant, explains NTech agronomist Robert Mullen. The football-sized sensors mount on the sprayer toolbar and work in real time, without GPS, to analyze plant needs and deliver a customized amount of nitrogen, on a two-foot-square basis.

“Other precision spraying systems involve time-consuming, GPS-guided, acre-by-acre field mapping and wasteful broadcast spraying,” says company president John Mayfield. “GreenSeeker sensors give plants a physical, write a prescription and deliver the optimal amount of fertilizer as the spray rig travels across the field. It delivers less where less is needed and more where more is needed to realize full crop yield potential.”

“Conventional inputs of nitrogen, based on yield goals [historical averages] have been a good guide for farmers to use in planning fertilizer rates,” explains Gordon Johnson, OSU regents professor and nutrient management specialist. “However, this approach, on average, results in two-thirds of the fertilizer being lost to the environment from the soil-plant system. Only one-third is accounted for in the harvested crop.”

He claims the technology used in the GreenSeeker will increase nitrogen use efficiency by 80 to 90%, reducing the amount lost to the environment from current figures of 65% to as low as 10%.

Because the optical sensor uses artificial light, the variable rate system works for both day and night spraying. Spraying at night can reduce fertilizer volatility and wind drift, Johnson notes.

The company claims wheat farmers can expect to add $10 to $12/acre to the bottom line with GreenSeeker. In field tests conducted by Burlington Co-op, Burlington, OK, the unit was used to top-dress 10 fields, from 90 to 160 acres, including two co-op fields, says co-op agronomist Kenneth Failes. “We saw increased yields of 4 and 9 bu. in our fields. That means a significant return in dollars to the farmer,” he says.

Cost of installing the system on an existing sprayer is about $1,000 per boom foot. But the company claims its product will save enough money to pay for itself in two years on a 2,500-acre farm.

The company also has a handheld sensor unit that allows you to monitor changing crop conditions throughout the season. It uses the same sensor, mounted on a telescoping pole with padded, adjustable shoulder strap, for taking spot samples as you walk through the field.

The 13-lb. unit comes with a 16-mB CompactFlash memory card, 120-VAC battery charger, USB card reader, screen protectors and carrying case. For more information, contact NTech Industries Inc., Dept. FIN, 740 S. State St., Ukiah, CA 95482, 888/728-2436, visit www.ntechindustries.com or www.freeproductinfo.net/fin.

Flexible map-based system

Cargill's InSite VRN system takes a more map-based approach to developing fertilizer prescriptions for fields. But this GPS-based service offers the flexibility of using a variety of mapping systems to generate its nutrient recommendations. “This system will fit the needs of farmers in the start-up process of field mapping as well as those who are very sophisticated at it,” says Ron Olson, manager of research and development for Cargill Crop Nutrition. “It can make use of grid soil sampling data, zone sampling data and yield maps, but it doesn't require them. The basic requirements are a field composite map, a farmer's yield goals and, ideally, a three-year field history.”

All available field data are sent to Cargill's mapping center, and within 48 hours, a prescription application map is created and sent to the dealer, where it can be electronically plugged into any type of fertilizer applicator.

“The benefit of using historic satellite imagery is that you can calculate organic matter levels in the field and generate yield potential maps,” says Dan Froehlich, Cargill agronomist. “That, in turn, allows you to more effectively calculate the nitrogen available through mineralization, so we can make more accurate nitrogen recommendations.”

Another benefit to this type of system, he notes, is that you can determine the variability in the field before you spend any money. “With grid sampling or electrical conductivity systems, you need to spend a lot of money up front to determine if a field has enough variability to justify variable rate application,” Froehlich says. “And if you're renting ground, you can't always afford to make that investment.”

The company introduced the system through certain dealers in Minnesota, Iowa, Nebraska, North and South Dakota, Texas and Ontario last summer, where it was used on about 50,000 corn and wheat acres. This coming season, in addition to prescribing variable nitrogen rates, the InSite VRN system also will be able to provide prescriptions for potassium and phosphorus applications.

Exact pricing will be determined by each dealer, Olson says, but expect the cost of this service to be included in a variable rate application package price. For more information, contact Cargill Crop Nutrition, Cargill Fertilizer Inc., Dept. FIN, 8813 Hwy. 41 S., Riverview, FL 33569, 800/237-2024, visit www.cargillfertilizer.com or www.freeproductinfo.net/fin.