Are You Ready for Variable Rate?

November 6, 2017 03:32 PM
Reaping the benefits of new technology demands a systems approach to crop production

A short decade ago, the ability to make every field produce to its maximum using variable-rate and multi-hybrid planting technology didn’t exist. Today, the benefits of varying seed, fertilizer and pesticide rates and changing hybrids are catching on, but you can’t just pull the technology off the dealer’s lot or shelf and run with it—not if you want a return on your investment. You, and your fields, must be prepared to use it.

“When a farmer asks me if he is ready to implement variable-rate technology [VRT], I ask him if he has implemented a systems approach to crop production,” Ferrie says. (A systems approach removes yield-limiting factors throughout the production process.) “Once you have removed the obstacles, you are ready to benefit from the next step: VRT,” Ferrie says.

The foundation of the systems approach, as illustrated by the pyramid on page 15, consists of four blocks: planting practices; field history, records and yield maps; soil testing; and tillage practices (including no-till) and soil conditions.

“Note variety/hybrid selection is part of the system, but it’s farther up the pyramid,” Ferrie says. “If you fail to lay the foundation with good planting practices, you won’t reap all the benefits of correct variety selection.”

Examining the blocks one by one will help you determine if you’re ready for VRT.

  • Planting practices include preparing a good seedbed, whether you use no-till, strip-till, vertical tillage or conventional horizontal tillage. Planting must be timely and occur in ideal soil conditions and uniform spacing and depth. In other words, you need to have mastered the secrets of picket-fence stands.  
  • Field history and maps showing spatial variability are essential for VRT. “From soil surveys, available on the internet, we can pull up a field’s soil types, slope and, usually, topography,” Ferrie says. “To develop management zones for VRT, we need maps that show spatial variability. These can be produced with a calibrated yield monitor. If a yield monitor isn’t calibrated, the information it generates shows nothing but inventory.”

Aerial imagery can also be used to determine spatial variability across the field, which is necessary to know when establishing management zones and implementing VRT. “The best yield maps are from wet and dry years, but the more years of data, the more accurate our management zones,” Ferrie says.

  • Soil tests provide the basis for many VRT decisions. “You can have the best hybrid selection and nitrogen program, but if your field is 6 tons per acre short on lime, you won’t maximize yield potential,” Ferrie says. “As someone once said, a fertile soil won’t always be productive, but a productive soil will always be fertile.”
  • Tillage practices and soil conditions are combined in one block  because tillage, or the lack of it, influences soil health. The condition of your soil will influence your ability to use VRT practices. “Learn to recognize healthy or unhealthy soil,” Ferrie says. “To fully benefit from VRT, your soil needs to be healthy. That requires removing compaction, installing drainage, maintaining the correct pH and other practices.”
  • Weeds, insects and disease are the next bricks above the foundation. To effectively vary herbicide, insecticide and fungicide rates, your management staff must include a pest boss—one person in charge of everything that falls under the heading of pest management.

The pest boss’s job is complicated, which is why you need one, and it becomes even more complex when you add VRT. “For example,” Ferrie explains, “if you plant multiple hybrids in a field, the pest boss must know the weed and insect resistance traits of each one. One might be glyphosate-resistant, while the other isn’t. One might contain genetic insect resistance, while the other must be treated with insecticides.”  

  • Hybrid/variety selection and harvest loss are interrelated. “Choosing the right hybrids to take advantage of varying your population on light and heavy soil is critical,” Ferrie says. “But you must be aware of each hybrid’s maturity and its effect on standability. If you select a 102-day hybrid for your light soil and a 112-day hybrid for your heavy soil, you must plan how to manage harvest to avoid harvest loss, from standability or at the combine header, for that earlier-maturing hybrid. Planning for timely harvest must be done when you plant the crop.”
  • Fertility rests on top of all the other blocks. “If you have mastered every other aspect of production, fertility can be what knocks yield out of the park,” Ferrie says. “But the best fertility program can be derailed by soil compaction or poor planting practices.”

Once you’ve implemented a systems approach, capitalize on VRT by evaluating every brick in the pyramid. “For example,” Ferrie says, “varying your seeding rate changes plant density. So you or your seed rep must understand hybrid ear type (flexible, determinate or semi-determinate) and plant structure (tall, short, upright, semi-upright or pendulum leaves). Ear type dictates population, and structure affects plants’ ability to capture sunlight and protect itself in dry conditions.”

Varying plant population lets you take advantage of each soil type’s moisture characteristics. First, you’ll need to know how much water you have to work with in a growing season. You can estimate that from 30-year rainfall records and/or the rate at which you can irrigate. That’s just the first step to a better understanding of your soil.

“You need to understand each soil’s infiltration rate,” Ferrie adds. “In other words, how much of your seasonal rainfall goes into the soil rather than running off. Slope plays a factor in absorption; some water might run off slopes and infiltrate in lower areas. Zones with poor infiltration can be planted to different hybrids and populations.”

You’ll also need to learn each soil’s water-holding capacity, which is influenced by type, texture and soil health. You’ll want to consider the transpiration and evaporation rates. Transpired water is used for production, while evaporated water is wasted. Row spacing, cover crops (which reduce evaporation) and other factors come into play.

With variable-rate nitrogen, it’s best not to apply all your nitrogen in the fall. “It’s far too risky,” Ferrie says. “With VRT, we want to lower our nitrogen rate on soils that need less, but we have no idea how much nitrogen we might lose on that soil by June, July or August.”

VRT application options include preplant, sidedressing and with the planter. You’ll need to understand how
nitrogen fertilizer requirements are influenced by environmental conditions and how soils vary in their capacity to supply nitrogen.

“Some soils can supply 30% to 70% of the nitrogen required by a corn crop,” Ferrie says. “How much they supply in a given season is determined by biological activity. Microbial activity results in periods of net mineralization (which makes nitrogen available to plants) and net immobilization (which makes it unavailable). That activity is influenced by tillage and fertility practices, as well as weather during the growing season.

“If you don’t grasp these concepts, you are not ready for variable-rate nitrogen application,” Ferrie says.

Getting ready to implement VRT takes effort, but higher yields from more efficient input use make everything worthwhile, for farmers and for the environment. Besides, Ferrie thinks the best part of VRT is just around the corner: the ability to plant multiple hybrids in the same field based on soil conditions. “That technology is going to be a game changer in terms of yield,” he predicts.

“Knowledge—whether your own, your employees’ or your suppliers’—is the mortar between the blocks that holds the systems pyramid together, laying the foundation for VRT,” Ferrie concludes.


Adopting Variable Rate Technology Requires Preperation



Systems Approach Pyramid
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