8 Ways to Match Hybrids to Management Zones Based on Water Supply

Matching yield goals to water supply lets you choose the right hybrids and populations for each management zone. ( Darrell Smith )

Variable-input technology (VIT) is exciting because it allows you to apply exactly the right kind and amount of inputs on every zone of your field to minimize cost and maximize yield. (That protects the environment too.)

Multihybrid planters are one of the main tools needed to fully implement VIT, says Farm Journal Field Agronomist Ken Ferrie. But even if you’re not yet equipped to switch hybrids as you plant, you can benefit from more efficient use of fertilizer, seed, pesticides and water.

The foundation of VIT is understanding your water supply in each management in zone. That lets you select the best hybrid and population.

Whether you farm irrigated or dryland, the amount of water available in every soil management zone determines how you will apply other inputs. “Assuming there are no other limiting factors, such as diseases or a nematode infestation, yield variations within a field usually are directly related to a soil’s ability to handle water,” Ferrie says. “Some soils tend to have too much water, while others have too little.”

Here’s what you must know about water in order to match hybrids to management zones:

1. Use yield maps and knowledge to pinpoint water issues in fields. “Some zones just can’t hold much water, which causes crop stress most years,” Ferrie says. “Some soils can hold more water, but it’s tied so tightly to clay particles that microbial organisms and plants can’t strip it away, so it’s useless.”

The higher the sand and silt content, the less water a soil can typically hold. The more clay content, the more water it can hold but less is usable. “Some soils have good water-holding capacity and a high percentage of usable water, but due to slope, texture or structure, they have poor infiltration,” Ferrie says. “That means they might only capture 50% of the water that falls during a rainfall event.”

2. Understand how much water you need. “It takes 3,000 gal. of water to grow 1 bu. of corn,” Ferrie says. “If you compare yield maps from wet and dry years and find some management zones yielded 20 bu. per acre more during the dry year, those higher-yielding soils must have provided 60,000 more gallons of water per acre. It might have come from better infiltration, or it could be water that ran off other parts of the field. It also could be from deeper soil with a higher usable water-holding capacity.”

3. Know how much water your soil can store. “In the Midwest, the amount of usable water held by various soils can range from ¼" to 2½" per foot of soil,” Ferrie says. “Depending on soil depth, the amount of usable water in the plants’ root zone can range from less than 1" to 9". This stored water can meet the crop’s needs when rainfall or irrigation doesn’t.”

4. Why is stored water so important? The average evapotranspiration rate (water moving upward from the soil through plants and into the atmosphere, along with soil evaporation) the past six years in Ferrie’s central Illinois area is 5.1" per acre in May, 5.9" in June, 5.9" in July and 5.2" in August. But the 25-year average rainfall across three regions of Iowa and Illinois is 4.2" in May, 4.5" in June, 4.4" in July and 4.1" in August.

“Comparing the need for water to the rainfall amount, from May through August, we are 4.9" short,” Ferrie says. “The situation might be worse if some of the rain didn’t infiltrate the soil. If only 90% infiltrated, we are 6.6" short of the amount required by crops. We must come up with the difference to avoid crop stress.”

Note: Infiltration rate varies according to moisture content of the soil and surface conditions (see chart below).

“If soil has a 4' rooting zone and must provide 6.6" of water, it must store 1.7" of usable water per foot,” Ferrie says.

Soils with low water-holding capacity might cause stress to crops multiple times during the growing season. “By the end of the year, we can wind up with average rainfall, but still stress the crop during long periods without rain,” Ferrie says. “In some soil zones, 10 days between rains and high temperatures are enough to do it. By harvest time, farmers might forget the crop was stressed, but the effect shows up in yield maps.”

5. Match yield goals to water supply. That lets you choose the right hybrids and populations for each management zone.

“Remember each year is different,” Ferrie says. “If you don’t receive sufficient rainfall from fall through spring, your soil will not recharge. In tile-drained fields, you will know soil is at its peak water-holding capacity if your tile lines are running. In untiled fields, you might need to rely on soil moisture sensors.”

6. How to set yield goals. “Setting yield goals too low causes you to apply too few inputs and sacrifice potential yield,” Ferrie says. “I also see farmers setting goals 50 bu. per acre above the soil’s water-holding capacity, resulting in wasted fertilizer and seed.”  

Zero in on a realistic yield goal by studying the yield of each soil management zone over a period of years. Separate wet seasons from dry ones.

7. How to set yield goals on newly-acquired land. What if a new field has no yield history? If the soils are comparable to some you already farm, that will give you a good idea of its water-supplying power.

“There are other ways to estimate your water supply,” Ferrie says. “Study the rainfall history for the past 25 or 30 growing seasons. In central Illinois, for example, the average rainfall is 24.3" from May through August. Look at the pattern for your region, not just your county.”

Next, determine the infiltration rate for each soil management zone. Conduct an infiltration test or consult a soil survey on the internet. Multiply the infiltration percentage times the annual rainfall to see how much water you can harvest. For example, say one soil management zone has an infiltration rate of 1.3" per hour. During the growing season, the average rainfall is 25.3", 60% of which falls at 1.3" per hour or less. That means you can capture 15" of water.

Your own observations can be useful. “If you receive ½" of rain in 30 minutes (a rate of 1" per hour), and water is running down your waterways at the conclusion of the storm, your soil is infiltrating less than 1" of water per hour,” Ferrie says.  

Now you must find out how much of the stored water can be used by the crop. You can determine the percentage of usable water in the soil by sending a sample to a soil test lab, or you can estimate it based on cation exchange capacity and soil texture.

Add the soil supply of usable water to the rainfall amount. In this example, 15" of rainfall will infiltrate the soil. The soil’s water-holding capacity is 9". “This gives us 24" of water to work with,” Ferrie says. “One inch of water equals 27,154 gal., so 24" of water equals 651,696 gal. Divide by 3,000 (gallons of water to produce 1 bu. of corn) and your yield goal will be 220 bu. As a rule of thumb, each 1,000 seeds planted produces 6.5 bu. of corn, so you need around 33,000 seeds per acre to achieve that yield. In succeeding seasons, you’ll gain more information from yield maps, soil testing and topographic data to fine-tune your planting rate. ”

8. Find the best hybrid for each management zone. Become a student of data to identify strengths and weaknesses in each zone. Look for hybrids that maximize the strengths and farm around the weaknesses.

Understand the difference between whole-field weaknesses and management zone weaknesses. For example, Goss’s Wilt affects the whole field, forcing you to select a more resistant hybrid. “If a zone has nematodes, with corn you can plant nematicide-treated seed in that area,” Ferrie explains. “With soybeans, you can plant nematicide-treated seed or a resistant variety.”

Within each management zone, focus on the greatest yield-limiting factor, and then find as many hybrids as possible that might fit.

Yield is paramount. “If hybrids meet every criteria for a management zone except yield, they must be cut from the team,” Ferrie says.

Don’t confuse yield with price per bag. “The cheapest hybrid might not be the best buy,” he says. “But the highest-priced hybrid might not be the best fit either. Initially, leave price out of the equation and look only at which hybrids fit your requirements. If, after studying all available data, two or three of them can meet your needs equally well, then consider the price.”

Spend as much time, or more, selecting varieties as you spend on choosing a piece of machinery and finding the best deal. Machinery can be fun, and maybe even glamorous, but plants pay the bills.

Water Storage Varies by Soil Type

Infiltration Varies as Soil Conditions Change

Manage Your Irrigation Water

Irrigation increases your opportunities to manage inputs. “In areas of poor infiltration, you can use variable-rate irrigation technology to apply lower amounts of water more frequently, so more water percolates into the soil,” says Ken Ferrie, Farm Journal field agronomist.

“You also can reduce the plant population on areas that supply less water. Install moisture sensors in multiple management zones to monitor the water content of various soils,” he says. “In unirrigated corners, lower your yield expectation to the soil’s water-holding capacity and reduce your plant population.”

That’s the promise of Variable Input Technology—matching the right amount of inputs to every soil zone to maximize yield and ROI.