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dfp-brad-robb-robb.dedman.jpg Brad Robb
Southeast Arkansas crop consultant Robb Dedman was a presenter at the 23rd Annual National Conservation Systems Cotton and Rice Conference.

Timely fertility, avoiding plant stress lead to high soybean yields

Southeast Arkansas consultant offers down-to-earth recommendations for soybean production.

Timely fertility applications and avoiding in-season stress are keys to record-yielding soybeans, according to an Arkansas consultant.

Robb Dedman prefers to space fertilizer applications based on plant need. "That's why we're moving away from 'front loading' our nutrient applications," says Dedman at the National Conservation Systems Cotton & Rice Conference held recently in Memphis, Tenn.

"We're putting more fertilizer out when it fits the plants' nutrient use curves, and we're getting better results. I know these curves aren't 100% accurate for the area where I work, but they are a good guideline."

Fertility

A successful fertility program starts in the fall with a quality grid or zone soil sample. "Every farmer has his preference. The key is consistency," Dedman says. "Make sure your crew pulls samples the same way. We like to sample half the farm one year and half the next."

Proper techniques include taking each sample at a uniform depth. Verify each one is properly identified so data can be applied to that specific sample. "It's important not to contaminate the current sample with soil from previous samples," Dedman says.

If you have multiple years of sampling data, look for trend lines. "Sampling results usually have minimal variations," Dedman says. "Use them to your advantage when you write variable rate prescriptions. I isolate details in our nutrient program based on years of sampling data, and it's starting to make a difference in our soils."

Poultry litter is the base fertility on Miles Bros Farms, a multi-thousand-acre southeast Arkansas operation where Dedman consults. They broadcast 1 to 2 tons in the fall and incorporate it. "If you don't incorporate, you won't get the full benefit from the nitrogen, and you might see some off-field movement during heavy rainfall," Dedman says.

"Nitrogen from the litter speeds decay of the previous year's crop residue and releases additional tied-up nutrients to the soil. We also variable-rate a commercial fertilizer on any high or low areas we find in-season."

The Miles farm uses tissue sampling to an extent, but not over the entire farm. Dedman calls it a guide, not the gospel. "We'll tissue sample a few fields of each crop and sample test plots separately. "Tissue sampling helps, but if you're trying to run your fertility program based on their results, you'll drive yourself crazy because one week they will be bad, and the next week good," Dedman says. "I draw a median line through the results. If the line is sloping downward, we need to make fertility adjustments."

If they find an in-field fertility problem during the growing season, they use a foliar fertilizer, but Dedman does not place great value on them. "They're not a primary source of fertilizer, or a cure-all. They're a Band-Aid," Dedman says. "If the Lord had wanted us to use foliar fertilizers as our primary source of fertility when soybeans start stressing, He would have put the roots where the leaves are located. Nutrient loss is just one factor we see in plant stress."

Preventing Plant Stress

Stress equals fruit loss. "When experiencing stress, a soybean plant's natural reaction is to shed its fruit," Dedman says. "To avoid that stress, you have to be proactive with irrigation, insect, and weed control."

As farmers continue to battle pigweed, Dedman remembers advice he was given as a young student by veteran Arkansas weed scientist Ford Baldwin. "Dr. Baldwin told me the best weed is the weed you never see," Dedman says. "They are easier to control below the soil than above."

Dedman likes current irrigation technologies and relies on moisture sensors to schedule irrigation. "Sensors help us stay ahead of low soil moisture levels," he says. "Terminating irrigation is just as important as starting it. Yields can be devastated by overwatering."

Variety selection, Dedman says, also helps manage stress. Mitigating soybean diseases can be easier by choosing a variety adapted to your specific growing environments and production practices. "Even though we have resistant varieties, they're not resistant to everything. We still usually apply a fungicide at the R2 to R3 stage," Dedman says.

Dedman and his client, Matt Miles, believe in on-farm variety trials and product testing. They dedicate ground to varieties and new products each year to see how they perform on their soils before expanding them to larger acreage. "We're seeing some plant health benefits from two new fungicides we tested last year — Revytek and Miravas Top," Dedman says. "Our plant canopies look healthier. That means good photosynthesis is taking place, which leads to improved yields."

Dedman offered his audience a few words of advice. "Do everything you can to avoid plant stress. Be timely in everything you do on the farm. Chuck Wilson, former director, Arkansas field services for the USA Rice Federation, shared this quote with me a long time ago: 'If you're five minutes early, you're on time. If you're on time, you're late. If you're late, you're left."

Dedman uses that mindset when making any farm-related recommendations.

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