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Soil testing remains basis of fertility programSoil testing remains basis of fertility program

Checking nutrient level is an absolute in devising an efficient fertilization plan, but  digging down as far as 48 inches could reveal leftover nutrients  and significant savings on a fertilizer bill.

Ron Smith 1

August 26, 2014

5 Min Read
<p>MARK MCFARLAND, Texas AgriLife Extension soil fertility specialist, discusses wheat nutrient management at the recent Big Country Wheat Conference in Abilene.</p>

It’s almost as predictable as the lunch menu at an Extension production meeting. Soil fertility specialists will encourage producers to soil test before they determine type and rate for crop nutrients. And attendees can expect barbecue and baked beans. Count on it.

Mark McFarland’s message, however, goes a bit, well, deeper. He’s adamant that checking nutrient level is an absolute in devising an efficient fertilization plan, but he also recommends digging down as far as 48 inches to see if leftover nutrients might be available to offer significant savings on a fertilizer bill.

“We buy fertilizer per pound of nutrients,” McFarland told participants in the recent Big Country Wheat Conference in Abilene. “And with prices ranging from 40 cents a pound to 60 cents a pound, it can be an expensive investment. We want to do it right because we know what it takes to grow a crop.”

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With wheat, end use is a critical factor. Nutrient demands for grazing, grain or dual purpose are different. “First, we need to know the end use and then determine how much nitrogen, phosphorus, potassium, secondary nutrients and micro-nutrients we need to achieve yield goals. If we leave one nutrient out, the other things we do will not matter. If we short one nutrient, that’s the one that will determine yield potential. So we need to get as close as we can.

“Soil test,” he said, to no one’s surprise. “I’ve been preaching that for 20 years.”

He also cautioned farmers to consider field history when planning nutrient programs. “See if any nutrient remains in the soil. Residual nutrients may be more valuable now than when they were applied. Price may have gone up.”

Nitrogen is wildcard

He says nitrogen is “the wildcard in nutrient management. It moves in the soil and can volatilize. We know a lot of ways we can lose nitrogen out of the system.”

Application rate, timing and method will determine how much nutrient gets into the plant. “Higher yield and better quality depend on rate and timing. Also, crop use—grain, grazing or dual purpose—require different rates. Yield goal will affect nutrient demand, too.”

Wheat needs part of the necessary nitrogen applied pre-plant or at-planting. The rest should wait, and rate will depend on crop conditions and yield potential in-season. “During wheat development, farmers can make adjustments. Use what’s needed to produce what the crop can make.”

For grazing only, McFarland said the crop may need nothing, depending on the field history. Drought, hail, or freezes of previous crops may have left ample nutrients in the soil. “Typically, we add pre-plant or at-planting nitrogen, 20 to 60 pounds depending on moisture and other factors.”

He recommends incorporating nitrogen, at least 2 inches deep, and 5 inches to 6 inches may reduce potential for volatization.

“Add phosphorus and potassium if needed and get the nutrients into the moisture zone of the crop where the plant is able to secure them for a longer period of time compared with surface applied.”

Row spacing, soil texture and soil type also may affect fertilizer rates. “Stand and moisture level will affect topdress rates,” McFarland said. Applying all fertilizer early increases the chance of losing nutrients. “Producers can meter out nutrients in-season based on condition of the crop.”

For grain only, wheat requires 1.5 pounds of nitrogen per bushel of grain. “Consider residual, too. Also, growers may pick up nitrogen from irrigation water, so consider that as well to determine application rate. For a 50-bushel wheat yield goal, figure 75 pounds of nitrogen, either residual or applied.”

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Split applications

He recommends split application with one-third of nitrogen demand applied early and two-thirds applied prior to jointing. That topdress timing, he says, reduces potential for freeze damage and disease pressure. “It also reduces potential for leaching and denitrification.

“Farmers may adjust topdress rates based on yield potential, but they should allow time for rain or snow to incorporate the nitrogen into the soil. It’s better to topdress nitrogen too early than too late since jointing is a critical time for nitrogen. That’s when yield potential is determined. After that, nitrogen applications will not affect yield but may improve quality.”

Dual purpose wheat needs more fertilizer, 2 pounds per bushel from a combination of residual fertilizer, irrigation water and applied fertilizer.

McFarland says split applications are still best. And he encourages soil testing at the typical 6-inch depth as well as deeper analyses.

“Wheat roots may go as deep as 3 or 4 feet deep, and nitrogen can move deeper than typical testing limits and still be in the crop rooting zone. Take soil samples at the 6-inch depth and also down to 4 feet to measure the plant’s available nitrogen.”

Dig deeper

He says tests across Texas have shown available plant nitrogen from 80 pounds to 200 pounds per acre found at depth. “At 50 cents to 60 cents per pound and considering 40 pounds of residual nitrogen, that’s a significant amount of money.”

Further studies show that with adequate residual nitrogen crop yields can be maintained with no additional nitrogen added. Studies have been conducted with cotton, corn and grain sorghum with similar results—maximum yield with zero added nitrogen.

“I’m not saying don’t fertilize,” McFarland said. “I am saying test first. Any money you don’t spend is profit.”

The extra samples only cost $4 each. “And make those deep samples complete, not just for nitrogen. Sulfur can move down, too, and potassium can be deeper.”

He said wheat farmers have many options for nitrogen sources. “The best one to buy is the cheapest,” he said. “But remember, calculate cost on pounds per nutrient.

“And don’t overlook phosphorus. It’s especially important for forage, and it is stable.” Placement is critical, however, and a band, 5 inches to 6 inches deep, is the most effective and most efficient application method. “We see a substantial yield response with phosphorus applied deep and find that 30 pounds deep is better than 90 pounds surface applied. Farmers can reduce phosphorus rate by 50 percent.

“Don’t skimp on potassium,” he added.

McFarland also warned wheat farmers to be wary of “non-traditional” fertilizer products with “no significant amount of research on when and how they work.”

University studies on some of these have found no improvements and in some cases resulted in “significant yield reductions. Be cautious about what you buy. Some of these products may make you feel better but they will not help your wheat crop.”

He said farmers can count on soil testing—and barbecue at farm meetings.




About the Author(s)

Ron Smith 1

Senior Content Director, Farm Press/Farm Progress

Ron Smith has spent more than 40 years covering Sunbelt agriculture. Ron began his career in agricultural journalism as an Experiment Station and Extension editor at Clemson University, where he earned a Masters Degree in English in 1975. He served as associate editor for Southeast Farm Press from 1978 through 1989. In 1990, Smith helped launch Southern Turf Management Magazine and served as editor. He also helped launch two other regional Turf and Landscape publications and launched and edited Florida Grove and Vegetable Management for the Farm Press Group. Within two years of launch, the turf magazines were well-respected, award-winning publications. Ron has received numerous awards for writing and photography in both agriculture and landscape journalism. He is past president of The Turf and Ornamental Communicators Association and was chosen as the first media representative to the University of Georgia College of Agriculture Advisory Board. He was named Communicator of the Year for the Metropolitan Atlanta Agricultural Communicators Association. More recently, he was awarded the Norman Borlaug Lifetime Achievement Award by the Texas Plant Protection Association. Smith also worked in public relations, specializing in media relations for agricultural companies. Ron lives with his wife Pat in Johnson City, Tenn. They have two grown children, Stacey and Nick, and three grandsons, Aaron, Hunter and Walker.

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