Potassium deficiencies, even in heavy Blackland soils that typically have adequate levels, have shown up more often in the past few years, McFarland said. “In many cases it’s drought related. Potassium uptake occurs through diffusion, so without adequate moisture, uptake slows or stops. When clay soils dry, they shrink, collapse and trap potassium in the clay layers. It can’t get to the roots.” Compaction also may play a role.

Liquid potassium offers a viable option. “With band injection, the yield response has been substantial,” McFarland said. “It is an advantage to place potassium in the active moisture zone.”

He recommends growers soil test to determine if potassium is adequate. “If it’s marginal, 125 to 150 parts per million, it may justify adding potassium. Deeper samples also may show available potassium. If it’s adequate at depth, yield response to an application is not likely.”

pH effects

Soil pH also affects nutrient uptake and fertilizer efficiency. A pH below 6.0 can affect yield potential. “As pH drops, solubility of nutrients also drops.” A good range is 6.4 up to 7 and McFarland recommends growers “stay well away from low levels. As pH goes below 5.5, aluminum toxicity can begin to be a problem.”

Some Blacklands soils show pH levels as high as 7.4 to 8, but some soils in the area may be as low as 5.4.

Again, McFarland recommends sampling deeper than the typical 6-inch level. “Sometimes the pH is low just in the surface 6 inches, which may not be a problem.  But if it’s low to depth, it could be trouble. Anything below 5.6 or 5.7 will show a response to limestone. Below 5.5 applying limestone will likely provide a significant advantage.”

“It’s a good idea to test to depth.”

Tillage may be an adequate option if soil pH is low in just the top 6 inches. Mixing soil from 8 to 10 inches may correct the problem.

McFarland cautions Texas farmers to make certain of what they are buying when they purchase limestone. “There is no limestone law in Texas, so it’s up to growers to know the quality of the product. Content and fineness make a difference. Percent of limestone—50 percent or 100 percent—affects the value and dictates application rate.”

With fertilizer prices still extremely high, McFarland says farmers can ill afford to waste any, apply more than they need, or to pay for any product that will not provide an economic advantage. The best tool remains a thorough knowledge of soil nutrient levels—based on soil testing (including sampling at depth).

Paying attention to what fertilizer costs, he says, should drive that message home.