Wheat Scoop: Soil pH, Fertility Keys to Maximizing Wheat Profits

Given its importance to farmers, the soil in which crops grow is often the most misunderstood component of wheat production. Managing soil fertility and soil pH, according to Dr. Brian Arnall, soil fertility specialist at Oklahoma State University, is a must when trying to achieve profitable yield levels.

“Only about 10% of the wheat producers in Oklahoma soil test each year,” Arnall explained at the Profit Maximizer Wheat Summit, July 20 in Wichita. The Summit was sponsored by Bayer CropScience, the High Plains Journal, KFRM Radio and Kansas Wheat. “Yet, soil tests are one of the most important things producers can do.”

Arnall says the soil test – which can be performed by land-grant universities or private companies – should measure nitrogen, phosphorous, potassium and soil pH, or acidity. Soil pH levels affect the effectiveness of many common herbicides, such as atrazine and sulfonyurea products.

“In soils with a pH of 5, herbicides degrade three times faster than soils with a pH of 6,” Arnall explains. “We’re losing activity on our very important herbicides. If we have problems like Italian ryegrass and cheat, we don’t need to be losing activity on some of our pre-plant and early-season herbicide applications.”

Wheat breeders have had great success in developing wheat varieties that tolerate acidic soils. However, when farmers rotate out of wheat into other crops, there are no aluminum tolerant corn, soybean or grain sorghum varieties.

Arnall says nitrogen management is important, too. Many farmers apply most, if not all, of the wheat crop’s nitrogen needs pre-plant. However, nitrogen fertilizer is temporal; of the nitrogen fertilizer applied pre-plant, plan on just 30-40% nitrogen-use efficiency. If applied in January or February, efficiency jumps to 50-60%.

“Now you’re getting more bang for your buck. When anhydrous prices are close to UAN and urea, it does not make sense to put everything in anhydrous just because it’s cheaper then, because the efficiency is so much lower,” he explains.

Arnall adds that there is no wheat yield guarantee in much of Kansas. If a producer fertilizes for 50 bushels per acre each year and only obtains a 10 bushel yield, the extra nitrogen will be wasted. A split application of nitrogen, however, allows producers to gauge crop progress and fine-tune nitrogen applications accordingly.

Wheat growers can estimate crop progress based on four environmental factors. Oklahoma State University data indicates that early planting date, ample soil moisture at planting, moderate temperatures during flowering and good moisture during grainfill led to higher than average yields on research plots west of Enid, for three straight years. Odds are that yields will decrease incrementally as just three, two or one of these conditions are met.

“If you have yield potential that’s above average, then you should look at fungicides and additional inputs,” Arnall says. “If you start dropping out those ideal conditions, you’re looking at well below average yield and your inputs, or how you manage that crop, should change.”