500-acre corn farmer pulled 39.44 tons of nitrogen, 16.22 tons of phosphorus and 11.83 tons of potassium out of the soil—not including leeching or other nutrient losses. “The availability of nutrients changes during the year due to biological, chemical and physical properties,” says Leslie Glover, USDA soil scientist. “Using the same nutrient program [year over year] is like going to the doctor and getting the exact same medication without getting any examination to determine the current state.”
“With that extra 20 bu. of corn, I’ll need to put something on [double crop] wheat possibly,” he says.
Carefully consider the impact big yielding crops has on phosphorus and potassium levels in fields.While nitrogen might typically be the first nutrient you think about when it comes to high yields, it’s important to consider other nutrient needs as well. “When guys have 200-bu. corn and 70-bu. beans they’re taking about 130 lb. of phosphorus and 152 lb. of potash/potassium out of the soil [in that two year rotation],” says Bob Perry, general manager, Perry Agricultural Laboratory, a soil testing lab in Bowling Green, Mo. “A lot of folks are just putting on
100-lb./100-lb.—all of a sudden they’re behind.” Crops need phosphorus in full form early for root development and as the plant grows to promote healthy stalks, stems and flower production. Potassium plays a vital role in plant growth as well, and deficiency can result in stunted growth, defoliation and weakened response to weather changes such as drought. “When we have poor fertility we’re much more susceptible to any deviation in weather,” Perry says. “Going through any stress is harder when you don’t have the fertility you need.” Perry recommends soil to have at least 50 lb. of phosphate per acre (25 ppm) and 300 lb. of potassium per acre (150 ppm) each season.