The sample is important. He recommends that producers pull from 12 to 15 cores for each 40 to 50 acres of uniform field area. “Anything larger than 50 acres should be split and split where soil type or textures change.

“Send samples in promptly.” He said soil left in a truck for several days will change and will not reflect what was initially available in the sample.

A zero to 6 inch sample is the standard test depth, but he said pulling deeper samples may identify nutrient carryover and possibly reduce fertilizer cost. “At a 12-inch to 24-inch depth, a significant amount of nitrogen may be available,” he said. “Often, a producer can grow a crop with just available nitrogen in the soil, especially following a drought and a failed crop.”

Reducing nitrogen demand, he said, lowers production costs. Less nitrogen also may promote an earlier crop, and an earlier harvest, especially with cotton.

He said tests show that residual nitrogen in corn land has produced yields equal to similar areas where nitrogen was applied. In multiple years, corn, cotton and grain sorghum responded to residual nitrogen. In a seven-year cotton study on 55 sites, only 13 responded to added fertilization with 100 pounds of residual nitrogen present.

“In one study, the value of residual nitrogen was as high as $80 per acre,” McFarland said.

He recommends producers continue to take the zero to 6-inch sample every year. And when they pull deeper samples he recommends using two buckets, one for the standard sample and one for the deep one. “Bag the samples separately.

“Farmers will find nutrients and they will save money on fertilizer,” he said. “And they have several tools to help sampling. Some are pre-marked at 6 inches, 12 inches, 18 inches and 24 inches.  Cost ranges from $40 to $70—maybe less when bought in bulk.

“Also, moisture conditions need to good for best sampling.”

McFarland said farmers have several choices for nitrogen fertilizers. “Pick the cheapest one,” he said. “Plants don’t care, so buy based on the cost per pound of nutrient.”

McFarland said phosphorus is a critical nutrient, especially important for healthy plant root systems. “Phosphorus is very stable, insoluble and does not leach or volatize. That’s a blessing and a curse because it can stratify.”