Nitrogen is subject to leaching, runoff and volatilization, but enough may remain in the soil, especially following a poor crop year, to produce cotton the following season.

“More than 10 years of research has demonstrated that residual nitrogen measured to a 24-inch depth, can be credited at 100 percent,” he said. “Residual soil nitrogen in the major production regions of Texas is often substantial with cotton showing a yield response to supplemental nitrogen fertilization at only 23 percent of study sites.”

He said sulfur and boron also are easily leached deeper into the soil, down to 24 to 48 inches.

“Look deeper into the profile to determine the amount of nutrients available,” he said. “We recommend deep profile sampling.”

He said identifying residual nitrogen and adjusting supplemental application rates accordingly has benefits other than cutting back on fertilizer. “Farmers may be able to use less plant growth regulator, insecticide, and harvest aid. They also may be able to harvest earlier.”

Coker said tests evaluating advantages of slow-release nitrogen have shown no significant yield advantages.

He said phosphorus is a very stable, immobile element that is not prone to leaching or volatilization. He recommends band injecting phosphorus at about a six-inch depth.

He said additional work is needed “to determine if nitrogen losses can be reduced under high loss potential conditions.”