Using these products, however, adds to fertilizer costs. So Mitchell and Osmond ask: “Are the benefits worth the extra cost? Do these materials work effectively and consistently under the heat and humidity of the Southern U.S. and for the major crops produced in the region?”

Results vary, according to the Southern Region Water Quality Program Special Project funded through the USDA National Institute of Food and Agriculture (NIFA). That study was designed “to evaluate the effectiveness of several slow-release nitrogen fertilizers and nitrogen fertilizer stabilizer products, compared to standard nitrogen fertilizers … for selected major row crops in the cooperating southern region states: Arkansas, Alabama, Florida, New Mexico, North Carolina, Oklahoma, and Texas.”

In each state, research included alternative and new technology nitrogen sources tested independently. Trials compared these products to “traditional” nitrogen sources, using crops and management practices common to each state. “Rates, methods and timing of application(s) depended on the objectives for each experiment. Where possible, materials were applied according to the manufacturers’ recommended rate and method. However, because of the difficulty of comparing commercial products, each state used products differently.

The traditional nitrogen sources used included: ammonium nitrate, urea-ammonium sulfate, liquid urea-ammonium nitrate (UAN solution), urea, dairy manure, and poultry litter. Alternative products evaluated included: Agrotain (urease inhibitor), Nutrisphere N (urease and nitrification inhibitor), Nitamin Nfusion (a slow release nitrogen source), Environmentally Smart Nitrogen (ESN, a polymer-coated, controlled-release urea), NDemand 30L 30-0-0 (a slowly available, liquid nitrogen), CoRoN 25-0-0 (a controlled release liquid nitrogen), UCAN 23 (YaraLiva) (includes water-soluble calcium to reduce ammonia volatilization), New Suryamin (includes organic nitrogen and bio-enzymes).

Results across all the states indicate:

• Nutrisphere, Nitamin and Agrotain did not improve yields at any location for any crop tested.

• Pre-plant incorporated ESN (as compared to urea) improved the corn yield at one site in Arkansas. When tested at two sites in Arkansas, ESN improved seed cotton yield at one site but produced yields equal to urea at the second site. However, surface applied ESN performed similarly or worse than UAN solution or urea in Alabama (corn), North Carolina (corn and wheat), Oklahoma (wheat), and Texas (grain sorghum).

• Evaluation of three organic nutrient supplements on vegetables in Florida gave mixed results, depending upon the rate and method used but generally required regular fertilizer applications to maintain optimum yields.