ACA, has been sold locally for several years on Delmarva as a crop stimulant or yield enhancer. ACA stands for Agricultural Crop Additive. It was developed in the early 1970's and sold as an additive for anhydrous ammonia. It has been suggested that it acted as a nitrification inhibitor, although this has been proven not to be the case. It has been speculated that the zinc has been providing a micronutrient response.
More recent indications are that some sort of plant regulatory action is occurring.
Reported responses to ACA include more fibrous and extensive root systems, increase in the number of brace roots, faster and more vigorous early plant growth, wider and darker green leaves, and heavier ear and kernel weight. Positive yield responses have been the exception rather than the rule in controlled, replicated experiments conducted both in the Mid-Atlantic region and in the Midwest. Studies in Wisconsin did not generate higher yields in field corn. The results in the Mid-Atlantic region have, with a few exceptions, failed to demonstrate yield increases in several agronomic and vegetable crops. The University of Maryland has shown responses in small grains, but Virginia studies have not shown similar responses.