AVAIL Phosphorus Fertilizer Enhancer: Analysis of 503 Field Evaluations.

AVAIL, a maleic-itaconic copolymer product marketed to enhance phosphorus (P) fertilizers, has been the subject of considerable research, debate, and legal action in recent years. Much of the debate has focused on the feasibility of AVAIL’s proposed mode of action, compared to quantifying crop response in the field. Although some effort has been made to summarize field research on crop response to AVAIL, most have not adequately considered standard principles in soil fertility. A surprising number of studies on AVAIL were conducted under conditions where no P response would be expected with conventional P fertilizers, and consequently should be evaluated with this in mind. A meta-analysis was conducted on all of the available studies on AVAIL P fertilization and parsed this data based on soil test P (STP), pH, and P fertilizer rate – three factors fundamentally accepted to influence crop P response. When all of the possible data were considered (503 data points), AVAIL increased crop yields by 2.1% (P <0.0001). However, when only those data were considered where a P response would be expected (i.e. low STP, extreme pH, and low P fertilizer rate; 116 data points), AVAIL increased crop yields by 4.6% (P <0.0001), which increases to 5.8% when only peer-reviewed and thesis/dissertation literature were considered. AVAIL is therefore effective in significantly increasing crop yields when used under conditions where a P response would be expected and when it is used appropriately. We urge researchers to use fundamental soil fertility principles when evaluating crop response to AVAIL.