Field Walk (image) American Society of Agronomy Share Print E-Mail Caption Development of the modified phosphorus index involved farmers and farm advisors. Their hands-on experience helped ensure a more workable final product. Credit Q.M. Ketterings. Usage Restrictions Please use with story only. Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.