M. L. Agnew and S. M. Berkenbosch, Iowa State University, 1992
The purpose of this study was to compare nine natural organic fertilizers to urea.
Treatments included BioTurf 10-4-4, Sustane medium grade 5-2-4, Sustane fine grade 5-2-4, ISU experimental (10% N), Milorganite 6-2-0, Natures Preference 5-3-5, Ringer 10-2-6, Ringer 6-1-3, Howe 5-2-5 (added in 1990), Urea 46-0-0, and a control. All fertilizers were applied at 1 lb N/1000 ft2 on May 15, June 15, August 15, and September 15, 1989. This study was replicated three times in a randomized complete-block design. Individual plot dimensions are 5 ft by 10 ft.