REPLICATION REQUIREMENTS IN FIELD EXPERIMENTS FOR COMPARING PHOSPHATIC FERTILIZERS

Proliferation of new phosphatic fertilizers with diverse chemical properties necessitates much agronomic evaluation including comparison in field experiments. If such experiments lack the power to detect real and economically important differences between fertilizers, there is a danger of inferior products entering the fertilizer market. The ability of field experiments to detect differences in plant yield from different fertilizers depends not only on the intrinsic differences between fertilizers but also on site responsiveness to phosphate, experimental variability and degree of replication. Biometrical guidelines are provided to assist in the design of powerful field experiments and a formula is developed for determining the replication required to detect differences in specific situations. The number of replications required to have a high probability of detecting important differences between phosphatic fertilizers is more than sometimes used. It is concluded that extreme reserve is necessary in interpreting trial results which fail to show a significant difference between materials.