Measurement of residue cover with dot screens

Photographic color slides of crop residue covering soil surfaces were projected onto screens with 100, 200, and 300 randomly located dots and visually evaluated for the number of dots that were coincident with images of residue. Specially prepared simulated residue slides were also projected onto the screens. Accuracy was improved by using at least three screen replications. There was not a consistent trend in improvement of accuracy between the 100-, 200-, and 300-dot screens. The observed residue cover was considerably higher than the calibration values. The dot-screen procedure appears to be consistent enough to obtain relative comparisons among tillage practices with three replications of observations of the same photographic slide.