Training reduced subjectivity of comparative yield method of estimation of grassland biomass

Abstract

Measuring grassland biomass using objective, quick and accurate methods is important for practical purposes in agriculture and ecology. Most existing techniques are either expensive or require advanced technical skills making them unaffordable and impractical for farmers in developing countries. The comparative yield method is a quick technique that involves the estimation of grassland biomass from visual scores. Despite its potential for use by farmers with minimal technical skills, it has been criticized for being subjective, thus limiting its use for research purposes only. We hypothesized that training and establishment of agreed-upon ground rules can reduce this subjectivity. We compared data collected by 36 farmers in northern Ethiopia, who participated under three instruction groups. Group 1 was involved both in the selection of reference plots and calibration plots and agreed-on ground rules. Group 2 was shown the reference plots and orientated about the ground rules. Group 3 was neither shown reference plots nor orientated on ground rules. Levene's test for equality of variance was performed among the estimations made by individuals. Mean values of scores and biomass measurements varied among groups. The variability of records was higher in groups 3 and 2 than in group 1, indicating the need for training and agreed-upon ground rules to achieve objectivity. We conclude that with minimal training and agreement on ground rules, the comparative yield method can be used by farmers and ecologists in developing countries to estimate grassland biomass with better precision and accuracy.