Visual assessment of pasture degradation: validation by ground cover and seasonal variation

Resumo

Visual assessments of pasture degradation levels are widespread because they are rapid, practical and
inexpensive. However, they can be subjective, making it difficult to distinguish between degradation levels to establish
management practices. This fact, in association with the lack of standardization of the number of levels and the assessment
periods, suggests a need for further studies. The objective of this study was to evaluate the relation between the degradation
levels of visually evaluated pastures and the soil cover measured in fields in summer and winter. Percentages of Brachiaria
grass, bare soil, spontaneous vegetation (broad and narrow leaf) and mulch were evaluated in 35 areas with different levels
of visual degradation. Canonical discriminant analysis showed that a reduction in the visually assessed degradation level
correlates better with the field-measured soil cover in summer. Visual distinctions between the degradation levels were difficult
by the visual ambiguity between spontaneous vegetation and pasture in both assessment periods and the visual ambiguity
between bare soil and mulch in winter. Visual assessments of pasture degradation should be standardized in the summer period
and simplified to two degradation levels, making them more accurate and better related to the vegetation cover measured
directly on the field.