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Area-×-Time Equivalency Ratio: A Method For Evaluating The Productivity Of Intercrops

Hiebsch, C. K., McCollum, R. E.
Agronomy journal 1987 v.79 no.1 pp. 15-22
crop yield, duration, intercropping, land use, continuous cropping
Production systems involving interplanted food crops are widespread in tropical latitudes, and interest in quantifying the productive potential of intercrops is high. Published data often suggest a sizable gain in land-use efficiency by growing such crops in mixtures. Our thesis is that many of the large intercrop advantages reported in the literature are misleading because the conceptual basis on which the monoculture-vs.-intercrop comparisons were made is incomplete. In this paper, we review the various methods for estimating intercrop productivity, propose a concept which we believe will remove the principal limitation in conventional methodology, and test the new concept with intercrop data from the literature. The land equivalency ratio (LER) is the most-used convention for intercrop-vs.-monoculture comparisons, but LER is frequently inappropriate because cropping-system duration, i.e., time, is not included in its calculation. Duration of land occupancy by an intercrop is often longer than production-cycle duration for one or more of the interplanted species. We propose an area-×-time equivalency ratio (ATER) and suggest that it will correct this conceptual inadequacy in LER. When published intercrop data were reevaluated via the ATER concept, large land-use advantages ascribed to growing food crops in mixtures disappeared. We conclude that most crop mixtures utilize land area and time (area·time) at about the same efficiency as pure stands of the mixture's components.