Density interactions in tropical intercropping. I. Maize ( Zea mays L.) and climbing beans ( Phaseolus vulgaris L.)

Abstract

Densities of maize ( Zea mays L.) and climbing beans ( Phaseolus vulgaris L.) were studied in monoculture and in a number of intercrop combinations over two seasons in the Cauca Valley of Colombia (4°N Latitude, 1000 m elevation). Maize densities from 1.5 to 10.5 plants per m 2 were combined with bean densities from 5.6 to 37.5 plants per m 2. Bean/ maize density combinations included 48 treatments in the first season and 25 treatments in the second season. Yields and yield components of both crops were measured. Maize density had a greater influence than bean density on both maize and bean yields and yield components. Maize is taller and shades the developing bean crop. A vigorous intercropped climbing bean reduced maize yield in the second season, though not in the first. Maize yields were positively correlated with maize density and ears per plant. Bean seed yield was positively correlated with pods per m 2 and pods per plant, but not with bean density. Bean yields and yield components were consistently and negatively correlated with maize yields and yield components: negative correlations between maize and bean yields were r = −0.84 ∗∗ and r = −0.72 ∗∗ for the first and second seasons. Per plant yield is reduced in both intercrop components by increased density of either crop. One additional maize plant per m 2 reduces per plant maize grain yield about five to six times more than one additional bean plant added to the intercrop. Bean yield per plant is reduced two to three times as much by adding one additional maize plant per m 2 compared to adding one additional bean plant per m 2. Intra-specific competition appears to be more intense than inter-specific competition. Effects of one additional plant of either species decrease at higher densities in the intercrop as both components compete for scarce growth factors. Total grain yields did not show an advantage for either monoculture or intercropping at higher maize densities. Land equivalent ratios consistently were greater than one, and specific combinations reached LER = 1.20. Total protein yield was higher for intercrop systems over all density combinations. Net income was higher for monoculture beans and for intercrop patterns than for monoculture maize. Results suggest that a range in maize/ climbing bean density combinations can be used to obtain maximum or near maximum total production and net income.