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

Abstract

Densities of maize ( Zea mays L.) and bush beans ( Phaseolus vulgaris L.) were evaluated in monoculture and in several intercrop combinations over two seasons in the Cauca Valley of Colombia (4°N latitude, 1000 m elevation). To determine whether optimum density combinations existed for intercropping, maize densities from 1 to 10 plants per m 2 were combined with bean densities from 10 to 40 plants per m 2. Yields and yield components of both crops were measured, and net income and biological efficiency of intercrop patterns compared to monoculture of each component crop. Maximum maize yields in monoculture were 3640 kg ha −1 with a tall hydbrid in the first season, and 7000 kg ha −1 with a semi-dwarf hybrid in the second season. Bean yield maxima in monoculture were about 2100 kg ha −1 in each season. Highest intercrop yields were attained with low to moderate maize densities and a wide range of bush bean densities. Higher total grain yields were found in intercrops in each season than in the best monoculture treatment. Bush bean yield per plant was reduced by increasing bean or maize plants per m 2 in the intercrop, but not proportionally to the number of additional plants. Thus, bush beans under severe competition are more efficient in use of scarce resources. One tall maize plant was equivalent in competition to three-and-a-half to four bush bean plants, while one semi-dwarf maize plant was equivalent to two to three bush bean plants. Net income generally was higher in the intercrop patterns, followed by monoculture beans and monoculture maize. Biological efficiency as measured by the Land Equivalent Ratio was higher in intercrop than in monoculture, and one intercrop treatment in the first season showed a 65% advantage over the single crop alternatives.