YIELD STABILITY IN INTERCROPPING STUDIES OF SORGHUM OR MAIZE WITH COWPEA OR COMMON BEAN UNDER DIFFERENT FERTILITY LEVELS IN NORTHEASTERN BRAZIL

Experimental evidence on yield stability of intercropping is sparse. This work was carried out to examine the stability of four intercrop patterns: maize (Zea mays L.)/cowpea (Vigna unguiculata (L.) Walp); maize/common bean (Phaseolus vulgaris L.); sorghum (Sorghum bicolor (L.) Moench)/cowpea; and, sorghum/common bean against their component crops. Twenty-one trials were established from 1974 to 1978. The mean relative yield advantage of intercropping patterns as indicated by the land equivalent ratio (LER) was 32%. The combined analysis of variance for the absolute total yields revealed that most of the pattern × environment interaction is accounted for by the heterogeneity of regressions. Pulses were less responsive to environmental change. However, cereals were more responsive to improvement in the environment resulting in increased yield. The regression lines of the intercropping patterns and sole cereals were closer to each other, due to the low yield contribution of the pulses to the intercropping total yield. However, the slopes of the intercropping pattern lines were closer to b = 1.0. On the basis of mean yield and regression slope, it was demonstrated that sole cereals or intercropping have better performance stability than sole pulses in northeastern Brazil.Key words: Stability, intercropping, sorghum, maize, cowpea, common bean