Yield potential and land-use efficiency of wheat and faba bean mixed intercropping

In Ethiopia, food production for a rapidly growing population from a continually shrinking farm size is a prime developmental challenge. Rising input costs, decline in soil quality, and buildup of insect pests, diseases and weeds have threatened the ecological and economic sustainability of crop production. To address those issues, intercropping of cereals with pulse crops could increase total grain production, provide diversity of products, stabilize yield over seasons, reduce economic and environmental risks common in monoculture systems, and thereby enhance sustainability. Here, mixed intercropping of wheat (Triticum aestivum L.) with faba bean (Vicia faba L.) was compared with sole culture of each species in 2002 and 2003 at Holetta Agricultural Research Center, in the central highlands of Ethiopia. The treatments were sole wheat at a seed rate of 175 kg ha(-1), sole faba bean at a seed rate of 200 kg ha(-1), and an additive series of 12.5, 25, 37.5, 50 and 62.5% of the sole faba bean seed rate mixed with the full sole wheat seed rate. Our results showed that mixed intercropping increased the land equivalent ratio by +3% to +22% over sole cropping. Increasing the faba bean seed rate in the mixture from 12.5 to 62.5% reduced wheat grain yield from 3601 kg ha(-1) to 3039 kg ha(-1) but increased faba bean grain yield from 141 kg ha(-1)to 667 kg ha(-1). Sole culture grain yield exceeded mixed culture grain yield by +5 to +25% for wheat and by +172 to +1190% for faba bean. Nonetheless, we obtained the highest total grain yield of 4031 kg ha(-1), gross monetary value of US$ 823, system productivity index of 4629 and crowding coefficient of 4.70 when wheat at its full seed rate was intercropped with faba bean at a rate of 37.5%. On average, weed biomass was reduced from 40.4 g m(-2) in sole wheat to 31.1 g m(-2) in mixed culture and the chocolate spot disease score was reduced from 5.1 in sole faba bean to 3.4 in mixed culture. In conclusion, intercropping of wheat with faba bean may increase total yield and revenue, reduce weed and disease pressure, increase land-use efficiency, and thereby enhance sustainability of crop production in Ethiopian highlands.