Figure 4: Crops yields: (a) cowpea grain as affected by cropping system × cowpea variety interactions effects ( ), 2007 and 2008; (b) subsequent millet grain and above-gorund biomass dry yields as affected by year × cropping system × cowpea variety three-way interaction effects at Cinzana Agronomic Research Station, 2008 and 2009. Y1: year 1 (2008), Y2: year 2 (2009), S1: alternate rows intercropping (1 row millet/1 row cowpea), S2: interhills intercropping (2 hills millet/1 hill cowpea), S3: cowpea sole crop, cowpea varieties: IT89KD-374, CZ1-94-23-1, and CZ11-94-5C.