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Most early alley cropping studies in semi-arid Kenya were on fairly flat land while there is an increase in cultivated sloping land. The effectiveness of aging contour hedgerows and grass strips for erosion control on an about 15% slope of an Alfisol was compared. The five treatments were Senna siamea hedgerows with tree prunings applied as mulch to crops (H+M), hedgerows with crops with prunings removed (H), mulch only applied to crops (M), crops with Panicum maximum grass strips (G), and a sole crop control of a rotation of maize (Zea mays) and cowpea (Vigna unguiculata). Cumulative results for four consecutive seasons showed that most successful treatment H+M reduced soil loss from just over 100 to only 2 Mg ha(-1) (or t ha(-1)) and runoff from just below 100 to 20 mm as compared to the sole crop control C. Grass strips were less effective (15 Mg ha(-1) and 46 mm, respectively). Cumulative maize yields (1993-1995) were reduced by 35% in H+M, 55% in H, and by more than 60% in G. Generally, the M plot produced similar yields to those of C. Cowpea yields were less affected than maize because mean rainfall was well above average during the cowpea seasons. The hedgerows, particularly in combination with mulch, and grass strips kept soil loss on steep slopes at tolerable and sustainable rates. Strong trade-offs between erosion control and crop productivity need not be a major deterrent to adoption by farmers, if the grass and trees provide other significant benefits to farmers.