Effect of incorporation of legumes on selected soil chemical properties and weed growth in a potato cropping system at Timboroa, Kenya

The effect of incorporation of lupine and garden pea on selected soil chemical properties and growth of weeds in a potato cropping system was evaluated in North Rift, Kenya. The study was carried out in a well drained, extremely deep, dusky red to dark reddish brown, friable clay, acid humic top soil. Two weeding regimes (at legume incorporation stage and/or at 50% potato flowering stage), three nitrogen levels (0, 60 and 120 kg N ha-1) applied as CAN and two legumes plus a control (garden pea, lupine and none) were evaluated in a split-split plot design with weeding regimes as the main plots, N as sub-plots and legumes as the unit plots. Incorporation of legumes significantly (p < 0.05) raised soil pH from 3.6 - 3.9 and to 4.2; increased soil available P from 15 mg/kg to 25 and to 29 mg/kg for garden pea and lupine, respectively. The two legumes interacted with weeding regime and N reducing sheep sorrel weed density and biomass. The significantly higher lupine effects were attributed to its high biomass production suggesting that legumes may best improve soil fertility and reduce soil acidity when incorporated in the soil as green manure.