Interaction in intercropped Coffea Arabica L. and Phaseoulus Vulgaris L.
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Three experiments were conducted on intercropping beans with low and high density Arabica coffee trees pruned to different canopy densities. Growth and yield components of bean plants were measured while clean coffee yields and quality were assessed to determine how the two intercrops interact when grown in mixtures of varying proportions. Dry bean plants interp1anted in low density coffee dessicated the top Boil which resulted in lower quality coffee beans than that obtained from mulched coffee. Bean plants grown directly under the dense coffee canopy were etiolated, had fewer branches, pods and seeds per plant than dry bean plants grown in the wider space between the coffee trees. Assessment of dry bean seed yield per planted row showed that only the central 90cm to 120cm strip between the coffee rows was suitable for interplanting with beans. Low density coffee pruned .on capped multiple stem system carried the bulk of its crop in the top half of the canopy and the removal of the lower half of the canopy had no significant effect on clean coffee yields. Alteration of pruning time in the year had no significant effect on clean coffee yield, though the quality could be affected due to the timeliness of opening up the canopy for effective penetration of pesticides to control diseases. Bean plants interplanted in h~h density coffee in full production developed long internodes, few branches, pods and seeds per plant, culminating in low yields. The removal of the coffee canopy by block stumping resulted in viBorous grQwth of interplanted beans which developed short internodes, increased branching, podding and seed setting and consequently high seed yield. Application of calcium ammonium nitrate fertilizer significantly increased the bean Beed yields. Neither the nitrogenous fertilizer nor intercropping coffee with different bean rows per coffee inter-row space s~ificantly affected the clean coffee yields. The dry bean yields increased with the rise in the number of the bean rows per coffee inter-row space. Interplanting coffee with beans increased the proportions of grade TT and thus lowered the quality of the clean coffee from the intercropping system due to soil moisture stress. Intercropping Yield Advantage Ratio (IYAR) is proposed as a measure of yield advantage achievable when an annual crop is interplanted in an established perennial crop. The IYAR is obtained by dividing the sum of the interplanted perennial crop yields in a cropping cycle and the annual yield of the annual intercrop by the sole perennial crop yield in a cropping cycle. An IYAR value greater than unity confers yield advantage to the perennial/annual intercropping system. Due to the adverse shading effect of the dense coffee canopy on undersown bean plants, the only suitable period in the coffee cropping cycle for successful intercropping with beans is during the change of cycle, when the coffee canopy is drastically reduced for about two years, provided the soil fertility is high and appropriate to both intercrops. The main findings of this study were incorporated in the standard recommendations on intercropping dry beans in Arabica coffee in Kenya under Technical Circular No. 51 of 1982. Three to six dry bean rows may be intercalated in the coffee inter-row space during the first two years of young coffee or in mature coffee undergoing the change of cycle.