Field experiment was conducted for three years to evaluate the influence of plant population density of intercropped soybean with sorghum on its competitive ability and economic yield at Otobi, Benue State, Nigeria. The experiment was laid out in split-split plot with three replications. The main plot treatment comprised of cropping systems with two levels (sole cropping, intercropping), while the sub-plot treatment was soybean variety at three levels (TGX 536-O2D, Samsoy 2, TGX 923-2E) and the sub-sub-plot treatment was plant population density of soybean at three levels (200,000 plants/ha; 333,000 plants/ha and 400,000 plants/ha). Planting intercropped soybean at 333,000 plants/ha gave significantly higher seed yield than planting at 400,000 plants/ha, which in turn had greater seed yield than planting at 200,000 plants/ha during the three years of experimentation. Increased density of soybean beyond 333,000 plants/ha in the intercrop reduced sorghum yield. The results showed that all the intercrop combinations had land equivalent ratio (LER) and area- time equivalency ratio( ATER) above unity (1.63 - 1.97) and (1.41 - 1.47),respectively, under all the densities of soybean tested, suggesting a considerable benefit for intercropping soybean with sorghum. LER figures decreased with increase in soybean density. ATER was highest at 333.000 plants/ha, suggesting higher productivity at this density. Aggressivity values were consistently negative at 200,000 plants/ha with a mean value of -0.25 and it was inconsistent at 333,000plants/ha and 400,000 plants/ha. The competitive ratio of soybean increased (0.76 - 1.15) with increasing density of the soybean in the intercrop combinations, indicating higher competitiveness at higher densities than the sorghum component. The competitive ratio of sorghum had the opposite response (1.23 - 0.76). Relative crowding coefficient (K) was inconsistent at all densities, while land equivalent coefficient (LEC) was above 0.25 indicating intercrop advantages for all combinations. ‘Soybean yield equivalent’ was also highest at 333,000 plants/ha (1.70) implying general suitability of soybean to intercropping at this density. Dominance analysis revealed that sole crop treatments were dominated. Intercropped soybean planted at 333,000 plants/ha and 400,000 plants/ha gave significantly higher net benefits than those planted at 200,000 plants/ha. Marginal analysis showed that planting soybean at 333,000 plants/ha gave the highest marginal rate of return and this was 2825%.These results suggest that growing soybean under intercropping at Otobi is biologically efficient at 333,000 plants/ha and more profitable.
Key words: Intercropped soybean, density, competition, Otobi.
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