s:2478:"%T Resource capture and utilization in intercropping: non-nitrogen nutrients 
%A Morris R A 
%A Garrity, D.P. 
%X The capture and utilization of P and K, two non-mobile soil resources, were examined by decomposing crop production/unit area into uptake/unit area (capture) and production/unit uptake (utilization efficiency). Resource capture and utilization efficiencies by intercrops were compared to those of sole crops by contrasting intercrop means against the weighted means of sole crops. Weightings were based on the proportion of each species in the intercrop. On average, intercrops took up 43% more P (4 to 83%) and 35% more K ( 10 to 87%) than the sole crops. Where nutrients were not limiting, P and K uptake increased as dry-matter yield increased, evidence that uptake was a function of crop growth rather than conversely. Even where soil P was deficient, uptake by a dominated crop was decided more by factors that determined the outcome of competition than by P availability. The combined root systems, likely to be larger and functional for a longer duration under intercrops than under either sole crop, were postulated to explain the greater capture of non-mobile nutrients like P and K. An enlarged root system provides an expanded root surface area to which non-mobile nutrients can diffuse. For mobile nutrients which move to root surfaces largely by mass flow, shading of the dominated canopy may explain the positive association observed between intecrop dry-matter accumulation and Ca capture. Shading reduces carbon assimilation and transpiration of the understory canopy and, therefore, would reduce mass flow of Ca as well.Competition for P and K by intercropped species, even when nutrient supplies were abundant, was affected by degree of growth concurrency, canopy domination and planting geometry. When a dominating species was harvested much earlier than the dominated species, the uptake rate of the longer-duration crop usually recovered from competition after the first crop was harvested. Exceptions occurred when development of the dominated crop was so badly impaired during concurrent growth that vegetative enlargement was inhibited after harvest of the early species. Uptake rates by pigeon pea and cassava, which are exceptionally long-maturing species that have relatively low daily P and K uptake requirements, appeared capable of fully recovering even on soils in which nutrient availabilities were marginal for other species. 
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