Genotipic differences in productivity and nutrient uptake and use efficiency of cassava as influenced by prolonged water stress

الأسبانية؛ قشتالية. A 2-y field trial was conducted at CIAT experimental station at Santander de Quilichao, Cauca, Colombia, to study the effects of prolonged water stress on cassava (Manihot esculenta Crantz) productivity and on nutrient uptake and use efficiency. Four contrasting cultivars, CM 507-37, CM 523-7, M Col 1684 and CMC 40, were used with adequate fertílization and watering, except when water was excluded by covering the soil with plastic sheets from 2 to 6 months after planting (early stress), from 4 to 8 months after planting (míd-season stress) and from 6 to 12 months after planting (terminal stress). Saquential harvests were made at 2, 4, 6, 8 and 12 months after planting to determine LAl, top and root blomass production. At final harvest, N, P, K, Ca and Mg uptake in top and root biomass was determined. During both early and mid-season water stress, LAl, top and root bíomass were significantly reduced in all cultívars. After recovery from stress, LAl was greatly enhanced with less dry matter allocated to stems and at final harvest root yields approached those in the controls. One cultivar, CMC 40 had greater final root yíeld under both stress treatments. Nutrient uptake in root and top bíomass was significantly lower in early stress treatment in all cultivars resultlng in hlgher nutrient use effíciency for root and total biomass production. Under mid-season water stress, only P and K uptake was lower, resulting in higher use efficiency of these two elements. Neither LAl nor top biomass was significantly affected by terminal stress, while root yield was lower in all cultlvars except CMC 40 whose final root yield was significantly greater under stress. Nítrogen uptake was greater in root but lower in top biomass of all cultlvars under terminal stress resultlng in lower N use effíciency for total biomass production. CMC 40 was the only cultivar with consistently greater use efficiency of P, K, Ca and Mg for both root and total bíomass production under terminal water stress.