Genotypic Variation in Potassium Uptake in Dryland Cotton

ABSTRACT

The variation in potassium (K) uptake was studied by the analysis of leaf K concentration in cotton varieties grown under conditions of terminal drought. Youngest fully-expanded leaves (3rd- 4th from apex of main stem) were used for the analysis of leaf K concentration and physiological parameters (photosynthesis, stomatal conductance, leaf water content, etc). Sampling was performed several years at two different times during the cycle in two different experimental sites. Significant variation in leaf K concentration was recorded among genotypes sampled at flowering and fruiting stages. Leaf K concentration decreased from flowering to boll opening ranging from 2.3–1.36% to 1.29–0.85% and critical leaf K concentrations (below 1.7%K) were recorded at times of high nutrient requirement. Terminal drought imposed a severe restriction over seedcotton yield which varied from 574 up to 1612 kg ha⁻¹ depending on years and location. Boll production and seedcotton yield was positively correlated with leaf K concentration only in 1998. Stomatal conductance and specific leaf weight were the physiological traits more consistently related to leaf K concentration. The strong effect of water stress plant growth and yield components might have shaded any K effect. Environmental factors (drought intensity, soil properties) and genotypic intrinsic traits (variation in K use efficiency) may have interacted to provide a complex response. Genetic correlation for leaf K concentration was found when analyzing sampling dates in each site but it did not occur among sites. Under controlled conditions, differences in root K uptake were found in cultivars and the number of secondary roots was associated with greater shoot K contents.

Conditions of diminished K availability and root uptake in drying soils might have affected plant nutrition at times of high requirements. Our results demonstrate that variation in K uptake may be found among dryland-grown cotton genotypes. This feature might be exploited to improve plant K status and yield when cropping in water-limited environments. Search on specific traits related to K use efficiency and further selection of genotypes might contribute to improve cotton K nutrition and productivity under dryland conditions.

Keywords:

• Gossypium hirsutum L.
• dryland
• potassium
• stomatal conductance
• yield

ACKNOWLEDGMENTS

The technical help of Ms. Ana Ferrer and Asuncion de Castro for chemical analysis is greatly acknowledged.