Factors determining Zn availability and uptake by plants in soils developed under Mediterranean climate

Abstract

Zinc deficiency is an extended agronomic problem, particularly in staple food crops such as cereals. The availability of Zn to plants is ruled by soil properties, biological factors in the rhizosphere, and interaction with other nutrients. These factors may constrain the predictive value of Zn availability indices. This work aimed at assessing the soil factors that affect the absorption of Zn by plants and improving the predictive value of conventional indices. To this end, an experiment was performed using durum wheat (Triticum durum L.) grown on a set of soils developed under Mediterranean climate. In calcareous soils, Zn uptake by plants decreased with increased clay content and Olsen P (POlsen), meanwhile in non-calcareous soils it decreased with increased crystalline Fe oxides content. Biological factors such as microbial activity and organic anion exudation in the rhizosphere contribute to Zn uptake by plants. No relationship was found between Zn uptake by plants and the DTPA extractable Zn (ZnDTPA). Pyrophosphate extractable Zn (ZnPyro) was only related to Zn uptake by plants in calcareous soils (R2 = 0.29; P < 0.01). The best estimation of Zn uptake by plants in calcareous soils was obtained with a model involving ZnPyro/POlsen ratio and clay content (R2 = 0.57; P < 0.001). In non-calcareous soils, Zn uptake by plants was accurately estimated with a model involving Fe bound to crystalline oxides and rhizospheric oxalate (81% of the variance explained). Results reveal the need of discriminating soils according to its carbonate content and the use of soil properties related to Zn adsorption capacity, such as clay and Fe oxide content, and Olsen P for accurate estimation of Zn uptake by plants.