Zinc and phosphorus availability to wheat as affected by humic substances in calcareous and siliceous growth media

Aim of study: Humic substances (HS) have an impact on the dynamics of phosphorus (P) and zinc (Zn) in soil and consequently can affect the availability of both nutrients to plants. This work aimed to study the effect of humic substances on the availability of P and Zn to wheat depending on the main sorbent surfaces in growth media. Area of study: Growth chambers of the Higher Technical School of Agricultural Engineering, University of Seville, Spain Material and methods: To this end, a pot experiment was performed involving three factors: i) HS rates, ii) Zn fertilization, and iii) type of growth medium, calcareous and noncalcareous (siliceous). Main results: Biomass production and Zn uptake by plants decreased with increasing HS rates. Humic substances decreased zinc uptake more markedly in the siliceous medium. Negative effects of HS can be ascribed to altered crop nutrition and the high aromaticity of HS that can promote phytotoxic effects. The antagonistic effect between P and Zn was less evident in the calcareous medium than in the siliceous medium. This is probably explained by the reduced availability of Zn and the consequent decrease in uptake by plants in the calcareous medium compared to the siliceous medium. These differences observed between both media can be ascribed to different adsorption dynamics depending on the main sorbent surfaces. Research highlights: The addition of HS, at the intermediate rates studied, had a positive effect on the microbial activity of the rhizosphere in the calcareous medium. Thus, not only crop functioning, but also soil biology, can be affected by the application of HS. This effect can be different depending on the HS rates applied and the type of growth medium.