Physiological Changes in Maize Grown in Soil with Copper and Zinc Accumulation Resulting from the Addition of Pig Slurry and Deep Litter over 10 Years

The aim of the present study was to evaluate if increased Cu and Zn concentrations in soils, as a consequence of distribution at the field level for 10 consecutive years of pig slurry (PS) and pig deep litter (DL), would cause toxicity to maize plants affecting, in turn, the biomass production and grain yield. With this aim, maize was grown in two cycles in undisturbed samples from soil that had been fertilized with annual applications of 90 or 180 kg N ha−1, either as PS or DL, in a field experiment carried out for 10 years in southern Brazil. The PS180 and DL180 treatments resulted in Cu and Zn accumulation in soil, and PS180 resulted in Zn accumulation in the tissue of maize plants. The increased availability of Cu and Zn was associated to slight changes in stomatal density, chlorophyll content, and catalase and ascorbate peroxidase activities. Nevertheless, soluble carbohydrate and protein contents and plant dry matter accumulation were not significantly affected by exposure of plants to those high levels of either metal. The results here presented indicate that, although successive applications of PS and DL resulted in a really considerable increase of Cu and Zn in the soils, they do not cause toxic effects in maize plants as to impair their ability to produce biomass and grain.