Micronutrient Concentration in Horticultural Crops Grown on a Soil Amended with the Solid Phase of Pig Slurry

Previous studies carried out on metal fractionation have shown that more than 95% of metals are in the solid phase of pig slurries (SPPS), with copper (Cu), and zinc (Zn) being the commonly occurring micronutrients in animal slurries. The input of micronutrients associated with the application of SPPS could be an important pathway for the supply of these essential elements to arable crops in bioavailable forms, especially in calcareous soils, which induce the immobilization of these elements. The aim of this work was to study the effect of application of pig manures (fresh and composted) derived from the SPPS on the micronutrient-iron (Fe), Cu, Magnesium (Mn), and Zn-concentration on amended calcareous soils in horticultural plants (cucumber and Milan cabbage). In addition, the effect of composting and application rates were analyzed. The experiment was conducted in field conditions on a Xerofluvent soil with a clayey-loam texture. The organic wastes used in this study were uncomposted and composted solid fractions of swine manure slurry (UC-SPPS and C-SPPS, respectively) at two different rates (supplying 300 kg ha(-1) and 450 kg N ha(-1) respectively). A mineral fertilizer treatment equivalent to 300 kg N ha(-1) and a control treatment without fertilization were also included for comparison. The use of SPPS amendment induced a biomass production similar to the mineral fertilizer for cucumber, but higher in Milan cabbage plants, without any yield increment associated with the increased application rate of SPPS or composting. Micronutrient concentration in cucumber and cabbage plants was affected by the SPPS amendment, with an increase of Mn and Zn uptake and a decrease of Cu, compared to the control. The increasing application rate of SPPS did not induce a general increase in the plant uptake of micronutrients; the opposite was true for the crops grown in the C-SPPS-amended soils.