Evaluation of the application of pig slurry to an experimental crop using agronomic and ecotoxicological approaches

The agronomic and ecotoxicological effects of the application of pig (Sus scrofa) slurry during a maize (Zea mays L.) crop cycle under conditions of forced irrigation were evaluated. The 0.2-ha experimental area, of typical xerofluvent soil and of known vulnerability to nitrate (NO3-) contamination, was divided into 12 plots and provided with water measurement instruments (TDR-probes, vertical tensiometers, and ceramic candles). Samples of soil, water, soil organisms, and the crop were subjected to analytical, agronomic, and biological test procedures. The following fertilizer treatments were applied to triplicate plots: urea (U;170 kg N ha(-1)), and an optimized (P1; 162 kg N ha(-1)) and triple (P3; 486 kg N ha(-1)) dose of pig slurry. Unfertilized plots (P0) served as controls. Calculation was made of seasonal drainage and leached NO3- and sodium losses during the experimental period. Conductivity, heavy metal concentration, hardness, pH, and redox potential were determined in soil solutions. The ecotoxicological evaluation of the soil solution and matrix was based on ecotoxicity bioassays and the quantification of organic and inorganic compounds [phenols, indols, polychlorinated biphenyls (PCBs)]. The results suggest that the P3 treatment is highly contaminating due to the leaching of nitrates and increased soil salinity. Despite the fact that a Folsomia candida reproduction test indicated chronic ecotoxicological effects on the soil in plots treated with P1 and P3, the absence of organic compounds suggests that these effects may be attributable to contaminants not considered in this study.