Changes in Soil Biological Properties after Sewage Sludge and Pesticide Application in Wheat Cultivation

Abstract

One of the solutions implemented in order to improve the quality of soils exposed to pesticides is the application of sewage sludge, which is a by-product of wastewater treatment. As an organic substrate, it provides soil with important nutrients, such as nitrogen and phosphorus, and enriches it with organic matter, thanks to which it can be a valuable fertilizer. The aim of the presented research was to evaluate the influence of granulated sewage sludge (GSS) on the biological properties of soil treated with herbicides (MCPA and dicamba) and fungicides (thiophanate-methyl and azoxystrobin). The following aspects were investigated: the activity of selected soil enzymes, the genetic biodiversity of bacteria and fungi, and the abundance of the bacterial gene responsible for ammonia oxidation. A field experiment was conducted, in which granulated sewage sludge (GSS) was applied to soil at a single dose of 3 t/ha. Wheat (Triticum aestivum L.) was sown on the prepared plots. The herbicides (H) and fungicides (F) as well as their mixture (F + H) were applied to the plants in the appropriate growth phases in the doses recommended by the producer. The control was soil without sewage sludge (C). The samples taken were tested for: dehydrogenases, catalases and urease activities, genetic biodiversity structure of bacteria and fungi by TRFLP assay, and the abundance of the bacterial amoA gene by qPCR. On the basis of the obtained results, it was found that the application of pesticides to soil fertilized with sewage sludge influenced the enzymatic activity of soil, and their activity differed depending on the tested enzyme. The activity of URE and DHA on the plots with GSS was higher by approx. 20% and 30%, respectively, as compared to the plots without GSS application. Moreover, both the genetic biodiversity of microorganisms and the abundance of amoA gene differed depending on the variant of the experiment. The GSS treatment of soil significantly influenced the growth of the studied gene as compared to C, and its abundance was 9.15 log10 gene copies/g DW of soil. Due to the content of nutrients in sewage sludge, it can be a valuable fertilizer in agricultural crops treated with pesticides.