Soil microbial functionality in response to dairy sewage sludge and mineral fertilisers application under winter rape

Abstract

Microbial activity and the diversity of their catabolic potential would be stratified according to soil profile as a result of differing content of soil organic C and they would be altered by applying dairy sewage sludge (DSS) to the surface and subsequently ploughing. We applied 26 Mg ha−1 of DSS and the same nutrient dose of mineral fertilisers as an NPK reference to the soil before sowing winter rape (Brassica napus) in the field experiment. We evaluated the impact of the fertilisers on microbial activity, measured with dehydrogenase and respiratory activity, and diversity of the microbes’ catabolic potential from non-rhizosphere and rhizosphere soil at selected depths. In the surface rhizosphere soil, there were significant increases in microbial catabolic potential (>25 %) and respiratory activity (>20 %) due to DSS application. All of the microbial parameter values in non-rhizosphere soil were higher at 0–20 than at 25–30 cm. These results are important for improving the management approach of diary sewage sludge application to agricultural soils in the context of increasing microbial activity in the soil profile and reducing mineral fertiliser use.