Changes in carbon pools and enzyme activities in soil amended with pig slurry derived from different feeding diets and filtration process

Monitoring soil carbon content and pools and associated enzyme activities has become an important area of research in terms of the carbon cycle in agricultural lands in order to infer factors regulating soil carbon sequestration. Pig slurry (PS) is considered as a source of organic matter and nutrients for crop production. In recent years, because of the cost of conventional feed applications, manufacturers have preferred liquid feeding diets with decreases of 10–25% in production costs. Furthermore, physical and chemical filtration of PS by new techniques may prevent soil degradation and reduce the negative effects of PS, such as high salt, pathogen, and heavy metal contents. This research aimed to assess the effect of the application of raw pig slurry (R) and treated pig slurry (T) (derived from physical and chemical separation processes) from liquid (L) and solid (S) feeding diets on different soil organic carbon pools and enzyme activities in a sandy loam soil under a rainfed barley cropping system for two years. The solid diet consisted of maize/soya bean, tubers and roots, and supplementary vitamins and minerals. The liquid diet consisted of dairy products such as fresh whey, concentrated cheese or yogurt, skim milk powder, and beer by-products such as brewer's yeast. As a general pattern, the addition of the different types of PS (R or T) had no significant effect on most soil properties, except for microbial biomass C (Cmic), which increased with R. However, the type of diet did have a significant effect on most properties, both for R or T slurries, suggesting that this is more of a determinant factor in explaining changes in soil than the type of pig slurry. Solid diet favors the significant increase of soil organic carbon and arylesterase activity, suggesting higher stabilization of the organic compounds provided by the PS. However, the liquid diet contributed to increasing soluble C and Cmic, suggesting higher availability of nutrients and C sources. Hence, the use of treated pig slurry has no detrimental effect on organic carbon dynamics compared to raw pig slurry and can be suggested as an alternative to reduce the environmental impact, prevent soil pollution, and ensure sustainability.