Effects of biostimulants on soil enzyme activities, antioxidant capacity and bacterial community composition

Soil biostimulants are gaining importance in biological agriculture because of their ability to enhance crop yields by retaining micronutrients, and promote soil microbial growth and biodiversity, as well as enzyme activities. We studied the effects of two commercially available products, VIVA® and AU 15%® applied to soil at doses of 25 and 50 t ha-1 of organic matter, on soil biological activity, antioxidant capacity and the diversity of bacterial communities during 45 days of incubation. Results showed that both biostimulants led to a general increase in ATP content, catalase, dehydrogenase, lipase and urease activities, as well as soil antioxidant capacity. VIVA® appeared to be generally more effective than AU 15%®, but only AU 15%® maintained the same level of soil antioxidant capacity throughout the experiment. The soil antioxidant capacity was strictly related to the amount of soil phenolic compounds extracted by alkali from the soil. The parameters examined were influenced by the dose of application. The results of the PCR-DGGE analysis showed that the two biostimulants influenced the composition of the bacterial communities differently from the beginning of the experiment. AU 15%® visibly affected soil bacteria biodiversity, particularly in soil samples amended with higher doses. VIVA®, at both application doses, generally appeared to exert positive effects on the soil bacterial population with the occurrence, at the end of the experiment, of ecologically important orders of species such as Actinomycetales.