Impact of crop aerial and root biomass inputs on soil nitrifiers and cellulolytic microorganisms

GREGORUTTI, VIVIANA CAROLINA; CAVIGLIA, OCTAVIO PEDRO

SOIL & TILLAGE RESEARCH

ELSEVIER SCIENCE BV

Año: 2019 vol. 191 p. 85 - 97

0167-1987

In agricultural no-tillsystems, crop residue management has an important impact on the activity andabundance of soil microorganisms, which play a crucial role in soil health andquality. In these systems, when cover crops are included in order to increasethe amount of crop residues, aerial biomass remains on the soil surface,whereas root biomass is directly incorporated into the soil. Although bothaerial and root biomass may have a differential effect on the abundance and activity of nitrifers andcellulolytic microorganisms, to our knowledge, such effects have not been individually studied in theliterature. The aims of this research were to study the abundance and activityof nitrifers and cellulolytic microorganisms, and their efciency indexes (EIs),as affected by: i)aerial cover crop residues and roots of cover crops at two soil depths (0-0.5and 0.05-0.2 m), and ii) soil conditions at 30, 90, and 150 days after thecover crop killing date. We conducted an experiment during two consecutiveyears in Paraná, Argentina (-31°50.9′S; -60°32.3′W). Treatments included twocover crop species that were added to the soil either as aerial input or asroot input. Treatments were aerial input of wheat (Triticum aestivum L.) (AW) on fallowed soil, aerial input of white sweetclover (Melilotusalbus Medik.) (ASC) on fallowed soil,in situ grown roots of wheat (RW), in situ grown roots of white sweet clover(RSC) and a control (C) on fallowed soil without aerial or root inputs. In eachof the growing seasons, at 30, 75 and 150 days after the killing date, soilsamples were collected at depths of 0-0.05 m and 0.05-0.20 m. From the soilsamples, soil water content, activity and abundance of nitrifers andcellulolytic microorganisms were determined. The average activity of nitriferswas higher (p < 0.0001) in the topsoil layer than in the subsurface layer(0.06 vs. 0.04 mg NO3- g soil-1). However, the average cellulolytic activity did notdiffer amongdepths and treatments. The average abundance of nitrifers was similar betweensoil layers (ca. 5-log g soil-1), and the abundance of cellulolytic activity rangedfrom 6.7 to 8.4 log g-1 soil. Our results show that in the topsoil, themicrobiological variables under study had a more important effect via the source of the inputs, i.e. whether thesource belongs to the aerial or roots biomass rather than the cover cropspecies. In addition, we detected that in the topsoil, regardless of the cropspecies, aerial residues promoted cellulolytic activity, whereas root inputspromoted nitrifer activity. The study allowed us to identify how themicrobiological variables were affected by the source of the input at the feld level.