Odzivi talne mikrobne združbe na upravljanje z organsko snovjo in obdelavo tal v ekološkem poljedelstvu

Pintarič, Sara (author), Eler, Klemen (mentor), Suhadolc, Marjetka (co-mentor)

Cilj doktorske naloge je bil proučiti vpliv vnosov organske snovi in različne intenzivnosti obdelave tal v poljedeljstvu glede na vsebnost ter porazdelitev organskega ogljika (Corg) in hranil v tleh ter na velikost in sestavo mikrobnih združb, zlasti z vidika mikrobno pogojenih procesov (na primer cikla N). V več kot dvajset let trajajočem poskusu v Moškanjcih z različno intenzivnostjo obdelave tal se je v obdobju petih let po prehodu iz konvencionalnega na ekološki sistem kmetovanja značilno povečevala vsebnost Corg v zgornjih 10 cm tal, vendar le pri minimalni obdelavi tal (MT), kjer so bili tudi večji vnosi organske snovi v obliki plevelne biomase in biomase korenin poljščin kot pa pri oranju (CT). Večje zaloge Corg kot tudi večja vsebnost Corg ter dostopnost hranil v zgornjih 10 cm pri MT se je pokazala v večji mikrobni biomasi, večji številčnosti talnih mikrobnih združb (bakterije, arheje, glive in funkcionalni geni N cikla) ter spremenjeni pestrosti in sestavi združb bakterij in gliv (Illumina sekvenciranje). Odziv slednjih na obdelavo tal se je razlikoval med rizosfernimi tlemi in koreninami poljščine. Proučevali smo tudi kratkoročne učinke prehoda iz MT na direktno setev oz. brez obdelave tal (NT). Spremembe v mikrobni biomasi in številčnosti bakterij, arhej in gliv so se pokazale že v dveh letih, vendar še bolj omejeno na zgornji centimeter tal. Hiter odziv mikrobnih združb predvsem na dodatek labilne organske snovi, v našem primeru gnojevke, in nekoliko manj na različno upravljanje z rastlinskimi ostanki (vdelava v globino 10 cm vs. na površini vs. brez slame) se je pokazal tudi v lončnem poskusu. Vdelava slame, kjer je bil stik slame s tlemi tesnejši, je značilno vplivala na večjo številčnost gliv v zgornjih 10 cm tal, kar se je odrazilo tudi na večjem mikrobnem dihanju (tok CO2 iz tal) v začetni fazi razgradnje slame. Gnojenje je povečalo razpoložljivost C in N, in tako posredno vplivalo na večjo številčnost zlasti bakterij in gliv v zgornjih 10 cm tal in značilno večje mikrobno dihanje, kot če gnojevka ni bila dodana. Kombinacija vdelave slame in dodatka gnojevke je pozitivno učinkovala na številčnost gena nosZII v zgornjih 10 cm tal. Lahko zaključimo, da različne kmetijske prakse (obdelava tal, organsko gnojenje, upravljanje z rastlinskimi ostanki) svojstveno vplivajo na mikrookoljske razmere v tleh, kar se odrazi v spremenjeni velikosti (mikrobna biomasa, številčnost) in sestavi talnega mikrobioma.

• Language: Slovenian
• Keywords: ohranitveno kmetijstvo, ekološko poljedeljstvo, no-till, zaloge ogljika, dihanje tal, mikrobna biomasa, bakterije, glive, cikel dušika, oksidatorji amonijaka, denitrifikatorji
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: BF - Biotechnical Faculty
• Year: 2023
• PID: 20.500.12556/RUL-152373
• COBISS.SI-ID: 173962755
• Publication date in RUL: 23.11.2023

Secondary language

• Language: English
• Title: Soil microbial community responses to soil organic matter management and tillage in organic agriculture

Abstract

The aim of doctoral thesis was to examine the effects of organic matter inputs and different tillage intensities on the content and distribution of soil organic carbon (Corg) and nutrients, and on the size and composition of microbial communities, in particular in terms of the microbially mediated processes (eg. N cycle). In the long-term experiment (>20 years) in Moškanjci with different tillage intensities, the Corg content in the top 10 cm of the soil increased significantly over the five years after the transition from conventional to organic farming, but only under minimum tillage (MT), which also had higher inputs of organic matter in the form of weed and crop root biomass, than under conventional tillage (CT). The higher Corg stocks as well as Corg and nutrient content in the upper 10 cm of MT was also reflected in higher microbial biomass, abundance of soil microbial communities (bacteria, archaea, fungi and N cycle functional genes) and altered diversity and composition of bacteria and fungi (Illumina sequencing). The latter responded to tillage differently in rhizosphere soils and crop roots. We also studied the short-term effects of the transition from MT to direct sowing or no tillage (NT). Changes in microbial biomass and the abundance of bacteria, archaea and fungi were already evident after two years, but limited to the top cm of the soil. The rapid response of the microbial communities to the addition of labile organic matter, and less to the different straw management (incorporation to the top 10 cm vs. left on surface vs. no added), was also shown in the pot experiment. Straw incorporation, where the contact of the straw with the soil was closer, significantly increased fungal abundance in the top 10 cm of soil, which was also reflected in higher microbial respiration (CO2 efflux) in the initial phase of straw decomposition. The slurry increased availability of labile C and N forms, thereby indirectly affecting the higher abundance of bacteria and fungi in the top 10 cm of soil, and significantly higher microbial respiration compared to no-slurry treatments. The combination of straw incorporation and slurry addition had a positive effect on the abundance of the nosZII gene in the top 10 cm of soil. In conclusion, different agricultural practices (tillage, organic fertilisation, crop residue management) have a specific impact on soil microenvironmental conditions, which is reflected in the altered microbial size (biomass, abundance) and composition.

• Keywords: conservation agriculture, organic farming, no-till, carbon stocks, soil respiration, microbial biomass, bacteria, fungi, nitrogen cycle, ammonia oxidizers, denitrifiers