Trade‐offs and synergies of soil carbon sequestration: Addressing knowledge gaps related to soil management strategies

Soil organic carbon (SOC) sequestration in agricultural soils is an important tool for climate change mitigation within the EU soil strategy for 2030 and can be achieved via the adoption of soil management strategies (SMS). These strategies may induce synergistic effects by simultaneously reducing greenhouse gas (GHG) emissions and/or nitrogen (N) leaching. In contrast, other SMS may stimulate emissions of GHG such as nitrous oxide (N2O) or methane (CH4), offsetting the climate change mitigation gained via SOC sequestration. Despite the importance of understanding trade-offs and synergies for selecting sustainable SMS for European agriculture, knowledge on these effects remains limited. This review synthesizes existing knowledge, identifies knowledge gaps and provides research recommendations on trade-offs and synergies between SOC sequestration or SOC accrual, non-CO2 GHG emissions and N leaching related to selected SMS. We investigated 87 peer-reviewed articles that address SMS and categorized them under tillage management, cropping systems, water management and fertilization and organic matter (OM) inputs. SMS, such as conservation tillage, adapted crop rotations, adapted water management, OM inputs by cover crops (CC), organic amendments (OA) and biochar, contribute to increase SOC stocks and reduce N leaching. Adoption of leguminous CC or specific cropping systems and adapted water management tend to create trade-offs by stimulating N2O emissions, while specific cropping systems or application of biochar can mitigate N2O emissions. The effect of crop residues on N2O emissions depends strongly on their C/N ratio. Organic agriculture and agroforestry clearly mitigate CH4 emissions but the impact of other SMS requires additional study. More experimental research is needed to study the impact of both the pedoclimatic conditions and the long-term dynamics of trade-offs and synergies. Researchers should simultaneously assess the impact of (multiple) agricultural SMS on SOC stocks, GHG emissions and N leaching. This review provides guidance to policymakers as well as a framework to design field experiments and model simulations, which can address knowledge gaps and non-intentional effects of applying agricultural SMS meant to increase SOC sequestration

From soil quality to soil ecosystem services

Kakovost tal lahko definiramo kot kontinuirano sposobnost tal za zagotavljanje ekosistemskih storitev (ES). Znanost o tleh prepoznava pet glavnih funkcij tal, ki zagotavljajo ES: (i) primarna produkcija, (ii) čiščenje in uravnavanje vode, (iii) skladiščenje ogljika in uravnavanje podnebja, (iv) biotska pestrost in zagotavljanje habitatov ter (v) zagotavljanje in kroženje hranil. ES ocenjujemo po naslednjih pristopih: (i) na podlagi kazalnikov, pri katerih ocene ES tal temeljijo na poenostavljenih približkih izbranih lastnosti tal(ii) na empiričnih povezavah med lastnostmi tal in funkcijami tal (statični pristop) in (iii) na podlagi modeliranja talnih procesov v času (dinamični pristop). Število modelov in orodij za ocenjevanje ES tal narašča, vendar pa je vprašljivo, v kolikšni meri se ocene približajo realni porazdelitvi in zastopanosti posamezne ES v prostoru. Nujni so kakovostni vhodni podatki o tleh, izbor robustnih kazalnikov kakovosti tal za ocenjevanje ES in nadaljnji razvoj modelov ter orodij za ocenjevanje funkcij tal in ES v smeri zmanjševanja negotovosti. Slovenija šele postavlja koncept ES tal, zato je namen prispevka na osnovi pregleda literature osvetliti razvoj konceptov in pristopov njihovega ocenjevanja v mednarodnem prostoru

Mineral and organic fertilisation influence ammonia oxidisers and denitrifiers and nitrous oxide emissions in a long-term tillage experiment

Nitrous oxide (N$_2$O) emissions from different agricultural systems have been studied extensively to understand the mechanisms underlying their formation. While a number of long-term field experiments have focused on individual agricultural practices in relation to N$_2$O emissions, studies on the combined effects of multiple practices are lacking. This study evaluated the effect of different tillage [no-till (NT) vs. conventional plough tillage (CT)] in combination with fertilisation [mineral (MIN), compost (ORG), and unfertilised control (CON)] on seasonal N$_2$O emissions and the underlying N-cycling microbial community in one maize growing season. Rainfall events after fertilisation, which resulted in increased soil water content, were the main triggers of the observed N$_2$O emission peaks. The highest cumulative emissions were measured in MIN fertilisation, followed by ORG and CON fertilisation. In the period after the first fertilisation CT resulted in higher cumulative emissions than NT, while no significant effect of tillage was observed cumulatively across the entire season. A higher genetic potential for N$_2$O emissions was observed under NT than CT, as indicated by an increased (nirK + nirS)/(nosZI + nosZII) ratio. The mentioned ratio under NT decreased in the order CON > MIN > ORG, indicating a higher N$_2$O consumption potential in the NT-ORG treatment, which was confirmed in terms of cumulative emissions. The AOB/16S ratio was strongly affected by fertilisation and was higher in the MIN than in the ORG and CON treatments, regardless of the tillage system. Multiple regression has revealed that this ratio is one of the most important variables explaining cumulative N$_2$O emissions, possibly reflecting the role of bacterial ammonia oxidisers in minerally fertilised soil. Although the AOB/16S ratio aligned well with the measured N$_2$O emissions in our experimental field, the higher genetic potential for denitrification expressed by the (nirK + nirS)/(nosZI + nosZII) ratio in NT than CT was not realized in the form of increased emissions. Our results suggest that organic fertilisation in combination with NT shows a promising combination for mitigating N$_2$O emissionshowever, addressing the yield gap is necessary before incorporating it in recommendations for farmers

Trade-offs and synergies of soil carbon sequestration

Soil organic carbon (SOC) sequestration in agricultural soils is an importanttool for climate change mitigation within the EU soil strategy for 2030 and canbe achieved via the adoption of soil management strategies (SMS). These strategies may induce synergistic effects by simultaneously reducing greenhousegas (GHG) emissions and/or nitrogen (N) leaching. In contrast, other SMS maystimulate emissions of GHG such as nitrous oxide (N$_2$O) or methane (CH$_4$),offsetting the climate change mitigation gained via SOC sequestration. Despitethe importance of understanding trade-offs and synergies for selecting sustain-able SMS for European agriculture, knowledge on these effects remains lim-ited. This review synthesizes existing knowledge, identifies knowledge gapsand provides research recommendations on trade-offs and synergies betweenSOC sequestration or SOC accrual, non-CO$_2$ GHG emissions and N leachingrelated to selected SMS. We investigated 87 peer-reviewed articles that addressSMS and categorized them under tillage management, cropping systems, watermanagement and fertilization and organic matter (OM) inputs. SMS, such as conservation tillage, adapted crop rotations, adapted water management, OMinputs by cover crops (CC), organic amendments (OA) and biochar, contributeto increase SOC stocks and reduce N leaching. Adoption of leguminous CC orspecific cropping systems and adapted water management tend to create trade-offs by stimulating N$_2$O emissions, while specific cropping systems or application of biochar can mitigate N$_2$O emissions. The effect of crop residues on N$_2$O emissions depends strongly on their C/N ratio. Organic agriculture and agro-forestry clearly mitigate CH$_4$ emissions but the impact of other SMS requiresadditional study. More experimental research is needed to study the impact ofboth the pedoclimatic conditions and the long-term dynamics of trade-offs andsynergies. Researchers should simultaneously assess the impact of (multiple)agricultural SMS on SOC stocks, GHG emissions and N leaching. This reviewprovides guidance to policymakers as well as a framework to design fieldexperiments and model simulations, which can address knowledge gaps andnon-intentional effects of applying agricultural SMS meant to increase SOC sequestration