Enzyme activities and microbial nutrient limitations in response to digestate and compost additions in organic matter poor soils in Marches, Italy

Authors: GURMESSA, BIYENSA - Polytechnic University Of Marche; COCCO, STEFANIA - Polytechnic University Of Marche; Ashworth, Amanda; UDAWAGTTA, RANJITH - University Of Missouri; CARDELLI, VALERIA - Polytechnic University Of Marche; SERRANI, DOMINIQUE - Polytechnic University Of Marche; LLARI, ALESSIO - Polytechnic University Of Marche; PEDRETTI, ESTER - Polytechnic University Of Marche; FORNASIER, FLAVIO - Crea; CORTI, GIUSEPPE - Polytechnic University Of Marche

Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/24/2024
Publication Date: 5/6/2024
Citation: Gurmessa, B., Cocco, S., Ashworth, A.J., Udawagtta, R.P., Cardelli, V., Serrani, D., Llari, A., Pedretti, E.F., Fornasier, F., Corti, G. 2024. Enzyme activities and microbial nutrient limitations in response to digestate and compost additions in organic matter poor soils in Marches, Italy. Soil & Tillage Research. 242. Article 106136. https://doi.org/10.1016/j.still.2024.106136.
DOI: https://doi.org/10.1016/j.still.2024.106136

Interpretive Summary: Using digestate (byproduct of bioenergy production from decomposed feedstock under anaerobic digestion) as a fertilizer improves soil nutrient status and agronomic yield and has the potential to replace inorganic fertilizers. However, farmer adoption of digestate as fertilizer has been low for a variety of reasons, including cost of application, low nutrient content, and environmental concerns related to direct application. Despite interesting developments in the field of digestate valorization and its environmental risks, evidence on the dynamics of resources allocation for nutrients acquisition in cropping systems after digestate or compost derived from it has been used as fertilizer is still lacking. Plants and microbes produce various enzymes that help them uptake nutrients from the soil, which may rise when the supply is in short of the demand. Depending on the relative availability of a particular nutrient, the relative resource allocation in aiding acquisition of the nutrient can vary. Researchers set out to understand the pattern of resource allocation (investments in enzymatic activities) following applications of digestate on crop yield and soil properties. In this study authors concluded that microbial biomass growth following organic amendments can lead to an increased rate of nutrient recycling and soil carbon sequestration in resource poor soils.

Technical Abstract: This study aimed to understand the pattern of resource allocation (investments in enzymatic activities) in organic carbon and nutrients poor soils following applications of digestate, five types of composts derived from digestate, and N-fertilizer (NINORG) for sunflower (Helianthus annuus L.) production. A plot with no treatment (digestate, compost, or inorganic N fertilizer) was considered as a control. The experiment was arranged in a completely randomized block design. A plot without any kind of fertilizer applied was used as a control Activities of nine C-, N-, P-, and S-cycling enzymes were measured and stoichiometries were analyzed to understand resource allocation dynamics at three crop development stages: seedling, pre-blooming, and harvest. Resource allocations (mainly C-, N-, and P-cycling) increased along plant developmental stages, irrespective of treatments and had positive relationships with microbial biomass, soil organic carbon, and soil nutrients contents, suggesting that increased source of energy and nutrients promoted microbial growth, which in turn triggered investments for resource allocation for satisfying the increased demand for energy and nutrients, particularly in later crop developmental stages. However, the demands for the nutrients and energy were not similar as stoichiometric analysis showed greater investments for P compared to N and C, and no treatment was able to reverse this pattern, as the vector angle persistently becoming greater than 60º at the three sampling times for all treatments. The investments in P acquisitions were at least four-fold greater than that of N and at least seven times greater than that of C, which reduced at harvest for all treatments except NINORG and control. As suggested by a strong negative correlation (p<0.001) with vector angle, increased bioavailable P through organic amendment applications narrowed the gap towards converging to the global 1:1:1 ratio of C:N:P. In conclusion, in soils with high imbalance in microbial nutrients and energy demand, organic amendments exacerbate microbial growth and lead to increased investments in nutrients acquisitions, although the investment for P acquisition per unit investments for C and N showed a declining trend over the cropping period. Therefore, organic fertilizers may help correct the energy-nutrients supply imbalance in soils under conventional farming systems, thus leading to healthy ecosystem functioning and provisioning of services.