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- Title
Exploring the Impacts of Digestate Application on the Carbon Cycle in Grassland Soils.
- Authors
Cattin, Marta; Semple, Kirk T.; Stutter, Marc; Brotons, Alfonso Lag; Parry, Chris; Surridge, Ben W.J.
- Abstract
Digestate may be applied to agricultural soils as a replacement for inorganic fertilizer, butalso potentially acting as a soil conditioner (e.g. increasing soil organic carbon[SOC] levels). However, digestate application to agricultural soil can have variedinteractions with microorganisms in the soil, depending on factors such as the quality ofdigestate applied (e.g. in terms of C:N ratio) and soil nutrient status. The net balanceof these interactions affects the carbon use efficiency [CUE], which is defined asthe capability of microorganisms to use organic carbon sources for growth. HighCUE generally occurs when microorganisms are growing mainly using C fromexogenous sources (anabolic pathway favoured), leading to a SOC stabilization.Low CUE occurs when bacteria are not using the C source efficiently (catabolicpathway favoured), leading to elevated soil respiration, CO2 production and reducednet C sequestration. Soil nutrient status (C, N, P level) can influence positively ornegatively the CUE. Organic materials with C:N <20 applied to a high nutrient soil(rich in C, N and P) increase the CUE, whilst their application to a low nutrientsoil (depleted in C, N and P) decreases it. Contrastingly, organic materials withC:N >20 (lignin-like) are virtually inaccessible to microbial decomposition in theshort term, thus no effect on CUE is expected. Based on this context, the aim of theexperiment described here was to understand how different digestate fractions (whole[WD] C:N=4 and solid [SD] C:N=22) applied at a fixed dose (170 Kg NH4/ha/y)affected CUE in two soils with contrasting fertility (high and low plant-availablenutrients). A 21-d incubation under controlled conditions was carried out (T=23˚ C) to assess soilmicrobial responses. Soil respiration was continually monitored using an automatedrespirometer and a set of destructive samples were prepared to analyse the changes inmicrobial biomass C (Cmicro). In both soils, Cmicro increased strongly following SDaddition, while WD was only associated with increased Cmicro in the high nutrient soil. Therate of CO2 efflux from the high nutrient soil was strongly promoted by WD application, yetthis rate decreased rapidly after day 7 of the incubation. In comparison, maximumCO2 efflux rates were lower under the SD treatment, yet this rate did not decreasethrough the 21-d incubation. In the low nutrient soil, maximum CO2efflux rateswere slightly higher under SD compared to WD treatment, and again SD effluxremained relatively constant throughout the incubation, whilst WD efflux decreasedafter 96h. Our results suggest that varying CUE responses are likely to be observedfollowing the application of digestate to agricultural soils, dependent on C-source(digestate fraction) and on the initial nutrient status of the receiving soil. Under certaincircumstances, digestate application may lead to an increased CO2 efflux from soils and adecrease of SOC. Therefore, digestate application rates and soil management should becarefully planned in order to avoid adverse impacts of digestate application to land.
- Subjects
CARBON cycle; SOIL respiration; HISTOSOLS; SOIL conditioners; SOIL management; GRASSLAND soils; SOIL stabilization
- Publication
Geophysical Research Abstracts, 2019, Vol 21, p1
- ISSN
1029-7006
- Publication type
Article