Response of subsoil organic matter contents and physical properties to long‐term, high‐rate farmyard manure application

Abstract

Application of farmyard manure (FYM) is common practice to improve physical and chemical properties of arable soil and crop yields. However, studies on effects of FYM application mainly focussed on topsoils, whereas subsoils have rarely been addressed so far. We, therefore, investigated the effects of 36-year FYM application with different rates of annual organic carbon (OC) addition (0, 469, 938 and 1875 g C m À2 a À1 ) on OC contents of a Chernozem in 0-30 cm (topsoil) and 35-45 cm (subsoil) depth. We also investigated its effects on soil structure and hydraulic properties in subsoil. X-ray computed tomography was used to analyse the response of the subsoil macropore system (≥19 μm) and the distribution of particulate organic matter (POM) to different FYM applications, which were related to contents in total OC (TOC) and water-extractable OC (WEOC). We show that FYM-C application of 469 g C m À2 a À1 caused increases in TOC and WEOC contents only in the topsoil, whereas rates of ≥938 g C m À2 a À1 were necessary for TOC enrichment also in the subsoil. At this depth, the subdivision of TOC into different OC sources shows that most of the increase was due to fresh POM, likely by the stimulation of root growth and bioturbation. The increase in subsoil TOC went along with increases in macroporosity and macropore connectivity. We neither observed increases in plant-available water capacity nor in unsaturated hydraulic conductivity. In conclusion, only very high application of FYM over long periods can increase OC content of subsoil at our study site, but this increase is largely based on fresh, easily degradable POM and likely accompanied by high C losses when considering the discrepancy between OC addition rate by FYM and TOC response in soil. Highlights• A new image processing procedure to distinguish fresh and decomposed POM.• The increase of subsoil C stock based to a large extend on fresh, labile POM.

Long‐term manure application enhances organic carbon and nitrogen stocks in Mollisol subsoil

“…Overall, our findings are in line with the speculation that prolonged persistence of OC in subsoil mainly relies on the (1) binding of SOC with the mineral surfaces and less accessibility to the microbes, and (2) additionally the lower oxygen concentration in the subsoil layers could hamper microbes to acquire sufficient energy from the recalcitrant compounds for sustaining microbial activity, thereby greatly decreasing the SOC decomposition (Chabbi et al, 2009; Dungait et al, 2012; Fontaine et al, 2007; Preusser et al, 2017), and hence increased SOC stocks in the deeper layers (Figure 1a). The primary OC inputs in the deep layers are root exudates, and dissolved OC from surface layers (Rumpel & Kögel‐Knabner, 2011) transferred by bioturbation (Leuther et al, 2022).…”

“…T A B L E 4 Relationship between SOC stock and TN stock and wheat-maize-soybean grain yield under long-term mineral and manure fertilization along with different layers of a Mollisol profile microbes to acquire sufficient energy from the recalcitrant compounds for sustaining microbial activity, thereby greatly decreasing the SOC decomposition (Chabbi et al, 2009;Dungait et al, 2012;Fontaine et al, 2007;Preusser et al, 2017), and hence increased SOC stocks in the deeper layers (Figure 1a). The primary OC inputs in the deep layers are root exudates, and dissolved OC from surface layers (Rumpel & Kögel-Knabner, 2011) transferred by bioturbation (Leuther et al, 2022).…”

Biochar and Farm Yard Manure Synergy: Enhancing Soil Health and Mitigating Climate Change Impacts in Cotton Production

“…Additionally, biochar can enhance microbial activity, providing the habitat for microbes (Palansooriya et al 2019). FYM, on the other hand, provides a direct source of organic matter to the soil (Khan et al 2023), enriching it with readily decomposable materials and nutrients that support microbial communities and organic carbon accumulation (Leuther et al 2022). The synergistic effect observed in the Biochar + FYM treatment suggests that the combination of these amendments enhances their individual contributions to carbon sequestration.…”

Pore Distances of Particulate Organic Matter to Predict N2o Emissions from Intact Soil at Moist Conditions

“…It is at the lower end of the range of densities of biochemicals (0.8-1.7 g/cm 3 ) and consistent with the fact that operationally, in the method proposed by Balesdent et al (1996), POM are separated by flotation in water. However, it is smaller than the density of soil POM, usually considered in the literature to range between 1.20 and 1.64 g/cm 3 in studies where fractionations were carried out with heavier liquids (Chenu and Plante, 2006;Mayer et al, 2004;Leuther et al, 2022).…”