Long-term continuous farmyard manure application increases soil carbon when combined with mineral fertilizers due to lower priming effects

Soil organic carbon and nitrogen in aggregates in response to over seven decades of farmyard manure application

“…The combined application of manure and chemical fertiliser also increased SOC and N content associated with all aggregate fractions, compared to +m (Figure 2B,C), indicating that the mineral fertiliser is more beneficial for SOC sequestration when applied in combination with manure. Such findings were explained by the lower priming effect causing a reduction in SOC decomposition rate in +s+m due to the abundance of nutrients, mainly dissolved N, compared to +m (Abdalla et al., 2022; Essel et al., 2021). The higher soil N abundance limits the soil microbial need for soil organic matter mining for nutrients, thus reducing the decomposition rate and promoting C stabilisation (Chen et al., 2022).…”

“…No significant change occurred to the manure fertilised plots (+m and +s+m) from 1904 to the sampling date in 2019, but the +s and the unfertilised plots received ≈ 2.5 tonnes of dry matter manure ha −1 year −1 before 1942. The current study considered four treatments (same as Abdalla et al., 2022): fertilised with mineral fertiliser in a similar amount of nutrients as compared to the manure application (+s), with cattle farmyard manure (+m), with mineral fertiliser and with manure (+s+m), and unfertilised control (uf; Table 1). There was no change in the four fertilisation practices after 1942 to the sampling date in 2019, thus maintaining the practices over the last 77 years.…”

“…Basal CO 2 efflux was measured from the composite samples (16 samples) used for the aggregate fractionation over 33 days in controlled conditions incubation using a CO 2 isotope analyser (CCIA−38d‐EP, Los Gatos Research (LGR) (Abdalla et al., 2022). In the current study, the cumulative basal respiration over the incubation period was used to further investigate its relationships to the aggregate stability and SOC and N associated with the aggregate fractions.…”

“…The study aimed at evaluating the effects of the three fertilisation practices on the aggregate size distribution and the associated SOC and N content in connection to soil basal respiration. Our previous study from the same experimental plots showed that the combination of manure and mineral fertiliser (+s+m) yields a higher net SOC gain, which was explained by the lower priming effects, compared to mineral fertiliser or unfertilised soil (Abdalla et al., 2022). Here, we aim to test whether the increased SOC content in combined fertilised soils can further be explained by the higher stability of soil aggregates and aggregate‐associated SOC and N, compared to other fertilisation practices, in addition to lower priming effects.…”

“…Within the fertilisation types, organic fertilisers are found to perform better than chemical ones alone in enhancing soil aggregation (Du et al., 2022; Wu et al., 2022; Zhou et al., 2013), mainly because of the fresh C input, which promotes microbial processes. Some studies reported that combining organic and synthetic mineral fertilisers is highly effective in improving soil C sequestration (Abdalla et al., 2022; Zhou et al., 2013). Such findings were mainly explained by the abundance of the important nutrients for microbial growth and activity from the mineral fertilisers in combination with a C source from organic fertilisers.…”