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Vermicomposting converts organic wastes into high-quality nutrient-rich compost and has been considered as a suitable technology for developing countries, especially at the household and community level as it is a simple and natural technology that does not require sophisticated machinery and frequent process monitoring. In addition, attempts to address SOM and nutrient losses in a sustainable manner in sub Saharan Africa countries require careful optimization of use of organic amendments such as through vermicomposting. We performed a vermicomposting experiment using three-earthworm species, exotic (Eisenia fetida and Eisenia andrei) and indigenous (Eudrilus eugeniae), fed on six different substrates made from agricultural wastes (cow and donkey manure separately spiked with three types of equally mixed crop residues (maize with soybean (MS), maize with banana (MB) and soybean with banana (SB)) to assess the nutrient stabilization in the resulting compost; and performed an incubation experiment using a selection of these vermicomposts to study the net N mineralization of the composts, and how they affected soil microbial properties such as microbial biomass C, dehydrogenase and β-glucosidase activities, in Nitisols. Earthworm activities during vermicomposting of agricultural wastes accelerated the rapid decomposition of mixed substrates and resulted with a significant reduction of TOC (C mass loss > 65%) and C:N ratios (twofold compared to the control without earthworm) and an increase in N mineralization and the total concentration of P, K and S. The effect of vermicompost on N availability and soil microbial quality significantly varied depending on vermicompost sources. The vermicompost made from cow manure mixed with soybean and banana residues using Eudrilus eugeniae had the highest net N mineralization (32.4 µgNg-1 soil, 75% of N added). Regardless of vermicompost type, amended soils had significantly higher microbial and enzymatic activities than unamended control. Our results suggest that vermicompost sources tested could reliably use for long-term improvement of soil nutrient mineralization and microbial activity under Nitisols of Ethiopia due to their greatest microbial activities and nutrient dynamics during vermicomposting.

Soil texture determines microbial activity and organic matter (OM) decomposition in several ways. Next to direct physicochemical stabilization of OM, the location of moisture in the soil matrix also depends on soil texture. At lower moisture content, the contact between soil moisture and OM might be critical for OM decomposition, because such areas of contact could function as a ‘bridge’ for transport of moisture, substrates and microorganisms. Additionally, water absorption by porous OM itself likely also depends on soil texture and this may thus bring about another indirect textural control on OM mineralization. However, the relevance of such indirect soil textural controls on OM mineralization has not been investigated. We therefore compared the mineralization of 13C-labeled maize particles (Cmaize-min) in a loamy sand and silt loam soil at three levels of water-filled pore space (20, 40 and 60%WFPS). The distribution of maize particles and moist soil volume was assessed at the microscale using X-ray μCT and contrast-enhancing agents. We hypothesized that a lower contact between OM and soil in the loamy sand soil would lead to a reduced OM decomposition compared with the silt loam soil. On the other hand, we expected that OM itself could attract more moisture from the surrounding loamy sand soil due to a higher water potential than in the silt loam soil at equal WFPS level. Contrary to our expectation, we found a lower contact between zones of moist soil and the added OM in the silt loam soil. But as expected, OM was able to attract more water from the loamy sand soil, and it preserved a moist state even when soil was at a low moisture content, which may explain the surprisingly limited inhibition of Cmaize-min in drier loamy sand soil. This finding suggests that such a ‘sponge-effect’ of OM may be a relevant yet largely overlooked element in studying the relationship between soil moisture and OM decomposition. Contrary to our expectation, Cmaize-min was higher in the silt loam soil texture across all three moisture levels (P

Soil microbial communities (bacteria, fungi, archea, protozoa) directly and indirectly influence all other trophic interactions in soil. Partial soil sterilization by gamma irradiation is emerging as a promising defanauting technique to remove specific target group of organisms with minimal soil disturbance. While considering the selective elimination of a target organism, it is crucial that microbial community has recovered to its original state. The microbial community should return back to its original state shortly after partial sterilization, but to date there are no studies on the dynamics of microbial recovery following partial sterilization.

Pseudomonas isolates from tropical environments have been underexplored and may form an untapped reservoir of interesting secondary metabolites. In this study, we compared Pseudomonas and cyclic lipopeptide (CLP) diversity in the rhizosphere of a cocoyam root rot disease (CRRD) suppressive soil in Boteva, Cameroon with those from four conducive soils in Cameroon and Nigeria. Compared with other soils, Boteva andosols were characterized by high silt, organic matter, nitrogen and calcium. Besides, the cocoyam rhizosphere at Boteva was characterized by strains belonging mainly to the P . koreensis and P . putida (sub)groups, with representations in the P . fluorescens , P . chlororaphis , P . jessenii and P . asplenii (sub)groups. In contrast, P . putida isolates were prominent in conducive soils. Regarding CLP diversity, Boteva was characterized by strains producing 11 different CLP types with cocoyamide A producers, belonging to the P . koreensis group, being the most abundant. However, putisolvin III‐V producers were the most dominant in the rhizosphere of conducive soils in both Cameroon and Nigeria. Furthermore, we elucidated the chemical structure of putisolvin derivatives—putisolvin III‐V, and described its biosynthetic gene cluster. We show that high Pseudomonas and metabolic diversity may be driven by microbial competition, which likely contributes to soil suppressiveness to CRRD.

In Western Europe, winter fallow could last 9 months, for example between a winter wheat and a cabbage crop. On bare soil, the risks of erosion and nitrogen leaching are high. The introduction of winter cover crop or agro-ecological service crop (ASC) could deliver several benefits to the environment and the agricultural system. How to manage them ? For which benefits ?

The soil environment impacts carbon turnover in a multitude of ways. It has been shown that C emissions are higher when exogenous carbon is locally concentrated than when it is spread in the soil matrix. Hence, the spatial separation between decomposers and substrate may cause ineffective dispersion of the produced enzymes within the soil matrix. It is not clear, however, if and how lower doses of exogenous C impact its degradability and if an interaction exists with native soil organic matter (SOM) level. Therefore, a seventy-day incubation experiment with six varying exogenous OM doses (0-6 g C kg-1) in soil mesocosms of loamy sand subsoil (WFPS 50%) with three different native SOM contents (i.e. 0.1, 0.5, and 1.0 %) was carried out. C emission and isotopic signature measurements of 13CO2 by means of a CRDS-analyser were used to track the degradation of added maize shoots with a δ13C=-12.7‰ that contrasts to native SOM (δ13C=-25‰). Mineral N was added, and the redox potential (Eh) monitored. Eh suggested that O2 may have not become limiting for C mineralisation, even at higher doses, but it did not clearly relate to the added C dose. Cumulative CO2 emissions increased proportionally with C dose and so our hypothesis that a lower dose dispersion limits microbial activity was disproved. However, a higher native SOM level led to higher relative degradability of added C for the highest doses (i.e. 3 and 6 g kg-1 soil). Furthermore, a negative impact of OM doses above 1 g kg-1 soil on native SOM degradation was found. We conclude that positive priming of native SOM mineralisation did not occur. A disproportional response of microbial biomass carbon and soil C mineralisation at lower doses suggests that dose does impact the microbial metabolic quotient. Ongoing PLFA analyses will help us interpret these observations.

Mineral nitrogen (N) availability to heterotrophic micro-organisms is known to impact organic matter (OM) decomposition. Different pathways determining the N accessibility depend to a large extent on soil structure. Contact between soil mineral and OM substrate particles can facilitate N transport toward decomposition hot spots. However, the impact of soil structure on N availability to microbes and thus heterotrophic microbial activity and community structure is not yet fully understood. We hypothesized that carbon mineralization (Cmin) from low-N substrate would be stimulated by increased N availability caused by closer contact with soil particles or by a higher moisture level, enhancing potential for N-diffusion. Under opposite conditions retarded heterotrophic activity and a dominance of fungi were expected. A 128-days incubation experiment with CO2 emission monitoring from artificially reconstructed miniature soil cores with contrasting soil structures, viz. high or low degree of contact between soil particles, was conducted to study impacts on heterotrophic activity. The soil cores were subjected to different water filled pore space percentages (25 or 50% WFPS) and amended with either easily degradable OM high in N (grass) or more resistant OM low in N (sawdust). X-ray μCT image processing allowed to quantify the pore space in 350 μm around OM substrates, i.e., the microbial habitat of involved decomposers. A lower local porosity surrounding sawdust particles in soils with stonger contact was confirmed, at least at 25% WFPS. Mineral N addition to sawdust amended soils with small particle contact at 25% WFPS resulted in a stimulated respiration. Cmin in the latter soils was lower than in case of high particle contact. This was not observed for grass substrate particles or at 50% WFPS. The interactive effect of substrate type and soil structure suggests that the latter controls Cmin through mediation of N diffusion and in turn N availability. Phospholipid fatty acid did not reveal promotion of fungal over bacterial biomarkers in treatments with N-limited substrate decomposition. Combining X-ray μCT with tailoring soil structure allows for more reliable investigation of effects on the soil microbial community, because as also found here, the established soil pore network structure can strongly deviate from the intended one.

soilbeg findings in soil and fertility

The role of soil structure in organic matter (OM) stabilization has been primarily investigated through physical fractionation studies operative at the scale of aggregates and smaller organo-mineral particles. By narrowing down soil structure to an arrangement of mineral and organic particles, the majority of studies did not explore the spatial organization of the soil pore network, the actual habitat of microorganisms. In a lab experiment we incubated a sandy loam soil (with application of ground grass or sawdust) in 18 small aluminum rings (Ø 1 cm, h 1 cm). Bulk density was adjusted to 1.1 or 1.3 Mg m-3 (compaction) and 6 rings were filled at a coarser Coarse Sand:Fine Sand:Silt+Clay ratio.