[Objective] The paper was to study highly efficient utilization of biogas slurry and the effect of highly efficient biogas slurry on vegetables, so as to provide basis for wide and effective application of biogas slurry. [Method] Using secondary aerobic fermentation technology, a small amount of humic acid was added into biogas slurry to enhance the biological activity of biogas slurry. Through greenhouse experiment, the effect of highly efficient nutrient solution of biogas slurry on yield and quality of green pepper, tomato and cucumber was studied. [Result] Compared with control and traditional application of biogas slurry, application of highly efficient nutrient solution of biogas slurry increased the yield of green pepper, tomato and cucumber, and the increase extents were 12.4%, 47.4%, 19.9% and 2.7%, 15.9%, 9.1%, respectively. Compared with traditional application of biogas slurry, application of highly efficient nutrient solution of biogas slurry significantly increased Vc content of green pepper and cucumber with the increase extent of 16.8% and 43.8%, respectively. [Conclusion] Application of highly efficient nutrient solution of biogas slurry can effectively promote the yield of green pepper, tomato and cucumber and change the qualities of vegetables, and significantly enhance the biological activity of biogas slurry.

The composition and function of the soil microbial community can be strongly influenced by soil structure and tillage. Soil total microbial biomass C (MBC), microbial biomass N (MBN), and fungal and bacterial biomass associated with different soil aggregate-size fractions were measured for a long-term no-till subtropical rice soil ecosystem to determine how tillage shifts microbial community structure and to detect the spatial scale at which microorganisms are the most sensitive to disturbance. Surface soil (0–20cm) was fractionated into aggregate-sizes (>4.76mm, 4.76–2.0mm, 2.0–1.0mm, 1.0–0.25mm, 0.25–0.053mm, <0.053mm) under three tillage regimes. Soil MBC, MBN, fungal biomass and bacterial biomass were significantly higher under no tillage (NT) than conventional tillage (CT) and CT flooded paddy field (FPF) in whole soil (p<0.05). Microbial biomass C, N and fungal biomass were significantly higher under NT than CT and FPF for all aggregate sizes. No significant tillage effects on microbial biomass C:N ratio were observed, but analysis of soil aggregates revealed significant differences due to tillage. Microbial biomass C:N ratio averaged 8.8, 8.5, and 8.4 for CT, NT, and FPF, respectively, while the ratio was significantly higher under CT than NT for macroaggregates >1.0mm, indicating a tillage-induced N limitation in macroaggregates. The fungal:bacterial biomass ratio ranged from 0.5 to 4.5, and was highest in 4.76–2mm aggregates for all tillage regimes. Fungal:bacterial ratios were significantly higher for aggregate sizes >1.0mm (2.4) than for <1.0mm aggregates (0.7). Tillage effects on fungal over bacterial dominance were not significant for whole soil and most aggregate sizes. The NT regime increased microbial biomass, but this increase was proportional for both bacteria and fungi. The soil microbial biomass and community structure was likely controlled by particle size at the aggregate-scale (0.05–5.0mm), while tillage played a role in regulating the microbial community structure.

The spatial organization of soil microbial communities over large areas and the identification of environmental factors structuring their distribution have been liUle investigated. The overall objective of this study was to determine the spatial paUerning of microbial biomass in soils on wide extent and to rank the environmental fiUers most influencing this distribution, by using the French Soil Quality Monitoring Network. This network covers ail the French terrilory and soils were sampled at2,150 sites along a systematic grid sampling. The soil DNA extracted from ail these soils was expressed in terms of soil molecular microbial biomass and related to other soil and land use data over the French territory. This study provides the first extensive map of microbial biomass and reveals the heterogeneous and spatially structured distribution of this biomass on the scale of France. The main factors driving biomass distribution are the soil physico-chemical properties (texture, pH and totai organic carbon) and land use also. Intensive agricultural crops, especially monoculture and vineyards, exhibited the smallest biomass pools in solI. Interestingly, factors known to influence the large scale distribution of macro organisms, such as dimatic factors, were not identified as important drivers for microbial communities. Microbial abundance is spatially structured and dependent on local filters such as soil characteristics and land use but is relatively independent of global fiUers such as climatic factors or the presence of natural barriers. Our study confirms that the biogeography of microorganisms differs fundamentally from the biogeography of "macroorganisms" and that soil management can have significant large-scale effects.

Affiche - résumé. Session GC: Microbes in the Changing Environmenl: Global Climate Change and Soif under Human Impact | International audience | The spatial organization of soil microbial communities over large areas and the identification of environmental factors structuring their distribution have been liUle investigated. The overall objective of this study was to determine the spatial paUerning of microbial biomass in soils on wide extent and to rank the environmental fiUers most influencing this distribution, by using the French Soil Quality Monitoring Network. This network covers ail the French terrilory and soils were sampled at2,150 sites along a systematic grid sampling. The soil DNA extracted from ail these soils was expressed in terms of soil molecular microbial biomass and related to other soil and land use data over the French territory. This study provides the first extensive map of microbial biomass and reveals the heterogeneous and spatially structured distribution of this biomass on the scale of France. The main factors driving biomass distribution are the soil physico-chemical properties (texture, pH and totai organic carbon) and land use also. Intensive agricultural crops, especially monoculture and vineyards, exhibited the smallest biomass pools in solI. Interestingly, factors known to influence the large scale distribution of macro organisms, such as dimatic factors, were not identified as important drivers for microbial communities. Microbial abundance is spatially structured and dependent on local filters such as soil characteristics and land use but is relatively independent of global fiUers such as climatic factors or the presence of natural barriers. Our study confirms that the biogeography of microorganisms differs fundamentally from the biogeography of "macroorganisms" and that soil management can have significant large-scale effects.

Designed soils are used in specialized urban areas, such as under sidewalks or on roof-tops. These substrates have coarse light-weight aggregates to meet load-bearing specifications with soil in voids for rooting medium. A full-factorial microcosm approach was used to study Lumbricus terrrestris (two adult worms added and no-worms added), compaction (bulk density of 1.95 and 1.48 g cm⁻³), and litter (litter and no-litter additions) in a designed soil. Earthworm biomass, soil physical, chemical, and biological properties, anion leaching and surface C efflux was measured on days 0, 7, 14, 21, 28, 72, 112, and 140. Earthworms decreased bulk density in compacted soil, but did not impact density of un-compacted soil. Earthworm biomass increased days 7 to 14, but declined from days 28 to 140, likely as result of the abrasiveness of the aggregate component and relatively shallow depth of the soil (25 cm). During the period of increasing earthworm biomass, surface C efflux, microbial biomass N, soil Ca²⁺ and NH ₄ ⁺ increased with earthworms. During the period of declining earthworm biomass, surface C efflux, microbial biomass N, soil Ca²⁺ and NO ₃ ⁻ , and leachate NO ₃ ⁻ increased, and soil pH decreased with earthworms. While alive and dying, Lumbricus terrestris stimulated microbial activity and biomass and nutrient availability, but an apparent shift to nitrification was observed as earthworm biomass declined. The results show Lumbricus terrestris to improve designed soil properties for plants, but the improvements may be short-lived due to the inability of these earthworms to survive in the designed soil.

Nitrogen losses from agricultural grasslands cause eutrophication of ground- and surface water and contribute to global warming and atmospheric pollution. It is widely assumed that soils with a higher fungal biomass have lower N losses, but this relationship has never been experimentally confirmed. With the increased interest in soil-based ecosystem services and sustainable management of soils, such a relationship would be relevant for agricultural management. Here we present a first attempt to test this relationship experimentally. We used intact soil columns from two plots from a field experiment that had consistent differences in fungal biomass (68 ±Â 8 vs. 111 ±Â 9 μg C g⁻¹) as a result of different fertilizer history (80 vs. 40 kg N ha⁻¹Â y⁻¹ as farm yard manure), while other soil properties were very similar. We performed two greenhouse experiments: in the main experiment the columns received either mineral fertilizer N or no N (control). We measured N leaching, N₂O emission and denitrification from the columns during 4 weeks, after which we analyzed fungal and bacterial biomass and soil N pools. In the additional ¹⁵N experiment we traced added N in leachates, soil, plants and microbial biomass. We found that in the main experiment, N₂O emission and denitrification were lower in the high fungal biomass soil, irrespective of the addition of fertilizer N. Higher ¹⁵N recovery in the high fungal biomass soil also indicated lower N losses through dentrification. In the main experiment, N leaching after fertilizer addition showed a 3-fold increase compared to the control in low fungal biomass soil (11.9 ±Â 1.0 and 3.9 ±Â 1.0 kg N ha⁻¹, respectively), but did not increase in high fungal biomass soil (6.4 ±Â 0.9 after N addition vs. 4.5 ±Â 0.8 kg N ha⁻¹ in the control). Thus, in the high fungal biomass soil more N was immobilized. However, the ¹⁵N experiment did not confirm these results; N leaching was higher in high fungal biomass soil, even though this soil showed higher immobilization of ¹⁵N into microbial biomass. However, only 3% of total ¹⁵N was found in the microbial biomass 2 weeks after the mineral fertilization. Most of the recovered ¹⁵N was found in plants (approximately 25%) and soil organic matter (approximately 15%), and these amounts did not differ between the high and the low fungal biomass soil. Our main experiment confirmed the assumption of lower N losses in a soil with higher fungal biomass. The additional ¹⁵N experiment showed that higher fungal biomass is probably not the direct cause of higher N retention, but rather the result of low nitrogen availability. Both experiments confirmed that higher fungal biomass can be considered as an indicator of higher nitrogen retention in soils.

International audience | 1. Regional above-ground biomass estimates for tropical moist forests remain highly inaccurate mostly because they are based on extrapolations from a few plots scattered across a limited range of soils and other environmental conditions. When such conditions impact biomass, the estimation is biased. The effect of soil types on biomass has especially yielded controversial results. 2. We investigated the relationship between above-ground biomass and soil type in undisturbed moist forests in the Central African Republic. We tested the effects of soil texture, as a surrogate for soil resources availability and physical constraints (soil depth and hydromorphy) on biomass. Forest inventory data were collected for trees >= 20 cm stem diameter in 2754 0.5 ha plots scattered over 4888 km(2). The plots contained 224 taxons, of which 209 were identified to species. Soil types were characterized from a 1:1 000 000 scale soil map. Species-specific values for wood density were extracted from the CIRAD's data base of wood technological properties. 3. We found that basal area and biomass differ in their responses to soil type, ranging from 17.8 m(2) ha(-1) (217.5 t ha(-1)) to 22.3 m(2) ha(-1) (273.3 t ha(-1)). While shallow and hydromorphic soils support forests with both low stem basal area and low biomass, forests on deep resource-poor soils are typically low in basal area but as high in biomass as forests on deep resource-rich soils. We demonstrated that the environmental filtering of slow growing dense-wooded species on resource-poor soils compensates for the low basal area, and we discuss whether this filtering effect is due to low fertility or to low water reserve. 4. Synthesis. We showed that soil physical conditions constrained the amount of biomass stored in tropical moist forests. Contrary to previous reports, our results suggest that biomass is similar on resource-poor and resource-rich soils. This finding highlights both the importance of taking into account soil characteristics and species wood density when trying to predict regional patterns of biomass. Our findings have implications for the evaluation of biomass stocks in tropical forests, in the context of the international negotiations on climate change.