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Soil Biological Activity
Carbon Flow from Roots to Microbes to Soil Humic Substa... Featured
Plant residue decomposition rates in soils have been shown to be increased and decreased in the presence of living roots and their exudates. Living roots also have been shown to promote the conservation or mineralization of native soil organic matter (SOM). Plant effects on soil water status and N availability may partly explain many of the contradictory results from greenhouse and field studies. The actual mechanisms involved, however, are still elusive.
Preferential Accumulation of Microbial Carbon in Aggreg... Featured
We examined the effect of reduced tillage on the accumulation of fungal- versus bacterial-derived organic matter within the soil matrix by quantifying the amino sugars glucosamine (Glc), galactosamine (Gal), and muramic acid (MurA) in aggregate-size fractions isolated from no-tillage (NT) and conventional-tillage (CT) soil. Intact soil cores (0- to 5- and 5- to 20-cm depth) were collected from the long-term tillage experiment at Horseshoe Bend in Athens, GA. Four water-stable aggregate-size fractions were isolated: large macroaggregates (>2000 µm), small macroaggregates (250–2000 µm), microaggregates (53–250 µm), and the silt + clay fraction (<53 µm). Small macroaggregates were further separated into coarse particulate organic matter (POM) (>250 µm), microaggregates contained within macroaggregates, and the silt + clay fraction. Amino sugars were extracted from all fractions, purified, and analyzed by gas chromatography. Fungal-derived amino sugar C (FAS-C) comprised 63%, while bacterial-derived ...
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Soil organic matter, biota and aggregation in temperate... Featured
La stabilisation à long terme de la matière organique du sol (MOS) dans les régions tempérées et intertropicales est sous la dépendance de l'activité biologique (champignons, bactéries, macrofaune et racines), de la structure du sol (agrégation) et de leurs interactions. En moyenne, si le turnover du carbone du sol (C) est environ deux fois plus rapide en régions intertropicales qu'en régions tempérées, peu de différences apparaissent toutefois quant à la qualité de la MOS sous ces climats différents. La stabilité de l'agrégation est plus élevée pour les sols des régions intertropicales, ceci étant probablement dû à leur minéralogie dominée par des argiles de type 1:1 associés à des oxihydroxides métalliques. Toutefois, pour les sols tropicaux, la corrélation entre teneur en C et stabilité de l'agrégation est plus faible et de moindres quantités de C sont associées avec les éléments fins (argile+limon). Aussi bien sous climats tempéré que tropical et subtropical, une ...
Living Soil: Training Exercises for Integrated Soils Ma... Featured
Living Soils: Training Exercises for Integrated Soils Management'Living Soils' consists of 31 exercises with accompanying reference materials which were compiled and edited by Dr William Settle, Senior Ecology Consultant to the FAO Programme for Community IPM in Asia. All exercises have been field tested in training sessions in Indonesia, Thailand, Cambodia and Bangladesh.
Standard methods for assessment of soil biodiversity an... Featured
A major feature of global change in the tropics is that of landuse associated with agricultural intensification (Lavelle et al. 1997). In addition to plants, soil is the habitat of a diverse array of organisms: archaea, bacteria, fungi, protozoans, algae and invertebrate animals, the activities of which contribute to the maintenance and productivity of agroecosystems by their influence on soil fertility (Hole 1981, Lavelle 1996, Brussaard et al. 1997).
Native earthworms communities, soil processes and susta... Featured
Tropical savannas cover 43% of the plains of Latin America, with an area of 243x106 ha. They are traditionally used for extensive cattle ranching of low productivity (Rippstein et al. 1996; Vera and Seré 1985). Common agroecosystems range from pure grass or legume/grass-based improved pastures, to high input annual crops (Thomas et al. 1995). The substitution of the native savanna by introduced grasses from Africa has been a widely accepted practice in the Colombian “Llanos” during the last 20 years. As a result agricultural production has increased rapidly but the long-term sustainability of these agroecosystems is limited. Such an evolution has important economical implications, and still scarce knowledge exists about biological processes involved in these land use changes and how these can alter fundamental ecosystem processes and services.
Plant covers, soil macrofauna and geranium cropping Featured
In the highlands of western Réunion, the abandonment of fallowing, the use of monocropping and crop rotations under bare soil conditions, and excessive application of pesticides has led to physical, chemical and biological soil degradation. The technical and socioeconomic performances of farms with geranium (Pelargonium x asperum) as main crop have been markedly affected by these trends. They have also had a detrimental effect on the environment—already weakened by serious natural constraints. Cropping over plant covers could enhance the sustainability of such farms under these adverse conditions.
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