Soil organisms in organic and conventional cropping systems.

Apesar do crescente interesse pela agricultura orgânica, são poucas as informações de pesquisa disponíveis sobre o assunto. Assim, num Argissolo Vermelho-Amarelo distrófico foram comparados os efeitos de sistemas de cultivo orgânico e convencional, para as culturas do tomate (Lycopersicum esculentum) e do milho (Zea mays), sobre a comunidade de organismos do solo e suas atividades. As populações de fungos,bactérias e actinomicetos, determinadas pela contagem de colônias em meio de cultura, foram semelhantes para os dois sistemas de produção. A atividade microbiana, avaliada pela evolução de CO2, manteve-se superior no sistema orgânico, sendo que em determinadas avaliações foi o dobro da evolução verificada no sistema convencional. O número de espécimes de minhoca foi praticamente dez vezes maior no sistema orgânico. Não foi observada diferença na taxa de decomposição de matéria orgânica entre os dois sistemas. De modo geral, o número de indivíduos de microartrópodos foi superior no sistema orgânico do que no sistema convencional, refletindo no maior índice de diversidade de Shannon. As maiores populações de insetos foram as da ordem Collembola, enquanto para os ácaros a maior população foi a da superfamília Oribatuloidea. Indivíduos dos grupos Aranae, Chilopoda, Dyplopoda, Pauropoda, Protura e Symphyla foram ocasionalmente coletados e de forma similar entre os sistemas

Decomposition of 14C-labelled plant material in a salt-affected soil

Sodicity and salinity are each known to influence the decomposition of plant residues, but the effects of their interactions are not well understood. In this study, a loamy topsoil was adjusted to 3 values of exchangeable Na (0, 3 and 25%), for each of 3 values of salinity (0.1, 0.5 and 1.5 dS m−1 in a 1:5 soil-to-water extract), by equilibration with solutions containing appropriate amounts of NaCl and CaCl2. 14C-labelled Trifolium subterraneum shoots, either finely ground or unground, were added to the soils at a rate of 2.22 g kg−1 soil. Samples were kept for 82 days at −50 kPa water potential, or 97 days with drying-rewetting cycles. Mineralisation of ground plant C increased with increasing sodicity, and decreased with increasing salinity. The influence of both sodicity and salinity were less with unground than ground plant material because of reduced interaction of substrates with the soil matrix. The effects of the treatments on mineralisation of plant C were established within the first 20 days of incubation. Mineralisation of native soil C was increased by sodicity throughout the incubation at low salinity, but was unaffected by sodicity at high salinity. At the end of the incubation, neither plant- nor soil-derived microbial biomass C were greatly affected by sodicity or salinity. Total microbial biomass C was significantly higher in the soils kept at constant water content than in those submitted to drying-rewetting, in which it was approximately the same as in the soils before incubation. Of the total microbial biomass C, 50–93% was derived from the plant material. Drying-rewetting cycles decreased mineralisation and microbial biomass C (both plant- and soil-derived), but did not influence the effects of sodicity and salinity. At each value of salinity, mineralised plant C was positively correlated with water-extractable organic C derived from plant material. This was also true for soil-derived C at low, but not at high values of salinity. Mineralisation generally resulted in a reduction in the amount of carbohydrate C relative to other forms of organic C, as determined by 13C CP-MAS nuclear magnetic resonance

Elimination de la matière organique dissoute des effluents de caves et de distillerie par épandage = Removal of dissolved organic carbon in winery and distillery wastewater by application to soil

A mathematical model was used to describe the removal of water-soluble (extractable) 14C from synthetic winery and distillery wastewaters, following addition to a sandy loam and a sand. Extractable 14C showed an immediate decrease attributed to adsorption, which was followed 14C due to oxidative microbial decay. Near complete (>95 % ) removal when higher amounts of carbon were added to the soils, and by soil which had not been previously exposed to the wastewaters. The implications of the above for the management of sites irrigated with wine industry wastewaters are outlined. / Un modèle mathématique a été utilisé pour décrire l'élimination du carbone C14 hydrosoluble (extractible) d'effluents vinicoles synthétiques de cuviers et de distilleries suivant l'addition à un terreau sableux ou à du sable. Le carbone C14 extractible montre une diminution immédiate attribuée à l'adsorption, précédent une deuxième période de déclin du carbone C14 extractible dû à la décomposition microbienne oxydative. Une élimination quasi complète du carbone C14 extractible (>95 % ) a été achevée en quelques heures à quelques jours. Des temps plus longs furent nécessaires à l'élimination du carbone 14 quand des quantités plus importantes de carbone étaient ajoutées aux sols et quand le sol n'était pas préalablement mis en contact avec des effluents vinicoles. Les implications de ces résultats dans la gestion des sites irrigués par les effluents vinicoles provenant de l'industrie du vin ont été résumées

Sites of microbial assimilation and turnover of soluble and particulate C-labelled substrates decomposing in a clay soil

Different types of 14C-labelled substrates, two soluble (glucose and starch) and two particulate (legume and wheat leaves), were incubated in a Vertisol to test the importance of substrate-soil matrix relationships in the processes of soil organic matter decomposition and the location of microorganisms. Mineralized C (CO2 12C, CO2 14C) were measured within 66 d of incubation. Sieving and sedimentation procedures were used to fractionate (Light fractions (Lf) > 250 micrometers, Lf 50-250 micrometers, Heavy fractions (Hf) > 50 micrometers, Hf 2-50 micrometers, and Hf 0-2 micrometers) the soil. Biomass C (12C and 14C) in unfrationated soil and in fractions was assayed after 3, 38 and 66 d. Comparisons with an unamended soil (control) were made. Decay rates of substrate 14C were highest during the first 3 d of incubation. After 66 d, substrate-derived CO2 14C represented 63, 64, 59 and 51%, of input 14C in soils amended with the glucose, starch, legume and wheat, respectively. Unlike 14C, rates of mineralization of 12C in amended and unamended soils remained more uniform throughout. Total biomass C in soluble substrate-amended soils was similar to that in the control, despite about 60% of total biomass C being derived from 14C substrate amendments. By contrast, decomposition of particulate substrates increased total biomass C concentration at day 3. There was little or no turnover of 14C apparent within the first 3 d, as indicated by high (0.60) growth efficiencies (biomass 14C/[biomass 14C + CO2 14C]). Fraction weights were constant. Irrespective of treatments, the silt-size fraction (Hf 2-50 micrometers) was the most abundant (about 51% of total soil weight). This fraction concentrated 65% of the clay fraction as microaggregates. The fraction (Hf > 50 micrometers) approximated sand particles (> 50 micrometers)... (D'après résumé d'auteur