M.J. Acea

Seasonal changes in microbial biomass and nutrient flush in forest soils

Microbial biomass and N, P, K, and Mg flushes were estimated in spring, summer, autumn, and winter samples of different forest soils. The microbial biomass showed significant seasonal fluctuations with an average distribution of 880±270 μg C g-1 soil in spring, 787±356 μg C g-1 soil in winter, 589±295 μg C g-1 soil in summer, and 560±318 μg C g-1 soil in autumn. The average annual concentrations of C, N, P, K, and Ca in the microbial biomass were 704, 106, 82, 69 and 10 μg g-1 soil, respectively. Microbial C represented between 0.5 and 2% of the organic soil C whereas the percentage of microbial N with respect to the total soil N was two-to threefold higher than that of C; the annual fluctuations in these percentages followed a similar trend to that of the microbial biomass. Microbial biomass was positively correlated with soil pH, moisture, organic C, and total N. The mean nutrient flush was 31, 15, 7, and 4 μg g-1 soil for N, K, P, and Mg, respectively, and except for K, the seasonal distribution was autumn ≥spring ≫ winter ≥summer. The average increase in available nutrient due to the mineralization of dead microbial cells was 240% for N, and 30, 26, and 14% for P, K, and Mg, respectively. There was a positive relationship between microbial biomass and the N, P, K, and Mg flushes. All the variables studied were significantly affected by the season, the type of soil, and the interaction between type of soil and season, but soil type often explained most of the variance.

PHYSICAL AND CHEMICAL CHARACTERIZATION OF FOUR COMPOSTED URBAN REFUSES

Abstract The physical and chemical characteristics of four composted urban refuses (one of them amended with CaCO 3 during the composting process) from Spanish industrial composting plants were studied from the point of view of their use as organic fertilizers. The four composts were very fine in texture with low bulk density and high salinity. The pH was close to neutrality; the organic matter content ranged from 42 to 60% and the C/N ratio from 16 to 22 (7 for the amended urban refuse). Most of the total N was in organic forms; NH 4 + -N largely predominatedNO 3 − -N in the composts, except for the amended composted refuse where the predominant inorganic form was NO 3 − -N. Calcium was the most abundantnutrient followed by K, Na, Mg and P. Most of the Ca and Na were in available forms; available K and Mg were lower and available P very small. Total Al and Fe were extremely abundant followed by Zn, Mn, Pb, Cu, Cr, Ni and Cd. The percentage of available Mn was very high, followed by available Cu and Pb in two of the composts, and available Zn and Cd. Available Al, Fe, Ni and Cr were very low or negligible. Most of the total Zn, important percentages of total Pb, Mn, Al and Fe, but very low proportions of total Cr and Ni and only traces of Cd, were complexed with organic matter; these compounds seemed to be soluble organo-metallic complexes, except part of those formed by Al and Cd that could be stable complexes. Although the four composted refuses were unbalanced with regard to the main nutrients they all had potential agronomic value. Total C contents and C/N ratios in the three non-amended composts were in the range for stabilized composts; however, the NH 4 + -N content seemed to point to the presence of non-stabilized substances.

Seasonal fluctuations in microbial populations and available nutrients in forest soils

Viable microorganisms, soil respiration, and available N, Ca, Mg, Na, K, and P contents were determined in samples of five different forest soils collected in spring, summer, autumn, and winter. Viable microorganisms and soil respiration were positively correlated and showed a clear seasonal trend. The soils exhibited high microbial population values in spring and autumn and low values in summer and winter; total respiration values were largely higher in autumn than in the other seasons. Seasonal variations in available Ca, Na, and K contents were much more marked than those found for available N, Mg, and P. Available N and K and the microbial population showed similar seasonal trends whereas available Ca, Mg, Na, and P did not exhibit a distinguishable and uniform seasonal pattern. The quantities of available nutrients in soils followed the order Ca>K=Na>Mg>P>N. Soils developed over basic rocks showed higher values of both microbial density and microbial activity than those in soils developed over acid rocks. All the variables analysed were clearly related to the type of soil but varied with the date of sampling; a significant seasonal effect on the microbial population, microbial activity and available nutrients was detected in all the soils studied.

Microbial populations of poultry pine-sawdust litter

Abstract The average density of viable microorganisms in poultry pine-sawdust litter was 6·3 × 10 7 /g dry material (DP); 1·6% of the population were aerobic heterotrophic bacteria. Acidophile bacteria, aerobic spore-forming bacteria, actinomycetes and fungi were, respectively 4·8 × 10 4 , 8·1 × 10 4 , 5·2 × 10 4 and 8·9 × 10 4 CFU/g DP. However the latter did not have a measurable mycelium. Algae were in low densities (18/g DP) and cyanobacteria were not detected. Most of the population had proteolytic and ammonificant capacities, but there were very few ammonium oxidizers and nitrite oxidizers. Denitrifiers were in relatively high density and the anaerobic free-nitrogen fixers were more abundant than the aerobic ones. Aerobic cellulolytics were scarce, but anaerobic cellulolytics, amylolytics and pectolytics showed a similar, and relatively high average density. Sulphate reducers and anaerobic mineralizers of organic sulphur were more abundant than the elementary-sulphur oxidizers, and sulphide oxidizers were not detected. Except for algae, microbial populations generally tended to decrease with time of use of the litter. This decline affected mainly nitrifiers, anaerobic and aerobic cellulolytics and amylolytics while sulphate reducers and anaerobic free-nitrogen fixers increased.

Microbial response to organic amendments in a forest soil

Abstract Wheat straw or poultry Pinus -sawdust litter were added to a forest acid soil and changes in the microbial community were studied during a 3-month soil incubation. Soil amendment did not alter the relationships between microbial groups. In all the samples most microbes were aerobic heterotrophic bacteria which predominated over fungal propagules and actinomycetes; fungal hyphae were relatively well developed, whereas the densities of cyanobacteria and algae were relatively low. Among the N-cycle microbes, there was a relatively high number of ammonifiers, while both ammonium- and nitrite-oxidizers were scarce. Although soil amendment did not significantly alter the pattern of growth of most microbial groups, it drastically changed their numbers, alterations due to poultry addition being much more marked than those due to straw addition. Among the heterotrophic microbes, straw addition to soil increased fungal population but decreased bacteria and especially actinomycetes, while those that were able to carry-out ammonification were unaffected. Conversely, poultry manure addition favoured all the microbial groups, the increase in number following the order: bacteria > fungi > actinomycetes, the ammonium-producers being particularly stimulated. Autotrophic microbes, whether photo- or chemo-autotrophs, were decreased by straw and manure. The response of microbes indicated that the use of wheat straw could lead to a reduction in taxonomic and functional diversity in the microbial community and that, in general, poultry manure seems to be better for applying to soil.

Microbial fluctuations after soil heating and organic amendment

Abstract Microorganisms in heated (200°C, 1 h) soil not inoculated (H) or inoculated with 0.5% of fresh soil (Hi) and amended with wheat straw (Hi+WS) or poultry manure (Hi+PM) were determined during a 3-month soil incubation. Heating completely sterilised the soil, although the normal soil manipulation in the laboratory contaminated H with a few microbes. In the inoculated soil samples, whether amended or not, microbes were able to actively proliferate, but soil inoculation was essential to develop field microbial conditions. Organic amendment (WS or PM) neither inhibited microbial proliferation nor changed the order of the sizes of the various subgroups. Saprophytic bacteria predominated over the other microbial groups, followed by fungal propagules and actinomycetes; fungal mycelium was relatively well developed, whereas the numbers of photoautotrophs, cyanobacteria and algae were low. With regard to the N-mineralizers, there was a relatively high number of ammonifiers, while chemoautotrophic nitrifiers, both NH4+- and NO2−-oxidizers, were scarce. Microbial groups, however, differed in their response to treatment. In regard to the heterotrophic microbes, amendment with WS increased counts of fungal propagules and hyphae length, while bacteria, particularly actinomycetes and ammonifiers, were lowered; conversely, PM treatment favoured bacterial, actinomycetal, ammonifier and fungal mycelium development and propagule generation. All the autotrophic microbes, whether photo- or chemo-autotrophs, were decreased by the addition of organic residues and, in general, the effect was more negative with PM than with WS. The results indicated that WS could restore the numbers of fungi in the heated soil, but it could cause a reduction in other microbial groups, whereas PM increased the numbers of all the taxonomic groups and the ammonifiers. However, neither residue favoured the recovery of autotrophic C- and N-fixers and nitrifiers in the heated soil.

Poultry slurry microbial population composition and evolution during storage

Abstract In poultry slurry bacteria, most of them being strict or facultative anaerobes, predominated over actinomycetes and fungi, and algae were in low densities. Most of the population could carry out proteolysis, ammonification, denitrification, anaerobic cellulolysis, anaerobic N 2 -fixation, amylolysis, pectolysis, reduction of sulphates and anaerobic mineralization of organic sulphur. Conversely there were few nitrifiers, aerobic cellulolytics, aerobic free-living N 2 -fixers and sulphur-oxidizers, and cyanobacteria, fungal hyphae and sulphide oxidizers were undetected. At the beginning of slurry storage, the population of viable microorganisms and most of the microbial groups abruptly declined. Thereafter, the viable population rapidly multiplied, being five-fold greater than its initial value after 14 weeks. This increase was mainly attributed to anaerobic bacteria, while aerobic heterotrophic bacteria, including the sporulating and acidophilic ones, actinomycetes and fungi were negatively affected. After the fall in numbers, proteolytics, ammonificants, amylolytics, anaerobic cellulolytics and anaerobic N 2 -fixers actively grew, regaining or even surpassing, their initial densities. Conversely aerobic free-living N 2 -fixers, ammonium-oxidizers, nitrite-oxidizers, aerobic cellulolytics, pectolytics and sulphur-oxidizers remained at densities significantly lower than their initial values. Only denitrifiers, algae and sulphate-reducers were favoured from the initial stage of the storage.

Microbial composition of poultry excreta.

Abstract Total microbial populations, bacteria, actinomycetes, fungi and algae of three samples of poultry excreta were studied. The physiological groups involved in C, N and S cycles have been determined. The results were compared with the common numbers in soils and organic wastes. Poultry excreta had a high density of micro-organisms. Bacteria, most of them being strict or facultative anaerobes, predominated. Actinomycetes and fungi were also in relatively high density. Fungi were mainly as propagules and their mycelium was nearly indetectable. Algae were in low density. A small percentage of aerobic bacteria was acidophilic or acid-tolerant, a lesser number was spore-forming, and cyanobacteria were not detected. Most of the microbial population had proteolytic, ammonificant, anaerobic cellulolytic, denitrificant and anaerobic nitrogen-fixing capacities, followed by amylolytics, pectolytics, sulphate reducers and anaerobic mineralizers of sulphur; whereas micro-organisms favoured by aerobic conditions as aerobic cellulolytic, aerobic free-living nitrogen fixers, ammonium oxidizers, nitrite oxidizers and sulphur oxidizers were in low densities, and sulphide oxidizers were not detected.

MICROBIAL BIOMASS AND C AND N MINERALIZATION IN FOREST SOILS

Abstract Microbial biomass and activity were determined in three Cambisols and two Rankers developed over different kinds of rocks. The soils contained 0·3−1·7 g C kg−1 soil as biomass, which represented 0·8−1·5% of the total C. Whether the fumigation-incubation or fumigation-extraction method was employed, non-significant differences were found in microbial biomass values. The microbial density, which ranged from 107 to 108 microorganisms g−1 soil, was drastically reduced by CHCl3-fumigation; however, the liberation of cell metabolites significantly increased the microbial growth rate. During 10 days of soil incubation at 25°C 0·1−0·2 g C kg−1 soil (0·1−0·5% of total soil C) was released and 1−5 mg N 100 g−1 soil (0·1−1·5% of total soil N) was mineralized. A significant increase (approximately threefold) in the average C and N mineralization was found as a consequence of microbial lysis by fumigation. The results indicated that these soils have a considerable quantity of microbial biomass but a relatively low metabolic activity and that C and N mineralization may be significantly improved when microbial constituents are liberated into the soil.