Evaluation of the total biomass has been done for the first time in four zonal soil types. A certain correlation has been found between the biomass pool in soils and potential respiration intensity. The microbial biomass is composed mainly the biomass of eucariots (88-99 %), while the biomass of procariots ranges within 1 % (chestnut soil) and 12 % (grey forest soil). In terms of their microbial biomass the soils under study may be arranged in a following sequence: grey forest soil (5.7 t/ha) sod-podzolic (14 t/ha) chernozem (15 t/ha) chestnut soil (32 t/ha). The biomass of microbial coenoses is rather regularly distributed in the profile, not being concentrated in the upper soil horizons, as it was assumed earlier

The effects of a range of fertilizer applications and of repeated low-intensity prescribed fires on microbial biomass C and N, and in situ N mineralization were studied in an acid soil under subalpine Eucalyptus pauciflora forest near Canberra, Australia. Fertilizer treatments (N, P, N + P, lime + P, sucrose + P), and P in particular, tended to lower biomass N. The fertilizer effects were greatest in spring and smaller in summer and late autumn. Low-intensity prescribed fire lowered biomass N at a soil depth of 0-5 cm with the effect being greater in the most frequently burnt soils. No interactions between fire treatments, season, and depth were significant. Only the lime + P and N + P treatments significantly affected soil microbial biomass C contents. The N + P treatment increased biomass C only at 0-2.5 cm in depth, but the soil depth of entire 0-10 cm had much higher (> doubled) biomass C values in the lime + P treatment. Frequent (two or three times a year) burning reduced microbial biomass C, but the reverse was true in soils under forest burn at intervals of 7 years. Soil N mineralization was increased by the addition of N and P (alone or in combination), lime + P, and sucrose + P to the soil. The same was true for the ratio of N mineralization to biomass N. Soil N mineralization was retarded by repeated fire treatments, especially the more frequent fire treatment where rates were only about half those measured in unburnt soils. There was no relationship between microbial biomass N (kg N ha-1) and the field rates of soil N mineralization (kg N ha-1 month-1) The results suggest that although soil microbial biomass N represents a distinct pool of N, it is not a useful measure of N turnover.

Long-term fertilization with ammonium sulphate [(NH4)2SO4] or amendment with sewage sludge have resulted in a reduction in the ratio of microbial biomass-C to soil-C in the Ultuna Long Term Soil Organic Matter Experiment. We explored whether a reduced substrate utilization efficiency and higher loss of substrate-derived biomass-C over an extended incubation period could account for the smaller biomass in these soils. Samples were taken from four soils of this field experiment, representing soils of contrasting pH, soil organic matter and heavy metal status. Soils were amended with either no substrate, [U-13C]-labelled glucose, [U-14C]-labelled straw or both substrates. The addition of glucose-C corresponded approximately to the amount of biomass-C in the soil, whilst the addition of straw-C was 5 times greater. The soils were incubated at 15 degrees C and were sampled at intervals for CO2-C and biomass-C for up to 134 days. There was initially a larger increase in biomass total-C than ninhydrin-N upon substrate addition, but by day 7 this ratio had fallen to that in the unamended soils. On day 7 less glucose-C was incorporated in the biomass of the (NH4)2SO4-fertilized soil with a pH of 4.4 and in the biomass of a sewage-sludge-amended soil, compared to a calcium-nitrate [Ca(NO3)2] fertilized and a farmyard-manure-amended soil. The proportion of glucose-C respired by day 7 was higher in the sewage-sludge-amended soil, but not the (NH4)2SO4-fertilized soil. The biomass of the (NH4)2SO4-fertilized soil had also incorporated less straw-C 7 days after addition, but this was not lower in the sewage-sludge-amended soil. Loss from the biomass of initially incorporated substrate-C over a period of more than 3 months was not higher in the (NH4)2SO4-fertilized and the sewage-sludge-amended soil. At the end of the incubation the sum of respired and biomass-incorporated glucose-C did not differ between soils, but less straw-C was metabolized in the (NH4)2SO4-fertilized and the sewage-sludge-amended soil compared to the Ca(NO3)2-fertilized and farmyard-manure-amended soil. The combined addition of glucose and straw resulted in an increased loss of glucose-derived C from the biomass in the first week, with most soils also showing an increased rate of 13CO2 production during this period. Microbial utilization of straw was reduced as a result of glucose addition, so that when considering both substrates combined the microbial utilization efficiency was markedly lower compared to when the substrates were added separately.

In recent publications, relatively great attention has been paid to the biomass of soil mycromycetes. This study was undertaken to measure soil micromycete biomass in three soils in southern Slovakia. The membrane filter determination method was used in order to distinguish separately from total soil biomasss the micromycete portion. The Haplic Chernozem contained the highest quantity of micromycete biomass and the Calcaric Fluvisol, the youngest soil, the least. The micromycete biomass was highly variable due to the great effect of environmental factors. Distinct maxima were observed over the investigated period, corresponding to temperature and humidity.

Soils with greater levels of microbial biomass may be able to release nutrients more rapidly from applied plant material. We tested the hypothesis that the indigenous soil microbial biomass affects the rate of decomposition of added green manure. Cowpea [Vigna unguiculata (L.) Walp.] leaves were added to four soils with widely differing microbial biomass C levels. C and N mineralization of the added plant material was followed during incubation at 30 degrees C for 60 days. Low levels of soil microbial biomass resulted in an initially slower rate of decomposition of soil-incorporated green manure. The microbial biomass appeared to adjust rapidly to the new substrate, so that at 60 days of incubation the cumulative C loss and net N mineralization from decomposing cowpea leaves were not significantly affected by the level of the indigenous soil microbial biomass.

International audience | The Dehérain long-term field experiment was initiated in 1875 to study the impact of fertilization on a wheat-sugarbeet rotation. In 1987, the rotation was stopped to be replaced by continuous maize. Crop residues were soil-incorporated and the mineral fertilization was doubled in some plots. The impact of those changes on the microbial biomass and activity are presented. In spring 1987, the soil was still in a steady-state condition corresponding to the rotation. The microbial biomass was correlated with total organic C and decreased in the order farmyard manure>mineral NPK>unfertilized control. Microbial specific respiratory activity was higher in the unfertilized treatments. The soil biomass was closely related to soil N plant uptake. In 1989, after 2 years of maize and crop residue incorporation, the steady-state condition corresponding to the previous agricultural practices disappeared. So did the relationship between the biomass and total organic C, and the soil N plant uptake. Biomass specific respiratory activity increased because of low efficiency in the use of maize residues by microbes under N stress.

We carried out an experiment to investigate the contribution of microbial biomass N to soil N which was made available by soil heating treatment, and was analyzed by an 15N-labelled technique. The soils used were Dark red soils and Andosols collected from Chiba prefecture. After labelling the microbial biomass N with 15N, the soils were heated (50, 100, 150 degrees C) and fumigated. The mineralized N and 15N were measured at 0, 10, and 20 days after incubation. In both soils, the amount of N mineralized from the heated soil increased with the increase in the temperature of heating treatment. However, the 15N abundance of the N mineralized from the heated soil decreased with it. The 156N abundance of the N mineralized from the heated soil at 50 degrees C and from the fumigated soil was approximately equal to that of the 15N-labelled microbial biomass. Based on these results, we suggest that the N mineralized from the heated soil at 50 degrees C is mainly derived from the microbial biomass N, and that the ratio of the contribution of non-biomass N to the mineralized N increase with the temperature of heating treatment

Nitrogen status of upland soils were assessed for soil samples collecting from the Northern, Northeastern, and Southern parts of Thailand. Soil organic matter, total nitrogen, mineralizable N and biomass N were analyzed and compared among these soil samples. Results revealed that soil samples from the North had finer texture and contained more organic matter and total nitrogen than soil sample from the Northeast and the South. Furthermore, nitrogen mineralization and nitrification was more efficient in Northern than in Northeastern and Southern soils. Nitrogen loss due to denitrification was observed only in some incubated Southern soils. The amount of soil microbial biomass was found in correlation with the amount of soil organic matter in all soil samples. Moreover, the mineralizable N derived from the biomass N in the North was lower than that in the Northeast.