Amounts of fungal biomass in adjacent cultivated and uncultivated soils in central Iowa were estimated and compared by quantifying soil ergosterol concentrations and lengths of fungal hyphae present. Both indices of fungal biomass, with one exception, indicated that there was at least twice as much fungal biomass in uncultivated soil as in cultivated soil. Levels of microbial biomass carbon in uncultivated soils were also determined to be at least twice that in cultivated soils. Data collected in this study indicate that fungi may be more significantly affected by agricultural soil management practices than other components of the soil microbial community. For two of the soils examined, calculated estimates denote that fungal biomass carbon represented approximately 20% of the total microbial biomass carbon in cultivated soil and about 33% of the microbial biomass carbon in uncultivated soil. Results of this study indicate that conventional agricultural practices result in a significant reduction of fungal biomass production in soil. Implications of differences in fungal biomass between the soils are discussed.

Soil microbial biomass carbon (biomass C) and its activity were measured in soil from Gabuzkoa (Spain) contaminated with heavy metals from a mine spoil tip. Soil was collected along a natural gradient of heavy metal contamination characterized by different organic C contents, clay contents, cultivation and topography. Biomass C and ninhydrin-N were measured by fumigation-extraction (FE), substrate induced respiration (SIR) and by soil ATP content. Microbial activity was measured by CO2 production and the arginine ammonification rate. The maximum soil concentration of zinc (about 6500 micrograms Zn g(-1) soil) was up to 27 times current European Union (EU) limits for agricultural soils. Microbial biomass, arginine ammonification rate and biomass C as a percentage of soil organic C decreased with increasing soil Zn concentration, while CO2 production and specific respiration rate increased. Soil biomass C was negatively (% variance accounted for = 45) and CO2 evolution positively (% variance accounted for = 72) significantly correlated with Zn concentration, in exponential relationships. Both biomass specific respiration rate (% variance accounted for = 83) and biomass as percentage of soil organic C (% variance accounted for = 76) were more significantly correlated to soil Zn concentration than was biomass alone. It was concluded that both biomass and activity measurements could serve as indicators of environmental stress due to metals in non-experimental sites. Additionally, these 'linked' measurements generally provided more sensitive indicators of environmental stress by heavy metals than either biomass C or CO2 evolution alone.

The purpose of this hay is to compare the root biomass among five tropical grasses, which affects the level of organic matter supply into soil and mineral nutrients acquisition. Experimental pastures of Brachiaria decumbens cv. Basilisk (BD). B. brizantha cv. Marandu (BB). Panicum maximum cv. Tanzania (TA), P. maximum cv. Tobiata (TO) and Andropogon gayanus cv. Baeti (AN) were established with two different levels of phosphorus and potassium. These pastures were grazed for three years, and then root biomass was measured in 0-10, 10-20 and 20-40cm of soil layers. Measured root biomass represented 53-76% of total biomass of the five grasses. Among the five grasses, root biomass level per square meter was in the order of BB BD TA TO AN, with the root biomass of BB significantly higher than those of the other grasses. Root biomass in the high fertilized soil was greater than those with low fertilizer levels. Root biomass decreased quickly with the increase of soil depth, whereas the percentage of root biomass to dry soil of BB was highest among the five grasses in all of the soil layers. It is concluded that BB is the best option to be introduced in crop-pasture rotation for soil quality improvement, in terms of quantity and distribution of root biomass. The relationship between root biomass and growth response of the examined species to soil fertility is also discussed

The soil physicochemical characteristics and amounts of microbial biomass C, N, and S in 19 soils (10 grassland, 2 forest, and 7 arable soils) were investigated to clarify the S status in granitic regosols in Japan, in order to determine the relationships between biomass S and other soil characteristics and to estimate approximately the annual S and N flux through the microbial biomass. Across the sites, the amount of biomass C ranged from 46 to 1,054, biomass N from 6 to 158, and biomass S from 0.81 to 13.44 mg kg(-1) soil with mean values of 438.8, 85.8, and 6.15 mg kg(-1) soil, respectively. Microbial biomass N and S accounted for 3.4-7.7% and 1.1-4.0% of soil total N and S, respectively. The biomass C : N, C : S, and N : S ratios varied considerably across the sites and ranged from 3.0-10.4, 32.5-87.7, and 5.0(-1)8.8, respectively. Microbial biomass S was linearly related to biomass C and biomass N. The regression accounted for 96.6% for biomass C and 92.9% for biomass N of the variance in the data. The amounts of biomass C, N, and S were positively correlated with a number of soil properties, particularly with the contents of organic C, total N, SO4-S, and electrical conductivity and among themselves. The soil properties, in various linear combinations showed a variability of 84-97% in the biomass nutrients. Stepwise multiple regression indicated that biomass C, N, and S were also dependent on SO4-S as a second factor of significance which could limit microbial growth under the conditions prevailing at the study sites. Annual flux of N and S was estimated through the biomass using the turnover rates of 0.67 for N and 0.70 for S to be approximately 129 kg k and 9.7 kg S ha(-1)y(-1), respectively, and was almost two times higher in grassland than arable soils

A soil incubation experiment was conducted to determine the effects of N application on microbial biomass C and P and to estimate the minimum requirement of available N for microbial biomass P formation. A granitic regosol soil was amended with N (as(NH4)2SO4) at rates of 0, 200, 400 or 800 mg N kg(-1), C (as rice straw) at 2100 mg C kg(-1) and P (as KH2PO4) at 500 mg P kg(-1) soil. With increasing N application up to 200 mg N kg(-1) soil, microbial biomass C significantly increased and remained constant or slightly decreased at higher N rates, while microbial biomass P increased up to 400 mg N kg(-1) soil and remained constant or slightly increased at the highest N contents. The concentration of P in microbial biomass (assuming that dry biomass contained 50% C) increased with increasing N rate and ranged from 32 to 76 mg g(-1). Among the P fractions in soil, microbial biomass P and inorganic P (available P) fractions increased with increasing N rates, whilst the Ca-P fraction decreased. The critical P concentration in microbial biomass (defined as that required to achieve 80% of the maximum synthesis of microbial biomass C) was estimated to be 60 +/- 4.1 mg P g(-1) biomass. The corresponding minimum amount of available N in the soil required to increase the biomass was estimated as 425 +/- 12 mg N kg(-1) soil. The specific respiration of the microbial biomass was little affected by the N concentration and was very high even above an N concentration considered to be the optimum for microbial biomass C and P but also microbial activity.

The scale dependency and landscape patterns of fungal and bacterial biomass, soil pH, organic C and moisture were examined in four hardwood forests in southern Ohio. Analysis of variance revealed significant differences in microbial biomass and soil chemistry among four forests (regional scale), among three contiguous watersheds within each forest (local scale), along gradients of moisture within watersheds (topographic scale) and upslope and downslope of individual red oaks (individual tree scale). Fungal and bacterial biomass varied significantly along gradients of moisture within watersheds while only bacterial biomass varied among sites and fungal biomass among watersheds. Fungal-to-bacterial biomass (F-to-B) ratio varied only among forests. Soil chemical properties varied at all scales examined except among watersheds. Hierarchical modeling of microbial patterns independent of scale revealed that while bacterial biomass and organic C are constrained by soil moisture present at the time of sampling and soil chemistry, fungal biomass is constrained by measures of long-term moisture patterns and soil texture. The resultant models also revealed that strong scale-independent models of bacterial biomass and organic C could be produced by scaling-up results from sampling points to the region, whereas this was not possible for fungal biomass and F-to-B ratio due to poor resolution at the local scale.

In order to investigate the influence of iron and aluminium oxide on microbial biomass in volcanic ash soils, we examined the relationships between the amounts of soil microbial biomass, evolved carbon dioxides and free iron and aluminium oxides. Eight soils were treated with H2O2 to remove organic matter, sterilized, inoculated with nonsterile soil, and incubated for 98 days with or without the addition of rice straw. The results obtained are as follows. The amount of soil organic C was decreased, while the amounts of free iron and aluminiumoxides were increased by treatment with H2O2. The amount of "stable" microbial biomass held in the soil at the latter period of incubation was also decreased. Therefore, it was suggested that soil organic matter could increase the amount of stable microbial biomass. Furthermore, within H2O2-treated soils, a negative correlation was obtained between the amount of evolved carbon dioxide and the amount Of stable microbial biomass and the amount of free aluminium oxides, suggesting that free aluminium oxides retard the decomposition of organic matter by soil micro-organisms and reduce the amount of stable microbial biomass

To detect the humification of organic compounds in soil that bypasses biomass incorporation, selective extraction procedures for radiocarbon from soil biomass and humus were evaluated. Following the incubation of C-glucose and C-benzoate in soil, fumigation-0.5 M K2SO4 extraction and 0.15 M Na4P2O7 extraction selectively removed biomass-associated and humus-associated radiocarbon, respectively. Applying the recovery correction of 3.4 × to biomass and 3.5 × to humus, radiocarbon balances of 95 to 107% were obtained during a time window following the degradation of these substrates. Negligible overlap between the extractions renders the technique suitable for investigating the fate of organics that, through cometabolism, attain unusual radiocarbon distributions in soil.

Microbial community composition may be an important determinant of soil organic matter (SOM) decomposition rates and nutrient turnover and availability in agricultural soils. Soil samples were collected from six long-term tillage comparison experiments located along two climatic gradients to examine the effects of no-tillage (NT) and conventional tillage (CT) management on bacterial and fungal abundance and biomass and to examine potential controls on the relative abundances of bacteria and fungi in these two systems. Samples were divided into 0-5 and 5-20 cm depth increments and analyzed for bacterial and fungal abundance and biomass, total C and N, particulate organic matter C and N (POM-C and N), soil water content, texture, pH, and water-stable aggregate distributions. Soil moisture, which varied by tillage treatment and geographically with climate, ranged from 0.05 to 0.35 g g(-1) dry soil in the surface 0-5 cm and 0.15 to 0.28 g g(-1) dry soil at 5-20 cm. Measured organic matter C and N fractions and mean weight diameter (MWD) of water-stable aggregates were significantly higher in NT relative to CT at three of the six sites. Fungal hyphal length ranged from 19 to 292 m g(-1) soil and was 1.9 to 2.5 times higher in NT compared to CT surface soil across all sites. Few significant tillage treatment differences in soil physical and chemical properties or in fungal abundance and biomass were observed at 5-20 cm. Bacterial abundance and biomass were not consistently influenced by tillage treatment or site location at either depth. The proportion of the total biomass composed of fungi ranged from 10 to 60% and was significantly higher in NT compared to CT surface soil at five of six sites. Proportional fungal biomass was not strongly related to soil texture, pH, aggregation, or organic C and N fractions, but was positively related to soil moisture (r = 0.67; P < 0.001). The relationship between soil moisture and the degree of fungal dominance was due to the positive response of fungal biomass and the lack of response of bacterial biomass to increasing soil moisture across the range of measured soil water contents. Tillage treatment effects on fungal biomass and proportional fungal abundance were not significant when the data were analyzed by analysis of covariance with soil moisture as the covariate. These results suggest that observed tillage treatment and climate gradient effects on fungi are related to differences in soil moisture. Further research is needed, however, to determine how tillage-induced changes in the soil environment shape microbial community composition in agroecosystems.

A study was made of the effect of liming (Ca(OH)2) on the numbers and biomass of bacteria (B) determined by a direct method in two textural types of soil; loamy sand (ls) and a loose sandy soil (lss) during 90 days in laboratory conditions. The liming of lss caused a marked and comparatively permanent increase in the bacterial biomass highly correlated with changes in soil acidity. The raising of pH from 4.5 to 7.0 and 9.0 brought about an increase in the mean size of biomass by 74 and 170 percent, respectively, in comparison with the control. The response of bacterial communities in the loamy sandy soil to the raising of pH was less enduring than that found in loose sandy soil, although even after 3 months their biomass sizes were 10 percent greater than the control