Relationships were established between the properties of 23 soils. Particularly identified were those soil properties correlated with (i) native biomass C, with (ii) the extent of decomposition of added [14C]glucose and [14C]Medicago littoralis plant residues after 44 and 66 weeks incubation respectively, and with (iii) the concentrations of substrate-derived C found in the microbial biomass and non-biomass residues. The native biomass C and biomass 14C from glucose and M. littoralis were highly correlated with each other and with soil clay content and other related soil properties, e.g. CEC and total soil pore space. For glucose-amended soils total residual 14C was also correlated with soil clay content. Differences between soils in the concentration of total residual organic 14C were due entirely to differences in the amounts of 14C present in the microbial biomass. Thus, statistically non-biomass 14C accounted for a constant proportion of input 14C. In contrast with glucose decomposition, total residual organic 14C from M. littoralis decomposition was not significantly correlated with clay content and related properties except when the statistical analyses were confined to soils of neutral to alkaline pH. Soils of mildly acidic pH retained more residual non-biomass 14C than did neutral to alkaline soils of similar clay contents. The close direct correlations between biomass 12C, and biomass 14C from glucose and plant material metabolism, and soil properties indicated that soil charge or structure or both are important factors influencing microbial biomass accumulation in soils. These factors may override such influences as substrate type, concentration and efficiency of utilisation in determining biomass C concentration in soils after long (1 yr) incubation.

A review of methods used for the determination of soil microbial biomass is given. The indirect methods are based on counting of microbial colonies developed on various cultivation media. Applying microscopical methods, length and thickness of the hyphae of micromycetes was measured, and bacterial cells in the range of the microscope view were counted. The chemical method indicates the biomass defining ATP - as the cell component. The essence of physiological or biochemical methods is based on adding to the soil such compound, which would affect the microbial processes in the soil sample. The course and the changes of these processes were then observed. The results obtained when using different methods, are comparable after calculation for identical units of each soil sample, e.g. 10 g C.

The effects of clearfelling a tropical rainforest and establishing pasture on soil microbial biomass and nitrogen transformations were assayed monthly over 1 yr in three adjacent systems in the central Amazon region; (1) virgin rainforest; (2) slashed-and-burnt forest; and (3) recently established pasture. The amounts of soil organic matter (SOM) and soil microbial biomass-carbon (biomass-C) were substantial in all systems. Total soil-C ranged between 1.9 and 5.2% depending on management and soil layer, whereas biomass-C ranged between 3.5 and 5.3% of total soil-C. The soil biomass-C decreased upon slashing-and-burning to 64% of its original value (1287 micrograms g-1) in the forest (0-5 cm soil layer) and increased after establishment of pasture to 1290 micrograms g-1, but remained unchanged in the deeper 5-20 cm soil layer. No significant seasonal variation was measured in any system or soil layer. Soil respiration responded to management like microbial biomass-C but varied significantly over the season with the smallest respiration found in the driest month (October) and the largest respiration at end of the rains in May. Pools of mineral N varied considerably in all systems and soil layers and displayed identical seasonal variations. The forest topsoil contained the highest amounts (on average 47 micrograms N g-1) and the pasture soil the smallest amounts (on average 24 micrograms N g-1). The transition of the forest ecosystem to a pasture resulted in increased NO3(-1) concentrations. Net N-mineralization and net NO3(-1) production monitored during short-term laboratory incubations were used as indices of N mineralization and nitrification. No significant differences in N-mineralization indices were measured between systems, but substantial within season variations were recorded in all systems and soil layers. The variations were synchronized in time with extreme net N-mineralization in September and net N-mineralization in October. Significant nitrification indices were measured in all systems. They were identical in the systems, except for small indices found in topsoil of the slashed and burnt area, where, on the other hand, certain localized areas with extreme nitrification rates were detected.

Using the chloroform fumigation incubation (CFI) method, an 8-10-day incubation proved suitable for the determination of the biomass: this period was sufficient for the CO2 production of the fumigated and control soils to become almost identical for the soils tested. During the 10-day incubation after chloroform fumigation, the rate at which the biomass was mineralized depended on the soil type. In the substrate-induced respiration (SIR) method, the first 4 h of incubation can be used for the determination of the biomass, due to the linearity of the process. No correlation could be demonstrated between the biomass-C determined using the CFI and SIR methods and the total numbers of bacteria, actinomycetes and fungi. The biomass-C values obtained using the SIR method exhibited no correlation with any of the soil properties examined. A weak correlation was found in the 21 soil samples between the CFI biomass-C and the organic C, total N, Olsen-P and saccharase activity of the soils tested.

Abundance and distribution of earthworms were studied on the Georgia Piedmont of the Southeastern U.S.A., at sites representing various ecosystem types, management practices, landscape positions, soil textures and soil erosion status. Earthworm abundance showed distinct seasonal patterns, with winter/spring maxima and summer minima. Numbers and biomass ranged from zero in plowed, mono-cropped soil at an upland site to over 1000 m-2 (> 25 g ash-free dry wt m-2) in no-tillage, double-cropped soil on bottomlands. Numbers and biomass in plowed, double-cropped soil, in a bottomland forest, and in grass meadows at both upland and bottomland sites were intermediate. Soil texture, as influenced by water erosion, strongly affected earthworm abundance. Moderately and severely eroded sandy clay loam supported significantly higher earthworm numbers and biomass than did slightly eroded soil with higher sand content. This effect may have resulted from low organic content and water holding capacity of the sandy soils. Of the soil texture variables, silt content was most highly correlated with earthworm biomass. Earthworm abundance was also related to quantity and quality of plant residue inputs in the agroecosystems, and to standing stocks of soil organic carbon across all sites studied. At most agroecosystem and forest sites, the predominant earthworm species were European lumbricids; native Diplocardia spp were most prominent in a meadow soil with high organic content.

Understanding microbial dynamics is important in the development of new management strategies to reverse declining organic-matter content and fertility of agricultural soils. To determine the effects of crop rotation, crop residue management, and N fertilization, we measured changes in microbial biomass C and N and populations of several soil microbial groups in long-term (58-yr) plots under different winter wheat (Triticum aestivum L.) crop rotations. Wheat-fallow treatments included: wheat straw incorporated (5 Mg ha-1), no N fertilization; wheat straw incorporated, 90 kg N ha-1; wheat straw fall burned, no N fertilization; and wheat straw incorporated, 11 Mg barnyard manure ha-1. Annual-crop treatments were: continuous wheat, straw incorporated, 90 kg N ha-1; wheat-pea (Pisum sativum L.) rotation (25 yr), wheat and pea straw incorporated, 90 kg N ha-1 applied to wheat; and continuous grass pasture. Total soil and microbial biomass C and N contents were significantly greater in annual-crop than wheat-fallow rotations, except when manure was applied. Microbial biomass C in annual-crop and wheat-fallow rotations averaged 50 and 25%, respectively, of that in grass pasture. Residue management significantly influenced the level of microbial biomass C; for example, burning residues reduced microbial biomass to 57% of that in plots receiving barnyard manure. Microbial C represented 4.3, 2.8, and 2.2% and microbial N 5.3, 4.9, and 3.3% of total soil C and N under grass pasture, annual cropping, and wheat-fallow, respectively. Both microbial counts and microbial biomass were higher in early spring than other seasons. Annual cropping significantly reduced declines in soil organic matter and soil microbial biomass.

The effect of temperature and soil moisture content on the influence of Afalon, Gramoxone, and Afalon + Gramoxone mixtures on the amount of soil microbial biomass was studied. The herbicides were applied at dosages of 1, 10, 100 and 1000 mg/kg. The soil was incubated at temperatures of 10, 20, 30 and 40 degrees C, and at water contents of 10, 50, and 90 % max. water capacity. After 0, 7, 14, and 21 days the amount of microbial biomass in soil was determined, using the physiological method of ANDERSON and DOMSCH (SIR method). The results show the inhibitory effect of Afalon on the microbial biomass, and stimulation caused by lower dosages of Gramoxone and Afalon + Gramoxone combinations. The inhibitory effect of all herbicides increased with increasing dosages. The inhibitory effect of the herbicides is significantly different at the different temperature and moisture conditions. It increases with increasing difference of the values of these parameters from optimum. The influence of each herbicide, or their combinations, on the amount of microbial biomass depends in a different manner on soil temperature and moisture content