An incubation study on soil amendment was carried out with sugarcane trash (ST), press mud (PM), mustard oil cake (MOC), and cow dung (CD) to investigate the periodic changes in mineral nitrogen (N), microbial biomass carbon (C), and N formation in soil. Nitrogen mineralization and microbial biomass C and N were measured at 0, 7, 14, 28, 42, 56, 70, and 84 days of incubation. Organic material (OM) amended soils significantly increased mineral N over control except ST that encouraged N immobilization. Significantly higher amount of microbial biomass C and N were produced in all the amended soils over control. Biomass C and N were increased rapidly within 7 days and decreased thereafter and reached a constant level after 28-42 days of incubation. A significantly higher amount of microbial biomass C (246.33 mg kg-1 soil) was found in ST-amended soil followed by MOC (229.39 mg kg-1 soil), PM (220.27 mg kg-1 soil), CD (189.05 mg kg-1 soil), and control (123.41 mg kg-1 soil). Similarly, a higher significant quantity of microbial biomass N (43.60 mg kg-1 soil) was found in ST-amended soil followed by MOC (41.38 mg kg-1 soil), PM (39.76 mg kg-1 soil), CD (37.05 mg kg-1 soil), and control (22.04 mg kg-1 soil). The apparent percentage of N assimilation in microbial biomass from added OM was linearly and positively correlated with the C:N ratios of added OM, both at the time of maximum biomass formation (r = 0.997**) and the end of incubation (r = 0.999**).

Abstract Relation between larval train millipede density and soil microbial biomass under two different forest. Ayu Toyota and Nobuhiro Kaneko (Soil Ecology Research Group, Graduate School of Environment and Information Sciences, Yokohama National University, 79-7 Tokiwadai, Yokohama, 240-8501, Japan). The relationship between larval train millipede, Parafontaria laminata (Attems, 1909) density and soil microbial biomass in larch, Larix kaempferi (Lamb.), oak, Quercus mongolica Fischer ex Turcz. var. grosserrata (Bl.) Rehd. et Wils. forest soils was examined. The larvae were found in soil at high density as all individuals in a population consisted of a single cohort (same age) in the study site. The effects of the train millipede on soil microbial biomass were observed for two growing seasons at 6th instar and 7th instar larval stages. Distribution of both instars was similar between the larch and oak forests. Sixth instar larvae reduced soil microbial biomass with increasing density in the larch forest, whereas they gave a non-linear density effect on soil microbial biomass in the oak forest. However, at 7th instar, there was no decrease in soil microbial biomass even at high density spot. These effects of larval train millipede on soil microbial biomass were considered to result from feeding behavior, such as geophagous at 6th instar larvae, and litter and soil mixed feeding at 7th instar larvae.

We estimated fine root biomass in a Japanese cedar (Cryptomeria japonica) plantation using a minirhizotron technique. Since data obtained from minirhizotrons are limited to the length and diameter of fine roots observed on minirhizotron tubes, data conversion is necessary to determine the fine root biomass per unit soil volume or unit stand area. We first examined the regression between diameter squared and weight per unit length of fine roots in soil core samples, and calculated the fine root biomass on minirhizotron tubes from their length and diameter. Then we determined conversion factors based on the ratio of the fine root biomass in soil core samples to that on minirhizotron tubes. We examined calculation methods, using a single conversion factor for total fine root biomass in the soil for depths of 0–40 cm (Cal1), or using four conversion factors for fine roots in the soil at 10-cm intervals (Cal2). Cal1 overestimated fine root biomass in the lower soil or underestimated that in the upper soil, while fine root biomass calculated using Cal2 better matched that in soil core samples. These results suggest that minirhizotron data should be converted separately for different soil depths to better estimate fine root biomass.

Grasslands have an underground biomass component that serves as a carbon (C) storage sink. Switchgrass (Panicum virgatum L.) has potential as a biofuel crop. Our objectives were to determine biomass and C partitioning in aboveground and belowground plant components and changes in soil organic C in switchgrass. Cultivars Sunburst and Dacotah were field grown over 3 yr at Mandan, ND. Aboveground biomass was sampled and separated into leaves, stems, senesced, and litter biomass. Root biomass to 1.1-m depth and soil organic C to 0.9-m depth was determined. Soil C loss from respiratory processes was determined by measuring CO₂ flux from early May to late October. At seed ripe harvest, stem biomass accounted for 46% of total aboveground biomass, leaves 7%, senesced plant parts 43%, and litter 4%. Excluding crowns, root biomass averaged 27% of the total plant biomass and 84% when crown tissue was included with root biomass. Carbon partitioning among aboveground, crown, and root biomass showed that crown tissue contained approximately 50% of the total biomass C. Regression analysis indicated that soil organic C to 0.9-m depth increased at the rate of 1.01 kg C m⁻² yr⁻¹ Carbon lost through soil respiration processes was equal to 44% of the C content of the total plant biomass. Although an amount equal to nearly half of the C captured in plant biomass during a year is lost through soil respiration, these results suggest that northern Great Plains switchgrass plantings have potential for storing a significant quantity of soil C.

Soil microbial biomass (hereafter referred to as microbial biomass), defined holistically as the living component of soil organic matter (i.e., all organisms with a volume less than 5,000 micro cubic m, e.g., bacteria, fungi, protozoa), is actively involved in biogeochemical processes that occur in soil microniches of paddy soils. These processes include organic matter decomposition, microbial oxidoreduction, and cycling of N, C, and plant nutrients. The nature and extent of these biogeochemical processes cannot be approximated without understanding the involvement of microorganisms in these processes. Microbially-mediated biogeochemical processes, such as photosynthesis, N2-flxation, organic matter decomposition, subsoil oxidoreduction, and nutrient immobilization, lead to increases in the content of microbial biomass, while processes, such as biomass turnover and mineralization, lead to its decrease. In addition, the level of microbial biomass in the paddy soil ecosystem is affected by many biotic and abiotic factors, such as N fertilization, organic matter applications, soil type, flooded-upland soil rotation, and soil depth. Methods to measure soil microbial biomass as a single pool of organic matter include substrate-induced respiration, chloroform fumigation-incubation, chloroform fumigation-extraction, and adenosine triphosphate. However, these holistic methods provide little information about the community composition and physiological state of the soil microbial biomass and reasons why the soil microbial biomass changes over time and under different conditions. However, these methods are useful in understanding of cycling and dynamics of soil organic matter, especially where whole suites of organisms are involved. Culturing and isolation of microorganism provide answers to the shortcomings of the single pool biomass methods. Newer methods that can provide valuable information about the physiological state of soil microbial communities and provide more sensitivity to detect changes in these communities include: gene-based analytical methods, microbial activity, tracer isotopes, and analysis of biomarkers. Depending upon the objectives of a study or the problem to be addressed, any of the analytical methods described offer a best and efficient approach to analyze soil microbial biomass.

The paper presents the results referring to soil salinity influence on the content of microorganism's biomass. Soil contamination was applied in a form of NaCl at following concentrations: 10, 100 and 1 000 mmol/kg. The soil with no salt addition was the control. Content of living microorganism's biomass was determined using physiological method according to Andersen and Domsch. Regardless the soil type, NaCl diminished the amount of biomass, but by 20 percent stronger in sandy than loamy soil. It was also found that negative influence of NaCl decreased in time in loamy soil, which was not observed in the sand

A glasshouse study using Tephrosia vogelii was conducted on ferralsols with soil pH 5.0 and 5.9, and low available P (2.5-2.9 mg P kg soil(-1)), to assess the effects of soil pH and application of P on seedling performance and quantity and quality of biomass. The two soils were treated with Minjingu phosphate rock (MPR) at 0 and 400 mg P kg(-1) soil and planted to T. vogelii, which grew for 12 weeks. The parameters assessed were plant height and nodule numbers for seedling performance, shoot and root dry matter yield for biomass quantity, and shoot N and P contents for biomass quality. Both soil pH and application of MPR significantly (p less than or equal to 0.05) affected all the parameters assessed. Increase in soil pH from 5.0 to 5.9 increased plant height by 13%, nodule number by 256%, shoot biomass by 110%, and N and P uptake by 121% and 125%, respectively. Minjingu PR application in the soil of pH 5.0 increased plant height by 14%, nodule number by 31%, shoot biomass by 94%, N uptake by 193% and P uptake by 200%. In the soil of pH 5.9 the corresponding increases due to MPR application were 5% for plant height, 65% for nodule number, 36% for shoot biomass, 35% for N and 100% for P uptake. The results indicated that in acidic ferralsols with low available P, biomass yield and quality of T. vogelii were enhanced when such soil conditions were corrected.

A laboratory study was conducted at Bangabandhu Sheikh Mujibur RahmanAgricultural University, Bangladesh during 1997. The changes in microbialbiomass carbon due to incorporation of different organic materials in soil werestudied to determine the contribution of microbial biomass C to carbon pool ofsoil. The organic materials incorporated into the soil were; rice straw, wheatstraw, Napier, azolla, water hyacinth and town refuse. Individual organicmaterials were incorporated in the soil immediately after soil moistureadjustment (50% of maximum water holding capacity) at the rate of 150 mg/20g air dried soil and were incubated for 98 days. The C account in the form ofCO2 (CO2-C) was measured up to 98 days at different time intervals. All thesoil samples incorporated with different sources of organic matter showedhigher biomass C as compared to untreated soils. At 98 days of incubation,wheat straw treated soil gave higher CO2-C (133.93 mg/100 g air dry soil) andbiomass C (215.31 mg/100 g air dry soil) followed by town refuse treated soil(CO2-C 123/61 mg/100 g air dry and biomass C 192.37 mg/100 g air dry soil).The amounts of CO2-C and biomass C recorded at 7 days of incubationgradually increased in soil treated with all the organic materials up to 98 daysof incubation but the amounts varied with respect to different organicmaterials. Maximum CO2-C and biomass C were produced at the primary stageof incubation (7 to 21 days). With the increase of incubation period, CO2-C andbiomass C production rates were decreased. Contribution of biomass C toorganic C was higher in the soil treated with Napier (1.81%) followed by thesoil treated with town refuse (1.58%). It was concluded that among organicmatter sources wheat straw had greater ability to increase CO2-C and biomassC.

Ecosystem‐level studies of producer–decomposer interactions have focused primarily on plant production and soil texture as regulators of decomposer abundance but have rarely considered the role of grazers in mediating such interactions. Here, we conducted replicated exclosure experiments at both high and low levels of soil fertility to investigate the effects of large, mammalian grazers on decomposer biomass and activity patterns in a semiarid grazing ecosystem in Kenya. Within only two years of grazer exclusion, microbial biomass was greater in soil of fenced grassland across all levels of soil fertility. This consistent negative effect of grazers on microbial biomass occurred despite the fact that grazers stimulated aboveground plant production in nutrient‐rich sites and depressed it in nutrient‐poor sites. A consideration of all the potential pathways by which grazers influence decomposer populations suggests that observed grazing‐induced reductions in microbial biomass were predominantly associated with a depression in the amount of plant carbon inputs to soils. Finally, across all study sites, microbial biomass was highly correlated with soil carbon content, suggesting that landscape‐scale constraints on soil organic matter content and plant production overarch grazer effects on microbial abundance. Our results support previous ecosystem‐level studies showing that microbial biomass and growth are constrained by plant production and soil C availability. In addition, our findings demonstrate that decomposer abundance can be influenced by an ecosystem's trophic structure, with significant reductions in microbial biomass occurring as a result of herbivores diverting plant carbon away from soils.

The exclusion of insects from terrestrial ecosystems may change productivity, diversity and composition of plant communities and thereby nutrient dynamics. In an early-successional plant community we reduced densities of above- and below-ground insects in a factorial design using insecticides. Beside measuring vegetation dynamics we investigated the effects of insect exclusion on above- and below-ground plant biomass, below-ground C and N storage by plants, litter quality, decomposition rate, soil water content, soil C:N ratio, nutrient availability and soil microbial activity and biomass. The application of soil insecticide had only minor effects on above- and below-ground biomass of the plant community but increased carbon content in root biomass and total carbon and nitrogen storage in roots. In one of the three investigated plant species (Cirsium arvense), application of soil insecticide decreased nitrogen concentration of leaves (-12%). Since C. arvense responded positively to soil insecticide application, this effect may be due to drought stress caused by root herbivory. Decomposition rate was slightly increased by the application of above-ground insecticide, possibly due to an impact on epigeic predators. The application of soil insecticide caused a slightly increased availability of soil water and an increased availability of mineralised nitrogen (+30%) in the second season. We explain these effects by phenological differences between the plant communities, which developed on the experimental plots. Microbial biomass and activity were not influenced by insecticide application, but were correlated to above-ground plant biomass of the previous year. Overall, we conclude that the particular traits of the involved plant species, e.g. their phenology, are the key to understand the resource dynamics in the soil.