Addition Of Farmyard Manure Research Articles

The effect of long-term fertilization with organic or inorganic fertilizers on mycorrhiza-mediated phosphorus uptake in subterranean clover

A pot experiment was conducted with soil from a long-term (74-year) fertilization field experiment to compare the effects of organic and mineral fertilizers on mycorrhiza formation in clover, and mycorrhiza-mediated plant P uptake. Five treatments were selected from the field experiment representing different forms and levels of P. Mycorrhizal effects on plant growth and P uptake were estimated by comparing plants grown in untreated soil containing indigenous arbuscular mycorrhizal (AM) fungi, with plants grown in pasteurized soil. Short-term versus residual effects of fertilizer/manure were also measured by comparing treatments with or without fertilizers added at the start of the pot experiment. Mycorrhiza formation was greatest in soil that had received no P for 74 years, followed by soil having received 30 or 60 Mg ha–1 farmyard manure (FYM), and soil having received 25 or 44 kg P ha–1 in NPK fertilizers. Plant growth and P uptake were severely reduced in the absence of AM fungi for all mineral fertilizer treatments. In contrast, plants growing in soil that had received FYM grew equally well or better when non-mycorrhizal. Recent additions of NK fertilizer and FYM had no effect on mycorrhiza formation, while additions of NPK led to reduced colonization. It thus seems that moderate quantities of FYM have less adverse effects on AM than equivalent amounts of nutrients in NPK fertilizers, a phenomenon that is most likely due to a temporal difference in P availability and its gradual release that balance plant demand.

Role of edaphic factors in the development of downy mildew (Sclerospora graminicola) in pearl millet

Infection of pearl millet by downy mildew [Sclerospora graminicola (Sacc.) Schrot.] has been shown to be influenced by soil pH, soil bulk density, soil moisture content and addition of farmyard manure and nitrogen fixing bacteria. A pH value of 8·5 allowed disease to develop the most, with increases in acidity to pH 7·5 producing 70% reduction in disease. Higher soil bulk density and moisture content also led to reductions in disease but the effects were not as marked as for pH. The addition of farmyard manure to soil or the addition of Rhizobium, Azospirillum or Azotobacter inocula as combined seed and soil treatment also reduced disease with the best effects being from a cluster bean isolate of Rhizobium and from Azotobacter chroococcum. Assessment of rhizosphere microorganisms associated with the resistant and susceptible varieties of pearl millet showed that, overall, the fungal population was lower in the resistant varieties but that it was increased in both susceptible and resistant varieties by infection with downy mildew. Bacterial and actinomycete populations were also lower in resistant varieties but in this case downy mildew infection decreased the rhizosphere populations of both groups.Dehydrogenase activity of rhizosphere soil was higher in susceptible varieties but was decreased in both variety types by infection with S. graminicola.The results are discussed with reference to possible mechanisms to explain the observed effects.

Rainfall infiltration and runoff from an Alfisol in semi-arid tropical India. I. No-till systems

Alfisols, which are abundant in the semi-arid tropics, are fragile and subject to crusting, resulting in high runoff amounts and large soil losses. A field experiment was conducted at the International Crops Research Institute for the Semi-Arid Tropics, Hyderabad, India, over a 6-year period to study the runoff from Alfisols under no tillage without amendments, and with the addition of farmyard manure (15 Mg ha −1yr −1) and rice straw ( Oryza sativa) (5 Mg ha −1 yr −1). Each treatment had three replicates. A total of 211 runoff events were recorded for each plot. For runoff from no-till systems without any plant or straw cover, the infiltration rate was controlled by the surface crust. Infiltration rate through a surface crust was 9.6 mm h −1 and showed little change over time. Infiltration rates measured with a ring infiltrometer and disc permeameter were five to six times higher than that observed under natural rainfall. The data was divided into four groups with similar amounts of rain during the preceding 2 days and percent soil cover. The regression analysis found that the amount of precipitation, 30 min intensity, soil cover, and time since the beginning of the experiment were all significant factors in determining the runoff. More than 75% of the variation in runoff was explained by these variables for the zero tillage system without amendments and with farmyard manure applied. Straw amended systems were more difficult to predict. For events with less than 15 mm of rain during the previous 2 days, runoff was mainly related to the amount of rainfall when surface cover was less than 30% and to the product of rainfall amount and 30 min intensity when surface cover was greater than 30%. For events with more than 15 mm of rain during the previous 2 days, infiltration rates were generally higher than for dry soil. Runoff was related to a number of variables. Implication for management practices on Alfisols are that adding organic residue to no-till systems could significantly lower the runoff and increase the amount of water available for the crop.

Importance of environmental factors on the growth of Thermoactinomyces thalpophilus

The germination and growth of endospores from Thermoactinomyces thalpophilus in two soils, a sand silt loam and a silt clay loam was investigated under a range of environmental conditions. A 50-fold increase in the recovery of T. thalpophilus was observed after 28 d growth in silt clay loam soil, when compared to the original inoculum (8.85×10 4 cfu g −1 dry soil), with similar results obtained for this soil over a range of soil moisture contents (5–50% w/w) and at temperatures of 30 and 45°C. In contrast, no increase in the recovery of T. thalpophilus was detected when endospores (2.53×10 5 cfu g −1 dry soil) were inoculated into sand silt loam soil. However, when sterile farmyard manure (2% w/w) was added to sand silt loam soil, a 50-fold increase in the numbers of T. thalpophilus isolated was observed over 28 d incubation. Analysis of the sand silt loam soil showed that organic C and N content, pH, and the C-to-N ratio of the soil had all increased significantly upon addition of farmyard manure, resulting in the growth of T. thalpophilus endospores in a soil which previously could not sustain growth. Addition of manure to the silt clay loam led to a 70% increase in recovery of T. thalpophilus. Growth and respiratory measurements of T. thalpophilus released into sterile manure confirmed the ability of these endospores to show rapid germination, with respiratory activity detected after 7 h, reaching a maximum value (700 μmol CO 2 h −1 g −1 dry manure) 11 h after inoculation, resulting in a 600-fold increase (final recovery, 2.38×10 9 cfu g −1 dry manure) in the recovery of T. thalpophilus. We conclude that T. thalpophilus is capable of growth in soils at temperatures as low as 30°C and under a range of soil moisture conditions. Further, enhanced growth in soils with additions of manure could be observed. These results support the idea that Thermoactinomyces endospores isolated from ancient soils containing agricultural debris may have remained dormant in soil following a brief period of rapid growth immediately following deposition.

Use of crop residue and manure to conserve water and enhance nutrient availability and pearl millet yields in an arid tropical region

Crop residues and manures are often used in temperate regions to control soil erosion and maintain soil organic matter. Because crop residues and manures oxidize more rapidly in warmer climates, benefits from use of these materials may not be as evident for tropical as for temperate region agriculture, especially in drier regions where residues are limited. In 1991 and 1992, a field experiment was conducted to study the effect of crop residue incorporation in a loamy sand (Typic Camborthid) in Rajasthan, India. Residues of clusterbean [ Cyamopsis tetragonoloba (L) Taub], mung bean [ Vigna radiata (L) R. Wilczek], and pearl millet [ Pennisetum glaucum (L) R. Br.], and farmyard manure (FYM) were incorporated by disking in October. A pearl millet crop was grown the following Kharif (summer) season with and without fertilizer N. Crop residues increased soil water content at seeding in the order pearl millet > mung bean = farmyard manure > clusterbean. Addition of crop residues and FYM generally enhanced soil fertility status (N and P availability, organic matter, enzyme activity) 10 to 20%. Clusterbean residues and FYM increased pearl millet grain yield 0.1 to 0.2 mg ha −1, compared with no residue. These treatments also increased straw yields 0.4 to 0.6 mg ha −1, but mung bean and pearl millet residues increased pearl millet straw only marginally when compared with no residues. Crop residues plus 20 kg fertilizer N ha −1 provided pearl millet grain yield equivalent to that for 40 kg fertilizer N ha −1 with no residues, thus effecting a 50% savings of fertilizer N. The use of clusterbean residues or FYM with fertilizer N improved N-use efficiency 20 to 30%. Results indicate that like temperate regions, incorporation of crop residues and FYM in arid tropical soils benefits soil water storage, soil nutrient availability, and crop yield.

Comparison of d- and l-amino acid metabolism in soils with differing microbial biomass and activity

The rates of CO 2 production from soils over 6 h in response to addition of either the l- or the d-isomers of alanine, glutamine and glutamic acid have been determined for soils from 13 experimental grassland plots. These plots were established in the 1896–1997 winter and have received regular additions of farm yard manure (FYM) either with or without inorganic N, P and K applied, or factorial combinations of inorganic N (as (NH 4) 2SO 4), inorganic P (as basic slag and triple superphosphate) and K (as KCl), or no nutrient addition (control). As a result of these treatments, the soils have contrasting chemical and biological properties. Biomass C, determined from glucose-induced respiration, was well correlated with the l-amino acid- and d-alanine-induced respiration rates. The rates of d-amino acid-induced respiration were consistently lower than those of the corresponding l-isomers, except for alanine in the more acidic soils which had small microbial biomass contents. The d-amino acid-induced respiration accounted for smaller fractions of the variation in microbial biomass than that induced by the corresponding l-isomers. Relative to the control soil, l-amino acid-induced respiration rates were increased by FYM treatment, decreased slightly by the NPK treatment and decreased to a larger extent by the acidifying (NH 4) 2SO 4 treatments. In contrast, the rates of d-glutamine- and d-glutamic acid-induced respiration were reduced by addition of FYM, NPK and (NH 4) 2SO 4. The ratio of l-amino acid-induced respiration to d-amino acid-induced respiration ( d-to- d ratio) ranged between 6.3 and 1.4 for glutamine and 8.7 and 2.6 for glutamic acid. The l-to- d ratios for glutamine and glutamic acid increased with increasing soil microbial biomass and declined abruptly, but not linearly, with increasing rate of CO 2 evolution per unit of biomass (qCO 2). The declines in l-to- d ratios may have been related to increased physiological stress in the soil microbial community, since they occurred along a gradient of increasing soil acidity.

Nitrogen balance and N recovery after 22 years of maize-wheat-cowpea cropping in a long-term experiment

The influence of N, P and K application through inorganic and organic fertilizers on N recovery in crop plants and its balance in the soil-plant (maize-wheat-cowpea fodder) was studied for the first 22 years of a long-term experiment at Punjab Agricultural University farm, Ludhiana, India. The results showed. that N removal and apparent N recovery by both maize and wheat was directly related to the balanced application of N, P and K fertilizers. Averaged over the years, application of N alone (100% N) resulted in a recovery of 17.1% in maize and 31.7% in wheat. The application of P and K along with N almost doubled (32.8% in maize and 64.7% in wheat) the apparent N recovery in the crops. Increase in soil N concentration which was related to the build-up of soil organic carbon (OC) occurred at a very slow rate with the application of N, P and K fertilizers. Addition of farm yard manure (FYM) resulted in highest N removal in crops and build-up of soil N and OC status. Application of recommended N without P and K fertilizers resulted in relatively large amounts (64–71%) of fertilizer N lost from the surface soil as compared to that (41–49%) with N, P and K applied together. Higher rate of fertilizer application (150% NPK) resulted in comparatively greater N loss (58–62%). It was concluded that balanced and judicious use of N, P and K fertilizers coupled with the addition of any deficient element (e.g. Zn) help in minimizing N losses and environmental pollution.

Water-retention, organic-C and soil texture

Samples taken from the two textural phases of the surface soil of an irrigated natrixeralf and its clay subsoil were dried at wilting point and in air. Water retention increased linearly with C content, with values extrapolated to zero C content proportional to clay content. Emerson et al. (1994) (Aust. J. Soil Res., 32, 939-51) had already shown that water held by the surface samples at 10 kPa suction increased approximately linearly with C content, independently of clay content. Similar linear relations were deduced for other soils using values of field capacity and wilting point reported in the literature. A constant amount of water is considered to be held by portions of the silt/clay matrix. As the C content of the soil is increased, polysaccharide gels gradually fill additional 1-3 �m wide pores within the portions. It was calculated that, after a long period in grass, gel present increases available water on a weight basis, by 34% and 125% in loamy sand and sandy clay A horizons respectively. Where farmyard manure (FYM) was incorporated, gel only formed from the added C. Nevertheless the large increase in field capacity of a sandy loam produced by rotavation was temporarily preserved by prior addition of FYM. It is suggested that the gel here was mainly on microbial filaments.

Methane emission and methanogen status of Indian rice soil

A laboratory study was conducted to determine the rate of methane emission and the methanogenic population in an Indian rice soil. Methane emission was highest at 37°C. The dry rice soil had a low methanogen content but this increased after rice cultivation. Addition of farmyard manure increased the methane emission, while inorganic fertilizers suppressed methane emission in uncultivated rice soil. The soil after rice cultivation was a better source of incoulum for biogas production than the spent slurry from a cattle-waste-based biogas plant.

Nematodes as indicators of enhanced microbiological activity in a Scottish organic farming system

Abstract.The presence of spring barley plants increased the numbers of nematodes, particularly of plant‐feeders, compared with fallow plots in a Scottish organic farming system. The addition of farmyard manure (FYM) had no detectable effect on nematode populations but poultry manure (PM) caused a considerable increase. The application of PM also altered the types of nematode present and favoured bacterial‐feeders and rhabditids in particular. These changes suggest that PM causes shortterm (within a growing season) increases in microbiological activity and nutrient cycling, whereas FYM is more likely to bring about long‐term changes.

Microbial biomass nitrogen and mineralization-immobilization processes of nitrogen in soils incubated with various organic materials

Abstract The effects of the addition of organic materials on the change of the pattern of microbial biomass N in soils were assessed in relation to the mineralization — immobilization processes of N. Two types of field moist soils (Udifluvent and Melanudand) amended with chicken manure, clover leaves, farmyard manure, bark compost and rice straw were incubated for 16 weeks at 25°C, and the amounts of biomass N and inorganic N were measured periodically. The chloroform fumigation-extraction method was used for measuring the soil microbial biomass N. Chicken manure was rapidly mineralized from the onset of incubation and did not result in an appreciable increase of the amount of microbial biomass N (<4.0% of the added organic N). Clover leaves showed a lag period of 2 weeks before active N mineralization commenced and the amount of microbial biomass N increased during the lag period, reaching a value of 13.6% of the added organic N, while the amount of biomass N decreased rapidly. On the other hand, the addition of farmyard manure and rice straw resulted in N immobilization from the start of incubation, and N immobilization continued up to 4 weeks for the farmyard manure-treated soils and during the entire incubation period for the rice straw-treated soils. The amount of soil microbial biomass N increased within 2 weeks (10.5–13.5% of the added organic N) by the addition of farmyard manure or rice straw and the increase was maintained throughout the immobilization phase. Bark compost induced a slight N mineralization and immobilization, and the amount of microbial biomass N increased was low (<5.8% of the added organic N). Thus the addition of organic materials resulted in the increase in the amount of microbial biomass N regardless of the soil types. However, the changes in the pattern of microbial biomass N were related to the N mineralization and immobilization processes of each organic material.

Microbial biomass turnover and enzyme activities following the application of farmyard manure to field soils with and without previous long-term applications

We studied the build-up and turnover of microbial biomass following the addition of farmyard manure to an unmanured soil and to soils from a long-term experiment in which different levels of farmyard manure had been applied for the last 23 years. The application of farmyard manure at 15–90 t ha-1 to previously unmanured soil increased the microbial biomass during the first 3 months of incubation but a gradual decline occurred with further incubation for up to 12 months. Microbial biomass C was positively correlated with soil organic C and ranged from 1.8% to 2.2% of organic C after 12 months of farmyard manure applications. Biomass turnover increased with the application of farmyard manure, ranging from 0.81 to 0.87 year-1 with various levels of manure. Amendment of soils from the long-term manure experiment with various levels of farmyard manure led to a build-up and decline in biomass C as seen in the unmanured soils, but biomass C was higher in all treatments compared to the corresponding unmanured soil treatments. Biomass turnover was greater compared to the unmanured soil treatments and it decreased with increasing levels of farmyard manure. The average soil respiratory activity increased with increasing levels of farmyard manure, but respiratory activity per unit of biomass C decreased with increasing levels of manure. Enzyme activities were greater in long-term manured soils compared to unmanured soils amended with various levels of manure. There was a significant correlation between biomass C and enzyme activities.

Organic matter-microbial biomass relationships in field experiments under tropical conditions: Effects of inorganic fertilization and organic amendments

The analysis of continuous fertilizer and manurial experiments in tropical conditions of India have shown that soil microbial biomass C and N increased with balanced fertilization. The additions of organic amendments increased microbial biomass even when the organic C content of the soil did not increase. The increase in microbial biomass was attributed to better plant growth resulting in higher rhizodeposition. The crop yields and N uptake were higher with the addition of farm yard manure or Sesbania green manure.

Fixation and release of ammonium by two typical paddy soils after incorporation of farmyard manure

In a pot experiment with two typical paddy soils from the province Zhejiang (People's Republic of China) the fixation of NH4+ by clay minerals after incorporation of farmyard manure (FYM) and the utilization of non-exchangeable NH4-N by plants was investigated.The following results were obtained:In the entisol, with vermiculite as the main clay mineral, about 40 % of the soluble NH4-N supplied with FYM and 55 % of the NH4-N supplied as (NH4)2SO4 were fixed by clay minerals. During the growing season all of the NH4+ fixed after the fertilizer addition was released. There was a highly significant correlation between the N uptake of the plants and the HCl-extractable NH4-N which included exchangeable NH4-N as well as the plant-available portion of the non-exchangeable NH4-N. However the HCl extraction underestimated the amount of non-exchangeable NH4-N which was released during the growing season.In the ultisol, containing mainly kaolinite, the amount of NH4+ fixed after the addition of FYM and (NH4)2SO4, respectively, and the amount of non-exchangeable NH4-N released during the growing season was negligible.It is concluded that in paddy soils with expandable clay minerals the N efficiency after the application of FYM or ammonium-containing and ammonium-forming fertilizers, respectively, is higher than in soils with mainly 1 : 1 clay minerals. After the penetration of the NH4 ions into the interlayers, the conversion of ammonium to nitrate is blocked, resulting in lower N losses by denitrification or leaching after flooding. Further N losses by NH3 volatilization are reduced.

Effect of elemental sulphur on some properties of calcareous soils and growth of date palm seedlings

Abstract Seedlings of date palm (Khlas cultivar) were grown in two soils with similar contents of CaCO3 and different clay contents. After addition of farmyard manure, elemental sulphur was added to both soils at rates of 0, 500, 1000, 2000, 5000, 10000, 20000 and 30000 μg S0 g−1. After five months, height, fresh and dry weight of plants were measured, and leaf contents of N, S, P and micronutrients were determined. Soil pH and contents of CaCO3, soluble salts and available P and micronutrients were determined. The results showed that the content of CaCO3 and pH values decreased with an increase in S0, and salinity was increased. This effect was more pronounced in soils containing less clay. Availability and uptake of P, Fe, Mn, and Zn were increased at high addition rates of S0. Growth of seedlings was reduced at S0 rates over 5000 μg g−1, possibly due to the salinity and imbalance between N and S.

The effect of fertilisation on soil nitrifier activity in experimental grassland plots

Soil nitrification was compared in soils from 89-year-old grassland experimental plots with diverse chemical characteristics. Measurements of NaClO3-inhibited short-term nitrifier activity (SNA) and deamination of 1,2-diamino-4-nitrobenzene were used to study nitrification and deamination activities, respectively, in soil from each of 12 plots. Using multiple regression analysis, an expression for the relationship between SNA, soil pH and fertiliser N additions was derived which indicated that both the frequency and the quantity of farmyard manure additions were important in determining the rate of nitrification. SNA was greatest where there were large and frequent additions of farmyard manure. In soil with pH below 5.2 SNA was very low or insignificant. The effect of (NH4)2SO4 additions could not be assessed because they acidified the soil. We suggest that additions of farmyard manure increase the potential for NO3− leaching or for denitrification. Deaminase assays indicated that soils with a higher pH showed greater N mineralisation than soils with a lower pH, except at the low extreme. There was no obvious relationship between SNA and deaminase activity at higher levels of pH.

Retrospective analysis of an archived soil collection I. Metals

Soil samples collected and stored from the mid-1800s to the present-day have been analysed recently for a number of elements. The samples from long-term experiments under permanent grassland and continuous arable crops at Rothamsted Experimental Station (U.K.) were selected to investigate time trends in elemental composition due either solely to atmospheric deposition or to a combination of atmospheric deposition and various soil treatments. There was no measurable increase in soil Pb from atmospheric deposition during 100 years in one experiment at Rothamsted, and ∼ 15% increase since the mid/late-1800s in two others. A predicted increase of ∼ 11% in the plough layer Pb burden this century was derived from estimates of Pb deposition between 1900 and the present day. Treatment effects due to additions of farmyard manure (FYM) (for Cu, Pb and Zn) were also observed, although there were none due to additions of phosphate fertilisers. Soils receiving annual applications of 35t FYM ha −1 now have concentrations of 37 mg Cu kg −, 70 mg Pb kg −1 and 142 mg Zn kg −1 in the plough layer; unmanured plots contain 28 mg Cu kg −1, 40 mg Pb kg −1 and 83 mg Zn kg −1. Soil Sr has declined from 104 mg kg −1 in 1856 to 66 mg kg −1 in 1980 in neutral or slightly calcareous soils under wheat; no such change was observed in acid soils, relatively high in organic matter and under permanent grassland. The elements Co, Cr, Mo, Ni, Rb, V, Y and Zr showed no consistent changes which could be associated with either atmospheric or treatment inputs.

Effect of various organic materials on the mobility of heavy metals in soil

The mobility patterns of four divalent heavy metals—Zn 2+, Cu 2+, Pb 2+ and Cd 2+—were determined under varying acidities in an artificially contaminated sand and a naturally polluted soil after the addition of various organic materials—farm yard manure (FYM), peat, humic acid (HA) and tetraethylene pentamine (Tetren). Due to dissolution and decomplexation, the mobility of the heavy metals increased considerably upon progressive acidification. Metal pairs ZnCd and CuPb showed almost similar mobility patterns. In the case of artificially contaminated scand, the addition of FYM and peat enhance the mobility of heavy metals at lower pH values and decreased it at higher pHs. Humic acid and Tetren had little effect.

Zinc equilibria in submerged sodic soils as influenced by application of amendments

In a pot culture experiment, the effect of gypsum (50% of soil requirement), pyrites (equivalent to gypsum), farmyard manure (0.5 g per 100g soil) and Zn (10mg Zn kg−1 soil) on Zn equilibria in Ghabdan and Langrian series of sodic soils was studied. The equilibrium soil solutions collected anaerobically after 1, 14, 28, 42, 56, 70 and 84 days of submergence were analysed for pH, EC, HCO3 and Zn. Submergence markedly decreased soil solution pH and Zn up to 14 days and thereafter, the former slightly increased and the latter continued to decrease. Addition of amendments decreased soil solution pH in the order gypsum, pyrites and farmyard manure (FYM) and increased Zn concentration in the order FYM, gypsum and pyrites. The values of Zn potential (pZn + 2pOH) were within the range of pKsp for Zn(OH)2-Zn2+ (aq) from 16 to 84 days of submergence in Ghabdan soil and from 9 to 42 days of submergence in Langrian soil, where later it shifted to ZnCO3-Zn2+ (aq) system. Addition of FYM, pyrites and gypsum shortened the period of predominant existence of Zn(OH)2-Zn2+ (aq) system to 40, 30 and 12 days in Ghabdan soil and 30, 20 and 6 days in Langrian soil respectively. After these periods the system was saturated with respect to ZnCO3-Zn2+ (aq) except gypsum treatment where Zn-soil (unknown solid phases) -Zn2+ (aq) system controlled the solubility of Zn after 38 and 28 days of submergence of Ghabdan and Langrian soil respectively.

Microbial biomass and activity in an agricultural soil with different organic matter contents

Changes in soil fertility caused by various organic and N-fertilizer amendments were studied in a long-term field trial mostly cropped with cereals. Five treatments were included: (I) fallow, (II) cropping with no C or N addition, (III) cropping with N-fertilization (80 kg ha −1 yr −1), (IV) cropping with straw incorporation (1800kg Cha −1 yr −1) and N-fertilization (80 kg ha −1yr −1), and (V) cropping with addition of farmyard manure (80 kg N + 1800kg Cha −1yr −1). The treatments resulted in soil organic matter contents ranging from 4.3% (I) to 5.8% (V). Microbial biomass and activity were determined by chloroform fumigation, direct counting of fungi (fluorescein diacetate (FDA)-staining and Jones-Mollison agar-film technique) and bacteria (acridine orange staining), most probable number determinations of protozoa, esterase activity (total FDA hydrolysis) and respiration. Both biomass estimates and activity measurements showed a highly significant correlation with soil organic matter. Microbial biomass C ranged from 230 to 600 μg C g −1 dry wt soil, as determined by the fumigation technique, while conversions from direct counts gave a range from 380 to 2260 μg C. Mean hyphal diameters and mean bacterial cell volumes decreased with decreasing soil organic matter content.