Effects of lime and phosphate additions on changes in enzyme activities,microbial biomass and levels of extractable nitrogen,sulphur and phosphorus in an acid soil

Summary The effects of adding lime and/or phosphate to an acid, phosphate-deficient soil on microbial activity, enzyme activities and levels of biomass and extractable N, S and P were studied under laboratory conditions. Following rewetting there was, as expected, an initial flush in microbial growth and activity, as shown by large increases in CO₂ evolution, in levels of biomass N, S and P and by accumulation of extractable mineral N and sulphate in the soil. Following rewetting, additions of lime and phosphate further stimulated mineralization of C, N and S. In the first 4 weeks of incubation, the mineralized N accumulated in the soil as ammonium N and there was a concomitant rise in soil pH. After this initial period, nitrification increased substantially and soil pH decreased again. Additions of lime generally increased protease and sulphatase activities but decreased phosphatase activity. Additions of phosphate decreased the activities of all three enzymes. The positive effect of liming on protease and sulphatase activities persisted for the duration of the experiment while accumulation of mineral N and sulphate effectively ceased after about 4 weeks. Furthermore, although phosphate additions decreased the activities of protease and sulphatase they increased the accumulation of mineral N and sulphate. Thus, protease and sulphatase activities were not reliable indicators of the relative amounts of mineral N and sulphate accumulated in the soil during incubation. Some uncertainty surrounded the validity of biomass S and P values estimated by the chloroform fumigation technique because differing proportions of the sulphate and phosphate released from the lysed cells may have been extracted from the different treatments.     

Effects of pine roots on microorganisms,fauna, and nitrogen availability in two soil horizons of a coniferous forest spodosol

Summary We investigated the effects of pitch pine seedling roots on extractable N, microbial growth rate, biomass C and N, and nematodes and microarthropods in microcosms with either organic (41% C, 1.14% N) or mineral (0.05% C, 0.01% N) horizon soils of a spondosol. Root quantity was manipulated by varying plant density (0, 1, 2, or 4 seedlings) and rhizosphere soil was separated from non-rhizosphere soil by a 1.2 m mesh fabric. In the rhizosphere of organic soil horizons, moisture, microbial growth rate, biomass C and N, and extractable N declined as root density was increased, but there was little effect on nematodes or microarthropods. High levels of extractable N remained after 5 months, suggesting that N mineralization was stimulated during the incubation. In the rhizosphere of mineral soil horizons, microbial growth rate, and nematode and microarthropod abundances increased at higher root density, and in the absence of roots faunal abundance approached zero. Faunal activity was concentrated in the rhizosphere compared to non-rhizosphere soil. In organic soil horizons, roots may limit microbial activity by reducing soil moisture and/or N availability. However, in mineral soil horizons, where nutrient levels are very low, root inputs can stimulate microbial growth and faunal abundance by providing important substrates for microbial growth. Our results demonstrate a rhizosphere effect for soil fauna in the mineral soil, and thus extends the rhizosphere concept to components of the soil community other than microbes for forest ecosystems. Although our results need to be verified by field manipulations, we suggest that the effects of pine roots on nutrient cycling processes in coniferous forests can vary with soil nutrient content and, therefore, position in the soil profile.     

长期施肥对红壤旱地土壤活性有机碳和酶活性的影响

以江西进贤长期肥料定位试验为平台,研究了红壤旱地不同施肥措施对土壤微生物生物量、活性有机C、C库管理指数以及土壤酶活性的影响。研究结果表明:与不施肥和单施化肥土壤相比,施有机肥处理土壤的pH、CEC、有机C、全N、全P、无机N、速效P、速效K及土壤微生物生物量均显著增加,土壤活性有机C和C库管理指数也较试前土壤和其他处理土壤明显提高,此外,土壤的转化酶、脱氢酶、脲酶和酸性磷酸酶活性也较其他处理显著增加。土壤微生物生物量、活性有机C以及4种土壤酶活性之间的相关关系显著,且它们均与土壤有机C、全N、全P、无机N、速效P等土壤养分呈显著正相关。因此,红壤旱地通过长期施用有机肥或与无机肥配施,不仅能显著提高土壤有机质的数量和质量,而且能增加土壤微生物生物量和酶活性,从而显著提高土壤肥力和土壤持续生产力。     

Relationships between C and N availability, substrate age, and natural abundance C and N signatures of soil microbial biomass in a semiarid climate

Soil microbial organisms are central to carbon (C) and nitrogen (N) transformations in soils, yet not much is known about the stable isotope composition of these essential regulators of element cycles. We investigated the relationship between C and N availability and stable C and N isotope composition of soil microbial biomass across a three million year old semiarid substrate age gradient in northern Arizona. The δ¹⁵N of soil microbial biomass was on average 7.2‰ higher than that of soil total N for all substrate ages and 1.6‰ higher than that of extractable N, but not significantly different for the youngest and oldest sites. Microbial ¹⁵N enrichment relative to soil extractable and total N was low at the youngest site, increased to a maximum after 55,000 years, and then decreased slightly with age. The degree of ¹⁵N enrichment of microbial biomass correlated negatively with the C:N mass ratio of the soil extractable pool. The δ¹³C signature of soil microbial biomass was 1.4‰ and 4.6‰ enriched relative to that of soil total and extractable pools respectively and showed significant differences between sites. However, microbial ¹³C enrichment was unrelated to measures of C and N availability. Our results confirm that ¹⁵N, but not ¹³C enrichment of soil microbial biomass reflects changes in C and N availability and N processing during long-term ecosystem development.     

Microbial biomass and N mineralization in relation to N supply of sugar beet under reduced tillage

Reduced tillage may affect N supply of plants by influencing soil microbial biomass and thereby N release. The aim of this study was to evaluate changes in microbial biomass due to tillage in relation to N mineralization and to assess the contribution to the N supply of sugar beet. For this purpose, in a field trial near Göttingen in 1995 microbial biomass and net N mineralization were determined in an in situ incubation of ploughed and reduced tilled soil in plots which were not given application of mineral N fertilizer. In reduced tilled soil the increase in mineral N concentration in the upper 10 cm of soil was mainly attributed to an increase in microbial biomass. The organic matter was more easily decomposable, indicated by the increase in C_mic/C_org and N_mic/N_t ratios; this was further supported by the enhanced turnover of microbial biomass in reduced tillage plots. A regression function was used to relate seasonal fluctuations of microbial biomass, soil moisture and soil temperature to N mineralization rate. There was a good agreement between measured and calculated N mineralization rate. Reduced tillage affected N mineralization by affecting the quantity and quality of microbial biomass. In 0–30 cm soil depth 169 kg N/ha were mineralized, 30 kg more N than in ploughed soil. However, despite improved N availability, the N uptake of sugar beet was decreased in reduced tilled soil. Because the N concentration in plants did not differ, it was concluded that sugar beet growth in reduced tilled soil was impaired due to other factors than N supply.     

A comparison of aggregate stability and biological activity in earthworm casts and uningested soil as affected by amendment with wheat or lucerne straw

The mechanisms responsible for stabilization of earthworm casts were investigated in a laboratory study. Earthworms (Aporrectodea caliginosa) were fed soil or soil amended with either ground wheat straw or lucerne hay. Cast material and uningested soil material were incubated for 56 days, and changes in aggregate stability (measured by wet sieving), soil biological activity and macronutrient availability were measured periodically. In general, aggregate stability and microbial biomass C tended to increase during the incubation for both cast and soil material, whereas hot-water extractable carbohydrate content declined. For amended treatments, basal respiration rate and microbial metabolic quotient were large at the first sampling (7 days) but declined rapidly thereafter. There was a transitory increase in extractable P in fresh casts compared with uningested material, a sustained increase in mineral N concentrations but no change in exchangeable K content. For unamended treatments, the casts were less stable than soil material, but this difference diminished during incubation. Drying aggregates before analysing them did not reverse this trend. The casts contained more microbial biomass C than soil material did, but the basal respiratory rate, respiratory quotient and hot-water extractable carbohydrate content were less. By contrast, for wheat- and lucerne-amended treatments casts were more stable than soil material, and the microbial biomass was less at all sampling times. For wheat treatments, respiratory quotient and hot-water extractable carbohydrate content were larger for cast than soil material, but the opposite was the case for lucerne treatments. We attribute the stability of casts in amended treatments to the intimate mixing of part-decomposed organic fragments with comminuted soil particles, binding by microbial mucilage associated with the organic fragments and linking and binding by fungal hyphae.     

Recovery of Soil C and N in a Tropical Pasture: Passive and Active Restoration

Soil degradation by deforestation and introduction of exotic grasses is a grave consequence of land‐use change in tropical regions during the last decades. Soil restoration following natural succession (i.e., passive restoration) is slow because of low tree establishment. Introduction of tree plantings by human intervention (i.e., active restoration) results in a promising strategy to accelerate forest succession and soil recovery in tropical region. The present research was carried out to explore the restoration of soil properties after cattle exclusion and of grazing combined with native tree planting introduction (legumes and nonlegumes) in a tropical pasture in Veracruz, southeast Mexico. Results indicate that land‐use changes decreased soil C and N pools in both litter and mineral soil. In addition, soil heterogeneity increased by land‐use changes at both temporal and spatial scales. In the short term, passive succession (i.e., cattle exclusion) favors the recovery of C and N content in labile soil pools, indicated by the increase in litter C and N masses as well as C and N concentrations in soil microbial biomass. Soils under active restoration showed trends to recover the N cycling, such as a greater accumulation of N in litter, in soil total N concentrations, soil microbial biomass N concentrations, rates of net N transformations, and extractable water and microbial biomass C:N ratios mainly under legumes species. Active restoration including legume introduction is a key factor for rapid recovery of soil fertility. Copyright © 2013 John Wiley & Sons, Ltd.     

Changes in soil–biological quality indices after long‐term addition of shredded shrubs and biogenic waste compost

Long‐term effects on soil chemical and soil biological properties were analyzed after an 8 y period with addition of biogenic household‐waste compost and shredded shrubs with and without N fertilization to an arable field. The addition of compost and shredded shrubs to soil increased significantly all soil organic matter–related properties. The effects of compost addition on soil chemical properties were in most cases stronger than those of adding shredded shrubs, especially the effects on total N, 0.5 M K₂SO₄‐extractable C_org and 0.5 M NaHCO₃‐extractable phosphate. In the shredded‐shrubs treatments, basal respiration and the contents of soil microbial‐biomass C, biomass N, and fungal ergosterol were significantly increased by 40%, 45%, 67%, and 90%, respectively. In the compost treatment, only microbial‐biomass C and biomass N were significantly increased by 25% and 38%, respectively. Microbial‐biomass P remained unaffected by both organic‐amendment treatments. Nitrogen fertilization had significantly negative effects on the NaHCO₃‐extractable P fraction (–22%) and on the basal respiration (–31%), but positive effects on the ergosterol content (+17%).     

Comparison of chloroform fumigation-extraction, phospholipid fatty acid, and DNA methods to determine microbial biomass in forest humus

Techniques developed to measure microbial biomass in mineral soils may not give reliable results in humus. We evaluated the relationships between three techniques to estimate microbial biomass in forest humus: chloroform fumigation-extraction (CFE), total extractable phospholipid fatty acids (PLFA), and extractable DNA. There was a good relationship between PLFA and CFE (R²=0.96), with a slope slightly different from that previously reported for mineral soils (1 nmol PLFA corresponded to a flush of 3.2 μg C released by fumigation in humus cf. 2.4 μg C in mineral soil). There was no relationship between DNA concentration and the other two measurements of microbial biomass. This may be due, in part, to the high fungal biomass in forest humus, as DNA concentration per unit biomass is much more variable for fungi than bacteria.     

Transformation of nitrogen compounds in the tundra soils of Northern Fennoscandia

The transformation of organic nitrogen compounds in the soils of tundra ecosystems of Northern Fennoscandia has been studied under laboratory and natural conditions. Tundra soils contain significant reserves of total nitrogen, but they are poor in its extractable mineral and organic forms. The potential rates of the net mineralization and net immobilization of nitrogen by microorganisms vary among the soils and depend on the C: N ratio in the extractable organic matter and microbial biomass of soil. Under natural conditions, the rate of nitrogen net mineralization is lower than the potential rate determined under laboratory conditions by 6–25 times. The incubation of tundra soils in the presence of plants does not result in the accumulation of mineral nitrogen compounds either in the soil or in microbial biomass. This confirms the high competitive capacity of plants under conditions of limited nitrogen availability in tundra ecosystems.     

黄土丘陵区垂直陡壁表面不同类型生物土壤结皮养分与微生物养分限制特征

生物土壤结皮的发育类型对土壤养分和微生物代谢起着重要作用。为进一步明确在生物结皮发育过程中微生物的限制性养分与影响因素,研究选择黄土丘陵区垂直陡壁表面上的裸土(CK)、浅色藻结皮(LA)、深色藻结皮(DA)、藻藓混合结皮(AM)和藓结皮(M)为研究对象,分析了不同生物土壤结皮类型下碳(C)、氮(N)、磷(P)养分状况与胞外酶活性,并通过胞外酶化学计量来量化微生物的代谢限制。结果表明:LA,DA,AM和M这4种类型生物土壤结皮C,N,P养分含量和微生物生物量C,N,P均显著高于CK(p<0.05),并且SOC,TN,TP和微生物生物量C,N,P随CK,LA,DA,AM和M的顺序逐渐增大,藓结皮微生物量C,N,P分别是CK处理的18.3,27.6,14.1倍。生物土壤结皮的发育显著提高了C,N,P循环酶的活性,冗余分析结果表明土壤养分与酶活性密切相关。此外,通过酶计量的矢量模型结果来看,生物土壤结皮的发育造成微生物相对碳限制的增大与相对磷限制的减小,并受到速效养分含量的影响。偏最小二乘路径模型结果也表明生物土壤结皮的类型会间接影响微生物的代谢限制。总的来说,生物土壤结皮类型的变化会改善土壤养分状况与微生物量等性质,养分资源的供应状况会造成微生物养分代谢的变化。     

Microbial biomass in organic soils: Estimation of biomass C,and effect of glucose or cellulose amendments on the amounts of N and P released by fumigation

The microbial biomass C in forest humus from beneath Scots pine (Pinus sylvestris L.), Japanese larch [Larix kaempferi (Lamb.) Carr.] and surface soil from Calluna heath, was estimated by both direct microscopy and by the substrate-induced-respiration (SIR) method of Anderson and Domsch. There was reasonable agreement between the methods with the larch and heath land samples, but with the pine, the SIR method gave much lower estimates of the biomass.Total biomass C was greatest in the larch samples and in all sites was dominated (>89%) by fungi.The effect of glucose, cellulose and NPK salts on the SIR biomass C and on the amounts of N and P released by CHCl₃-fumigation of the pine and larch humus, and a mineral soil, were compared. In general, the effects of glucose and cellulose were similar—the biomass C was increased, but the “flushes” of soluble N and inorganic P decreased. The addition of NPK along with the C substrate did not increase the flushes of N and P.The SIR method appears a useful technique to estimate the biomass C on acid organic soils, but the flushes of N and P were not a reliable measure of the nutrient content of the biomass, especially on C-amended samples.     

The influence of soil and biosolids type,and microbial immobilisation on nitrogen availability in biosolids‐amended agricultural soils – implications for fertiliser recommendations

Soil microbial biomass interactions influencing the mineralisation of N in biosolids‐amended agricultural soil were investigated under field conditions in two soil types, a silty clay and a sandy silt loam, with contrasting organic matter contents. Soil treatments included: dewatered raw sludge (DRAW); dewatered and thermally dried, mesophilic anaerobically digested biosolids (DMAD and TDMAD, respectively); lime‐treated unstabilised sludge cake (LC); and NH₄Cl as a mineral salt control for measuring nitrification kinetics. Soil mineral N and microbial biomass N (MBN) concentrations were determined over 90 days following soil amendment. Despite its lower total and mineral N contents, TDMAD had a larger mineralisable pool of N than DMAD, and was an effective rapid release N source. Increased rates of mineralisation and nitrification of biosolids‐N were observed in the silty clay soil with larger organic matter content, implying increased microbial turnover of N in this soil type compared with the sandy silt loam, but no significant difference in microbial immobilisation of biosolids‐N was observed between the two soil types. Thus, despite initial differences observed in the rates of N mineralisation, the overall extent of N release for the different biosolids tested was similar in both soil types. Therefore, the results suggest that fertiliser guidelines probably do not need to consider the effect of soil type on the release of mineral N for crop uptake from different biosolids products applied to temperate agricultural soils.     

The use of polyethylene mulches to change soil microclimate as revealed by enzyme activity and biomass nitrogen,sulphur and phosphorus

Summary The effects of white, black and clear polyethylene mulches on temporal fluctuations in protease, sulphatase and phosphatase activities and levels of available and biomass N, S and P in raised beds of soil under a strawberry crop were investigated under field conditions. During spring, summer and early autumn, clear and, to a lesser extent black, polyethylene mulch increased both maximum and minimum mean monthly temperatures over those recorded with white mulch or no mulch. During summer and autumn, soil moisture content measured at monthly intervals was higher under mulched than unmulched conditions. Levels of extractable nitrate and sulphate in soils during autumn followed the order: clear mulch = black mulch > white mulch > no mulch. However, there were no significant differences in levels of enzyme activity or concentrations of biomass N, S or P between treatments. There were significant seasonal fluctuations in estimates of biomass N, S and P, but there was no close relationship between fluctuations in any estimate. This discrepancy was attributed to errors in the chloroform fumigation technique. Enzyme activities showed significant temporal fluctuations but the three enzymes did not show similar times of minimum and maximum activity. The complexity of interactions between soil microbial and biochemical properties and nutrient availability was exemplified by the absence of a discernible relationship between seasonal fluctuations in enzyme activities and levels of biomass N, S and P and/or levels of extractable mineral N, S and P in the soil. Strawberry fruit yields and vegetative growth followed the order : clear mulch = black mulch>white mulch>no mulch. Clear, and to a lesser extent black mulch increased the percentage of total yields produced in the first 2 months of cropping.     

Tillage effects on microbial biomass and nutrient distribution in soils under rain-fed corn production in central-western Mexico

Quantifying how tillage systems affect soil microbial biomass and nutrient cycling by manipulating crop residue placement is important for understanding how production systems can be managed to sustain long-term soil productivity. Our objective was to characterize soil microbial biomass, potential N mineralization and nutrient distribution in soils (Vertisols, Andisols, and Alfisols) under rain-fed corn (Zea mays L.) production from four mid-term (6 years) tillage experiments located in central-western, Mexico. Treatments were three tillage systems: conventional tillage (CT), minimum tillage (MT) and no tillage (NT). Soil was collected at four locations (Casas Blancas, Morelia, Apatzingán and Tepatitlán) before corn planting, at depths of 0–50, 50–100 and 100–150 mm. Conservation tillage treatments (MT and NT) significantly increased crop residue accumulation on the soil surface. Soil organic C, microbial biomass C and N, potential N mineralization, total N, and extractable P were highest in the surface layer of NT and decreased with depth. Soil organic C, microbial biomass C and N, total N and extractable P of plowed soil were generally more evenly distributed throughout the 0–150 mm depth. Potential N mineralization was closely associated with organic C and microbial biomass. Higher levels of soil organic C, microbial biomass C and N, potential N mineralization, total N, and extractable P were directly related to surface accumulation of crop residues promoted by conservation tillage management. Quality and productivity of soils could be maintained or improved with the use of conservation tillage.     

Organic matter extracted with 0.01 M CaCl2 or with 0.01 M NaHCO3 as indices of N mineralisation and microbial biomass

A pot experiment was carried out with three soils at ambient temperature in which temporal changes in fractions of soil organic matter that were extractable with either 0.01 M CaCl₂ or 0.01 M NaHCO₃ were compared with changes in N mineralisation and microbial biomass C. UV spectral analysis of soil extracts was also carried out on sub-samples taken at the beginning of the experiment. The objective was to quantify the fractions of extractable soil organic matter and determine whether these could be used to estimate the mineralisable organic N content of the soils. The results suggested that part of the NaHCO₃-extractable organic matter originated in the microbial biomass but that non-biomass material was also present. The non-biomass material was not identified directly, but was composed of compounds with high UV absorbance. In the case of CaCl₂, the results suggested that extracellular proteins were contained in the extract and that some material released from the actively growing microbial biomass may also have been present. A supplementary study with 16 soils was carried out to determine the ability of the organic matter solubilised by either extractant to predict soil N uptake by barley seedlings. A significant relationship (P<0.01) was found between N uptake and CaCl₂-extractable material only.     

半干旱农田生态系统作物根系和施肥对土壤微生物体氮的影响

盆栽和大田试验表明,作物根系显著影响土壤微生物体氮的含量。在田间试验条件下,根际土壤微生物体氮比非根际土壤平均高出N54.7μg/g;盆栽试验中,根际土壤微生物体氮平均含量为N77.1±13.6μg/g,而非根际土壤为N65.2±17.0μg/g,差异达显著水平,根际微生物体氮含量为非际根际土壤的1.10～2.04倍。施肥能明显增加土壤微生物体氮含量,但影响程度因肥料种类而不同。秸秆和富含有机物质的厩肥对土壤微生物体氮的影响远大于化学肥料,而且土壤微生物体氮含量随秸秆施用量增加而增加。在红油土上进行的20年长期田间定位试验结果表明,对不施肥和施氮磷处理,0—20cm土层的微生物体氮分别是N102.2和110.4μg/g;在施氮磷的基础上,每公顷配施新鲜玉米秸秆9375kg、18750kg、37500kg和厩肥37500kg时,相应土层微生物体氮分别是N147.5、163.2、286.4和265.3μg/g。培养条件下,当有效能源物质缺乏时,微生物对NH4+-N的同化固定能力远大于NO3--N,但在加入有效能源物质葡萄糖后,微生物对2种形态氮的固定量大幅度增加,且对2种形态氮的固定量趋于一致。     

Extractability of labelled microbial biomass N by electro-ultrafiltration and CaCl2 extraction

A laboratory soil incubation and a pot experiment with ryegrass were carried out in order to examine the extractability of microbial biomass N by using either 10-mM CaCl₂ extraction or the electro-ultrafiltration (EUF) method. The aim of the experiment was to test the hypothesis whether the organic N (Norg) extracted by EUF or CaCl₂ from dried soil samples represents a part of the microbial biomass. For the laboratory incubation a ¹⁵N-labelled Escherichia coli suspension was mixed with the soil. For the pot experiment a suspension of ¹⁵N-labelled bacteria was applied which had previously been isolated from the soil used. Soil samples of both treatments, with and without applied bacterial suspension, were extracted by EUF and CaCl₂. The extractability of applied microbial biomass was estimated from the difference in extractable Norg between the two treatments. In addition, the N isotopic composition in the upper plant matter, in the soil, and in organic and inorganic N fractions of EUF and CaCl₂ extracts was analysed. Both experiments showed that the applied microbial biomass was highly accessible to mineralization and thus represented potentially mineralizable N. However, this mineralizable N was not extractable by CaCl₂ or by the EUF method. It was, therefore, concluded that the organic N released on soil drying and which was thus extractable was derived from the non-biomass soil organic matter. The result suggests that both extraction methods may provide a suitable index for mineralizable N only in cases where the decomposable organic substrates are derived mainly from sources other than the living soil biota.Dedicated to Professor J. C. G. Ottow on the occasion of his 60th birthday     

Hydrochar amendment promotes microbial immobilization of mineral nitrogen

Hydrochars and biochars are products of the carbonization of biomass in different conversion processes. Both are considered suitable soil amendments, though they differ greatly in chemical and physical composition (e.g., aromaticity, inner surface area) due to the different production processes (pyrolysis, hydrothermal carbonization), thus affecting their degradability in soil. Depending on the type, char application may provide soil microorganisms with more (hydrochars) or less (biochars) accessible C sources, thus resulting in the incorporation of nitrogen (N) into microbial biomass. A soil‐incubation experiment was conducted for 8 weeks to determine the relationship between mineral‐N concentration in the soil solution and microbial‐biomass development as well as soil respiration. An arable topsoil was amended with two hydrochars from feedstocks with different total N contents. Biochars from the same feedstocks were used for comparison. Both char amendments significantly decreased mineral‐N concentration and promoted microbial biomass compared to the nonamended control, but the effects were much stronger for hydrochar. Hydrochar application increased soil respiration significantly during the first week of incubation, simultaneous with the strongest decrease in mineral‐N concentration in the soil and an increase in microbial biomass. The amount of N detected in the microbial biomass in the hydrochar treatments accounted for the mineral N “lost” from the soil during incubation. This shows that microbial immobilization is the main sink for decreasing mineral‐N concentrations after hydrochar application. However, this does not apply to biochar, since the amount of N recovered in microorganisms was much lower than the decrease in soil mineral‐N concentration. Our results demonstrate that while both chars are suitable soil amendments, their properties need to be considered to match the application purpose (C sequestration, organic fertilizer).     

Relationship between acidity and microbiological properties in some tea soils

The present study was conducted to investigate the effects of different forms of soil acidities on microbial biomass C, ergosterol content, microbial metabolic quotient, microbial respiration quotient, and fluorescein diacetate-hydrolyzing activity of some tea-growing soils of India. Total potential and exchangeable acidity and extractable and exchangeable aluminum were higher in Tripura followed by Jalpaiguri and Kharagpur soil. Different forms of acidity were significantly and positively correlated with each other. All the microbiological properties investigated were significantly and positively correlated with soil organic C content. The ratio of organic C with microbial parameters was significantly and negatively correlated with different forms of acidity. Principal component analysis indicated that the microbial activities were not directly affected by the extractable aluminum and total potential acidity. Although the tea soils had higher microbial biomass and activities because of higher organic matter content than other soils, the ratios of microbial parameters/organic carbon indicated that inhibition of microbial growth and activities had occurred because of acidity stress.