Classification of soils of Russia: Discussion on the internet site

The work of the Dokuchaev Soil Institute site on soil classification during the last three years is analyzed. The main subject of the discussion is the Classification and Diagnostics of Soils of Russia (2004) as compared to the classification of 1977. The website’s visitors, mainly soil scientists performing survey under contracts or involved in organizing environmental monitoring consult the diagnostics and names of their objects according to the new classification. The principles and structure of the classification system and criteria for distinguishing the basic taxa are accepted by practically everybody; the proposals on the correction of the diagnostics of soil horizons and their characteristics are made for a wide spectrum of soils. Many of the suggestions were taken into account by the authors in the last edition of this classification (2008). The users of the site are especially interested in anthropogenically modified soils, primarily in urban soils and soils disturbed by mining operations. Among the site’s visitors are many students and postgraduates, who are especially active during the examination periods.     

Chemical properties and pedogenesis of yellowish/yellow brown forest soils in the submontane and mountain zones of Kyushu district,southwestern Japan

Abstract

This study aimed to clarify pedogenetic processes and classification of yellowish Brown Forest Soils according to the Classification of Forest Soils in Japan and the Yellow Brown Forest soils according to the Unified Soil Classification System of Japan in the warm and cool temperate forest of Kyushu district, Japan. In addition, the study aimed to clarify a problem with the Unified Soil Classification System of Japan. Thirty-six soil profiles of Brown Forest Soils, including 13 yellowish Brown Forest Soils and 15 Yellow Brown Forest soils, were compared with regard to their chemical properties and the relationship with climatic conditions was assessed. The yellowish Brown Forest Soils had thin A horizons, low pH and low levels of free oxides in the B horizons, and a low amount of silica and a high aluminum and iron to silica ratio. These features were related to the paleo reddish weathering. The immaturely developed A horizon of the yellowish Brown Forest Soils was caused by these weathered, low-activity substances. The Yellow Brown Forest soils had low levels of active iron oxides and a low activity ratio of free iron oxides compared with the Haplic Brown Forest soils in the same thermal climatic conditions. The activity ratio of free iron oxides was correlated to mean annual air temperature with the carbon stocks and with many other chemical properties. Accordingly, classification of Brown Forest Soils was clearer according to thermal climatic conditions. The activity ratio of free iron oxides can become an effective index that distinguishes Yellow Brown Forest soils under warm temperate lucidophyllous forest and Haplic Brown Forest soils under cool temperate broad-leaved deciduous forest with considerable vertical soil zonality.     

Assessing the technogenic contamination of urban soils from the profile distribution of heavy metals and the soil bulk density

The contamination of soils with heavy metals in the city of Moscow has been assessed using the conventional procedure and a new resource approach developed at the Faculty of Soil Science of Moscow State University. The approach involved the consideration of the profile distribution of a pollutant and the variation in the bulk density of the enclosing soil. The integral parameter of contamination was the reserve of the pollutant in a conventional normative soil layer 1 m in thickness according to the Moscow Law On the Urban Soils. In the soil samples taken in the main administrative districts of Moscow, the contents of heavy metals of the first (zinc, lead, cadmium, arsenic, and mercury) and second (nickel and copper) hazard classes were determined. For each profile, distribution graphs of all of the above elements have been developed, and the element reserves have been calculated in the upper 1-m-thick layer with consideration for the changes in the soil density with depth. The obtained data have been compared with the normative reserves of heavy metals and the estimates of technogenic contamination derived using the conventional procedure. An increase in the total reserves of pollutants has been observed at the increase in their concentrations with depth; therefore, a clean soil according to the conventional procedure can be classified as contaminated. Analogously, a decrease in the total reserve of a pollutant in the upper 1-m-thik layer and, hence, a decrease in the degree of soil contamination have been observed when the concentration of the pollutant reduced with the depth. In general, the profile distributions of heavy metals and the soil bulk density strongly interfere with the estimation of the contamination of the soil as a spatially heterogeneous body and should be taken into consideration in the development of a present-day system of quality criteria and norms for urban soils.     

Correction of a large-scale soil map with the use of the new classification system of Russian soils

A large-scale soil map of one of the farms in the south of Karelia has been analyzed. This map was initially compiled in 1979 on the basis of the official Classification and Diagnostics of Soils of the Soviet Union (1977). We have corrected it with the use of the new Classification and Diagnostics of Russian Soils. Both the names of the map units and the particular delineations on the map have been changed. These changes are related to differences in the principles of soil diagnostics in the old and new classification systems and to real changes in the soil cover that have taken place after the map’s compilation. In particular, large areas of peat bogs have been drained, and the cultivated peat soils have been subjected to accelerated mineralization. Surface planing works after digging drainage channels have also changed the soil cover pattern. The revised large-scale soil map developed on the basis of the new classification system gives more adequate information about the real soil cover.     

Micro flora related to the nitrogen cycle in the tropical upland farm soils

Samples of upland-farm surface soils (0–10 em in depth) belonging to various great soil groups were collected in 28 upland sites in Thailand during the rainy season.

Among the microbes related to the transformation of nitrogen, namely ammonifiers, ammonia oxidizers, nitrite oxidizers and denitrifiers, the count of denitrifier showed the maximum value amounting to 10⁴ to 10⁵ per 1 g of dry soil, followed byammonifier. The population level of nitrogen-fixing blue green algae was unexpectedly high, being 10³ to 10¹

The microbial counts in Brown Forest Soils, Rendzinas and Grumusols with high content of organic matter, available phosphorus and exchangeable potassium tended to be high.

Non-calcic Brown Soils, Reddish Brown Lateritic Soils, Alluvial Soils, Red-Yellow Podzolic Soils and Gray Podzolic Soils which lack in some nutrients showed intermediate levels of microbial populations, while the counts of nitrogen-fixing blue green algae in Alluvial Soils and those of denitrifier in Red-Yellow Podzolic Soils were markedly high. In the case of Low Humic Gley Soils and Regosols with low content of organic matter, available phosphorus and available potassium, the population of microbes was generally small.

The relationship between the organic matter content and the microbial population of soils was positively significant at 0.1 % level only in the case of fungal population (r=0.551), while the relationship between the available phosphorus content and the microbial population was positively significant at 0.1% level only in the case of Azotobacter (r=0.682).

The relationships between the total nitrogen, the exchangeable potassium, the amount of NH₄+^-N, the amount NO₂ ^--N, or the amount of NH₄ ⁺-N+NO₂ ^--N and each microbial population were not significant in any microbial groups.

The count of denitrifiers in upland farm soils of Thailand was 9 times as high as that in non-volcanic upland-farm soils of Japan and was 23 times higher than that in volcanic soils though large variations were seen among the great soil groups of Thailand. Conversely, the population of non-spore-forming nitrite oxidizers in the upland farm soils of Thailand was 1/100 that in non-volcanic soils of Japan and 1/280 that in volcanic soils. In the case of Azotobacter, the count in upland farm soils of Thailand averaged 2,800 per 1 g of dry soil. while that in non-volcanic upland farm soils of Japan was 77 on the average.

The ratio of aerobic bacteria to actinomycetes in upland farm soils of Thailand was 2.31, while that of non-volcanic soils of Japan was 7.28.     

Determining weathering rates of soils in China

As an important parameter for critical load calculation and soil acidification simulation, weathering rates of soils in China were studied using different methods of calculation. The approaches used were the mass balance approach, the soil mineralogical classification, the total analysis correlation, the PROFILE model, the MAGIC model and a simulated leaching experiment. Since chemical weathering of secondary minerals usually plays a much more important role in neutralizing the long-term acidification of soils in China than that of parent material, soil mineralogy rather than parent rock/material type, which is regarded as the most suitable factor representing weathering rates in Europe, should be adopted as the basis for soil classification. The weathering rate assigned to each soil should also be corrected when the effect of temperature is considered. Due to the variation in experimental conditions, the weathering rates of soils from laboratory experiment may be difficult to compare with field determined rates, and should be adjusted by pH and percolation rate. The comparison of various methods in this study shows that the weathering rates of soils estimated by the PROFILE model coincide well with those from other independent methods such as the dynamic modeling by MAGIC and the modified leaching experiment. The weathering rates were very low (usually lower than 1.0 kEq·ha⁻¹·year⁻¹) for Allites (including Latosol, Lateritic Red Earth, Red Earth, Yellow Earth and Yellow-Brown Earth) in south China and Silalsols (consisting of Dark Brown Forest Soil, Black Soil and Podzolic Soil) in northeast China, and very high for Alpine Soils, Desert Soils and Pedocals in west China. The content of weatherable minerals in soil is the most important factor in determining the spatial distribution of weathering rate in China, while the difference in temperature may be the reason why the weathering rate of soil in northeast China was lower than that in southeast China.     

The particle-size distribution in soils: Problems of the methods of study,interpretation of the results,and classification

The analysis of literature sources and a database on soil physical properties collected by the Department of Soil Physics and Amelioration of Soils of the Faculty of Soil Science of Moscow State University made it possible to compare three major constituents of the particle-size distribution analysis (PSDA): (a) the classification of soil separates with respect to their sizes and the classification of soil textures, (b) the procedures used to prepare soil samples for the PSDA, and (c) the specificity of the determination of the particle-size distribution by different methods. It was shown that there are good physical and statistical grounds for the conversion of data on the particle-size distribution from the Russian classification system into other systems. Much larger problems are related to the pretreatment of soil samples for the PSDA. The diversity of existing methods, classification schemes, and technical devices based on different physical principles (sedimentation and laser diffractometry) should be taken into account in the analysis and quantitative conversion of particle-size distribution data from a given classification system into another system. The Russian classification of soil textures and soil particle-size groups developed by N.A. Kachinskii has certain advantages and can be easily converted into other systems. In the choice of a particular system, it is important to take into account the goals of the study. Agreement between soil scientists concerning the major constituents of the PSDA has to be reached.     

美国土壤Salic层研究

The taxonomic hierarchy and nationwide distribution of soils with a salic horizon were studied using the USA Natural Resources Conservation Service Soil Survey Geographic (SSURGO) Database to provide a more holistic view of the role of soil-forming factors in pedogenesis than from isolated case studies.Soils with a salic horizon occupied an area of 11 000 km2,i.e.,0.1% of land area in the contiguous USA.These soils occur narrowly in three great groups(Aquisalids,Haplosalids and Halaquepts),11 subgroups,and 97 soil series.Soils with a salic horizon commonly had a mesic (50% of soil series) or thermic (19%) soil-temperature class,an aquic (89%) soil-moisture class,a mixed mineral class (79%),a calcareous (52%)reaction class,a superactive (59%) cation exchange activity class,and a fine (24% of soil series),fine-loamy (24% of soil series),or fine-silty (19% of soil series) particle-size class.Soils with a salic horizon were concentrated in the Basin and Range Province of western USA.The key pedogenic processes leading to the development of salic horizons were salinization,gleization,and calcification,with some evidence for argilluviation and silicification.     

Possibilities of including the taxonomy of soils and parent materials of Moscow city into the classification system of the soils of Russia

The analysis of the taxonomy of the soils and soil-forming rocks of Moscow city was performed in view of the compatibility of the taxonomy proposed with the new classification system of the soils of Russia. The common platform, which determines the possibility to incorporate the taxonomy of urban soils into the new classification system, is the principle of the priority of the diagnostic horizons, which provides the properties-oriented conceptual background of the compared systems. It was shown that the considered classification developments do not have any fundamental differences either in ideology or in concrete manifestations. Some contradictions in place can be eliminated by respective discussions and agreements.     

Soil quality and fertility in sustainable agriculture,with a contribution to the biological classification of agricultural soils

Soils and crops are particularly vulnerable to climate change and environmental stresses. In many agrosystems, soil biodiversity and ecosystem services provided by soils are under threat from a range of natural and human drivers. Agricultural soils are often subject to agronomic practices that disrupt soil trophic networks and make soils less productive in the long term. In this scenario, sustainable soil use aimed at improving plant/root status, growth and development plays a crucial role for enhancing the biological capacity of agricultural soils. This commentary paper is divided into the following four main sections: (i) the contentious nature of soil organic matter; (ii) soil biological quality/fertility; (iii) soil classification; and, (iv) which agricultural practices can be defined as sustainable? The published literature was analyzed within a holistic framework, with agrosystems considered as living systems where soil, vegetation, fauna and microorganisms co-evolve and are reciprocally influenced. Ultimately, this article will suggest a better stewardship of agricultural soils as a natural capital.     

Die Böden von Wallhecken in Schleswig-Holstein I. Klassifikation und Genese

Soils of Mound Hedges in Schleswig-Holstein I. Classification and Genesis In typical landscapes of Schleswig-Holstein soils of mound hedges were investigated (FAO (1989): Cumulic Anthrosol). New soils have been developed from the deposit of the mound hedge in less than 250 years. A classification with regard to the German classification of natural soils is suggested. The soil genesis from sandy deposits has reached the step of Dystric Regosols, groundwater has induced gleyic features. Soil genesis could be described chronologically, if time of deposition of these mound hedges is known. Some of the natural soils are conserved below the deposit. Pedogenesis in an area, changed by man, could be reconstructed. This is why systematic, scientific soil investigations of mound hedges may be very interesting.     

Classifying soils at the ultimate stage of weathering in the tropics

Oxisols cover ≈ 23% of the land surface in the tropics and are utilized extensively for agricultural purposes in the tropical countries. Under the variable input types of agricultural systems practiced locally, some of these soils still appear to have problems in terms of proper soil classification and subsequently hinder attempts to implement sustainable agro‐management protocols. The definition for Oxisols in Soil Survey Staff (1999) indicates that additional input is still required to refine the definition in order to resolve some of the outstanding classification problems. Therefore, the objective of this study is to examine the properties of some Oxisols and closely related soils in order to evaluate the classification of these soils. Soils from Brazil, several countries in Africa, and Malaysia were used in this study. Field observations provided the first indication that some of the presently classified kandi‐Alfisols and kandi‐Ultisols were closer to Oxisols in terms of their properties. Water‐retention differences and apparent CEC of the subsurface horizons also supported this idea. The types of extractable Fe oxides and external specific surface areas of the clay fractions showed that many kandic horizons have surface properties that are similar to the oxic horizons. Micromorphology indicated that the genetic transition from the argillic to the oxic involves a diminishing expression of the argillic. Properties, such as CEC, become dominant. The kandic horizon is therefore inferred as a transition to the oxic horizon. It is proposed that the Oxisols be keyed out based only on the presence of an oxic horizon and an iso–soil temperature regime. The presence of a kandic horizon will be reflected at lower levels in Oxisols. The Oxisols will now be exclusive to the intertropical belt with an iso–soil temperature regime. The geographic extend of the Oxisols would increase and that of kandi‐Alfisols and Ultisols would decrease. A few kandi‐Alfisols and Ultisols in the intertropical area will have low CEC which would fail the weatherable mineral contents. The kandic subgroups of some Alfisols and Ultisols will be transitional between the low (< 16 cmol_c [kg clay]^–1)‐ and high (> 24 cmol_c [kg clay]^–1)‐activity clay soils. The proposed changes to classification will contribute to a better differentiation of the landscape units in the field. Testing of the proposed classification on some Malaysian soils showed that the new definition for Oxisols provides a better basis for the classification of the local soils and the development of meaningful soil‐management groups for plantations.     

类似但成土因素不同的土壤：巴西始成土的趋同演变

Soils result from the interaction of five independent formation factors.If one factor varies,while the others remain constant,different soils can be produced.Herein,we demonstrated an opposing trend,wherein two soils were similar,despite considerable differences in all factors of soil formation.We sampled two Inceptisols (Oxic Dystrudepts) formed on different parent materials (gneiss vs.mica schist),climate (tropical altimontane vs.warmer,drier plateau),topography (1 650 m,45％ slope vs.1000 m,8％ slope),time (rejuvenated vs.old,stable surface),and vegetation (rainforest vs.Cerrado savanna).The two soils had similar chemical properties,whereas the soil on mica schist had finer particle size distribution,lower porosity,and lower saturated hydraulic conductivity.These properties were related to a coarser blocky microstructure compared to the soil on gneiss.Both soils presented active mineral weathering and pronounced pedoplasmation,demonstrated by clay contents ＞ 300 g kg-1,although only the Dystrudept on gneiss possessed coarse rock fragments.The C horizons of both soils presented fragmented clay coatings suggestive of argilluviation,likely relict,because they were not observed in the B horizons.The similarities in many properties of the two Dystrudepts,despite contrasting factors of soil formation,suggest converging evolution and that soil classification at the subgroup level was efficient in grouping similar formative processes in tropical conditions.Moreover,this work revealed that similar pedogenic processes acting on different factors of soil formation can result in similar soil properties,at least for Inceptisols where further soil development is hindered by topographic limitations.     

Plant litter decomposition and microbial characteristics in volcanic soils (Mt Etna,Sicily) at different stages of development

Soils at different developmental stages were sampled from eight sites on the slopes of Mt Etna, Sicily (Italy) and characterized for total C, microbial biomass and microbial respiration. The values of these parameters were greatest for the most developed soils, but differences in recent management and site characteristics limited analysis of trends with soil development across the eight sites. The decomposition kinetics of both intact leaf litter and the water-insoluble fraction of leaf litter from three common species on Etna [Etnean broom (Genista aetnensis), European chestnut (Castanea sativa), and Corsican pine (Pinus nigra)] were determined in four of the soils (the two with the smallest and the two with the largest organic C contents) in a laboratory experiment over 168 days to test two hypotheses. First, that the readily mineralized fraction of added plant C is greater when the plant material decomposes in well-developed soils compared to less developed soils, and second, that the microbial communities in less developed soils are less efficient at mineralizing C from low quality plant residues. The first hypothesis held for Genista and Pinus litter, but not Castanea litter. The second hypothesis was supported for the Castanea and Pinus litter, but not for the Genista litter. Thus, the general applicability of the hypotheses was dependent on the precise source and characteristics of the litter.     

Characteristics and classification of anthropogenic soils in the Osnabrück area,Germany

Soils in the area around Osnabrück/Northwest Germany have been strongly influenced by man. The classification of these soils based on the German and international classification systems is problematical. Eight representative soils, two Anthrosols (plaggic and hortic), four soils affected by the coal and steel industry and consisting of distinct monosubstrata (coal and ore mining heaps, slag heap, sludge area) as well as two deposits of heterogeneous waste components (reclaimed wet land, filled quarry) were investigated. The sites are assessed in relation to their contamination by heavy metals and PAH as well as suitability for plant growth. An attempt was made to classify the soils using the current classification of World Reference Base for Soil Resources (WRB), German Soil Science Society Classification, FAO and the USA. These systems enables a satisfactory classification of two Anthrosols compared with the other soils. In the US taxonomy, the pedogenesis of technological substrata was not considered. In the FAO taxonomy, it is not acceptable to term all soils as Urbic Anthrosols without any further differentiation. This differentiation was enabled in both the WRB and the German taxonomy. In the WRB taxonomy, however, only anthropic subunits of the Regosols are included. An improvement could be achieved by the introduction of comparable subunits of the Arenosols, Durisols, Gleysols, and Leptosols. In the German taxonomy (normally soil and substrata are classified separately), the induction of toxic subunits in the presence of high soil contamination influencing the edaphon would be helpful. Furthermore, soils hardened by silica should be classified as respective varieties.     

Phosphorus sorption kinetics in different types of alkaline soils

This study investigated phosphorus sorption kinetics of three different soils from three sites within the Sahel region of Tunisia; iso-humic soils from Chott-Mariem site, calcic-magnesic soils from Enfidha site and saline-sodic soils from Kondar site. Soils from all sites were sampled (0–25 cm) and analysed for their physico-chemical proprieties. In previous works, we determined the adsorption efficiency of these different soils. In this study, we focused on the influence of contact time on phosphorus adsorption by the different soils. The analytic data were approached from the following kinetics models: pseudo-first-order, pseudo- second-order and Elovich model. The second order model was shown to be the best fit for describing phosphorus adsorption by each soil sample, as seen from the correlation coefficient R² which ranged from 0.68 to 0.96 for the pseudo-first-order model, 0.91 to 0.99 for pseudo-second-order model and 0.84 to 0.94 for Elovich model.     

Potential of Tamarix africana and other halophyte species for phytostabilisation of contaminated salt marsh soils

Purpose

Salt marsh plants are colonising wastes from a steel plant deposited on the Coina River Banks posing a potential contamination risk to the Tagus estuary ecosystem. The objectives of this study were to assess the uptake, accumulation and translocation of hazardous elements/nutrients in three spontaneous halophytic species, to evaluate the capacity of Tamarix africana to stabilise a contaminated salt marsh soil, and to evaluate the ecotoxicity of the pore water and elutriates from phytostabilised soils.

Materials and methods

The work comprises the following: fieldwork collection of soil samples from Coina River (an affluent of Tagus River) bank landfill, estuarine water and spontaneous plants (Aster tripolium, Halimione portulacoides and Sarcocornia sp.), and greenhouse studies (microcosm assay) with T. africana growing in one landfill salt marsh soil, for 97 days, and watered with estuarine water. Soils were analysed for pH, EC, C_organic, NPK, iron and manganese oxides. Soils total (acid digestion) elemental concentrations were determined by ICP/INAA. Estuarine waters, plants roots and shoots (acid digestion), soils available fraction (diluted organic acids extraction-RHIZO or pore water), and salts collected from the T. africana leaves surface were analysed for metals/metalloids (ICP-MS). Ecotoxicity assays were performed in T. africana soil elutriates and pore waters using Artemia franciscana and Brachionus plicatillis.

Results and discussion

Soils were contaminated, containing high total concentrations of arsenic, cadmium, chromium, copper, lead and zinc. However, their concentrations in the available fraction were <4 % of the total. The estuarine waters were contaminated with cadmium, but negligible ecotoxicological effect was observed. The spontaneous plants had significant uptake of the above elements, being mostly stored in the roots. Elemental concentrations in the shoots were within the normal range for plants. These species are not hazardous elements accumulators. Tamarix africana was well adapted to the contaminated saline soils, stored the contaminants in the roots, and had small concentrations of hazardous elements in the shoots. Excretion of hazardous elements by the salt glands was also observed. Elutriates from soils with and without plant did not show ecotoxicity.

Conclusions

The salt marsh species play an important role in the stabilisation of the soils in natural conditions. Tamarix africana showed potential for phytostabilisation of saline-contaminated soils. The low translocation of the elements from roots to shoots and/or active excretion of the elements by the salt glands was a tolerance mechanism in T. africana.

     

Labile lead in polluted soils measured by stable isotope dilution

It is well known that lead (Pb) is strongly immobilized in soil by adsorption or precipitation. However, the reversibility of these reactions is poorly documented. In this study, the isotopically exchangeable Pb concentration in soils (E‐value) was measured using a stable isotope (²⁰⁸Pb). Soils were collected at three industrialized sites where historical Pb emissions have resulted in elevated Pb concentrations in the surrounding soil. Lead concentrations ranged from background values, in the control soils collected far from the emission source, to highly elevated concentrations (5460–14440 mg Pb kg^?1). The control soil of each site was amended in the laboratory with Pb(NO₃)₂ to the same total Pb concentrations as the field‐contaminated soils. The %E values (E‐value relative to total Pb content) were greater than 84% in the laboratory‐amended soils, and ranged from 45% to 78% (mean 58%) in the field‐contaminated soils. The relatively large labile fractions of Pb in the field‐contaminated soils show that the majority of Pb is reversibly bound despite the fact that the binding strength is large. The Pb concentrations in soil solution were up to 3500‐fold larger for the laboratory‐amended soils than for field‐contaminated soils at corresponding total Pb concentrations. These differences cannot be explained by differences in labile fractions of Pb but are attributed to the decrease in soil solution pH upon addition of Pb²⁺‐salt.     

Strengths and weaknesses of the new classification system of Russian soils

Strengths and weaknesses of the new classification system of Russian soils are discussed. It is argued that the diversity of Russian soils and the ecological conditions of their formation are incompletely represented in this system. In particular, several specific groups of soils in the south of European Russia cannot be adequately classified within the framework of the new classification system. Several important tasks have to be solved before its adoption as an official document. First, it is necessary to compile correlation tables between the soil taxa of the previous classification (1977) and the new classification (2004). Second, a key for the field diagnostics of soils within the framework of the new system has to be developed. Third, the soils that are missing in the new system have to be introduced into it.     

Mineralization of carbon and nitrogen from cowpea leaves decomposing in soils with different levels of microbial biomass

Soils with greater levels of microbial biomass may be able to release nutrients more rapidly from applied plant material. We tested the hypothesis that the indigenous soil microbial biomass affects the rate of decomposition of added green manure. Cowpea (Vigna unguiculata L.) Walp.] leaves were added to four soils with widely differing microbial biomass C levels. C and N mineralization of the added plant material was followed during incubation at 30°C for 60 days. Low levels of soil microbial biomass resulted in an initially slower rate of decomposition of soil-incorporated green manure. The microbial biomass appeared to adjust rapidly to the new substrate, so that at 60 days of incubation the cumulative C loss and net N mineralization from decomposing cowpea leaves were not significantly affected by the level of the indigenous soil microbial biomass.