Enzyme activities and microbial community structure in semiarid agricultural soils

This study investigated the effect of management on -glucosidase, -glucosaminidase, alkaline phosphatase, and arylsulfatase activities and the microbial community structure in semiarid soils from West Texas, USA. Surface samples (0–5 cm) were taken from a fine sandy loam, sandy clay loam, and loam that were under continuous cotton ( Gossypium hirsutum L.) or in cotton rotated with peanut ( Arachis hypogaea L.), sorghum ( Sorghum bicolor L.), rye ( Secale cereale) or wheat ( Triticum aestivum L.), and had different water management (irrigated or dryland), and tillage (conservation or conventional). The enzyme activities were higher in the loam and sandy clay loam than in the fine sandy loam. Soil pH was not affected by management, but the soil organic C and total N contents were generally affected by the different crop rotations and tillage practices studied. The trends of the enzyme activities as affected by management depended on the soil, but in general crop rotations and conservation tillage increased the enzyme activities in comparison to continuous cotton and conventional tillage. The soil enzyme activities were significantly correlated with the soil organic C ( r -values up to 0.90, P< 0.001), and were correlated among each other ( r -values up to 0.90, P <0.001). There were differences in the fatty acid methyl ester profiles between the fine sandy loam and the sandy clay loam and loam, and they reflected the differences in the enzyme activities found among the soils. For example, a 15:0 ranged from 1.61±0.25% in cotton-peanut/irrigated/no-till in the fine sandy loam to 3.86±0.48% in cotton-sorghum/dryland/conservation tillage in the sandy clay loam. There were no differences due to management within the same soil.Trade names and company names are included for the benefit of the reader and do not infer any endorsement or preferential treatment of the product by USDA-ARS     

土地利用和轮作方式对旱地红壤生化性质的影响

研究不同土地利用和轮作方式对旱地红壤肥力的影响对提高红壤质量具有十分重要的指导意义。本研究以湖南省桃源县的林地、大豆-油菜轮作、玉米-休闲轮作土壤为研究对象,明确了林地、农地土壤及农地不同轮作方式对土壤化学和生物性质的影响。结果表明,林地土壤的pH、有机碳、速效养分、微生物生物量碳及酶活性(纤维素酶、酸性磷酸酶、转化酶、蛋白酶)均显著高于农地土壤;大豆-油菜轮作土壤的pH、养分含量、微生物生物量碳含量及其微生物熵在大多数情况下高于玉米-休闲轮作,但轮作处理对各酶活性的影响并不完全一致。这种不一致性可能与不同酶对由不同利用和轮作方式导致的土壤性质差异的敏感性不同所致。土壤有机碳和pH与各生物指标均呈显著正相关关系,表明提高该地区的土壤有机碳含量对于维持土壤的生化性质具有重要的作用。     

Differences in soil enzyme activities,microbial community structure and short-term nitrogen mineralisation resulting from farm management history and organic matter amendments

Changes in soil microbial biomass, enzyme activities, microbial community structure and nitrogen (N) dynamics resulting from organic matter amendments were determined in soils with different management histories to gain better understanding of the effects of long- and short-term management practices on soil microbial properties and key soil processes. Two soils that had been under either long-term organic or conventional management and that varied in microbial biomass and enzyme activity levels but had similar fertility levels were amended with organic material (dried lupin residue, Lupinus angustifolius L.) at amounts equivalent to 0, 4 and 8 t dry matter lupin ha^?1. Microbial biomass C and N, arginine deaminase activity, fluorescein diacetate hydrolysis, dehydrogenase enzyme activity and gross N mineralisation were measured in intervals over an 81-day period. The community structure of eubacteria and actinomycetes was examined using PCR–DGGE of 16S rDNA fragments. Results suggested that no direct relationships existed between microbial community structure, enzyme activities and N mineralisation. Microbial biomass and activity changed as a result of lupin amendment whereas the microbial community structure was more strongly influenced by farm management history. The addition of 4 t ha^?1 of lupin was sufficient to stimulate the microbial community in both soils, resulting in microbial biomass growth and increased enzyme activities and N mineralisation regardless of past management. Amendment with 8 t lupin ha^?1 did not result in an increase proportional to the extra amount added; levels of soil microbial properties were only 1.1–1.7 times higher than in the 4 t ha^?1 treatment. Microbial community structure differed significantly between the two soils, while no changes were detected in response to lupin amendment at either level during the short-term incubation. Correlation analyses for each treatment separately, however, revealed differences that were inconsistent with results obtained for soil biological properties suggesting that differences might exist in the structure or physiological properties of a microbial component that was not assessed in this study.     

Soil organic matter, microbial biomass and enzyme activities in a tropical agroforestry system

 The effects of growing trees in combination with field crops on soil organic matter, microbial biomass C, basal respiration and dehydrogenase and alkaline phosphatase activities were studied in soils under a 12-year-old Dalbergia sissoo (a N₂-fixing tree) plantation intercropped with a wheat (Triticum aestivum) – cowpea (Vigna sinensis) cropping sequence. The inputs of organic matter through D. sissoo leaf litter increased and crop roots decreased with the increase in tree density. Higher organic C and total N, microbial biomass C, basal soil respiration and activities of dehydrogenase and alkaline phosphatase were observed in treatments with tree-crop combination than in the treatment without trees. Soil organic matter, microbial biomass C and soil enzyme activities increased with the decrease in the spacing of the D. sissoo plantation. The results indicate that adoption of the agroforestry practices led to an improved organic matter status of the soil, which is also reflected in the increased nutrient pool and microbial activities necessary for long-term productivity of the soil. However, tree spacing should be properly maintained to minimize the effects of shading on the intercrops. Received: 21 February 1997     

Mobile and readily available C and N fractions and their relationship to microbial biomass and selected enzyme activities in a sandy soil under different management systems

Within different land‐use systems such as agriculture, forestry, and fallow, the different morphology and physiology of the plants, together with their specific management, lead to a system‐typical set of ecological conditions in the soil. The response of total, mobile, and easily available C and N fractions, microbial biomass, and enzyme activities involved in C and N cycling to different soil management was investigated in a sandy soil at a field study at Riesa, Northeastern Germany. The management systems included agricultural management (AM), succession fallow (SF), and forest management (FM). Samples of the mineral soil (0—5, 5—10, and 10—30 cm) were taken in spring 1999 and analyzed for their contents on organic C, total N, NH₄⁺‐N and NO₃^—‐N, KCl‐extractable organic C and N fractions (Corg_(KCl) and Norg_(KCl)), microbial biomass C and N, and activities of β‐glucosidase and L‐asparaginase. With the exception of Norg_(KCl), all investigated C and N pools showed a clear relationship to the land‐use system that was most pronounced in the 0—5 cm profile increment. SF resulted in greater contents of readily available C (Corg_(KCl)), NH₄⁺‐N, microbial biomass C and N, and enzyme activities in the uppermost 5 cm of the soil compared to all other systems studied. These differences were significant at P ≤ 0.05 to P ≤ 0.001. Comparably high C_mic:C_org ratios of 2.4 to 3.9 % in the SF plot imply a faster C and N turnover than in AM and FM plots. Forest management led to 1.5‐ to 2‐fold larger organic C contents compared to SF and AM plots, respectively. High organic C contents were coupled with low microbial biomass C (78 μg g^—1) and N contents (10.7 μg g^—1), extremely low C_mic : C_org ratios (0.2—0.6 %) and low β‐glucosidase (81 μg PN g^—1 h^—1) and L‐asparaginase (7.3 μg NH₄‐N g^—1 2 h^—1) activities. These results indicate a severe inhibition of mineralization processes in soils under locust stands. Under agricultural management, chemical and biological parameters expressed medium values with exception for NO₃^—‐N contents which were significantly higher than in SF and FM plots (P ≤ 0.005) and increased with increasing soil depth. Nevertheless, the depth gradient found for all studied parameters was most pronounced in soils under SF. Microbial biomass C and N were correlated to β‐glucosidase and L‐asparaginase activity (r ≥ 0.63; P ≤ 0.001). Furthermore, microbial biomass and enzyme activities were related to the amounts of readily mineralizable organic C (i.e. Corg_(KCl)) with r ≥ 0.41 (P ≤ 0.01), suggesting that (1) KCl‐extractable organic C compounds from field‐fresh prepared soils represent an important C source for soil microbial populations, and (2) that microbial biomass is an important source for enzymes in soil. The Norg_(KCl) pool is not necessarily related to the size of microbial biomass C and N and enzyme activities in soil.<?show $6#>     

Effect of rotation, nitrogen fertilization and management of crop residues on some chemical, microbiological and biochemical properties of soil

A long-term experiment, which started in 1971 near Perugia, central Italy, was performed to investigate the effect of different crop residue management practices and rotation systems on some soil properties. Twenty years after the beginning of the experiment, chemical (organic C, total N, humified organic C, humic and fulvic acids), microbiological and biochemical parameters (microbial biomass, global hydrolase activity, dehydrogenase and catalase activities) were investigated. Two crop residue management practices were used in the experiment, i.e. removal (RCR soils) and burial (BCR soils). These treatments were factorially combined with eight rotation systems, i.e. five maize-wheat rotations of different lengths (M-1W, M-2W, M-3W, M-4W and M-5W) and three continuous wheat systems with different fertilization inputs, from 150 to 250 kg N ha^–1. Soil samples were collected in the spring of 1991 for chemical determinations, and in the spring and autumn of 1992, 1993 and 1994, for microbiological and biochemical determinations. All soil chemical, microbiological and biochemical parameters investigated showed significant differences depending on the management of the crop residues. The BCR soils showed more favourable characteristics. In contrast, few significant effects were observed in relation to rotation and N-fertilization treatment. Significant correlations were found between organic-C content and all microbiological and biochemical parameters, as well as between the microbiological and biochemical parameters themselves, indicating that organic-C content plays an important role in determining the level of soil enzyme activity and, consequently, of soil fertility. This experiment showed that burying crop residues in soil can be considered good agronomic practice, which may help limit the gradual depletion of soil organic matter and improve the chemical properties of the soil. Received: 11 January 1996     

Long-term management effects on organic C and N pools and activities of C-transforming enzymes in prairie soils

Changes in soil microbial and biochemical properties in response to management practices reflect changes in the functional capacity of soil ecosystems. The objectives were to evaluate effects of long-term management practices on different soil organic C and N pools and activities of glycoside hydrolases, including α- and β-glucosidases, α- and β-galactosidases, cellulase, and invertase, in semiarid prairie soils. Soils were sampled from five long-term management systems including: undisturbed, abandoned from cultivation, moderately grazed, heavily grazed, and cultivated with winter wheat (Triticum aestivum L.). Activities of C-transforming enzymes were sensitive in discriminating soil ecosystems under various land uses and can be used as indicators for detecting impact of soil management practices on the soil capacity to cycle C. Long-term cultivation (more than 30 yr) decreased total organic C and N, microbial biomass, and activities of C-transforming enzymes, and led to development of a microbial community with enhanced metabolic activity. Grazing, especially at moderate intensity, did not lessen soil capacity to support microbial life and cycle C. The intermediate status of the chemical, microbial, and biochemical properties in the abandoned from cultivation soils suggested that through secondary succession the soil ecosystem is restoring its capacity to sequester C and support microbial life.     

Influence of organic and mineral amendments on microbial soil properties and processes

Microbial diversity in soils is considered important for maintaining sustainability of agricultural production systems. However, the links between microbial diversity and ecosystem processes are not well understood. This study was designed to gain better understanding of the effects of short-term management practices on the microbial community and how changes in the microbial community affect key soil processes. The effects of different forms of nitrogen (N) on soil biology and N dynamics was determined in two soils with organic and conventional management histories that varied in soil microbial properties but had the same fertility. The soils were amended with equal amounts of N (100 kg ha⁻¹) in organic (lupin, Lupinus angustifolius L.) and mineral form (urea), respectively. Over a 91-day period, microbial biomass C and N, dehydrogenase enzyme activity, community structure of pseudomondas (sensu stricto), actinomycetes and α proteobacteria (by denaturing gradient gel electrophoresis (DGGE) following PCR amplification of 16S rDNA fragments) and N mineralisation were measured. Lupin amendment resulted in a two- to five-fold increase in microbial biomass and enzyme activity, while these parameters did not differ significantly between the urea and control treatments. The PCR–DGGE analysis showed that the addition of mineral and organic compounds had an influence on the microbial community composition in the short term (up to 10 days) but the effects were not sustained over the 91-day incubation period. Microbial community structure was strongly influenced by the presence or lack of substrate, while the type of amendment (organic or mineral) had an effect on microbial biomass size and activity. These findings show that the addition of green manures improved soil biology by increasing microbial biomass and activity irrespective of management history, that no direct relationship existed among microbial structure, enzyme activity and N mineralisation, and that microbial community structure (by PCR–DGGE) was more strongly influenced by inherent soil and environmental factors than by short-term management practices.     

Seasonal changes in microbial biomass in soils cropped with palmarosa (Cymbopogon martinii L.) and Japanese mint (Mentha arvensis L.) in subtropical India

Changes in microbial C, N, and P were investigated for 1 year in two soils with similar physicochemical properties but supporting different crops under subtropical conditions. One was cropped with palmarosa (Cymbopogon martinii L.) and the other with Japanese mint (Mentha arvensis L.). Both the season and the type of cropping had a significant influence on changes in the soil microbial biomass. In general, soil microbial biomass C, N, and P were highest in summer months and lowest in midwinter. Soil microbial biomass levels and microbial C:N and C:P ratios were higher and N:P ratios lower under palmarosa soil than under mint.     

Organic matter, microbial biomass and enzyme activity of soils under different crop rotations in the tropics

Soil organic matter level, soil microbial biomass C, ninhydrin-N, C mineralization, and dehydrogenase and alkaline phosphatase activity were studied in soils under different crop rotations for 6 years. Inclusion of a green manure crop of Sesbania aculeata in the rotation improved soil organic matter status and led to an increase in soil microbial biomass, soil enzyme activity and soil respiratory activity. Microbial biomass C increased from 192 mg kg^–1 soil in a pearl millet-wheat-fallow rotation to 256 mg kg^–1 soil in a pearl millet-wheat-green manure rotation. Inclusion of an oilseed crop such as sunflower or mustard led to a decrease in soil microbial biomass, C mineralization and soil enzyme activity. There was a good correlation between microbial biomass C, ninhydrin-N and dehydrogenase activity. The alkaline phosphatase activity of the soil under different crop rotations was little affected. The results indicate the green manuring improved the organic matter status of the soil and soil microbial activity vital for the nutrient turnover and long-term productivity of the soil. Received: 7 January 1996     

Changes of Soil Microbial Biomass Carbon and Nitrogen with Cover Crops and Irrigation in a Tomato Field

ABSTRACT

In order to understand how soil microbial biomass was influenced by incorporated residues of summer cover crops and by water regimes, soil microbial biomass carbon (C) and nitrogen (N) were investigated in tomato field plots in which three leguminous and a non-leguminous cover crop had been grown and incorporated into the soil. The cover crops were sunn hemp (Crotalaria juncea L., cv ‘Tropic Sun’), cowpea (Vigna unguiculata L. Walp, cv ‘Iron clay’), velvetbean (Mucuna deeringiana (Bort) Merr.), and sorghum sudangrass (Sorghum bicolor × S. bicolor var. sudanense (Piper) Stapf) vs. a fallow (bare soil). The tomato crop was irrigated at four different rates, i.e., irrigation initiated only when the water tension had reached ?5, ?10, ?20, or ?30 kPa, respectively. The results showed that sorghum sudangrass, cowpea, sunn hemp, and velvetbean increased microbial biomass C by 68.9%, 89.8%, 116.8%, and 137.7%, and microbial N by 58.3%, 100.0%, 297.3%, and 261.3%, respectively. A legume cover crop, cowpea, had no statistically significant greater effect on soil microbial C and N than the non-legume cover crop, sorghum sudangrass. The tropical legumes, velvetbean and sunn hemp, increased the microbial biomass N markedly. However, the various irrigation rates did not cause significant changes in either microbial N or microbial C. Soil microbial biomass was strongly related to the N concentration and/or the inverse of the C:N ratio of the cover crops and in the soil. Tomato plant biomass and tomato fruit yields correlated well with the level of soil microbial N and inversely with the soil C:N ratio. These results suggest that cover crops increase soil microbiological biomass through the decomposition of organic C. Legumes are more effective than non-legumes, because they contain larger quantities of N and lower C:N ratios than non-legumes.     

Soil sustainability indicators following conservation tillage practices under subtropical maize and bean crops

Conservation management systems such as no tillage may enhance sequestration of soil C. The soil properties that contribute to soil C storage under such systems are still largely unknown, especially in subtropical agroecosystems. We investigated the influence of tillage [mouldboard plough (MP) and no tillage (NT)] on soil organic C, microbial biomass and activity, structural stability and mycorrhizal status of a field cultivated with maize (Zea mays L.) or bean (Phaseolus vulgaris L.) on a Vertisol in Northern Tamaulipas, Mexico. Crop type, tillage system and soil depth had a significant effect on soil organic C, aggregate stability and bulk density. Soil organic C, microbial biomass C and N and dehydrogenase and phosphatase activities were greater with NT than with MP, particularly under bean cultivation. In the 0–5 cm layer, microbial biomass C and N were, on average, about 87 and 51% greater in the soils cultivated with bean and maize, respectively, under NT than under MP. Higher levels of mycorrhizal propagules, glomalin related soil protein (GRSP) and stable aggregates were produced under NT than under MP in both crops. The no-tillage system can be considered an effective management practice for carrying out sustainable agriculture under subtropical conditions, due to its improvement of soil physical and biochemical quality and soil C sequestration.     

有机和常规生产模式下菜田土壤酶活性差异研究

通过对露地及温室环境下有机和常规蔬菜栽培土壤采样,测定分析了5种参与土壤碳氮循环的酶活性,及其与土壤相关理化性质之间的关系。结果显示:温室及露地土壤EC值在有机生产中相应低于常规生产12%和16%;有机生产土壤微生物碳氮含量显著高于常规生产;不同生产模式下土壤酶活性差异显著,有机生产土壤中的蛋白酶、脲酶、脱氢酶、β-葡糖苷酶活性高于常规生产,而硝酸还原酶活性较常规生产低;有机与常规栽培对蛋白酶活性影响极显著(P=0.006 8),对脲酶活性影响程度达显著水平(P=0.012 4)。除脱氢酶以外,不同栽培模式环境对土壤中另外4种酶活性均有显著影响,温室栽培环境中的蛋白酶、脲酶和硝酸还原酶活性高于露地。除硝酸还原酶外,其他4种酶活性与可溶性全氮、微生物碳、微生物氮相关系数达到显著水平。分析表明,土壤酶活性受到栽培方式以及环境的影响,并且有机生产能够提高参与土壤碳氮循环的酶活性。土壤蛋白酶、脲酶、脱氢酶和β-葡糖苷酶活性能够作为表征土壤碳氮循环以及微生物活性的指标。     

Evaluation of microbial methods as potential indicators of soil quality in historical agricultural fields

In agricultural ecosystems that have had consistent cropping histories, standard microbial methods may be used to evaluate past and present practices. Our objective was to evaluate several microbial methods that best indicate cropping histories and soil quality on long-term plots. We selected soil microbial carbon (C), phospholipid analyses, direct counts of total fungal and bacterial biomass, and soil enzymes (phosphatases) to measure direct and indirect microbial activity on the Sanborn Field and Tucker Prairie. The Sanborn Field has been under various cropping and management practices since 1888 and the Tucker Prairie is an uncultivated site. Seven different plots were chosen on the Sanborn Field and random samples were taken in the summit area on the Tucker Prairie, which represented a reference site. Soil microbial biomass C, phospholipids, and enzyme activity were reflective of the cropping and management histories observed on the Sanborn Field. Enzymatic activity was highly correlated to soil organic matter. The direct counts of fungal and bacterial biomass showed that fungal populations dominated these soils, which may be attributed to soil pH. Soil microbial biomass C and enzyme assays seemed to be better potential indicators of cropping histories than the other methods tested in the long-term plots.This paper has been assigned by the Missouri Agricultural Experiment Station to Journal Series no. 12043     

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.     

Ramifications of crop residue loading for soil microbial community composition,activity and nutrient supply

Variable results have been reported on the effects of crop residue loads on soil microbial properties. We investigated changes in soil bacterial composition, β-glucosidase enzyme activity and nutrient bioavailability in response to wheat residue loading. The treatments included three levels of above-ground wheat residues (removed, retained or supplemented), with or without fertilizer N. Bacteroidetes, Firmicutes and Verrucomicrobia (the first two are copiotrophs) were less abundant where residues were removed than where residues were retained or supplemented, but the reverse was true for Actinobacteria, Cyanobacteria, Chloroflexi and Nitrospirae (all oligotrophs, although some Actinobacteria can be copiotrophic). Actinobacteria were also less abundant where fertilizer N was applied, and the abundances of their genera (including Arthrobacter and Mycobacterium) increased where residues were removed, confirming that they were oligotrophic in this study. β-diversity showed similar differences in the bacterial community structures because of residue management, but α-diversity was not affected by residue management or N fertilizer. β-glucosidase enzyme activities increased as C inputs increased with residue manipulation and N fertilizer. The enzyme activities increased with increasing residue loading in the 0–15 cm soil depth, but decreased with soil depth. Soil K supply increased with increasing residue loading, but nitrate-N supply was highest with residue retention. These results demonstrate remarkable resilience of soil microbial functioning under a wide range of crop residue inputs, without adverse effects on enzyme activity attributable to inorganic N fertilizer. The increasing β-glucosidase activity with increasing residue loading probably explains why crop residue return does not always increase soil C stocks.     

Evaluation of soil microbial indices along a revegetation chronosequence in grassland soils on the Loess Plateau,Northwest China

There is a growing interest in using soil microbial parameters as indicators of soil quality changes after revegetation of disturbed soils. This study investigated the changes in different soil microbial parameters as well as physico-chemical parameters as affected by vegetation rehabilitation of soil in the Loess plateau of China subjected to natural succession after enclosure. The results showed that the soil nutrients tend to be concentrated in the soil surface layer, especially the soil organic C, total N and alkali extractable N with soil organic C being doubled (up to 20 g kg⁻¹) after 50 years of revegetation. Soil enzyme activities and microbial biomass C (Cmic) and N (Nmic) increased with rehabilitation time up to 23 years. After 23 years, soil Cmic and Nmic and enzyme activities remained stable. Enzyme activities increased rapidly during the early stage of revegetation, about 15–20 years after enclosure. Soil Cmic and Nmic also increased about 20% faster up to 23 years since enclosure in the 0–20-cm soil layer. Soil basal respiration (BR) in the 23 years site was higher than in other sites, indicating high microbial activity in this site. These findings demonstrated significant impacts of natural vegetation succession in overgrazed grassland on the properties of the surface soils, including the soil nutrients, organic matter, soil microbial biomass, respiration, and enzyme activities.     

利用复合方法对不同耕作系统中的土壤微生物活性进行分析

Cropping activities may affect soil microbial activities and biomass,which would affect C and N cycling in soil and thus the crop yields and quality.In the present study,a combination of microcalorimetric,enzyme activity(sucrase,urease,catalase,and fluorescein diacetate hydrolysis),and real-time polymerase chain reaction(RT-PCR) analyses was used to investigate microbial status of farmland soils,collected from 5 different sites in Huazhong Agriculture University,China.Our results showed that among the 5sites,both positive and negative impacts of cropping activities on soil microbial activity were observed.Enzyme activity analysis showed that cropping activities reduced soil sucrase and urease activities,which would influence the C and N cycles in soil.Much more attentions should be given to microbial status affected by cropping activities in future.According to the correlation analysis,fluorescein diacetate hydrolysis showed a significantly(P 0.05) negative correlation with the time to reach the maximum power output(R ——0.898),but a significantly(P 0.05) positive correlation with bacterial gene copy number(R = 0.817).Soil catalase activity also showed a significantly(P 0.05) positive correlation with bacterial gene copy number(R = 0.965).Using combined methods would provide virtual information of soil microbial status.     

Soil carbon sequestration,plant nutrients and biological activities affected by organic farming system in tea (Camellia sinensis (L.) O. Kuntze) fields

There is growing interest in investigations into soil carbon (C) sequestration, plant nutrients and biological activities in organic farming since it is regarded as a farming system that could contribute to climate mitigation and sustainable agriculture. However, most comparative studies have focused on annual crops or farming systems with crop rotations, and only a few on perennial crops without rotations, e.g. tea (Camellia sinensis (L.) O. Kuntze). In this study, we selected five pairs of tea fields under organic and conventional farming systems in eastern China to study the effect of organic farming on soil C sequestration, plant nutrients and biological activities in tea fields. Soil organic C, total nitrogen (N), phosphorus (P), potassium (K) and magnesium (Mg), available nutrients, microbial biomass, N mineralization and nitrification were compared. Soil pH, organic C and total N contents were higher in organic tea fields. Soil microbial biomass C, N and P, and their ratios in organic C, total N and P, respectively, net N mineralization and nitrification rates were significantly higher in organic fields in most of the comparative pairs of fields. Concentrations of soil organic C and microbial biomass C were higher in the soils with longer periods under organic management. However, inorganic N, available P and K concentrations were generally lower in the organic fields. No significant differences were found in available calcium (Ca), Mg, sodium (Na), iron (Fe), manganese (Mn), copper (Cu) and zinc (Zn) concentrations between the two farming systems. These findings suggest that organic farming could promote soil C sequestration and microbial biomass size and activities in tea fields, but more N-rich organic fertilizers, and natural P and K fertilizers, will be required for sustainable organic tea production in the long term.     

Microbial biomass and N transformations in two soils cropped with annual and perennial species

A field study was undertaken to determine the effects of different plant species on soil microbial biomass and N transformations in a well drained silty clay loam (Typic Dystrochrept) and a poorly drained clay loam (Typic Humaquept). The crop treatments were faba bean (Vicia faba L.), alfalfa (Medicago sativa L.), timothy (Phleum pratense L.), bromegrass (Bromus inermis L.), reed canarygrass (Phalaris arundinacea L.), and wheat (Triticum aestivum L.). Measurements of microbial biomass C, denitrification capacity, and nitrification capacity were performed periodically in the top 2–10 cm of soil. On most sampling dates, all three parameters were higher under perennial than under annual species. The nitrification capacity was positively affected by the level of N applied to each species (r=0.65^** for the silty clay loam and 0.84^*** for the clay loam) and not directly by the plant. The differences found in microbial biomass C were significantly correlated with the water-soluble organic C present under each plant species (r=0.74^*** for the silty clay loam and 0.90^*** for the clay loam), suggesting differences in C deposition in the soil among plant species. In the silty clay loam, the denitrification capacity was positively related to the amount of organic C found under each plant species, while in the clay loam, it was dependent on the amount of N applied to each species. There was less denitrification activity per unit biomass under legume species than under graminease, suggesting that, depending on their composition, root-derived materials may be used differently by soil microbes.