Development and validation of numerical indexes integrating enzyme activities of soils

Three numerical indexes, based on soil enzyme activities, which can discriminate between altered and unaltered soils, are presented and validated. Seven enzymes were measured at three different agricultural sites subjected to contamination by municipal and industrial wastes (site 1), intensive cultivation without either crop rotation or organic fertilization (site 2), and irrigation with brackish water (site 3). At each site neighbouring, unaltered soils were sampled and analysed as control soils.The three indexes were developed by means of canonical discriminant analysis (CDA) using data from two sites, while the third site was kept aside as an independent test. The first index is built up using all of the enzyme activities studied; the second, using the most discriminating enzyme activities only; and the third was developed for testing against data in published papers that deal with enzyme measurements in soils under different management regimes.The three indexes were able to discriminate between altered and control soils when applied to the data set from the third site, i.e., that not used for index development. When tested against published data, the third index was usually able to discriminate altered soils from controls by higher index scores. This index was successful in most cases: it was consistently able to classify soils according to their reported degree of alteration. Our results confirm that enzyme activities are suitable indicators of soil alteration and may be usefully integrated to develop soil alteration indexes suitable for monitoring soil status under different conditions.     

Hydrolytic enzyme activities in agricultural and forest soils. Some implications for their use as indicators of soil quality

Although a great deal of information exists about the effect of land use on soil enzyme activities, much of this is contradictory and brings into question the suitability of soil enzyme activities as indicators of how land use affects soil quality. The purpose of this study was to investigate the effect of land use on different soil biochemical properties, especially hydrolytic enzyme activities, with the aim of providing knowledge about the problems related to the use of enzymes as indicators of soil quality. The data presented derive from various studies in which a large number of soils under different types of forest or agricultural management were analysed by the same methods. All of the soil samples were characterized in terms of their main physical and chemical properties, the activity of several hydrolases, microbial biomass C and soil basal respiration. The results indicate that soil use causes a large reduction in organic matter content and that the effect on enzyme activity varies depending on the type of land use or management and the type of enzyme. Furthermore, the enzyme activities per carbon unit (specific activities) in soils affected by land use are almost always higher than in maximum quality soils (climax soils under oak vegetation or oak soils), and land use also generates greater increases in the specific activity as the C content decreases. The mechanism responsible for these increases probably involves loss of the most labile organic matter. Enzyme enrichment is not always produced to the same degree, as it varies as a function of the enzyme and the type of land use under consideration. It is concluded that the complexity of the behaviour of the soil enzymes raises doubts about the use of enzyme activities as indicators of soil degradation brought about by land use.     

Assessing air-drying and rewetting pre-treatment effect on some soil enzyme activities under Mediterranean conditions

Soil enzyme activities are useful indicators of soil quality as they are very sensitive to disturbance. Sample storage or pre-treatments could affect the results in these assays, which are normally determined in fresh samples, kept cold or frozen. The objectives of this study were to (i) evaluate the effect of air-drying or air-drying and rewetting on β-glucosidase, acid phosphatase and urease activities in soils from different locations, degradation status and sampling seasons, and (ii) assess if air-drying or air-drying and rewetting is an accurate sample storage and pre-treatment procedure for enzyme activities in soil quality evaluations under semiarid Mediterranean conditions. Our results showed that urease, phosphatase and β-glucosidase activities were hardly affected by air-drying of degraded and non-degraded soils from the two locations studied in all seasons. Short incubations (4, 8 and 12 d at 23 °C) of rewetted air-dried soil at 55% of water-holding capacity showed different patterns depending on the enzyme studied. Urease and β-glucosidase activities were relatively stable during incubation, with several significant (P<0.05) shifts up and down in some soils and samplings. However, acid phosphatase showed an increase in activity with incubation, of between 5% and 50% relative to air-dried samples. These increases followed no pattern and were unrelated to soil characteristics or sampling date. Hence, urease, phosphatase and β-glucosidase activities determined in air-dried soil samples seem to be representative of those obtained under field-moist conditions. In contrast, short incubations of rewetted soil samples can produce fluctuations in these enzyme activities, mainly of acid phosphatase, and estimations in these conditions are not so representative of field-moist soil values.     

Effect of organic and mineral fertilizers on soil respiration and enzyme activities of two Mediterranean horticultural soils

The effects of municipal food waste compost addition and mineral fertilization on selected soil microbiological activities were investigated during 3 years of reiterated treatments on two Mediterranean agricultural soils with different organic carbon content. Compost at 15, 30 and 45 t ha⁻¹ (dry matter), mineral (NPK) fertilizers and combined fertilizers with 15 t ha⁻¹ of compost plus two reduced doses of mineral N were applied to both soils. At both sites, organic amendment increased soil respiration, fluorescein diacetate hydrolysis, phosphatase and arylsulphatase activities. The differences in soil microbial activities among treatments, found after 3 years of repeated treatments, were attributable to the variations of soil organic C content and to the impact of soil tillage. Our results show that, in Mediterranean intensively cultivated agroecosystems, annual organic amendments improve the microbial activity of soil and produce cumulative effects, suggesting the usefulness of repeated high-rate compost applications.     

Suitability of enzyme activities for the monitoring of soil quality improvement in organic agricultural systems

There is growing interest in the applications of soil enzymes as early indicators of soil quality change under contrasting agricultural management practices. However, despite there being an abundant literature on this subject, most comparative assessments have been based on a limited number of experimental farms and, therefore, conclusions are not as robust as desired. In this study, we compare 18 pairs of organic and neighbouring conventional olive orchards in southern Spain. These sites were selected to allow the definition of the relative contributions of site-landscape features, soil type, and time since organic accreditation and tillage intensity, on the soil quality. Soils were analysed for physico-chemical properties, the activities of dehydrogenase, β-glucosidase, arylsulphatase, acid and alkaline phosphatase, and potential nitrification. The geometric mean of the assayed enzymes (GMea) was validated with an independently performed Principal Component Analysis (PCA), and used as a combined soil quality index. The effects of tillage intensity and time since organic accreditation on the improvement of soil quality were also evaluated within the subset of organic farms. Overall for the 18 sites, contrasted management practices did not differ in their impact on basic soil physico-chemical properties, except for loss of on ignition and available inorganic N which were higher and lower in organic farms, respectively. Organic management resulted in significantly higher soil enzyme activities. However, differences were not significant in some of the paired comparisons when considered individually. This highlights the need for extensive comparative assessment, as in this study, to draw clear conclusions concerning the changes to soil quality under sustainable management practices. The GMea was significantly correlated with the first axis of the PCA and shown to be appropriate for condensing the set of soil enzyme values to a sole numerical value. Soil quality changes in organic versus conventional farms, as measured by the GMea, ranged from −23% to 97%, and was highly dependent on time since organic accreditation (r = 0.88; P < 0.01). On the other hand, tillage intensity clearly tended to delay any progress in soil quality in the organic farms.     

Effect of elevated O3 on rhizospheric enzymatic activities of ozone sensitive and tolerant wheat cultivars

Tropospheric ozone (O₃) is considered harmful to agriculture production and soil community. Wheat cultivars HD 2987 (O₃ sensitive) and Kharchiya 65 (O₃ tolerant) were grown under ambient and elevated (ambient + 30 ppb) levels of O₃ (EO) using open top chambers, and microbial biomass and enzymatic activities were investigated in soil rhizosphere. Elevated O₃ declined soil enzymatic activities related to carbon cycling viz. β-glucosidase, cellobiohydrolase, cellulase and amylase more in sensitive cultivar compared to tolerant. Enzymatic activities linked to nitrogen cycling like N-acetyl-glucosaminidase and urease decreased while protease and glycine aminopeptidase increased. Microbial biomass carbon and nitrogen declined more in sensitive cultivar by 11.1 and 21.2%, respectively. Root biomass reduced in wheat cultivars with an increase of their phenolics contents by 34.3 and 10.2% in HD 2987 and Kharchiya 65, respectively at 60 days after germination. Non-significant changes were observed in soil organic carbon and total nitrogen in both the cultivars. Redundancy analysis suggested that soil enzymatic activities were predominantly affected by O₃ induced changes in microbial biomass carbon and root biomass. Study also showed that rhizosphere of sensitive cultivar HD 2987 was affected more under EO as compared to tolerant Kharchiya 65.     

Effect of cattle slurry in grassland on microbial biomass and on activities of various enzymes

We examined the long-term effects of cattle slurry, applied at high rates, on microbial biomass, respiration, the microbial quotient (qCO₂) and various soil enzyme activities. In March, June, July, and October 1991, slurry-amended grassland soils (0–10 cm) contained significantly higher levels of microbial biomass, N mineralization and enzyme activities involved in N, P, and C cycling. With microbial biomass as the relative value, the results revealed that the slurry treatment influenced enzyme production by the microbial biomass. High levels of urease activity were the result not only of a larger microbial biomass, but also of higher levels of enzmye production by this microbial biomass. The ratio of alkaline phosphatase and xylanase to microbial biomass was nearly constant in the different treatments. The metabolic quotient (qCO₂) declined with increased levels of slurry application. Therefore it appears that microorganisms in slurry-amended soils require less C and energy if there is no competition for nutrients. The results of this study suggest that urease activity, nitrification, and respiration (metabolic quotient) can be used as indicators of environmental stress, produced by heavy applications of cattle slurry.     

Biochemical properties of range and forest soils in Mediterranean mountain environments

Biochemical properties are at present considered to be the best indicators for assessing soil quality, but their use is limited by the lack of available data, at least for certain ecosystems. In an attempt to offset this lack of data, the present study provides information on different biochemical properties of soils from Sierra Nevada and Sierra María (southern Spain), covering a range of altitudes between 1,000 and 3,000 m. In general, the values of the properties analyzed were similar to those of other mountain soils, although the values of basal respiration were particularly low, possibly due to the low levels of humidity at the time of sampling. The biochemical properties were closely correlated with each other, as observed in soils from other type of environments. Altitude had a clear effect on the biochemical properties because of its effect on climate and vegetation. At both sites, the soil samples showing the most homogenous pattern of biochemical properties (seen through star diagrams) were those corresponding to intermediate altitudes.     

土壤质量的酶学指标研究

土壤质量日益衰退,寻找能够准确标示其变化的敏感指标非常重要。土壤酶几乎参与了土壤中全部的生物化学反应,与土壤中多种生态过程密切相关。土壤酶的敏感性、专一性和综合性等特点使其可以作为一个反映土壤质量的生物学指标。本文在概述了土壤酶作为土壤质量指标可行性的基础上,综述了土壤肥力质量、环境质量等的土壤酶活性和酶动力学指标的研究,并对今后相关研究提出了几点建议。     

长期施用牛粪对松嫩平原盐渍化土壤质量的影响

在盐渍化土壤中,普遍存在土壤结构性和养分状况差以及土壤酶活性低等现象.这种现象主要是由于土壤中过量的交换性钠离子和较高的土壤pH所引起.长期施用有机肥(牛粪)是一项提升盐渍化土壤质量的重要措施.本研究依托东北农业大学盐碱土改良长期定位试验站,以腐熟的牛粪为改良材料,依据牛粪施用年限共设置5个处理,采用完全随机区组设计,每处理3次重复,供试作为玉米,各处理分别为:施用牛粪2年、6年、13年和18年,以不施用牛粪的盐渍化土壤作为对照.分别测定各处理的土壤理化指标和酶活性.采用因子分析法与土壤质量指数法评价长期施用有机肥对盐渍化土壤质量的影响.研究结果表明:长期施用有机肥能够改善盐渍化土壤的物理性状、提高土壤养分状况、降低土壤pH和盐分以及增加土壤酶活性.根据特征根>1原则,经因子分析后可提取2个公因子,分别表征"土壤结构性"(因子1)和"土壤盐碱性质"(因子2).与未施用有机肥的土壤相比,施用有机肥13年和18年的土壤具有较好的土壤结构性和较低的盐碱性质,而施用有机肥2年和6年的土壤仅具有较低的盐碱性质.比较土壤质量指数(SOI)可知:盐渍化土壤质量随有机肥施用年限而增加,有机肥施用18年处理的土壤质量最高.总之,土壤结构性差和盐碱性质高是影响松嫩平原盐渍化土壤质量的关键限制因子,其中以土壤结构性差最为主导;土壤容重、pH和盐分的降低是长期有机培肥措施下盐渍化土壤质量得以提升的重要特征,尤其是以土壤容重的降低最为重要.     

Biochemical characterization of biological activity in very young mine soils

Summary A number of biochemical parameters reflecting biological activity (respiration, ATP, enzyme activities) were determined in 0- to 7-year-old lignite mine soils. C (as CO₂) and ATP contents and hydrolytic enzyme activities all increased with soil age. The kinetics of CO₂ release showed that both labile and recalcitrant C-bearing substrates were mineralized, the mineralization constant of C decreased with soil age, but were always greater than those of native soils. The percentage of N mineralization, which tended to decrease with soil age, resulted in all cases in a predominance of ammoniacal forms. These findings suggest that since organic C and N accumulated with age in these soils, the C and N cycle is established progressively.     

Fuzzy classification of microbial biomass and enzyme activities in grassland soils

Soil microbial properties are widely used as indicators of soil quality. The interpretation of soil microbial processes, however, is difficult because of their regional and seasonal heterogeneity as well as the lack of reference values. One possibility to overcome these limitations to apply the fuzzy set theory. This approach more realistically describes ecological systems because it considers natural ambiguity and complexity. The present study applies a fuzzy rule-based classification model to define soil quality based on soil microbial biomass, N-mineralisation, enzyme activity data (urease, xylanase, phosphatase, arylsulfatase) and soil organic matter. The data have been collected from different grassland sites in the European Union over a period of 20 years. The fuzzy model is based on a rule system derived from a training set using simulated annealing as an optimisation algorithm. For each variable, nine triangular fuzzy sets were defined for consideration as possible rule arguments. The model uses the t-norm for combination of arguments, product inference, the weighted sum as rule combination and the maximum method for defuzzification. The output is the assignment of membership of the object to a given soil quality class. The soil quality classes (very poor, poor, medium, high, very high) were defined by five heavy metal contamination levels (very high, high, medium, low, no). A predefined number of fuzzy rules were assessed using a simulated annealing algorithm. The fuzzy model was validated by a test file by assigning the soils to the quality class with the highest response value. The fuzzy model yielded an overall coincidence of 88.8% between observed and simulated results. The most sensitive index of soil quality was microbial biomass. N-mineralisation was a good indicator for the high-quality soils, while urease and arylsulfatase were important indicators for heavily contaminated, poor soil quality. Xylanase and phosphatase behaved ambivalently. Including soil organic carbon in the model decreased its effectiveness by 6.5%. We suggest that the presented fuzzy model based on soil microbial properties could be applied not only to soil degradation, upscaling and prediction, but also to judge the response of soils to environmental changes.     

Effect of fractionation on the enzymatic state and behaviour of enzyme activities in different structural soil units

Summary The behaviour and state of soil catalase, dehydrogenases, urease and proteases associated with different soil structural fractions were studied. Assays of the enzymatic sensitivity to pH variation, thermal stability and the calculation of kinetics constants of Michaelis were performed. The results indicated that catalase and urease activity in these soils seem to be of the same type, because the activities presented a similar behaviour in the soil fractions studied. However, their state appeared different in each group of soil units. Dehydrogenases showed a similar state and behaviour while proteases were in a different state and behaviour in each soil fraction.     

Numerical characterization of forest soils using biological and biochemical properties

Summary To find if surface soils could be grouped by their biological and biochemical properties, soil samples (0–5 cm) were collected at 4-week intervals for 56 weeks from 48 woods in and around the English Lake District, and pH, loss-on-ignition (LOI), moisture content, oxygen uptake, and cellulase and phosphatase activities were measured. Results expressed on a loss-on-ignition basis were more informative than those on an oven-dry basis. In a principal component analysis of each property over the 14 samplings, the first component values represent smoothed between-plot differences; other components identify plots which behave differently from the majority at certain times. Analysis of variance showed very highly significant differences between plots for all the properties. pH and loss-on-ignition showed the smallest, but significant, differences between samplings. On a loss-on-ignition basis, the only significant correlations between first component values, and between plot means, were phosphatase with oxygen uptake and cellulase with pH. It is concluded that no individual physiological property can be used as a measure of soil bioactivity, which supports the conclusions of other authors. None of the principal component analyses of individual or combined properties showed any evidence of the existence of distinct clusters of plots. On a loss-on-ignition basis, a priori groups based on (1) pH < 3.8, (2) pH 3.8 – 5.0 and (3) pH > 5.0, showed no significant difference in moisture content. However, oxygen uptake was significantly lower in (1) than in (2). Cellulase activity was significantly greater in (3) than in (1) and (2). Phosphatase activity was significantly lower in (1) than in (2), and there appeared to be a peak at pH 3.8 – 5.0.     

Soil enzymatic activity as affected by long term application of farm yard manure and mineral fertilizer under a rainfed soybean–wheat system in N-W Himalaya

Long-term experimental sites are expected to provide important information regarding soil properties as affected by management practices. This study was designed to examine the effects of continuous fertilization, and manuring on the activities of enzymes involved in mineralization of C, N, and P on a long term (33 years) field trial under sub-temperate conditions in India. Treatments at the site included application of recommended doses of nitrogen and phosphorus (NP), nitrogen and potassium (NK), nitrogen, phosphorus and potassium (NPK), farmyard manure (FYM) with N (N + FYM), FYM with NPK (NPK + FYM) and un-amended control (C). The study was done under rainfed soybean–wheat rotation. Manure application increased soil carbohydrate, dehydrogenase, acid and alkaline phosphatases, cellulase, and protease activity significantly. Urease activity was not influenced by the manure treatment and the activity was highest in controls. Both acid and alkaline phosphatase activities were negatively influenced by chemical fertilizer treatment. Almost all the enzymes studied were significantly correlated with soil C content. The results suggest that application of FYM directly or indirectly influences the enzyme activity and it in turn regulates nutrient transformation.     

Microbiological rates and enzyme activities as indicators of functionality in soils affected by the Aznalcóllar toxic spill

This study focused on the potential of using soil enzyme activities and general microbiological rates (respiration, N-mineralisation, nitrification) to evaluate the quality of soils affected by a pyrite mud spill which contained high concentrations of heavy metals. The quality of soils after restoration was estimated by comparing enzyme activities and general microbiological rates in three different types of experimental field plots: (i) non-polluted, (ii) polluted but restored, and (iii) polluted but un-restored soils. Non-polluted soils showed the highest levels of enzyme activity. Significant differences were detected for acid phosphatase, β-glucosidase and urease activities between all types of plots. However, arylsulfatase and alkaline phosphatase activities showed no significant differences between the restored plots and polluted but un-restored plots. Geometric mean statistics were used as an index of soil quality in terms of overall: (i) bioavailable heavy metal concentrations, (ii) assayed enzyme activities, and (iii) general microbiological rates, in order to compare plots differing in the degree of pyritic mud pollution. The results indicate that it is important to consider these three criteria in to estimate the soil quality of heavy-metal contaminated soils. Typically, enzyme activities were negatively correlated with bioavailable Cd, Cu and Zn concentrations, but positively with soil pH values. In contrast, pH values were negatively correlated with bioavailable concentrations of Cd, Cu and Zn. It is unclear if the generalised lower enzyme activities found in restored soils, compared to non-polluted soils, is promoted by pH or bioavailable heavy metals concentrations, or a combination of both.     

Application of biological indicators to assess recovery of hydrocarbon impacted soils

Remediation programmes are considered complete when human risk-based criteria are met. These targets are unrelated to the ecological parameters that may be important with regard to future soil uses. As a consequence, there has been a move towards the consideration of biological indicators for hazard assessment in conjunction with the remediation of contaminated soils. This study uses a range of biological assays to assess the ecological health of soils from a former gas works site undergoing various remediation treatments. The indicators that optimally differentiated the extent of soil remediation were biomass-C, respiration, dehydrogenase activity, earthworm toxicity and mustard seed germination. Although they had different end-points, once robust and sensitive biological indicators were incorporated into a quantitative soil quality index, they gave a clearer representation of ecological health than chemical data alone by their integration of contamination effects at a number of trophic levels.     

A soil quality index based on the equilibrium between soil organic matter and biochemical properties of undisturbed coniferous forest soils of the Pacific Northwest

Recent studies have suggested that the organic matter contents of undisturbed soils (under natural vegetation) are in equilibrium with biological and biochemical properties. Accordingly, we hypothesised that such equilibria should be disrupted when soils are subjected to disturbance or stress, and that measurement of this disruption can be expressed mathematically and used as a soil quality index. In this study, we evaluated these hypotheses in soils from the H.J. Andrews Experimental Forest in Oregon. Both O and A horizons were sampled from nine sites in Spring 2005 and Fall 2006. Soil samples were analyzed for enzyme activities (phosphatase, β-glucosidase, laccase, N-acetyl-glucosaminidase, protease and urease), and other biological and chemical properties including N-mineralization, respiration, microbial biomass C (MBC), soil organic carbon (SOC) and total nitrogen content. In addition, soil samples from one old-growth site were manipulated in the laboratory to either simulate chemical stresses (Cu addition or pH alteration) or physical disturbances (wet-dry or freeze-thaw cycles). The results showed variation in biological and biochemical soil properties that were closely correlated with SOC. Multiple regression analysis of SOC levels against all soil properties showed that a model containing only MBC and phosphatase activity could account for 97% of the SOC variation among the sites. The model fit was independent of spatial and temporal variations because covariates such as site, stand age, sampling date, and soil horizon were found to be not statistically significant. Although the application of stress/disturbance treatments inconsistently affected most of the individual biochemical properties, in contrast, the ratio of soil C predicted by the model (C_p), and soil C measured (C_m) was consistently reduced in soils submitted to at least one level of stress and disturbance treatments. In addition, C_p/C_m was more affected in soils submitted to wet-dry cycles and Cu contamination than to freeze-thaw cycles or shifts in soil pH. Our results confirm previous evidence of a biochemical balance in high quality undisturbed soils, and that this balance is disrupted when the soil is submitted to disturbances or placed under stress conditions. The C_p/C_m ratio provides a simple reference value against which the degrading effects of pollutants or management practices on soil quality can be assessed.     

Soil organic matter quantity and quality in mountain soils of the Alay Range, Kyrgyzia, affected by land use change

 Changes in soil management practices influence the amount, quality and turnover of soil organic matter (SOM). Our objective was to study the effects of deforestation followed by pasture establishment on SOM quantity, quality and turnover in mountain soils of the Sui Checti valley in the Alay Range, Kyrgyzia. This objective was approached by analysis of total organic C (TOC), N, lignin-derived phenols, and neutral sugars in soil samples and primary particle-size soil fractions. Pasture installation led to a loss of about 30% TOC compared with the native Juniperus turkestanica forests. The pasture soils accumulated about 20% N, due to inputs via animal excrement. A change in land use from forest to pasture mainly affected the SOM bound to the silt fraction; there was more microbial decomposition in the pasture than in the forest silt fraction, as indicated by lower yields of lignin and carbohydrates, and also by a more advanced oxidative lignin side-chain oxidation and higher values of plant : microbial sugar ratios. The ratio of arabinose : xylose was indicative of the removal of carbohydrates when the original forest was replaced by pasture, and we conclude that this can be used as an indicator of deforestation. The accumulation of lignin and its low humification within the forest floor could be due to the extremely cold winter and dry summer climate. Received: 10 March 1999     

Effect of distillery effluents on plant and soil enzymatic activities and groundnut quality

A field experiment was conducted during the rainy season 2000 to examine the effect of distillery effluents, i.e., biomethanated spent wash (BSW), raw spent wash (RSW), and lagoon sludge (LS) versus recommended NPK+FYM (farmyard manure) on nutritional quality of groundnut (Arachis hypogaea L.) and enzyme activities of plant and soil. The distillery effluents did not affect the oil content (%), crude and true protein contents (%) in groundnut but increased the seed yield and the contents of methionine by 44 % (1.15 g (16 g N)^–1 vs. 0.80 g (16 g N)^–1 in control) and of cysteine by 24 % (1.36 g (16 g N)^–1 vs. 1.10 g (16 g N)^–1 in control). BSW produced the highest seed yield (619 kg ha^–1) followed by RSW (557 kg ha^–1) and LS (472 kg ha^–1). LS recorded the highest total chlorophyll content (2.94 mg (g FW)^–1) in groundnut leaves. Application of BSW and RSW significantly increased the activity of plant peroxidase whereas the plant polyphenol oxidase was higher in BSW only. The application of distillery effluents did not affect the nitrate reductase activity but BSW significantly increased the nitrate content in the rhizosphere soil. The three effluents significantly increased the dehydrogenase and alkaline phosphatase activity more than recommended NPK+FYM.