Sensitive Indicators Of Soil Quality Research Articles

Glomalin accumulated in seagrass sediments reveals past alterations in soil quality due to land-use change

Arbuscular mycorrhizal fungi (AMF), symbionts with most terrestrial plants, produce glomalin-related soil protein (GRSP), which plays a major role in soil structure and quality. Both fungi hyphae and protein production in soils are affected by perturbations related to land-use changes, implying that GRSP is a sensitive indicator of soil quality. Unfortunately, GRSP degrades within years to decades in oxic environments, preventing its use as palaeoecological proxy. However, GRSP is transported to marine, near-shore anoxic sediments, where it accumulates and remains non-degraded, enabling the assessment of its potential as a palaeoecological proxy for soil ecosystem's health. Exploiting this fact, we have obtained for the first time a long-term record (c. 1250years) of GRSP content using a Posidonia oceanica seagrass mat sediment core from the Western Mediterranean (Portlligat Bay, Spain). The trends in GRSP content matched well with land-use changes related to agrarian activities reconstructed by pollen analysis. In periods of cultivation, GRSP accumulation in the mat decreased. Given the role played by GRSP, the results suggest that agrarian intensification may have resulted in perturbations to soil quality. Thus, GRSP in seagrass mat sediments can be used to assess long-term trends in continental soil quality induced by human activities. These findings open new possibilities in long-term ecology research, as other anoxic environments could be potentially valid too. Testing them would open the possibility to identify long-term patterns in soil quality and other environmental stressors that could also affect AMF and GRSP production in soils.

Responses of absolute and specific soil enzyme activities to long term additions of organic and mineral fertilizer

Long-term phosphorus (P) and nitrogen (N) applications may seriously affect soil microbial activity. A long-term field fertilizer application trial was established on reddish paddy soils in the subtropical region of southern China in 1998. We assessed the effects of swine manure and seven different rates or ratios of NPK fertilizer treatments on (1) the absolute and specific enzyme activities per unit of soil organic carbon (SOC) or microbial biomass carbon (MBC) involved in C, N, and P transformations and (2) their relationships with soil environmental factors and soil microbial community structures. The results showed that manure applications led to increases in the absolute and specific activities of soil β-1,4-glucosidase(βG), β-1,4-N-acetylglucosaminidase (NAG), and leucine aminopeptidase (LAP). The absolute and specific acid phosphatase (AP) activities decreased as mineral P fertilizer application rates and ratios increased. Redundancy analysis (RDA) showed that there were negative correlations between absolute and specific AP activities, pH, and total P contents, while there were positive correlations between soil absolute and specific βG, NAG, and LAP enzyme activities, and SOC and total N contents. RDA showed that the contents of actinomycete and Gram-positive bacterium PLFA biomarkers are more closely related to the absolute and specific enzyme activities than the other PLFA biomarkers (P<0.01). Our results suggest that both the absolute and specific enzyme activities could be used as sensitive soil quality indicators that provide useful linkages with the microbial community structures and environmental factors. To maintain microbial activity and to minimize environmental impacts, P should be applied as a combination of inorganic and organic forms, and total P fertilizer application rates to subtropical paddy soils should not exceed 44kgPha−1year−1.

Assessment of soil quality under different tillage practices during wheat cultivation: soil enzymes and microbial biomass

Microbial processes, particularly enzyme activities, play crucial functional roles in soil ecology, hence serving as sensitive indicators of soil quality. We assessed the temporal dynamics of microbial biomass and selected soil enzymes (β-d-glucosidase, cellobiohydrolase, polyphenol oxidase, urease, glycine-aminopeptidase and alkaline phosphatase) during wheat cultivation, under four different tillage practices in the rice–wheat system. The four practices involved conventional tilling of soil before cultivating each crop (CTR-CTW); no tilling before cultivating rice but conventional tillage before wheat (NTR-CTW); conventional tilling before cultivating rice but no tilling before wheat (CTR-NTW) and no tilling before cultivation of each crop (NTR-NTW). Microbial biomass and activities of hydrolytic enzymes increased under NTR-NTW followed by CTR-NTW and NTR-CTW with respect to the conventional practice CTR-CTW, thus reflecting improvement in microbial activities with reduced tillage frequency. Enzyme activities generally depended on soil moisture and temperature, but nature of relationships varied among different practices. Nutrient demand appeared to be the strongest driver of alkaline phosphatase and urease, and soil temperature for glycine-aminopeptidase. Under CTR-CTW, activities of most of the extracellular enzymes were related with β-d-glucosidase or urease, but such relations altered under rest of the practices. The study showed that extracellular soil enzymes respond sensitively to tillage practices as well as environmental variables, particularly soil temperature and moisture and hence can serve as a sensitive indicator of changes in soil processes. Considering improvement in microbial biomass and enzymatic activities as indicators of better soil quality, adoption of no tillage apparently improved soil quality. Still, more number of field studies are required under tillage managements to explore the relationships between different enzyme activities and environmental factors.

Soil organic carbon fractions as influenced by vegetation type and land management: A case study in semiarid rangelands of Hamedan, Iran

Soil is an environmental component permanently changing due to the often cyclic processes of litter supply and vegetation cover. To investigate the influence of vegetation type on soil carbon fractions, six vegetation types, including rainfed wheat (RW), grasses (G), Astragallus–Bromus (A-B), Astragallus–lactuca (A-L), Astragallus–Artemisi (A-A), Astragallus–Euphorbia (A-E) were studied in similar environmental conditions in terms of parent material and slope aspect in Gonbad watershed, Hamadan. Total organic carbon (TOC), active carbon (AC), soil carbohydrates (Ch) and basal respiration (BR) were measured in surface soils (0-15 cm) in fall and spring. TOC, CH, and BR were significantly greater in A-B and A-A than other covers. A-B and A-A showed higher vegetation cover and litter compared to other types. TOC and Ch in RW and G were significantly lower than other types. The highest (711.7 mg/kg) and lowest (262.6 mg/kg) AC were observed in A-B and RW, respectively. RW had lowest values of selected soil quality indicators due to tillage and cultivation. The content of TOC and AC were significantly higher in spring than autumn. Amount of BR and Ch showed no significant difference in the two seasons. Significant positive correlations were observed between soil quality indicators, these correlations were stronger in spring than in autumn. In autumn, the highest correlations were observed between AC and Ch (0.701), as well as AC and BR (0.441). In spring, significant correlations were observed between all soil quality indicators at 1% level. It was concluded that AC and Ch are the most sensitive soil quality indicators that reflect land use and vegetation type differences.

Effects of soil C:N on growth and distribution of nitrogen and carbon of Malus hupehensis seedlings

Aims Soil C:N is a sensitive indicator of soil quality and an indicator for assessing carbon and nitrogen nutrition balance of soils. Our objective was to explore the effects of soil C:N on growth and distribution of nitrogen and carbon of Malus hupehensis seedlings.Methods Using the track technology of C and N double mark, we investigated growth parameters(height, stem diameter and dry matter of different organs),15N parameters(absorption, N derived from fertilizer, distribution and utilization) and13C parameters(distribution in different organs) of two-year old M. hupehensis seedlings under six different soil C:N treatments(T1–T6 were 4.70, 9.78, 14.70, 19.96, 25.60 and 28.83, respectively).Important findings With increase of soil C:N, dry matter of roots increased significantly, while the height, stem diameter and dry matter of above ground parts and total plant increased at first and then decreased. The highest value appeared in the T4 treatment. There were significant differences in15N utilization efficiency among the six different treatments.15N utilization efficiency increased from T1 to T4, and the rate of T4(18.46%) was 1.73 times than that of T1. But, the15N utilization efficiency decreased with a further increase of soil C:N, as the rate of T5and T6 reduced that of T4 by 1.59% and 2.58%, respectively. In the two lower soil C:N treatments(T1 and T2),the order of Ndff value(15N derived from fertilizer) in the organs was roots leaves stems. With increase of soil C:N, Ndff value in leaves was the highest, followed by roots and stems.15N distribution ratio in leaves increased,while13C distribution decreased with increase of soil C:N, but the changes were the opposite in roots. Considering plant growth and utilization of nitrogen, the suitable soil C:N was 21–23 under these experimental conditions.

Can Soil Organic Carbon Pools Indicate the Degradation Levels of Pastures in the Atlantic Forest Biome?

In Brazil, a large part of the Atlantic Forest was deforested in pastures, which were developed on the basis of natural fertility and organic matter content of the new deforested soil. However, as time went by the organic matter content in these areas have been decreasing causing soil degradation. The objective of this study was to evaluate the organic matter as a quality indicator of Ultisols in different levels of pasture degradation in the region of Governador Valadares-MG. Four sites of pastures were chosen at different levels of degradation, observed visually, two capoeiras in different stages of natural recovery and forest site (reference). Soil samples were collected at three depths (0.00-0.05, 0.05-0.10 and 10-0.20 m) in two seasons of the year (rainy and dry seasons) in the middle third of the landform with three replicates. The following attributes were determined: soil organic C, free light fraction, particulate organic matter, particulate organic C, mineral-associated organic C and dissolved organic matter. The experimental results showed that the soil organic matter appeared efficient in discriminating soil quality between degraded forest/pasture, as well as between degraded capoeira/pasture. But, it was not sensitive to discriminate within levels of degraded pastures. Among the organic matter pools studied, the most sensitive soil quality indicators were: particulate organic matter and dissolved organic matter, in the following degraded order verified from these indicators: forest < capoeira 1 = capoeira 2 < pastures (1, 2, 3 and 4).

Temporal changes of Collembola population and alterations of life history parameters and acetylcholinesterase and superoxide dismutase activities in Cyphoderus javanus (Collembola) as biomarkers of fly ash pollution in lateritic soil

Fly ash is applied in agricultural fields to improve soil quality and crop yield; however, there are concerns regarding environmental hazards and toxicity to ecologically important soil organisms. The soil microarthropod fauna is a vital component of detritus food web, and major groups like Collembola are sensitive indicators of soil quality; however, information is scanty on their biomarker potentials against xenobiotics in tropical soils. The present study was aimed to evaluate temporal changes of Collembola population in fly ash amended field plots, and assess the biomarker potentials of life history parameters and biochemical responses such as acetylcholinesterase (AChE) and superoxide dismutase (SOD) activities in Cyphoderus javanus Borner (Collembola, Insecta), exposed to fly ash treated soil in microcosms. The field study using 5% (50 t ha−1) and 20% (200 t ha−1) doses of fly ash revealed dose-dependent and persistent decline in the density and relative abundance of Collembola population in sandy loam lateritic soil. The microcosm experiments showed negligible lethal effect of fly ash on C. javanus, but major life history parameters namely survival success, fecundity, and molting were significantly inhibited by fly ash treatments. The activity of AChE was downregulated, whereas activity of SOD was upregulated within 7 days of exposure of C. javanus to fly ash treated soil. These biological and biochemical parameters in Collembola are potential biomarkers, and therefore, the effects of fly ash are significant in C. javanus, an ecologically relevant species in the tropical soils of India.

The Effect of Different Flooding Duration on Soil Organic Carbon and its Labile Fraction in the Riparian Zone of Three Gorges Reservoir Area

The labile fractions of organic carbon (OC) in soil can respond rapidly to changes in C supply and have been suggested as a sensitive indicator of soil quality. The object is to determine soil organic C and its labile fractions at the duration of different flooding. Three elevation gradient sites were chose: below 145m (permanently flooding site), 145-175m (seasonal flooding site), and above 175m (never flooding site) in the riparian zone of Three Gorges reservoir Area. The results showed that soil OC, dissolved organic C (DOC) and water-soluble carbohydrate (WSCh) were lower under seasonal flooding sites than those of never flooding upland and permanently flooding sites, whereas microbial biomass C (MBC) decreased with the flooding duration. Correlation analysis showed that soil OC and MBC had significantly positive relationship with DOC. The results suggested that seasonal flooding significantly affected soil OC and its labile fractions in the riparian zone of Three Gorges reservoir Area.

Characteristics of Soil Organic Carbon, Total Nitrogen, and C/N Ratio in Chinese Apple Orchards

Soil organic carbon and nitrogen are used as indexes of soil quality assessment and sustainable land use management. At the same time, soil C/N ratio is a sensitive indicator of soil quality and for assessing the carbon and nitrogen nutrition balance of soils. We studied the characteristics of soil organic carbon and total nitrogen by investigating a large number of apple orchards in major apple production areas in China. High apple orchard soil organic carbon content was observed in the provinces of Heilongjiang, Xinjiang, and Yunnan, whereas low content was found in the provinces of Shandong, Henan, Hebei, and Shaanxi, with the values ranging between 6.44 and 7.76 g·kg-1. Similar to soil organic carbon, soil total nitrogen content also exhibited obvious differences in the 12 major apple producing provinces. Shandong apple orchard soil had the highest total nitrogen content (1.26 g·kg-1), followed by Beijing (1.23 g·kg-1). No significant difference was noted between these two regions, but their total nitrogen content was significantly higher than the other nine provinces, excluding Yunnan. The soil total nitrogen content for Xinjiang, Heilongjiang, Hebei, Henan, and Gansu was between 0.87 and 1.03 g·kg-1, which was significantly lower than that in Shandong and Beijing, but significantly higher than that in Liaoning, Shanxi, and Shaanxi. Six provinces exhibited apple orchard soil C/N ratio higher than 10, including Heilongjiang (15.42), Xinjiang (13.38), Ningxia (14.45), Liaoning (12.24), Yunnan (11.03), and Gansu (10.63). The soil C/N ratio was below 10 in the remaining six provinces, in which the highest was found in Shaanxi (9.47), followed by Beijing (8.98), Henan (7.99), and Shanxi (7.62), and the lowest was found in Hebei (6.80) and Shandong (6.05). Therefore, the improvement of soil organic carbon should be given more attention to increase the steady growth of soil C/N ratio.

Evaluación de la calidad del suelo tras la implantación de cubiertas permanentes en viñedos de zonas semiáridas. Materia orgánica y propiedades físicas y biológicas del suelo

El establecimiento de cubiertas vegetales permanentes (PGC) en viñedos de zonas semiáridas, con manejo tradicional de suelo desnudo mediante laboreo y aplicación de herbicidas, es controvertido, porque tiene ventajas agronómicas y ambientales, pero puede inducir cambios negativos en la calidad física del suelo. Los objetivos de este trabajo fueron: (i) avanzar en el conocimiento del efecto de la implantación de PGC en la calidad física y biológica del suelo, e (ii) identificar los indicadores de calidad del suelo más apropiados para suelos calizos de viñedo en una zona semiárida. Se determinaron propiedades físicas y biológicas clave en un Calcisol Cámbico con PGC de diferente edad (1 y 5 años), con un control manejado convencionalmente. El análisis de correlaciones mostró una relación directa entre la estabilidad estructural (WSA), la capacidad de retención de agua útil (AWC), la biomasa microbiana y las actividades enzimáticas del suelo bajo PGC. El contenido de C orgánico total (SOC) y lábil (POM-C) estuvo también correlacionado con los parámetros microbianos. Los indicadores de calidad del suelo más sensibles se identificaron mediante análisis factorial por componentes principales (PCA). La actividad de lombrices, AWC, WSA, SOC y POM-C mostraron el mayor peso en los dos factores obtenidos con PCA, por lo que estas propiedades pueden considerarse indicadores adecuados de la calidad del suelo en este agrosistema. Estos resultados indican que tanto los atributos físicos como biológicos del suelo son diferentes bajo PGC, y necesitan ser evaluados al estudiar las consecuencias de su introducción en suelos de viñedo.

Assessing soil quality indicator under different land use and soil erosion using multivariate statistical techniques

Soil degradation associated with soil erosion and land use is a critical problem in Iran and there is little or insufficient scientific information in assessing soil quality indicator. In this study, factor analysis (FA) and discriminant analysis (DA) were used to identify the most sensitive indicators of soil quality for evaluating land use and soil erosion within the Hiv catchment in Iran and subsequently compare soil quality assessment using expert opinion based on soil surface factors (SSF) form of Bureau of Land Management (BLM) method. Therefore, 19 soil physical, chemical, and biochemical properties were measured from 56 different sampling sites covering three land use/soil erosion categories (rangeland/surface erosion, orchard/surface erosion, and rangeland/stream bank erosion). FA identified four factors that explained for 82 % of the variation in soil properties. Three factors showed significant differences among the three land use/soil erosion categories. The results indicated that based upon backward-mode DA, dehydrogenase, silt, and manganese allowed more than 80 % of the samples to be correctly assigned to their land use and erosional status. Canonical scores of discriminant functions were significantly correlated to the six soil surface indices derived of BLM method. Stepwise linear regression revealed that soil surface indices: soil movement, surface litter, pedestalling, and sum of SSF were also positively related to the dehydrogenase and silt. This suggests that dehydrogenase and silt are most sensitive to land use and soil erosion.

Assessing impacts of copper on soil enzyme activities in regard to their natural spatiotemporal variation under long-term different land uses

Enzymes are known to be sensitive indicators of soil quality. Nevertheless, the natural variability of their activities needs to be considered for a relevant interpretation of activity levels, especially in contaminated soils. We first monitored the variability of enzymatic activities (acid and alkaline phosphatases, β-glucosidase, N-acetyl-β-glucosaminidase, urease and dehydrogenase) in two agricultural sites in north-western France during a seasonal April–October cycle. For both sites, two types of long-term different agricultural managements, grassland and intensive cropping were considered. Our results revealed great variability of enzymatic activities in space and over time, yet more pronounced for grassland than for cropped soils. Then, we assessed the impact of copper on enzymes activity on Terrestrial Model Ecosystems (TMEs) filled with undisturbed soil, and incubated for 70 days in open-field conditions. Copper was added at two concentration levels corresponding to a regulated annual agronomic input (2 mg kg−1) or to a high soil contamination (200 mg kg−1). In comparison to effects of natural spatiotemporal variability of soil conditions, copper addition did not show significant impacts on enzymatic activities. Finally, our results confirmed that for assessing effective impacts of contaminants in soils under real field conditions, natural spatiotemporal soil variability must be considered.

Soil quality indicator responses to row crop, grazed pasture, and agroforestry buffer management

Soil enzyme activities and water stable aggregates have been identified as sensitive soil quality indicators, but few studies exist comparing those parameters within buffers, grazed pastures and row-crop systems. Our objective was to examine the effects of these land uses on the activities of selected enzymes (β-glucosidase, β-glucosaminidase, fluorescein diacetate (FDA) hydrolase, and dehydrogenase), proportion of water stable aggregates (WSA), soil organic carbon and total nitrogen content. Four management treatments [grazed pasture (GP), agroforestry buffer (AgB), grass buffer (GB) and row crop (RC)] were sampled in 2009 and 2010 at two depths (0 to 10- and 10 to 20-cm) and analyzed. Most of the soil quality indicators were significantly greater under perennial vegetation when compared to row crop treatments. Although there were numerical variations, soil quality response trends were consistent between years. The β-glucosaminidase activity increased slightly from 156 to 177 μg PNP g−1 dry soil while β-glucosidase activity slightly decreased from 248 to 237 μg PNP g−1 dry soil in GB treatment during 2 years. The surface (0–10 cm depth) had greater enzyme activities and WSA than sub-surface (10–20 cm) samples. WSA increased from 178 to 314 g kg−1 in row crop areas while all other treatments had similar values during the 2 year study. The treatment by depth interaction was significant (P < 0.05) for β-glucosidase and β-glucosaminidase enzymes in 2009 and for dehydrogenase and β-glucosaminidase in 2010. Soil enzyme activities were significantly correlated with soil organic carbon content (r ≥ 0.94, P < 0.0001). This is important because soil enzyme activities and microbial biomass can be enhanced by perennial vegetation and thus improve several other soil quality parameters. These results also support the hypothesis that positive interactions among management practices, soil biota and subsequent environmental quality effects are of great agricultural and ecological importance.

SEASONAL AND TEMPORAL VARIATION IN SOIL MICROBIAL BIOMASS C, N AND P IN DIFFERENT TYPES LAND USES OF DRY DECIDUOUS FOREST ECOSYSTEM OF UDAIPUR, RAJASTHAN, WESTERN INDIA

The soil microbial biomass of soil is being increa sing recognized as sensitive indicator of soil quality. Its knowledge is fundamental for sustainab le environment management. The soil microbial biomass C, N and P were studied in four different l and uses of dry tropical forest of Udaipur, Rajasth an, Western India to assess the influence of abiotic, p hysico-chemical variables and difference in differe nt land uses (mixed forest, butea plantation, grasslan d and agricultural lands) on the seasonal variation in soil microbial biomass. Microbial biomass C, N and P were highest during rainy season and lowest durin g winter in all the four different land use with the exception of microbial N which was lowest in summer in mixed forest and butea plantation. Microbial biomas s C and N were shown to be significantly correlated to the abiotic and physico-chemical variables of th e soil, such as soil temperature, relative humidity , soil moisture, organic C, total N, clay, and pH. Present study clearly shows that land use has a significan t effect on microbial biomass C, N and P in soil by a ltering natural soil characteristics under the same ecological conditions.

ROTATION IN CONSERVATION AGRICULTURE SYSTEMS OF ZAMBIA: EFFECTS ON SOIL QUALITY AND WATER RELATIONS

SUMMARYConservation agriculture (CA) systems are based on minimal soil disturbance, crop residue retention and crop rotation. Although the capacity of rotations to break pest and disease cycles is generally recognized, other benefits of crop rotations in CA systems are seldom acknowledged and little understood. We monitored different conventional and CA cropping systems over the period from 2005 to 2009 in a multi-seasonal trial in Monze, southern Zambia. Both monocropped maize and different maize rotations including cotton and the green manure cover crop sunnhemp (Crotalaria juncea) were compared under CA conditions, with the aim of elucidating the effects of crop rotations on soil quality, soil moisture relations and maize productivity. Infiltration, a sensitive indicator of soil quality, was significantly lower on conventionally ploughed plots in all cropping seasons compared to CA plots. Higher water infiltration rate led to greater soil moisture content in CA maize treatments seeded after cotton. Earthworm populations, total carbon and aggregate stability were also significantly higher on CA plots. Improvements in soil quality resulted in higher rainfall use efficiency and higher maize grain yield on CA plots especially those in a two- or three-year rotation. In the 2007/08 and 2008/2009 season, highest yields were obtained from direct-seeded maize after sunnhemp, which yielded 74% and 136% more than maize in the conventionally ploughed control treatment with a continuous maize crop. Even in a two-year rotation (maize-cotton), without a legume green manure cover crop, 47% and 38% higher maize yields were recorded compared to maize in the conventionally ploughed control in the two years, respectively. This suggests that there are positive effects from crop rotations even in the absence of disease and pest problems. The overall profitability of each system will, however, depend on markets and prices, which will guide the farmer's decision on which, if any, rotation to choose.

Effect of tillage system and straw management on organic matter dynamics

The choice of cultivation system in arable agriculture exerts a strong influence not only on soil health and crop productivity but also on the wider environment. Conservation tillage using non-inversion methods conserves soil carbon, reduces erosion risk and enhances soil quality. In addition, conservation tillage has been shown to sequester more carbon within the soil than inversion tillage, reducing carbon dioxide losses to the atmosphere. Stable, well structured topsoils that develop following long-term conservation tillage lead to more energy efficient systems due to the reduced power requirements for cultivation. Long-term experiments, e.g. more than 20 years, that confirm the impact of conservation tillage over an extended period are not common. Here we evaluate the impact of different tillage methods and winter wheat straw management, either incorporated or removed, on organic matter turnover and soil quality indicators. No-till, chisel and mouldboard ploughing was carried out for 23 years on a silty clay loam soil in South West England that was not considered suitable for non-inversion tillage due to weak soil structure. In order to assess the effect of contrasting cultivation and straw disposal method on soil carbon dynamics, a range of assays were conducted, including water extractable organic carbon, hot water extractable carbohydrate, microbial biomass carbon, activity of β-glucosidase and acid phosphatase enzymes, C sequestration and the natural abundance of 13C. Our results show that the soil organic carbon concentration in the topsoil was greater under no-till than mouldboard ploughing, while a reverse trend was observed in the lower depths. A 14–17% increase in soil organic carbon was observed in the topsoil for chisel plough and no-till treatments compared to mouldboard ploughing. Water extractable organic carbon was found to constitute only 1–7% of the microbial biomass carbon. Hot water extractable carbohydrate was one of the most sensitive indicators of soil quality and had a significant a negative correlation with bulk density and positive correlation with soil organic carbon microbial biomass carbon β-glucosidase and acid phosphatase. The choice of cultivation method exerted a major control on microbial and carbon dynamics. No-till and chisel ploughing maintained carbon in the soil surface horizons, which will benefit the stability of this weakly structured soil, but mouldboard ploughing distributed carbon more uniformly throughout the soil profile, particularly when straw was incorporated, hence leading to the retention of more carbon in the soil profile.

The conversion of overgrazed pastures to almond orchards and alfalfa cropping systems may favor microbial indicators of soil quality in Central Iran

Land use changes may have a major influence on soil quality that is important in sustaining ecosystem productivity. Yet, the effects of these changes on soil quality are not well understood, particularly in poor heterogeneous pastures overgrazed by sheep. The aim of this study was to determine the short-term response of soil quality indicators to changes in land use from permanent pastures overgrazed to almond orchards and then to alfalfa cropping systems occurring in Saman plain, Central Iran. Soil quality indicators were evaluated in four land use systems including permanent pastures (PP) overgrazed by sheep, pastures converted to almond orchards (AO) for more than 45 years, almond orchards converted to alfalfa fields for 5 years (FA) and almond orchards converted to alfalfa fields for 2 years (TA). Composite soil samples from each of the four random replicates of the land use systems were sampled to a depth of 30 cm, and analyzed for soil bulk density, total N, total organic C, wet aggregate stability, C mineralization, microbial biomass C, and phosphatase activities. Land use changes (i.e. conversion of pastures to almond orchards and then to alfalfa fields) resulted in significant increases in soil bulk density, and total organic C and N contents. Similarly, total organic C and N pools were far greater in TA and FA compared to PP and AO land use systems. The soil porosity and aggregate stability (MWD) in PP and AO land use systems were significantly greater than those in TA and FA land use systems. Carbon mineralization and microbial biomass C and the activity of acid and alkaline phosphatases were substantially higher in the alfalfa fields than those in overgrazed pastures and almond orchards. The microbial metabolic quotient ( qCO 2) increased in alfalfa fields, although the increases were marginal. It would appear that (1) the conversion of poor pastures to alfalfa cropping systems favors soil microbial properties, (2) microbial properties are the most sensitive soil quality indicators responding positively to short-term changes in land use. It is also concluded that improvement in soil quality and enhanced biological activity in alfalfa fields demonstrated the gradual resilience of the poor and overgrazed pastures once converted to a fast growing and N 2 fixing legume crop.

The application of bioassays as indicators of petroleum-contaminated soil remediation

Bioremediation has proven successful in numerous applications to petroleum contaminated soils. However, questions remain as to the efficiency of bioremediation in lowering long-term soil toxicity. In the present study, the bioassays Spirotox, Microtox ®, Ostracodtoxkit F™, umu-test with S-9 activation, and plant assays were applied, and compared to evaluate bioremediation processes in heavily petroleum contaminated soils. Six higher plant species ( Secale cereale L., Lactuca sativa L., Zea mays L., Lepidium sativum L., Triticum vulgare L., Brassica oleracea L.) were used for bioassay tests based on seed germination and root elongation. The ecotoxicological analyses were made in DMSO/H 2O and DCM/DMSO soil extracts. Soils were tested from two biopiles at the Czechowice oil refinery, Poland, that have been subjected to different bioremediation applications. In biopile 1 the active or engineered bioremediation process lasted four years, while biopile 2 was treated passively or non-engineered for eight months. The test species demonstrated varying sensitivity to soils from both biopiles. The effects on test organisms exposed to biopile 2 soils were several times higher compared to those in biopile 1 soils, which correlated with the soil contaminants concentration. Soil hydrocarbon concentrations indeed decreased an average of 81% in biopile 1, whereas in biopile 2 TPH/TPOC concentrations only decreased by 30% after eight months of bioremediation. The bioassays were presented to be sensitive indicators of soil quality and can be used to evaluate the quality of bioremediated soil. The study encourages the need to combine the bioassays with chemical monitoring for evaluation of the bioremediation effectiveness and assessing of the contaminated/remediated soils.

The Humus Content and Soil Biological Properties as a Function of Organic and Mineral Fertilization

There is a growing recognition for the need to develop sensitive indicators of soil quality that reflect the effects of land management on soil and assist land users in promoting sustainability of agro-ecosystems. Three soil enzymes (dehydrogenase, phosphatase and invertase) microbial biomass as biological variables and soil organic matter content (SOM) were investigated relative to fertilization and soil fertility (estimated by crop yield) at a long-term fertilization trial (Keszthely, Hungary). 0-34.7-69.4-104.1t farmyard manure (FYM) ha m 1 5 yr m 1 and the corresponding amount of mineral fertilizers (NPK) were applied in two different crop rotation systems. There were four straw and/or stalk incorporating treatments in the second crop rotation 'B'. Enzyme activities, microbial biomass and the amount of SOM were generally higher in the fertilized soils than in the unfertilized soils. The type of amendments (mineral, FYM or mixed) had significant effects only on the amount of SOM. The correlations among the biological variables and the crop yield were generally low (r < 0.250. The differences in field management resulted only in the invertase activity.

International approach to assessing soil quality by ecologically-related biological parameters

Soil quality represents an integral value of the compositional structures and natural functions of soil in relation to soil use and environmental conditions on site. Among the indigenous soil components, different organisms and especially microorganisms play a key role in ecologically important biogeochemical processes. In that way, soil microorganisms contribute to the maintenance of the matter and energy transfer in terrestrial environments. Under stress conditions caused by adverse anthropogenic effects such as dissemination of chemical pollutants, the development and biochemical activities of soil microorganisms undergo several alterations. To prevent negative ecological consequences, microbiologically-related parameters should be involved in the indication of soil quality. In order to indicate some reliable indicators, an international project was established in which scientists from the Czech Republic, Hungary, Russia, Slovak Republic and Germany were participating. Standardized methods for selected microbiological and biochemical soil parameters were repeatedly applied in the individual laboratories on soil samples from rather unaffected and anthropogenically-affected soil sites (49 in total). After evaluation of more than 20 individual parameters it was concluded that N2-fixing bacteria, total microbial biomass, soil respiration, dehydrogenase activity, and perhaps also the humification activity of soil microorganisms could serve as sensitive indicators of soil quality. Further research is necessary, however, to recognize critical limits with respect to the different soil types and uses. Seasonal oscillations in ecologically-related soil biological activities which regularly occur should be appropriately respected.