Key Soil Quality Indicators Research Articles

Direct measurement and prediction of bulk density on alluvial soils of central Chile

The significance of soil bulk density ( rb) as a key indicator of soil quality was examined in this study. Bulk density values obtained by direct methods (clod, cylinder, and excavation) with three sample sizes (small, medium, and large) were compared with those obtained by 10 published pedotransfer functions (PTFs) for two alluvial soils (a massive fine-textured Fluventic Haploxeroll and an aggregated, coarse-textured Fluventic Haploxerept) of central Chile. With the exception of small cylinders in fine-textured soil, there were nonsignificant differences between the methods and sample sizes assessed. On the coarse-textured soil, there were nonsignificant differences between the excavation and clod methods, but mediumsized cylinders differed from other cylinder sizes. In general, the clod technique tended to give higher values than the other methods. Using basic information (texture and organic matter/C content) from the existing PTFs for both sites, a better fit for coarse-textured than fine-textured soils was obtained. This indicates that it is necessary to define a set of locally calibrated PTFs that address the complexity of the soil resource throughout Chile.

Soil respiration dynamics in fire affected semi-arid ecosystems: Effects of vegetation type and environmental factors

Soil respiration (Rs) is the second largest carbon flux in terrestrial ecosystems and therefore plays a crucial role in global carbon (C) cycling. This biogeochemical process is closely related to ecosystem productivity and soil fertility and is considered as a key indicator of soil health and quality reflecting the level of microbial activity. Wildfires can have a significant effect on Rs rates and the magnitude of the impacts will depend on environmental factors such as climate and vegetation, fire severity and meteorological conditions post-fire. In this research, we aimed to assess the impacts of a wildfire on the soil CO2 fluxes and soil respiration in a semi-arid ecosystem of Western Australia, and to understand the main edaphic and environmental drivers controlling these fluxes for different vegetation types. Our results demonstrated increased rates of Rs in the burnt areas compared to the unburnt control sites, although these differences were highly dependent on the type of vegetation cover and time since fire. The sensitivity of Rs to temperature (Q10) was also larger in the burnt site compared to the control. Both Rs and soil organic C were consistently higher under Eucalyptus trees, followed by Acacia shrubs. Triodia grasses had the lowest Rs rates and C contents, which were similar to those found under bare soil patches. Regardless of the site condition (unburnt or burnt), Rs was triggered during periods of higher temperatures and water availability and environmental factors (temperature and moisture) could explain a large fraction of Rs variability, improving the relationship of moisture or temperature as single factors with Rs. This study demonstrates the importance of assessing CO2 fluxes considering both abiotic factors and vegetation types after disturbances such as fire which is particularly important in heterogeneous semi-arid areas with patchy vegetation distribution where CO2 fluxes can be largely underestimated.

Effect of Organic Manure and Crop Residue Based Long-Term Nutrient Management Systems on Soil Quality Changes under Sole Finger Millet (Eleusine coracana (L.) Gaertn.) and Groundnut (Arachis hypogaea L.) – Finger Millet Rotation in Rainfed Alfisol

ABSTRACTA long-term experiment was conducted to evaluate the effect of integrated use of organic and inorganic sources of nutrients on soil quality and its relation to finger millet yield under two predominant crop rotations viz., groundnut–finger millet and finger millet monocropping in hot moist semiarid rainfed Alfisol soils in South India. Two experiments were laid out separately for each cropping system in a randomized complete block design with five treatments individually with FYM and maize residue-based combinations viz., Control (T1), FYM @ 10t ha −1 or Maize residue (MR) @ 5t ha −1 (T2), farm yard manure (FYM) @ 10t ha −1 or Maize residue (MR) @ 5t ha −1 + 50% RDF (Recommended Fertiliser Dose) N, P2O5 & K2O (T3), FYM @ 10t ha −1 or Maize residue (MR) @ 5t ha −1 + 100% RDF N,P2O5 & K2O (T4), Recommended N, P2O5 & K2O (T5). Thus, four sets of nutrient management systems were evaluated. The results showed that farm yard manure or maize residue application in combination with recommended dose of fertilizer significantly improved the soil physical, chemical, and biological properties compared to control and application of inorganic fertilizers alone. Based on evaluation of 19 soil quality parameters under each of the four nutrient management systems, the common key soil quality indicators emerged out were: organic C (OC), available nitrogen (N), available sulfur (S), and mean weight diameter (MWD) of soil aggregates. A significant correlation between the finger millet yield and the relative soil quality indices (RSQI) indicates the importance of soil quality in these semiarid Alfisol soils. The results and the methodology adopted in the present study could be of importance in improving the soil quality not only for the region of the study, but also in other identical soils and cropping systems across the world.

Effects of land use and land cover on selected soil quality indicators in the headwater area of the Blue Nile basin of Ethiopia.

Understanding changes in soil quality resulting from land use and land management changes is important to design sustainable land management plans or interventions. This study evaluated the influence of land use and land cover (LULC) on key soil quality indicators (SQIs) within a small watershed (Jedeb) in the Blue Nile Basin of Ethiopia. Factor analysis based on principal component analysis (PCA) was used to determine different SQIs. Surface (0-15 cm) soil samples with four replications were collected from five main LULC types in the watershed (i.e., natural woody vegetation, plantation forest, grassland, cultivated land, and barren land) and at two elevation classes (upland and midland), and 13 soil properties were measured for each replicate. A factorial (2 × 5) multivariate analysis of variance (MANOVA) showed that LULC and altitude together significantly affected organic matter (OM) levels. However, LULC alone significantly affected bulk density and altitude alone significantly affected bulk density, soil acidity, and silt content. Afforestation of barren land with eucalypt trees can significantly increase the soil OM in the midland part but not in the upland part. Soils under grassland had a significantly higher bulk density than did soils under natural woody vegetation indicating that de-vegetation and conversion to grassland could lead to soil compaction. Thus, the historical LULC change in the Jedeb watershed has resulted in the loss of soil OM and increased soil compaction. The study shows that a land use and management system can be monitored if it degrades or maintains or improves the soil using key soil quality indicators.

Organic amendment influences soil quality in farmers’ field under rice-based cropping systems in Indo-gangetic plains of India

Indexing soil quality and identification of key soil indicators are essential for maintaining sustainability of agricultural soils. A minimum data set was developed for soils collected from farmers’ field under long-term rice-potato-sesame (R-P-S) and rice-wheat (R-W) cropping systems with NPK and NPK + organic amendment (FYM) under Alfisols in Indo-Gangetic Plains of India. Soil samples (40 geo-referenced) were collected at 0–0.20 m depth from the fields following the same cropping systems for the last ten years. The samples were analyzed for a large number of physical, chemical and biological attributes. The multivariate statistical analysis showed that out of the 38 attributes, organic C, aggregate ratio, microbial biomass C (Cmic), available zinc and β-glucosidase (β-glu) activity were screened as key indicators of soil quality for soils under R-P-S system; whereas, very labile C, mineralizable C and N (Cmin and Nmin), and β-glu activity were found as key indicators of soil quality for soils under R-W cropping system. The overall results indicated that oxidizable organic C and its labile fractions viz., very labile C, Cmic or Cmin and the C-cycle regulating enzyme viz., β-glu activity are the process based key master indicators for the assessment of soil quality. Application of organic amendment with inorganic fertilizer always maintained higher soil quality index for soils under long-term R-P-S and R-W cropping systems.

Soil quality index for evaluation of reclaimed coal mine spoil

Success in the remediation of mine spoil depends largely on the selection of appropriate tree species. The impacts of remediation on mine soil quality cannot be sufficiently assessed by individual soil properties. However, combination of soil properties into an integrated soil quality index provides a more holistic status of reclamation potentials of tree species. Remediation potentials of four tree species (Acacia auriculiformis, Cassia siamea, Dalbergia sissoo, and Leucaena leucocephala) were studied on reclaimed coal mine overburden dumps of Jharia coalfield, Dhanbad, India. Soil samples were collected under the canopies of the tree species. Comparative studies on the properties of soils in the reclaimed and the reference sites showed improvements in soil quality parameters of the reclaimed site: coarse fraction (−20.4%), bulk density (−12.8%), water holding capacity (+0.92%), pH (+25.4%), EC (+2.9%), cation exchange capacity (+46.6%), organic carbon (+91.5%), N (+60.6%), P (+113%), K (+19.9%), Ca (+49.6%), Mg (+12.2%), Na (+19.6%), S (+46.7%), total polycyclic aromatic hydrocarbons (−71.4%), dehydrogenase activity (+197%), and microbial biomass carbon (+115%). Principal component analysis (PCA) was used to identify key mine soil quality indicators to develop a soil quality index (SQI). Selected indicators include: coarse fraction, pH, EC, soil organic carbon, P, Ca, S, and dehydrogenase activity. The indicator values were converted into a unitless score (0–1.00) and integrated into SQI. The calculated SQI was significantly (P<0.001) correlated with tree biomass and canopy cover. Reclaimed site has 52–93% higher SQI compared to the reference site. Higher SQI values were obtained for sites reclaimed with D.sissoo (+93.1%) and C.siamea (+86.4%).

Soil Quality in Relation to Agricultural Production in the North China Plain

Sustainable agricultural production is of vital importance to food supply security. This study aimed to investigate crop yield response to spatial variability of soil quality at a county scale in the North China Plain (NCP) and subsequently derive key soil quality indicators. Soil samples were geo-referenced and taken in 2008 from both surface (0–20 cm) and subsurface (20–40 cm) layers in 132 fields throughout the Fengqiu County, located in the centre of the NCP, for subsequent soil properties' analyses. Annual crop yields were obtained from the same fields where soil samples were collected. Soil quality was evaluated based on a fuzzy set with 13 soil properties, and its spatial distributions were investigated by integrating geostatistical analysis and geographic information system (GIS) techniques. Soil quality indices were classified into five grades, and their spatial distributions were mapped within the county. The surface soil qualities were about one to two grades higher than the subsurface soil. The quality indices for surface and subsurface soils were positively associated with the annual crop yields, suggesting the importance of both. Soil organic matter, total nitrogen, available P, and available K contributed 50% of the combined weight to the soil quality index and were identified as key indicators of soil quality status in the area in terms of sustainability.

Evaluation of soil quality for agricultural production using visible–near-infrared spectroscopy

Soil quality (SQ) assessment has numerous applications for agricultural management. Conventional quantification of SQ is based on laboratory analysis and integrative indices that can be costly and time consuming to obtain. A rapid, quantitative method using soil spectra, following the successful process of soil characterization by visible (VIS)–near infrared (NIR) spectroscopy, can provide a robust approach for soil monitoring. ObjectiveTo predict specific soil indicator properties and soil quality indices for the productive function of the soil using VIS–NIR spectroscopy, and to evaluate the suitability of spectral data for assessing and monitoring the impact of arable and grassland management in a temperate maritime climate. MethodsThe study used 40 sites in Ireland under both arable (n=20) and grassland (n=20) management systems. Specific indicators and soil quality indices (SQIs) identified by Askari and Holden (2014) and Askari (2014) were used as the reference standard for estimation using VIS–NIR spectra. Partial least-squares regression was used to predict the indicators and SQIs. SQI was predicted from both spectrally derived indicator values and directly from the soil spectra, and accuracy was assessed by comparison with laboratory and field derived measurements. ResultsThe indicators of SQ could be predicted with excellent (soil organic carbon and carbon to nitrogen ratio in grassland soils; total nitrogen, carbon to nitrogen ratio, extractable magnesium and aggregate size distribution in arable soils), good (bulk density of <2mm fraction in grassland soils) and moderate (penetration resistance, soil respiration and bulk density in arable soils) accuracy. The SQIs were predicted directly with excellent accuracy under grassland (RPD=3.04, R2=0.92, RMSE=0.03) and arable (RPD=2.78, R2=0.89, RMSE=0.04) management. Soil structural quality class, management type and management intensity were differentiable by their characteristic reflectance. ConclusionThe reliability of SQI and key indicators of soil quality, and the ability to differentiate by management practices and soil structural quality confirmed the efficiency of VIS–NIR spectroscopy for monitoring and evaluating SQ as a reliable alternative to conventional laboratory methods. PracticeSpectroscopy has the potential to provide a reliable approach that will allow rapid, low cost, high frequency SQ monitoring for multiple purposes, and can play an important role in sustainable land management. ImplicationsVIS–NIR spectroscopy was shown to be suitable for quantitative assessment of soil quality, thus paving the way for development of an applied tool that can be used for agricultural management on the context of soil security, soil health, soil protection and soil quality.

Combined effect of tillage and organic fertilization on soil quality key indicators and indices in alluvial soils of Indo-Gangetic Plains under rainfed maize–wheat system

Inceptisols in the submountainous region of Indo-Gangetic Plains in India are known as low productive areas due to several constraints like decline in soil organic matter and fertility, deterioration of soil physical and biological properties. The present study was conducted with tillage as main treatments and integrated nutrient management as subtreatments to improve soil quality and to identify the key indicators of soil quality after 5 years of experimentation in maize–wheat cropping system at Ballowal Saunkhri. Conventional tillage (CT) + interculture (IC) maintained significantly higher soil quality indices (SQI) of 1.12 which was at par with 50% CT + IC + chemical weed control (CWC) (1.08). Application of nitrogen (N) through 50% (organic) + 50% (inorganic) maintained higher soil quality with SQI of 1.10 followed by application of 100% N through organics (1.08). The results indicated that reduction in the intensity of tillage to 50% with interculture practices and combined use of organic and inorganic fertilizers maintained higher soil quality in these degraded Inceptisols. The methods of principal component analysis and computation of SQI adopted will be highly useful to future researchers, land managers, and students at locations across the world having similar climatic and edaphic conditions.

Effects of Soil Management Practices on Key Soil Quality Indicators and Indices in Pearl Millet (Pennisetum americanum (L.) Leeke)–Based System in Hot Semi-arid Inceptisols

Rainfed Inceptisol soils, despite their agricultural potential, pose serious problems, including soil erosion, low fertility, nutrient imbalance, and low soil organic matter, and ultimately lead to poor soil quality. To address these constraints, two long-term experiments were initiated to study conservation agricultural practices, comprising conventional and low tillage as well as conjunctive use of organic and inorganic sources of nutrients in Inceptisol soils of Agra center of the All-India Coordinated Research Project for Dryland Agriculture (AICRPDA). The first experiment included tillage and nutrient-management practices, whereas the second studied only conjunctive nutrient-management practices. Both used pearl millet (Pennisetum americanum (L.) Linn) as test crop. These experiments were adopted for soil quality assessment studies at 4 and 8 years after their completion, respectively, at the Central Research Institute for Dryland Agriculture (CRIDA), Hyderabad, India. Soil quality assessment was done by identifying the key indicators using principal component analysis (PCA), linear scoring technique (LST), soil quality indices (SQI), and relative soil quality indices (RSQI). Results revealed that most of the soil quality parameters were significantly influenced by the management treatments in both the experiments. In experiment 1, soil quality indices varied from 0.86 to 1.08 across the treatments. Tillage as well as the nutrient-management treatments played a significant role in influencing the SQI. Among the tillage practices, low tillage with one interculture + weedicide application resulted in a greater soil quality index (0.98) followed by conventional tillage + one interculture (0.94), which was at par with low tillage + one interculture (0.93). Among the nutrient-management treatments, application of 100% organic sources of nutrients gave the greatest SQI of 1.05, whereas the other two practices of 50% nitrogen (N) (organic) + 50% (inorganic source) (0.92) and 100% N (inorganic source) (0.88) were statistically at par with each other. The various parameters that emerged as key soil quality indicators along with their percentage contributions toward SQI were organic carbon (17%), exchangeable calcium (Ca) (10%), available zinc (Zn) (9%), available copper (Cu) (6%), dehydrogenase assay (6%), microbial biomass carbon (25%) and mean weight diameter of soil aggregates (27%). In experiment 2, SQI varied from 2.33 to 3.47, and 50% urea + 50% farmyard manure (FYM) showed the greatest SQI of 3.47, which was at par with 100% RDF + 25 kg zinc sulfate (ZnSO4) (3.20). Under this set of treatments, the key soil quality indicators and their contributions to SQI were organic carbon (19%), available N (20%), exchangeable Ca (3%), available Zn (4%) and Cu (17%), labile carbon (20%), and mean weight diameter of soil aggregates (17%). The quantitative relationship established in this study between mean pearl millet yields (Y) and RSQI irrespective of the management treatments for both the experiments together could be quite useful to predict the yield quantitatively with respect to a given change in soil quality for these rainfed Inceptisols. The methodology used in this study is not only useful to these Inceptisols but can also be used for varying soil types, climate, and associated conditions elsewhere in the world.

Current status, uncertainty and future needs in soil organic carbon monitoring

Increasing human demands on soil-derived ecosystem services requires reliable data on global soil resources for sustainable development. The soil organic carbon (SOC) pool is a key indicator of soil quality as it affects essential biological, chemical and physical soil functions such as nutrient cycling, pesticide and water retention, and soil structure maintenance. However, information on the SOC pool, and its temporal and spatial dynamics is unbalanced. Even in well-studied regions with a pronounced interest in environmental issues information on soil carbon (C) is inconsistent. Several activities for the compilation of global soil C data are under way. However, different approaches for soil sampling and chemical analyses make even regional comparisons highly uncertain. Often, the procedures used so far have not allowed the reliable estimation of the total SOC pool, partly because the available knowledge is focused on not clearly defined upper soil horizons and the contribution of subsoil to SOC stocks has been less considered. Even more difficult is quantifying SOC pool changes over time. SOC consists of variable amounts of labile and recalcitrant molecules of plant, and microbial and animal origin that are often operationally defined. A comprehensively active soil expert community needs to agree on protocols of soil surveying and lab procedures towards reliable SOC pool estimates. Already established long-term ecological research sites, where SOC changes are quantified and the underlying mechanisms are investigated, are potentially the backbones for regional, national, and international SOC monitoring programs.

Improvement and Assessment of Soil Quality under Long-Term Conservation Agricultural Practices in Hot, Arid Tropical Aridisol

Soils in the hot, arid topical regions are low in organic matter and fertility and are structurally poor. Consequently, these soils suffer on account of poor physical, chemical, and biological soil quality traits, leading to miserably low crop yields. Long-term use of conjunctive nutrient management and conservation tillage practices may have a profound effect on improving the quality of these soils. Therefore, the objective of this study was to identify the key soil quality indicators, indices, and the best soil- and nutrient-management practices that can improve soil quality on long-term basis for enhanced productivity under a pearl millet–based system. The studies were conducted for the Hissar Centre of All-India Coordinated Research Project at the Central Research Institute for Dryland Agriculture, Hyderabad. Conjunctive nutrient-use treatments and conservation tillage significantly influenced the majority of the soil quality parameters in both the experiments. In experiment 1, the key soil quality indicators that significantly contributed to soil quality in a rainfed pearl millet–mung bean system were available nitrogen (N, 35%), available zinc (Zn; 35%), available copper (Cu; 10%), pH (10%), available potassium (K; 5%), and dehydrogenase assay (5%). The three best conjunctive nutrient-use treatments in terms of soil quality indices (SQI) were T3, 25 kg N (compost) (1.52) > T6, 15 kg N (compost) + 10 kg N (inorganic) + biofertilizer (1.49) > T5, 15 kg N (compost) + 10 kg N (green leaf manure) (1.47). In experiment 2, under a rainfed pearl millet system, the key indicators and their percentage contributions were electrical conductivity (15%), available N (19%), exchangeable magnesium (Mg; 18%), available manganese (Mn; 13%), dehydrogenase assay (19%), microbial biomass carbon (C; 5%), and bulk density (11%). The three best tillage + nutrient treatments identified from the viewpoint of soil quality were T1, conventional tillage (CT) + two intercultures (IC) + 100% N (organic source/compost) (1.74) > T3, CT + two IC + 100% N (inorganic source) (1.74) > T4, low tillage + two IC + 100% N (organic source/compost) (1.70). The findings of the present study as well as the state-of-the-art methodology adopted could be of much interest and use to the future researchers including students, land managers, state agricultural officers, growers/farmers, and all other associated stakeholders. The prediction function developed between long-term pearl millet crop yields (y) and soil quality indices (x) in this study could be of much use in predicting the crop yields with a given change in soil quality index under similar situations.

Effect of Soil and Nutrient-Management Treatments on Soil Quality Indices under Cotton-Based Production System in Rainfed Semi-arid Tropical Vertisol

Rainfed semi-arid tropical Vertisols of the Indian subcontinent encounter many problems on account of the physical, chemical, and biological soil qualities and consequently have poor crop yields. To ensure sustainable crop production, there is a need to improve and periodically assess the quality of these soils by adopting suitable soil and nutrient-management practices on a long-term basis. Hence, soil quality assessment studies were conducted at the Central Research Institute for Dryland Agriculture, Hyderabad, India, by adopting an ongoing long-term experiment from Akola Centre (Maharashtra) of All-India Coordinated Research Project for Dryland Agriculture (AICRPDA) for the rainfed Vertisol. This long-term experiment was initiated in 1987 with six soil and nutrient management treatments: T1, control; T2, 50 kg nitrogen (N) + 25 kg phosphorus pentoxide (P2O5) ha−1; T3, 25 kg N ha−1 through leuceana; T4, 25 kg N ha−1 through farmyard manure (FYM); T5, 25 kg N + 25 kg P2O5 + 25 kg N ha−1 through FYM; and T6, 25 kg P2O5 ha−1 + 50 kg N ha−1 through leuceana under cotton + greengram intercropping (1:1). Out of the 19 soil quality parameters studied, significant influence of the soil and nutrient-management treatments was observed on almost all the parameters except exchangeable calcium (Ca), available iron (Fe), labile carbon (LC), and bulk density (BD). A standard methodology using principal component analysis (PCA) and linear scoring technique (LST) was adopted to identify the key indicators and for computation of soil quality indices. The various key soil quality indicators identified for these Vertisols under cotton + green gram system were pH, electrical conductivity (EC), organic carbon (OC), available K, exchangeable magnesium (Mg), dehydrogenase assay (DHA), and microbial biomass carbon (MBC). The soil quality indices as influenced by different long-term soil and nutrient-management treatments varied from 1.46 to 2.10. Among the treatments, the conjunctive use of 25 kg P2O5 ha−1 + 50 kg N ha−1 through leuceana green biomass (T6) maintained significantly higher soil quality index with a value of 2.10 followed by use of 25 kg N + 25 kg P2O5 + 25 kg N ha−1 through FYM (T5) (2.01). The order of percent contribution of these identified indicators to soil quality indices was OC (28%) > MBC (25%) > available K (24%) > EC (7%) > pH (6%) = DHA (6%) > exchangeable Mg (4%). Thus, the findings of the present study could be of immense use to the researchers, land managers, farmers, nongovernment organizations (NGOs) and other stakeholders for making periodical assessment of key indicators of soil quality, identifying the best soil and nutrient-management treatments and practices, and planning for improving soil quality to achieve higher productivity goals on a sustainable basis in rainfed semi-arid tropical Vertisol regions. The methodology of the study could also be useful for other rainfed semi-arid tropical Vertisol regions of the world.

A review of soil quality indicators and five key issues after 12 yr soil quality monitoring in the Waikato region

AbstractAn ongoing programme of soil quality assessment in the Waikato region of New Zealand is providing baseline data and allowing identification of the impacts of land use and associated key soil quality issues. In this paper, we review the strengths and weaknesses of key soil quality indicators and provide summary statistics for chemical, physical and biochemical parameters in both background and production soils of the Waikato Region. Statistical comparison of production to background soils, time related trends, relative surface enrichments, and correlations enable us to infer likely and potential impacts of human activity on the region’s soil resource. Five key issues that cause loss of soil resource have been identified. These are soil compaction, loss of soil organic matter, excessively high fertility levels, erosion risk, and accumulation of contaminants. In addition, evidence exists for accelerated attack or weathering of aluminosilicate minerals in farmed soils [dealumination, Australian Journal Soil Research (2009) vol. 47, 828–838], a process previously only recognized in soils adjacent to aluminium smelters.

Soil quality evaluation and the interaction with land use and soil order in Tasmania, Australia

Soil quality information has been collected at 272 sites across Tasmania. Soil target values were developed for six key soil quality indicators, with values dependent on soil order and land use. The selected indicators were pH (H 2O), organic carbon, extractable phosphorus, exchangeable sodium percent, bulk density and aggregate stability. Soil quality monitoring sites were biased to agricultural land uses, which was justified due to these land uses being more likely to result in soil degradation than conservation or native forestry. Cropping and perennial horticulture land uses had a greater proportion of sites outside targets for organic carbon and bulk density than grazing pasture and forestry. Most intensively used soils were within pH targets. Aggregate stabilities at many sites were outside targets under cropping and irrigated pasture indicating that cropping sites had an increased risk of erosion. Extractable phosphorus levels were below target for most dryland pasture sites and above target for most irrigated pasture sites. Soil order explained more variability in organic carbon, aggregate stability, bulk density and ESP than land use but land use explained more of the variability in pH and Olsen P than soil order.

Comparison of Soil Organic Matter in Created, Restored and Paired Natural Wetlands in North Carolina

Soil organic matter (SOM) content is a key indicator of soil quality and is correlated to a number of important soil processes that occur in wetlands such as respiration, denitrification, and phosphorus sorption. To better understand the differences in the SOM content of created (CW), restored (RW), and paired natural wetlands (NWs), 11 CW/RW-NW pairs were sampled in North Carolina. The site pairs spanned a range of hydrogeomorphic (HGM) subclasses common in the Coastal Plain. The following null hypotheses were tested: (1) SOM content of paired CW/RWs and NWs are similar; (2) SOM content of wetlands across different HGM subclasses is similar; and (3) interactions between wetland status (CW/RW vs. NW) and hydrogeomorphic subclass are similar. The first null hypothesis was rejected as CW/RWs had significantly lower mean SOM (11.8 ± 3.9%) than their paired NWs (28.98 ± 8.0%) on average and at 10 out of the 11 individual sites. The second and third null hypotheses were also rejected as CW/RWs and NWs in the non-riverine organic soil flat subclass had significantly higher mean SOM content (31.08 ± 14.2%) than the other three subclasses (8.18 ± 2.5, 11.18 ± 8.2, and 10.38 ± 4.2%). Individual sites within this fourth subclass also had significantly different SOM content. This indicated that it would be inappropriate to include the organic soil flat subclass with either the riverine or non-riverine mineral soil flat subclasses when considering restoration guidelines. These results also suggested that if there is a choice in mitigation options between restoration or creation, wetlands should be restored rather than created, especially those in the non-riverine organic soil flat subclass.

Qualidade do solo em sistemas de manejo avaliada pela dinâmica da matéria orgânica e atributos relacionados

A matéria orgânica tem sido sugerida como um indicador-chave da qualidade do solo (QS), considerando sua influência nos demais atributos essenciais para que o solo desempenhe suas funções. Visando investigar o potencial desse indicador na avaliação de sistemas de manejo, foram utilizados dois experimentos de longa duração em Argissolos no Sul do Brasil. No primeiro, com dez anos, localizado na Universidade Federal de Santa Maria (RS), foram selecionados cinco tratamentos, sendo três sistemas de cultura (pousio/milho, azevém + vica/milho e mucuna/milho) estabelecidos sob sistema plantio direto, acrescidos de um tratamento mantido permanentemente sem plantas (solo descoberto) e mais um tratamento-referência mantido em campo natural. No segundo, com 15 anos, situado na Universidade Federal do Rio Grande do Sul, Eldorado do Sul (RS), foram avaliados os seguintes tratamentos: o sistema de cultura aveia/milho em preparo convencional sem adubação nitrogenada, o mesmo sistema (aveia/milho) em três diferentes sistemas de preparo do solo (convencional, reduzido e plantio direto) e o sistema de cultura aveia + vica/milho + caupi em plantio direto, todos os últimos quatro tratamentos com adubação nitrogenada (144 kg ha-1 ano-1 ). Neste experimento, foram ainda utilizados, como referência, uma área de campo natural e um tratamento com elevada adição de resíduos (guandu/milho). Inicialmente, os tratamentos foram hierarquizados em ordem crescente de QS, com base nos resultados disponíveis e na experiência acumulada pelos pesquisadores responsáveis pelos experimentos. Foram analisados os teores de Carbono Orgânico Total (COT) e Nitrogênio total (NT), COT e NT nas frações superiores e inferiores a 53 µm, potencial de mineralização do C e N do solo e C da biomassa microbiana. Somente as camadas de 0-5 e 0-20 cm foram utilizadas neste trabalho. A QS foi alterada pelos manejos adotados em ambas as áreas experimentais. O COT e NT, avaliados na camada de 0-5 cm, mostraram-se eficientes em discriminarem o impacto de sistemas de manejo sobre a QS, reproduzindo, em ambas as áreas, a ordenação proposta. Dentre as frações avaliadas, a &gt; 53 µm foi a mais sensível em detectar os impactos dos sistemas de manejo.

Long-term soil management effects on crop yields and soil quality in a dryland Alfisol

A long-term experiment was conducted with the objective of selecting the appropriate land management treatments and to identify the key indicators of soil quality for dryland semi-arid tropical Alfisols. The experiment was conducted using a strip split–split plot design on an Alfisol (Typic Haplustalf) in southern India under sorghum ( Sorghum vulgare (L))-castor ( Ricinus communis (L)) bean rotation. The strip constituted two tillage treatments: conventional tillage (CT) and minimum tillage (MT); main plots were three residues treatments: sorghum stover (SS), gliricidia loppings (GL), ‘no’ residue (NR) and sub plots were four nitrogen levels: 0 (N 0), 30 (N 30), 60 (N 60), and 90 kg ha −1 (N 90). Soil samples were collected after the sixth and seventh year of experimentation and were analyzed for physical, chemical and biological parameters. Sustainable yield index (SYI) based on long-term yield data and soil quality index (SQI) using principal component analysis (PCA) and linear scoring functions were calculated. Application of gliricidia loppings proved superior to sorghum stover and no residue treatments in maintaining higher SQI values. Further, increasing N levels also helped in maintaining higher SQI. Among the 24 treatments, the SQI ranged from 0.90 to 1.27. The highest SQI was obtained in CTGLN 90 (1.27) followed by CTGLN 60 (1.19) and MTSSN 90 (1.18), while the lowest was under MTNRN 30 (0.90) followed by MTNRN 0 (0.94), indicating relatively less aggradative effects. The application of 90 kg N ha −1 under minimum tillage even without applying any residue (MTNRN 90) proved quite effective in maintaining soil quality index as high as 1.10. The key indicators, which contributed considerably towards SQI, were available N, K, S, microbial biomass carbon (MBC) and hydraulic conductivity (HC). On average, the order of relative contribution of these indicators towards SQI was: available N (32%), MBC (31%), available K (17%), HC (16%), and S (4%). Among the various treatments, CTGLN 90 not only had the highest SQI, but also the most promising from the viewpoint of sustainability, maintaining higher average yield levels under sorghum–castor rotation. From the view point of SYI, CT approach remained superior to MT. To maintain the yield as well as soil quality in Alfisols, primary tillage along with organic residue and nitrogen application are needed.

Effect of military training on indicators of soil quality at Fort Benning, Georgia

Abstract The purpose of this research was to investigate the effects of soil disturbance on several key indicators of soil quality at Fort Benning, Georgia. Military activities at Fort Benning that result in soil disturbance include infantry, artillery, wheeled, and tracked vehicle training. Soil samples were collected along a disturbance gradient that included: (1) reference sites, (2) light military use, (3) moderate military use, (4) heavy military use, and (5) remediated sites. With the exception of surface soil bulk density, measured soil properties at reference and light use sites were similar. Relative to reference sites, greater surface soil bulk density, lower soil carbon concentrations, and less carbon and nitrogen in particulate organic matter (POM) were found at moderate use, heavy use, and remediated sites. Studies along a pine forest chronosequence indicated that carbon stocks in POM gradually increased with stand age. An analysis of soil C:N ratios, as well as soil carbon concentrations and stocks, indicated a recovery of soil quality at moderate military use and remediated sites relative to heavy military use sites. Measurements of soil carbon and nitrogen are ecological indicators that can be used by military land managers to identify changes in soil from training activities and to rank training areas on the basis of soil quality.

Hot-water extractable carbon in soils: a sensitive measurement for determining impacts of fertilisation, grazing and cultivation

Using pre-established trial sites on allophanic soils, we investigated the impacts of long to medium-term pastoral management practices, such as fertilisation and grazing intensity, on a range of soil biological and biochemical properties; hot water-extractable C (HWC), water-soluble C (WSC), hot-water extractable total carbohydrates, microbial biomass-C and N and mineralisable N. These properties were examined for their usefulness as soil quality indicators responding to changes in the rhizosphere caused by management practices. Adjacent cropping, market garden and native bush sites located on similar soil types were included to determine the changes in soil biological and biochemical properties resulting from changes in land use. The seasonal variability of HWC and its relationship with other labile fractions of soil organic matter was also examined. Microbial biomass-C, mineralisable N and extractable total carbohydrates showed promise in differentiating treatment and land use effects. However, HWC was one of the most sensitive and consistent indicators examined at 52 different sites. The impact of different land uses on the amounts of HWC in the same soil type was far greater than that was observed for the soil organic carbon. The average values of HWC for soil under different land use were: native (4000 μg C g −1 soil), sheep/beef pastures (3400), dairy pastures (3000), cropping (1000) and market gardening soils (850). HWC was also sensitive to differences within an ecosystem, e.g. effects of grazing intensities and effects of N or P fertilisers on pastures. The sheep and beef/cattle grazed pastures always had higher amounts of HWC than the intensively grazed dairy pastures. Nitrogen fertiliser application (200 and 400 kg N ha −1 yr −1) over the previous 5 yr had significant ( P<0.001) negative impacts on HWC and other soil microbial properties. In contrast, long-term application of P fertilisers had a significant ( P<0.001) positive effect on the HWC levels in pastoral soils. In the case of long-term P trials, HWC increased even though no increase in the total soil carbon pool was detected. HWC was positively correlated with soil microbial biomass-C ( R 2=0.84), microbial nitrogen ( R 2=0.72), mineralisable N ( R 2=0.86), and total carbohydrates ( R 2=0.88). All these correlations were significant at P<0.001 level of significance. The HWC was also positively correlated with WSC and total organic C. However, these correlations were poorer than those found for other soil parameters. Most of these measurements have been actively promoted as key indicators of soil quality. Given the strong correlations between HWC and other biochemical measurements, HWC could be used as an integrated measure of soil quality. When HWC is extracted, other pools of labile nutrients are also extracted along with C. Therefore it is suggested that decline in HWC would also indicate a decline in other labile organic pools of nutrients such as nitrogen, sulphur and phosphorus. About 40–50% of the C in the HWC extract was present as carbohydrates.