Sensitive Indicators Of Soil Quality Research Articles

Farm-Scale Mapping of Soil Microbiological Indicators Using Geostatistical Technique

Soil microbiological properties viz. soil microbial biomass carbon (MBC) and dehydrogenase activity (DHA) are sensitive soil quality indicators. Spatial modeling and prediction map of soil MBC and DHA were generated for a semiarid agricultural farm, New Delhi, India from 288 geo-referenced grid samples spaced 100 m × 100 m distance using geospatial techniques and geo-statistics. Soil microbial biomass carbon (MBC) ranged from 19.7 to 519.7 µg g-1 with standard deviation of 84.1 and soil DHA varied from 1.2 to 17.2 µg TPF g-1 dry soil hr-1 with sample variance of 10.89. Soil MBC and DHA had high data viability with coefficient of variation (CV) of 42.5 % and 53.2%, respectively. The best fit semivariogram for both soil MBC and DHA was exponential model and had practical spatial range of 1500 m and 1473 m respectively. Environmental disturbances or extrinsic factors dominantly influenced the spatial variability of soil MBC, expressing its weak spatial dependency. Besides, both soil structural/internal factors and extrinsic factors controlled soil DHA variability with moderate level of spatial dependency. Spatial variability map of soil MBC and DHA, prepared with good accuracy through ordinary kriging in GIS software, showed that major area of the farm had soil MBC ranging from 150 to 250 mg kg-1 and had DHA from 1.2 to 10 µg TPF g-1 dry soil hr-1.

Spatial change in glomalin-related soil protein and its relationships with soil enzyme activities and microbial community structures during urbanization in Nanchang, China

Rapid urbanization brings about drastic changes in land use and soil quality. Glomalin-related soil protein (GRSP), a sensitive indicator of soil quality, is possibly secreted by arbuscular mycorrhizal fungi (AMF). Besides, soil microorganisms and enzymatic activities play an irreplaceable role in improving soil quality and regulating soil nutrient circulation. However, little data are available on the interactions between GRSP, microorganisms, and enzymatic activities during urbanization. Here, we selected a built-up area (505 km2) in Nanchang, China, and collected soil samples from 184 sites from different urbanized areas. Soil microorganisms, soil physicochemical properties, soil enzymatic activities, vegetation characteristics, and land-use configurations were used to decouple the variations in total GRSP (TG) and easily extractable GRSP (EEG) during urbanization. Results showed that TG and EEG contents significantly decreased by 16.2 % and 19.4 % from low to heavy urbanization areas, respectively. Moreover, N-acetylglucosamine glycosidase (NAG), acid phosphatase (AP), and leucine aminopeptidase (LAP) activities, and the biomass of gram-positive bacteria (G+) and actinomycetes were significantly larger in lightly urbanized than in heavily urbanized areas (p < 0.05). EEG and TG positively correlated with β-1,4-glucosidase (BG), NAG, LAP, AP, G+, gram-negative bacteria, actinomycetes, and total soil microbial biomass (p < 0.05). Variance partitioning analysis showed that soil enzymatic activities are pivotal in GRSP production. However, no direct evidence shows that AMF secrete GRSP. Furthermore, structural equation modeling found that urbanization could diminish soil enzymatic activities by reducing vegetation cover and increasing the proportion of impervious surface area, indirectly causing a decrease in GRSP content. In conclusion, urbanization could indirectly reduce GRSP content by affecting land-use configurations and soil enzymatic activities. In the future, we shall consider improving soil quality by increasing GRSP content during urbanization.

Organic matter pools in a fluvisol after 29 years under different land uses in an irrigation region in northeast Brazil

Soil organic matter (SOM) is a critical component of the soil system and a sensitive indicator of soil quality. We aimed to investigate the response of SOM pools to different land uses and management in irrigated croplands of the semi-arid region of northeast Brazil. Four sites irrigated under long-term (29 years) land uses were selected: banana (B1 and B2); elephant grass (EG) - perennial systems; maize and cowpea succession (MCP) - annual system; B1 was cropped for 17 years +2 years of maize and cowpea +17 years banana, while B2 was continuously cropped. A native forest (NF) site was selected as reference of steady state. Soil samples were collected at four depths in the rows and inter-rows of each management system. The higher decline in SOM fractions was perceived at 0–0.05 m depth and microbial indices (microbial biomass C and N, and basal respiration and metabolic quotient) were very sensitive indicators of soil quality. Perennial systems (B1 and EG) maintained the C and N stocks at higher levels equivalent to NF at the 0–0.40 m layer, while MCP and B2 had lower total organic carbon (TOC) (15 and 17%, respectively) and total nitrogen stocks (4.27 and 8.67%, respectively). Perennial cultivation with B1 and EG showed also the highest soil C and N microbial biomass and stratification ratio and, the lowest respiratory quotients, all indications of elevated soil C sequestration. In general, land use change from native forest to annual crops reduced plant residue input and increased soil disturbance, favoring higher SOM mineralization, while perennial crops and grasses were the most effective in increasing C and N stocks due to the maintenance of crop residues on the soil surface and the absence of soil tillage.

Sensitivities of Physical and Chemical Attributes of Soil Quality to Different Tillage Management

Tillage management is a direct factor in affecting soil quality, which is a key factor in sustainable agriculture. However soil quality evaluation needs significant manpower, material resources and time. To explore the sensitive indicators of soil quality affected by tillage management, eight soil physical and chemical properties under three tillage managements, including plow tillage, subsoiling tillage and rotary tillage, were determined under a long-term experiment in North China Plain. The results showed that subsoiling tillage management had the highest soil organic carbon and total nitrogen in the 0–20 cm layer and the lowest soil bulk density in the 30–40 cm layer. Rotary tillage management had the highest soil water content in the 0–40 cm layer. Meanwhile, compared to 2002, the soil organic carbon, total nitrogen and soil bulk density had varied greatly in 2012, but there was no significant difference between 2012 and 2018. However, other property concentrations tended to increase in 2002, 2012 and 2018. In addition, there was a significant linear relationship between soil quality index and grain yield. Subsoiling tillage management had the highest soil quality index and gain yield both in 2012 and 2018. The soil quality can be evaluated through the sensitive indicator of soil organic carbon, total nitrogen, soil bulk density, total phosphorus and soil water content, which provides a scientific basis for selecting reasonable tillage management and evaluating soil quality in this agricultural production area or other similar areas.

Monitoring and molecular characterization of bacterial species in heavy metals contaminated roadside soil of selected region along NH 8A, Gujarat

Heavy metal contamination is a universal concern due to health risks associated with metal pollution. Soil contamination by heavy metals is known to affect microbial activities at elevated concentrations adversely. However, indigenous soil bacterial populations' response to added heavy metal and metal combinations is poorly understood. Microbes prevailing in the soil are the driving factors. Their properties are recognized as sensitive indicators of soil quality and health. Moreover, these microscopic organisms are accountable for the fertility and aeration of the soil that forms fundamental aspects of soil function. The current study was performed to explore the diversity of bacterial species in heavy metal polluted roadside soil. The roadside soil samples were collected from diverse sites and processed for physicochemical properties, microbial characterization, and heavy metals distribution in the selected locations. Serial dilution and spread plate techniques were used for the isolation of bacterial species. The 16S-rRNA gene sequencing identified bacterial species in roadside soil as Bacillus drentensis (MK217088), Bacillus safensis (MK774729), Bacillus haynesii (MK192808), Bacillus subtilis (MK217089), and Bacillus cereus (MK801278). In addition, the 16S rRNA sequences of isolated bacterial strains were aligned to generate a phylogenetic tree. Thus, the current research study provides a platform for efficiently investigating roadside soils by microbial profiling that may discover novel microbes of scientific significance and improved potential.

Labile Soil Organic Matter Pools Are Influenced by 45 Years of Applied Farmyard Manure and Mineral Nitrogen in the Wheat—Pearl Millet Cropping System in the Sub-Tropical Condition

Labile soil organic matter pools (LSOMp) are believed to be the most sensitive indicator of soil quality when it is changed rapidly with varied management practices. In sub-tropical climates, the turnover period of labile pools is quicker than in temperate climates. Organic amendments are of importance in improve the LSOMp for a temperate climate and may be helpful in sub-tropical climates as well. Hence, the status of LSOMp was studied in long term farmyard manure (FYM) amended soils under wheat (Triticum aestivum L.) and pearl millet (Pennisetum glaucum L.) cropping systems in sub-tropical arid conditions. At the same time, we also attempt to determine the impact of mineral nitrogen (N) application in these pools. In this study, dissolved organic matter (DOM), microbial biomass (MB), and light fraction (LF) were isolated in the management practices involving different modes and rates of FYM applications along with the application of nitrogenous fertilizer. C and N contents of the labile pools were analyzed in the soil samples at different periods after FYM applications. Among the different pools, microbial biomass carbon (MBC) and dissolved organic carbon (DOC) were changed significantly with different rates and modes of FYM application and mineral N application. Application of FYM at 15 Mg ha−1 in both the seasons + 120 kg ha−1 mineral N resulted in significantly higher MBC and DOC as compared to all of the other treatments. This treatment also resulted in 13.75% and 5.8% more MBC and DOC, respectively, as compared to the amount of MBC and DOC content in the control plot where FYM and mineral N were not applied. Comparing the labile organic matter pools of 45 years of FYM amendment with initial values, it was found that the dissolved organic carbon, microbial biomass carbon, and light fraction carbon were increased up to the maximum extent of about 600, 1200, and 700 times, respectively. The maximum amount of DOM (562 mg kg−1 of DOC and 70.1 mg kg−1 of DON), MB (999 mg kg−1 of MBC and 158.4 mg kg−1 of MBN), LF (2.61 g kg−1 of LFC and 154.6 g kg−1 of LFN) were found in case of both season applied FYM as compared to either summer or winter applied FYM. Concerning the different rates of FYM application, 15 Mg ha−1 FYM also resulted in a significantly higher amount of DOM, MB, and LF as compared to other FYM rates (i.e., 5 Mg ha−1 and 10 Mg ha−1). Amongst different pools, MB was found to be the most sensitive to management practices in this study. From this study, it was found that the long-term FYM amendment in sub-tropical soil along with mineral N application can improve the LSOMp of the soil. Thus, it can be recommended that the application of FYM at 15 Mg ha−1 in summer and winter with +120 kg ha−1 mineral N can improve SOC and its labile pools in subtropical arid soils. Future studies on LSOMp can be carried out by considering different cropping systems of subtropical climate.

Soil Quality Assessment after 25 Years of Sewage Sludge vs. Mineral Fertilization in a Calcareous Soil

The aim of this work was to identify the most sensitive soil quality indicators and assess soil quality after long-term application of sewage sludge (SS) and conventional mineral fertilization for rainfed cereal production in a sub-humid Mediterranean calcareous soil. The treatments included six combinations of SS at different doses (40 t ha−1 and 80 ha−1) and frequencies (every 1, 2 and 4 years), plus a control with mineral fertilization, and a baseline control without fertilization. Twenty-five years after the onset of the experiment, 37 pre-selected physical, chemical and biological soil parameters were measured, and a minimum data set was determined. Among these indicators, those significantly affected by treatment and depth were selected as sensitive. A principal component analysis (PCA) was then performed for each studied depth. At 0–15 cm, PCA identified three factors (F1, F2 and F3), and at 15–30 cm, two factors (F4 and F5) that explained 71.5% and 67.4% of the variation, respectively, in the soil parameters. The most sensitive indicators (those with the highest correlation within each factor) were related to nutrients (P and N), organic matter, and trace metals (F1 and F4), microporosity (F2), earthworm activity (F3), and exchangeable cations (F5). Only F3 correlated significantly (and negatively) with yield. From these results, we concluded that soil quality can be affected in opposite directions by SS application, and that a holistic approach is needed to better assess soil functioning under SS fertilization in this type of agrosystem.

Vertical distribution analysis of soil organic carbon and total nitrogen in different land use patterns of an agro-organic farm

While the quantity of soil organic carbon and nitrogen are used as indices of soil quality assessment and sustainable land use management, soil microbial activity is also a sensitive indicator of soil quality. Though the dynamics of carbon and nitrogen in terrestrial ecosystem can be largely affected by macro factors such as climatic conditions, local micro environmental factors such as land use history, plant functional type and management practices also play an important role in this regard. The present study was aimed at assessing and analyzing different types of land use patterns so as to understand their influence on the depth wise distribution of soil organic carbon (SOC), total nitrogen (TN) and microbial activity under the same management practices. The investigation was carried out in an organic farm located at Anand, Gujarat, India. Three different types of land use patterns viz., (i) fodder grass raising land, (ii) teak woodland, and (iii) wheat-pearl millet cropland were selected. Vertical (0–100 cm depth) variation in soil biophysical properties was recorded. Analysis of variance showed SOC (%) and TN (%) varied significantly (P < 0.001) with land use patterns (LU), depth (D), and LUxD. It was found that at all three land use patterns SOC and TN were highest at upper layer (0–10 cm) then decreased towards deeper layers (up to 40 cm) and then again increased with depth (40–100 cm) in soil profile. Highest values of SOC (%) and TN (%) (1.02% and 0.08% respectively), were reported in wheat-pearl millet cropland at 0–10 cm depth. Use of organic amendment made a great impact on SOC (%) in wheat pearl-millet cropland throughout the soil profile. We found almost same quantity of SOC (%) at 0–10 cm and 80–100 cm in teak woodland and grass raising land. The microbial biomass (carbon and nitrogen) and dehydrogenase activity were also found to be highest at upper layer (0–10 cm) in wheat-pearl millet cropland (418.2 µg/g, 52.9 µg/g and 104.05 TPF µg/g respectively) as compared to other two types of land use patterns. A significant positive correlation was observed between soil organic carbon and total nitrogen with microbial biomass and dehydrogenase activity at all three land use patterns. Our findings suggest that changes in land use pattern and management practices make a significant impact on vertical distribution of SOC and TN. Accurate investigation of SOC and TN storage at regional levels is important for detecting changes in carbon and nitrogen sequestration potentials induced by land use changes over a period of time to enable the rebuilding of SOC and TN in agro-ecosystems.

Soil quality index as affected by temporal long term tea cultivation in Jorhat District of Assam

Aim: The investigation was undertaken to identify the Minimum Data Set (MDS) for Soil Quality Index (SQI) assessment in continuouslong-term tea cultivation systems. Methodology: In the study under very deep, fine loamy, well-drained soil, five age groups of tea plantations viz. less than 15 years, 15-30 years, 30-45 years, 45-60 years and more than 60 years were selected and identified minimum data set and soil quality index. Results: In very deep, fine loamy, well-drained soil under continuous tea cultivation, SQI, 14.74 was obtained for less than 15 years, 14.06 for 15-30 years, 11.12 for 30-45 years, 12.94 for 45-60 years and 11.37 for more than 60 years of plantation, respectively. Interpretation: The most sensitive soil quality indicators identified in very deep, fine loamy, well-drained soil were pH for less than 15 years, total nitrogen for 15-30 years, available nitrogen for 30-45 years, organic carbon for 45-60 years and exchangeable aluminium for more than 60 years of continuous tea cultivation.

Arbuscular mycorrhizal fungi in the rhizosphere of soybean in integrated crop livestock systems with intercropping in the pasture phase

Arbuscular mycorrhizal fungi (AMF) are important microorganisms that act as sensitive soil quality indicators. The increase in plant diversity in Integrated Crop Livestock Systems under no-tillage (ICLS-NT) can also alter the diversity of species of fungi and bring benefits to the system. This study had the objective of evaluating the AMF diversity and its quantitative characteristics in ICLS-NT with intercrop in the pasture phase. The experiment was conducted in a dystrophic red latosol, with plots represented by the grasses Panicum maximun cv. BRS Tamani and Urochloa brizantha cv. Piatã, intercrop with the legumes (subplots): cowpea (Vigna unguiculata) cv. BRS Tumucumaque, pigeon pea (Cajanus cajan) cv. BRS Mandarim and single grass type only. The potential for inoculation was elevated in areas with legume intercrop, with either grass, and about 29% higher in areas with the C. cajan/P. maximun consortium. They may be associated with the benefits that the intercrop with legumes brings, through the relationship of rhizobia and AMF. The spore density and mycorrhizal colonization were higher with the use of grass from the genus Urochloa in relation to Panicum, reaching 92% and 88% higher, respectively, as well as an increase in species richness, being associated with a greater affinity of AMF with intercropped grasses. The insertion of the legumes into the intercrop with the grasses affected soybean productivity, positively correlating (74%) with mycorrhizal colonization. These results are related to the fact that intercrop promote the release of a high diversity of organic compounds, helping in the activity of soil microbiota, including AMF, increasing colonization and species diversity of these fungi. Thus, intercrops of grasses with legumes affected positively the activity and diversity of species of the AMF, reflecting in the increase in productivity of the soybean crop.

Biological indicators of soil quality under conventional, reduced, and no-tillage systems

ABSTRACT Soil microbial processes can serve as sensitive indicators of soil quality. A 2-year field experiment was conducted to determine the combined effects of tillage (conventional, CT; reduced, RT; and no tillage, NT) and residue (with or without residue removal) on soil microbial and enzyme activities under wheat (Triticum aestivum L.)- and corn (Zea mays L.) in a rotation, using a split-plot design with three replications near Shiraz, Iran. The highest microbial biomass (660.19 and 667.00 µg MBC g−1 soil in wheat and corn, respectively) was recorded under RT. Soil respiration was affected by tillage in order NT > RT > CT. The lowest microbial quotient (qCO2) was obtained under RT (15.60 in wheat and 5.94 in corn, respectively), while NT and CT either showed similar effects or NT was superior over CT. The highest acid phosphatase enzyme was obtained under RT (442.65 and 374.17 µg PNP g−1 soil h−1 in wheat and corn, respectively). Alkaline phosphatase and urease enzymes were highest under NT. Our research has shown that replacing CT with conservation tillage (especially RT) can greatly improve soil enzymes and microbial biomass and optimize qCO2 values under wheat- and corn in a rotation in a short term.

Inhibitory effect of microplastics on soil extracellular enzymatic activities by changing soil properties and direct adsorption: An investigation at the aggregate-fraction level

Microplastics (MPs), as a new type of environmental pollutant, pose a serious threat to soil ecosystems. The activities of soil extracellular enzymes produced by microorganisms are the potential sensitive indicators of soil quality. However, little is known about the response mechanism of enzyme activities toward MPs on a long-term scale. Moreover, information on differences in enzyme activities across different soil aggregates is lacking. In this study, 150 days of incubation experiments and soil aggregate fractionation were combined to investigate the influence of MPs on extracellular enzyme activities in soil. 28% concentration of polyethylene with size 100 μm was adopted in the treatments added with MPs. The results show that MPs inhibited enzyme activities through changing soil nutritional substrates and physicochemical properties or through adsorption. Moreover, MPs competed with soil microorganisms for physicochemical niches to reduce microbial activity and eventually, extracellular enzyme activity. Enzyme activities in different aggregate-size fractions responded differently to the MPs exposure. The catalase in the coarse particulate fraction and phenol oxidase and β-glucosidase in the micro-aggregate fraction exerted the greatest response. With comparison, urease, manganese peroxidase, and laccase activities showed the greatest responses in the non-aggregated silt and clay fraction. These observations are believed to stem from differences in the key factors determining the enzyme activities in different aggregate-size fractions.The inhibitory pathway of microplastics on activities of extracellular enzymes in soil varies significantly across different aggregate fractions.

Functional diversity of rhizosphere soil microbial communities in response to different tillage and crop residue retention in a double-cropping rice field.

Microbial community functional diversity is a sensitive indicator of soil quality, soil management such as tillage and crop residue which can affect the microbial community functional diversity of paddy field. However, there is still limited information about the influence of different tillage and crop residue management on rhizosphere soil microbial community functional diversity in a double-cropping rice (Oryza sativa L.) field. Therefore, four tillage treatments were set up in paddy field, tillage treatments were included: conventional tillage with residue incorporation (CT), rotary tillage with residue incorporation (RT), no-tillage with residue retention (NT), and rotary tillage with residue removed as control (RTO). And the effects of CT, RT, NT, and RTO treatments on the average well color development (AWCD), genetic diversity indices and carbon source utilization of rhizosphere soil were studied in the present paper. The results showed that the values of AWCD with CT, RT and NT treatments were higher than that of RTO treatment. It was implied that application of crop residue management resulted in the variation of the carbon utilization efficiency of rhizosphere soil microbial communities. At maturity stages of early and late rice, the Richness indices, Shannon indices and McIntosh indices with CT treatment were significantly higher than that of RTO treatment, and with the order as CT>RT>NT>RTO. Principal component analysis (PCA) results indicated that there were significant differences in carbon substrate utilization patterns among different tillage treatments. Carbohydrates and amino acids were the main carbon resources utilized by rhizosphere soil microbes. Therefore, the combined application of tillage with crop residue management could significantly increase the rhizosphere soil microbial community functional diversity in the double-cropping paddy field of southern China.

Variation in soil bacterial communities by long-term application of organic and inorganic fertilizers in rice

Fertilization plays important role in increasing the quality of soil and crop productivity. Soil bacterial communities are sensitive indicators of soil quality and their response to long-term fertilization in paddy soils of Kerala remains unexplored. In the present study, we analysed the long term effect of fertilizer regimes viz., organic inputs (ONM), integrated inputs (INM) and inorganic (INF) inputs on bacterial community in paddy soils using NGS sequencing of 16S rRNA genes. The results showed that relative abundance of bacterial communities varied across organic and inorganic fertilizer treatments. The dominant phyla across all the treatments were Actinobacteria followed by Acidobacteria, Proteobacteria and Firmicutes. The long term application of organic and integrated fertilizers clearly increased the abundance of beneficial microbes like Bacillus, Arthrobacter, Bradyrhizobium, Frankia etc in soil. In contrast, continuous use of chemical fertilizers, suppressed the growth of Rhizobium, Azospirillum, Pseudomonas and Burkholderia in rhizosphere soils. Overall, the present study enhanced our understanding of relationship between soil microbiota and functioning of agro ecosystem and support the use of integrated fertilization strategy in rice. DOI: https://doi.org/10.25174/2249-4065/2019/94878

Effects of different rotation periods of Eucalyptus plantations on soil physiochemical properties, enzyme activities, microbial biomass and microbial community structure and diversity

Eucalyptus is widely cultivated in southern China as a short-rotation fast-growing species for timber production. However, this kind of business model has aroused widespread concern on soil quality. This study aimed to determine the cutting period of Eucalyptus plantation by comparing the effects of different cultivation years on soil quality. Four Eucalyptus stands, including 2-, 6-, 10-, and 15-year-old (abbreviated as 2 yr, 6 yr, 10 yr, and 15 yr, respectively) were used, and 25 soil physicochemical and biological indicators were determined. Results showed that the soil texture of the 10 yr and 15 yr plantations significantly improved. Soil organic matter, macronutrients, enzyme activity, and microbial biomass decreased significantly at 6 yr and then increased at 10 yr. However, the contents of available nutrients and the activities of urease and catalase decreased again at 15 yr. Redundancy analysis showed that the contents of total phosphorus, available phosphorus, available potassium, available zinc, and available calcium considerably influenced the soil bacterial community, whereas the contents of total nitrogen and available nitrogen greatly affected the fungal community. Meanwhile, pH and soil texture exerted a significant impact on microbial community structure. Bacterial diversity showed an increasing trend with the rotation period, whereas the fungal diversity ranked by 2 yr > 6 yr < 10 yr > 15 yr. The relative abundances of soil major microbial taxa were closely related to the soil physicochemical properties and were roughly similar to ecological strategy. These results suggest that cultivation period significantly affected the soil quality. Thus, we propose to extend the rotation period of Eucalyptus plantation to 10 yr. Extending the cultivation period to 10 yr significantly improved soil quality, but the available nutrients and enzyme activity of the 15 yr plantation showed a decreasing trend. Microbial community structure may be a sensitive indicator of soil quality in Eucalyptus plantations.

Reduced tillage, but not organic matter input, increased nematode diversity and food web stability in European long-term field experiments.

Soil nematode communities and food web indices can inform about the complexity, nutrient flows and decomposition pathways of soil food webs, reflecting soil quality. Relative abundance of nematode feeding and life‐history groups are used for calculating food web indices, i.e., maturity index (MI), enrichment index (EI), structure index (SI) and channel index (CI). Molecular methods to study nematode communities potentially offer advantages compared to traditional methods in terms of resolution, throughput, cost and time. In spite of such advantages, molecular data have not often been adopted so far to assess the effects of soil management on nematode communities and to calculate these food web indices. Here, we used high‐throughput amplicon sequencing to investigate the effects of tillage (conventional vs. reduced) and organic matter addition (low vs. high) on nematode communities and food web indices in 10 European long‐term field experiments and we assessed the relationship between nematode communities and soil parameters. We found that nematode communities were more strongly affected by tillage than by organic matter addition. Compared to conventional tillage, reduced tillage increased nematode diversity (23% higher Shannon diversity index), nematode community stability (12% higher MI), structure (24% higher SI), and the fungal decomposition channel (59% higher CI), and also the number of herbivorous nematodes (70% higher). Total and labile organic carbon, available K and microbial parameters explained nematode community structure. Our findings show that nematode communities are sensitive indicators of soil quality and that molecular profiling of nematode communities has the potential to reveal the effects of soil management on soil quality.

Soil carbon pools and enzyme activities in aggregate size fractions after seven years of conservation agriculture in a rice–wheat system

Decline in soil organic carbon (SOC) due to intensive tillage and removal or burning of crop residues is considered a major threat to maintaining soil quality and meeting future challenges of food production at national and global scales. Adoption of conservation-agriculture practices (no till and residue retention) is necessary to promote soil structural stability and increases in SOC content and enzyme activities. We evaluated the impact of tillage and residue-management practices on yield, soil labile-C pools, aggregate stability and soil enzyme activities after seven cycles of a rice (Oryza sativa L.)–wheat (Triticum aestivum L.) system on the Indo-Gangetic Plain of India. Treatments included four combinations of tillage and crop establishment in rice (main plots), and three combinations of tillage and residue management in wheat (subplots). Irrespective of rice-establishment method, mean grain yield of no-till wheat with rice-residue mulch (NTW+RR) was 9% and 22% higher, respectively, than of conventional-till (CTW) or no-till wheat with no rice-residue mulch. Soil C pools (very labile, labile, less-labile and non-labile) were significantly higher under a no-till dry-seeded rice (NTDSR)–NTW+RR cycle than conventional-till puddled transplanted rice–CTW. Macro-aggregates (&amp;gt;0.25 mm) had higher labile C pools, glomalin content and enzyme activities than micro-aggregates. NTW+RR significantly increased soil C pools within both macro- and micro-aggregates. Compared with CTW, NTW+RR increased soil dehydrogenase, cellulase and alkaline phosphatase activities by 23%, 34% and 14%, and water-soluble organic C by 31%, and increased water-stable aggregates and mean-weight-diameter. NTDSR–NTW+RR increased SOC, enzyme activity, aggregate stability and wheat grain yield. Results indicated that soil labile-C pools across aggregate fractions were the most sensitive indicators of soil quality when determining the effects of changes in management practices. Furthermore, adoption of no till and residue retention may improve sustainability in rice–wheat systems of the Indo-Gangetic Plain.

Comparative analysis of soil deterioration under different land uses in southwestern Nigeria

Soil degradation associated with land use is a critical problem in Southwestern Nigeria and there is little or insufficient scientific information in assessing soil quality indicator. In this study 9 soil physical and chemical properties were measured from 5 different sampling sites covering three land use categories (arable farms, tree farms and natural forest). The quality of the soils was determined by comparing the physio-chemical parameters of soil samples from the farms with the Standard maximum allowable thresholds for agricultural lands. Two hundred (200) copies of questionnaire were administered purposively to elicit information on socio-economic status focusing on farm history and farm attributes. Analysis of Variance was used to identify the most sensitive indicators of soil quality for evaluating land use within the forest belt in Southwestern Nigeria and subsequently compare soil quality assessment using fieldwork and laboratory soil analysis method. The results indicated that soils in the study area were characterized with mean bulk density, cation exchangeable capacity that varied at F = 0.68, P

Dynamics of Bacterial Communities in a 30-Year Fertilized Paddy Field under Different Organic–Inorganic Fertilization Strategies

Fertilization plays important roles in improving soil fertility and in increasing crop yield. Soil microbial communities are sensitive indicators of soil quality and health, which could be affected by fertilization strategy. However, our knowledge on how organic–inorganic fertilizers application affects soil bacterial communities remains largely poorly understood. In this study, we investigated the long-term effects of different organic–inorganic fertilization strategies: without fertilizer (CK), fertilizers NPK (CF), fertilizers NPK, plus 30% organic manure (CFM1), and fertilizers NPK plus 60% organic manure (CFM2) on soil bacterial communities in paddy fields. Results showed that the bacterial 16S ribosomal DNA (rDNA) gene abundances in treatments CF, CFM1, and CFM2 were 1.44, 1.54, and 1.28 times higher than that in CK and the ACE index in treatment CFM1 was 9.0% greater than that in treatment CFM2, respectively. Fertilization strategy significantly changed the relative abundance of Nitrospirae, Gemmatimonadetes, and unclassified bacteria at the phylum level and bacteria belonging to order Nitrospira, candidate bacterium SBR2076, unclassified bacteria, Syntrophobacterales, and Solibacterales at the order level, respectively. High organic–inorganic fertilizer application rates inhibited the growth of Nitrospirae by 20–35%, and stimulated the growth of Gemmatimonadetes by 14–77%, relative to the rest of the treatments, respectively. Hierarchical cluster and principal coordinate analysis (PCoA) showed that the fertilization strategy affected the bacterial community structures, and the organic–inorganic fertilized treatments possessed similar bacterial community structures. Furthermore, soil pH, total nitrogen (TN), and soil organic carbon (SOC) were the main driving factors altering the bacterial communities. Our results suggested that combined organic–inorganic fertilizers application increased soil nutrient contents and bacterial abundances, and this could be an optimized fertilization strategy in regulating soil bacterial communities for rice production.

Comparison of Soil Physical Quality Indicators Using Direct and Indirect Data Inputs Derived from a Combination of In‐Situ and Ex‐Situ Methods

Core Ideas Soil quality indicators such as S and PAWC are considered as static indicators with low sensitivity. The soil quality indicator AWr is considered a dynamic indicator with high sensitivity. Indirect pedotransfer function based SWRCs are appropriate for static baseline indicators. Soil monitoring programs should use AWr as a sensitive and reliable soil quality indicator. The quality of a soil is its ability to deliver functions providing ecosystem services, human health and well‐being. Soil physical quality (SPQ) values use different parts of the soil water retention curve (SWRC) to calculate SPQ. For example, the plant available water capacity (PAWC) method is the difference in water content between permanent wilting point and field capacity. The S‐index uses the slope of the SWRC at its inflection point and the relative air‐water energy (AWr) is the integral of “dry” divided by the “wet” area of the SWRC. Increasing demand for soil monitoring policies calls for reliable and sensitive soil quality indicators (SQIs). The objectives of the study were to assess the sensitivity and applicability of SPQ indicators using direct and indirect data inputs. The indirect approach provided sufficient data complexity for the PAWC and S‐index values, but the more complex AWr required the direct approach. PAWC and S‐index values were identified as static SPQ indicators. The values obtained from these approaches should be used to form baseline static datasets and therefore have an indicative role only. The AWr value was identified as a dynamic SPQ indicator and provided required sensitivity to pick up temporal changes in SPQ. This indicator could be used at multiple scales and could even guide grassland management in terms of SPQ. Higher SWRC data resolution will require more complex hydraulic models to fit and will ultimately improve the accuracy of soil hydraulic data and improve the sensitivity of AWr as a SPQ indicator.