Soil Aggregation

The study examined aggregate size distribution and related structural indices in soils of natural forest, Cupressus lusitanica plantation and cultivated land through dry and wet sieving techniques. Variations in aggregate size distribution and structural indices were observed among land uses which might be ascribed to soil organic carbon (SOC) content and tillage practices. Alteration from natural forest to Cupressus lusitanica plantation and cultivated land apparently reduced the quantity of SOC and water stable aggregates (WSA) (> 1mm) but increased the quantity of WSA (1-0.25 mm) and micro-aggregates (< 0.25 mm). Long term cultivation leads to deterioration of soil structure and formation of clods. The mean percent by mass of agronomically most valuable aggregates (AVA) in soils of natural forest, Cupressus lusitanica plantation and cultivated land to the whole investigated depth were 86.61, 80.42 and 74.44%, respectively. Coefficient of stability (K ) ranged from 2.48 in s...

The assessment of soil attributes affected by land use changes or different cultivation management strategies is commonly based on a comparison between agricultural elds, neglecting the natural soil spatial variability. This study aimed to develop a methodology based on improved space series to differentiate between spatial variability of soil attributes and the effect of tillage direction when the evaluation is based on comparison between adjacent elds. The study area consists of two adjacent elds of different tillage directions, i.e. up-down tillage (UDT) and contour tillage (COT). Soil sampling was performed at 40 points in each led at 5 m intervals along a contour line at the mid-slope position. All measured soil attributes, i.e. sand, silt, clay, MWD, GMD, bulk density; SP, CCE, OM, of UDT were signi cantly (P<0.05) different from those of COT compared by independent sample T test. This analysis could not differentiate between the spatial variability of the soil and the changes induced by tillage. To determine the net effect of UDT on soil attributes, we (i) performed space series analysis on COT data, (ii) used autoregressive, moving average and autoregressive-moving average models to model the space series data on COT eld, and (iii) used the best model obtained for each soil attributes on COT to forecast the value of the property in ten adjacent points in the UDT eld. Comparison between the forecasted and measured data in UDT showed that the evaluation of tillage direction effect on soil attributes based on comparison between adjacent elds can be over or under estimated when the sampling coordinates and the spatial correlation among adjacent observations of data are ignored. The methodology used was able to differentiate between natural and management induced differences of soil attributes. Overall, the use of this methodology will improve the prediction and understanding of the effects of different cultivation practices on soil quality.

Enzymes play the most important role in the decomposition and deterioration of organic matter in the soil. Most of the microbial activity in the soil is determined by measuring the activities of the enzymes. The aim of this study is to examine the changes in dehydrogenase enzyme activity in different pedological development soils formed on the same parent material, but with different slopes, land cover and land use under semihumid climatic conditions. It was carried out on the soil formed on the basaltic parent material in different topographical positions within the Dağköy area of Engiz district, which is located at the south of the Samsun-Bafra Highway. In this study, dehydrogenase enzyme activity was assessed in order to reveal the biological properties of the soil of the study area and it was investigated the dehydrogenase enzyme activity in terms of soil biological property. For this aim, six soil profiles formed on weathered basaltic parent material and located on toposequence of north-south transect were described according to genetic horizon and classified as Lithic Ustorthent, Vertic Haplustept, Typic Haplustept and Typic Haplustert. It was determined that the dehydrogenase changed between 0.073-1.170 µg TPF in soils taken from each profiles. In addition, when the statistical relationship between dehydrogenase enzyme activity and different profiles, land use, and height along the north-south transect was investigated different profiles and different heights were found to be important at % 1 level of effect on dehydrogenase enzyme activity in the soil (P=0.006<0.01). Also the effect of different land use patterns were found to be important at % 5 level on the activity of dehydrogenase enzyme in the soil (P = 0.048<0.05).

This study investigated P sorption patterns of surface soils of forest, grazing and cultivated lands in the Guto Gida District located in western Oromia, Ethiopia. Soil P sorption was measured in the laboratory by batch experiment in which the soils were equilibrated with solution varying in initial concentration of P (0, 5, 25, 50, 100, 150 and 250 mmol P/L) for 24 hours. From each land use type, extractable Al, Fe and Mn ions were evaluated using different extractants and P sorption isotherms were described by Langmuir equation and provided a good fit for the equilibrium P concentration. Values of the P sorption maximum of the soils ranged from 588-1280 mmol kg . Soils of the cultivated land with high clay and extractable Al contents had high degree 1 of P sorption than the remaing land use systems. Additionally, results of the study indicated that soils with high clay and containing oxides and hydroxide of Al and Fe had a high P-sorption capacity resulting in P- deficiency in the...

A new theoretical and experimental framework that permits an accurate determination of aggregate‐size stability distribution is presented. The size‐stability distribution in addition to estimating aggregate‐size distribution distinguishes between amounts of stable and unstable macroaggregates (&gt;250 μm). The determination of aggregate‐size stability distribution involves the assumptions that soil aggregates can be categorized in terms of their size and water stability (slaking resistance). Experimentally this procedure involves the slaked and capillary‐wetted pretreatments; and a subsequent slaking treatment of aggregates &gt;250 μm in size. We also propose the stable aggregates index (SAI) and the stable macroaggregates index (SMaI) for studying soil stability based on aggregate resistance to slaking. These indices account for the total weighted average of stable aggregates and the total weighted average of stable macroaggregates, respectively. Both the SAI and the SMaI indices w...

Changes in soil structure often accompany changes in management practices and may affect the effectiveness of these practices. Parameters are needed to quantify these changes. Our objective was to see if fractal dimensions derived from `aggregate bulk density±aggregate size' and `aggregate number±aggregate size' relationships could be applied to quantify such changes. The study was conducted at the Experimental Farm of the School of Agronomy and Forestry Engineering, National University of La Plata, Argentina. A Vertic Phaeozem soil was sampled at seven locations differing in long-term management practices. The `aggregate bulk density±aggregate size' and `number of aggregates±aggregate size' data were obtained for seven ranges of aggregate sizes. Differences in treatments were re¯ected by the fragmentation fractal dimension but not the mass fractal dimension. The lowest fragmentation fractal dimensions corresponded to plots under long-term notillage and the highest to plots with a history of cultivation of rice (Oryza sativa L.) under water. The fragmentation fractal dimension re¯ected the differences in soil management whereas the mass fractal dimension appeared to be insensitive to those differences.

The intra-aggregate architecture of soil macroaggregates provides suitable microhabitats for nematodes to graze on microorganisms. However, it is not fully clear how nematodes and microbial communities interactively mediate soil organic carbon (SOC) turnover. Here, we aimed to illustrate the relationships between nematodes, microbial community, and SOC turnover in the macroaggregates of a red soil receiving long-term manure application. Soil macroaggregates (>2 mm) were sampled from an 11-year field experiment including four manure treatments: no manure (M0), low manure rate (M1), high manure rate (M2), and high manure rate with lime (M3). The abundances of nematodes and microbial communities were substantially increased under manure treatments. Bacterivores dominated under the M2 and M3 treatments, while plant parasites were enriched under the M1 treatment. Phospholipid fatty acid analysis indicated that the ratio of bacteria to fungi significantly increased, but the ratio of Gram-positive bacteria to Gram-negative bacteria declined with the increasing manure addition. Random forest modeling showed that soil porosity had a primary effect on nematode assemblages, while pH and SOC contributed profoundly to the structure of the microbial community and carbon metabolic capacity. Structural equation modeling suggested that nematode grazing promoted carbon metabolic activities predominantly due to increased microbial biomass. Taken together, the mechanistic understanding of nematode-microorganism interactions may have important implications for improving soil fertility by nematode-mediated microbial processes.

barley crops in their early stage of growth and then let the crops recover for grain harvesting (Yau and Mekni, In West Asia and North Africa, farmers may permit sheep (Ovis 1987). This practice of grazing cereals in early growth aries) to graze young barley (Hordeum vulgare L.) crops and then let the crops recover to allow grain harvest at maturity. The objective stages occurs in Morocco (Belaid and Morris, 1991), of this study is to test the hypothesis that in a semiarid area, clipping Syria (Nordblom, 1983; Mazid and Hallagian, 1983), and or grazing before stem elongation on a suitable barley cultivar planted Tunisia (Amara et al., 1985). early in the season may not reduce grain and straw yields. Field Farmers in some other areas of the world also allow experiments (1997-1998 to 1999-2000) were conducted in the Bekaa green-stage grazing on winter cereals. The most out-Valley of Lebanon at a site with Vertic Xerochrept soil and 513 mm standing example is in the USA where winter wheat in of long-term annual precipitation. Treatments were early planting the southern Great Plains is widely used for grazing by with no clipping or grazing (ENG), early planting with early clipping cattle (Redmon et al., 1995). In Australia, the practice or grazing (EG), and normal planting with no clipping or grazing is common in the Tablelands of New South Wales where (NNG). Hand clipping was performed in late winter to early spring oat (Avena sativa L.) has been the most popular cereal

The modulus of elasticity of dam concrete is difficult to determine directly from tests due to the necessity for large specimens and testing machines. In order to study the applicability of simple elastic models for predicting the modulus from standard size specimens, tests were conducted on prisms of 45×45×90 cm fabricated with dam concrete (maximum aggregate of 120 mm). The tests on standard 15×30 cm cylinders were made with the mortar and wet-screened components of this concrete. It is seen that the use of the data from these components together with estimated values of the modulus of the aggregates gives reasonable predictions of the moduli of the dam concrete. This has been verified for a range of ages, from 7 to 180 days.

Soil organic C (SOC) storage results when organic matter inputs to soil exceed losses through decomposition, and is strongly influenced by organic matter effects on soil aggregation. We evaluated the initial effects of lipid-extracted algae (LEA), a byproduct of biofuel production, on soil aggregate formation and SOC storage. In situ field incubations were conducted by amending soil with (1) 1.5% LEA, (2) 3.0% LEA, (3) 1.5% LEA + 1.5% wheat straw (WS) and (4) soil plus inorganic N (140 kg ha -1 NH 4 NO 3 ) and P [112 kg ha -1 Ca(H 2 PO 4 ) 2 •H 2 O] as the control. Soil samples were collected 0, 3, 6, 9, and 12 months after treatment application at 0-5, 5-15, and 15-30 cm. Soil was separated into macroaggregate (>250 µm), microaggregate (250-53 µm), and silt and clay (<53 µm) fractions by dry-sieving, and mean weight diameter was calculated. Soils and soil fractions were analyzed to determine C concentrations and associated δ 13 C values. Mean weight diameter 12 months after 3.0% LEA application was greater than the 1.5% LEA + 1.5% WS addition at the 5-15 cm depth. Soil amended with 1.5% LEA, 3.0% LEA or 1.5% LEA + 1.5% WS resulted in greater SOC after 12 months for all soil size fractions and depths. δ 13 C indicated that most LEA-C was initially associated with the silt and clay fraction, but later became more strongly associated with the macro-and microaggregate fractions after 12 months. Soil application of LEA enhanced initial aggregate formation and SOC storage by increasing aggregate MWD and macro-and microaggregate associated SOC over time. As the world population grows and resources become more limited, use of alternative energy sources, soil conservation, and environmental protection must be top research priorities. Our research emphasized all three and demonstrated that LEA can enhance soil structure and C storage.

Root exudation contributes to soil carbon allocation and also to microbial C and energy supply, which subsequently impacts soil aggregation around roots. Biologically-driven soil structural formation is an important driver of soil fertility. Plant genetic determinants of exudation and more generally of factors promoting rhizosphere soil aggregation are largely unknown. Here, we characterized rhizosphere aggregation in a panel of 86 pearl millet inbred lines using a ratio of root-adhering soil dry mass per root tissue dry mass (RAS/RT). This ratio showed significant variations between lines, with a roughly 2-fold amplitude between lowest and highest average values. For 9 lines with contrasting aggregation properties, we then compared the bacterial diversity and composition in root-adhering soil. Bacterial α-diversity metrics increased with the &quot;RAS/RT ratio.&quot; Regarding taxonomic composition, the Rhizobiales were stimulated in lines showing high aggregation level whereas Bac...

Tropical ecosystems have an important role in global change scenarios, in part because they serve as a large terrestrial carbon pool. Carbon protection is mediated by soil aggregation processes, whereby biotic and abiotic factors influence the formation and stability of aggregates. Nutrient additions may affect soil structure indirectly by simultaneous shifts in biotic factors, mainly roots, and fungal hyphae, but also via impacts on abiotic soil properties. Here, we tested the hypothesis that soil aggregation will be affected by nutrient additions primarily via changes in arbuscular mycorrhizal fungal (AMF) hyphae and root length in a pristine tropical forest system. Therefore, the percentage of water-stable macroaggregates (> 250 µm) (WSA) and the soil mean weight diameter (MWD) was analyzed, as well as nutrient contents, pH, root length, and AMF abundance. Phosphorus additions significantly increased the amount of WSA, which was consistent across two different sampling times. Despite a positive effect of phosphorus additions on extra-radical AMF biomass, no relationship between WSA and extra-radical AMF nor roots was revealed by regression analyses, contrary to the proposed hypothesis. These findings emphasize the importance of analyzing soil structure in understudied tropical systems, since it might be affected by increasing nutrient deposition expected in the future.

A Field experiment was carried out to evaluate the effects of some bacterial fertilizers on some parameters growth and yield of two cultivars of watermelon during the season 2018-2019. The study included two factors the first factor was two cultivars of watermelon (Top yield and Charleston Gray) the second factor was bacterial fertilizer {control, Azospirillium barsilense (B1), Azotobacter chrococum (B2), Azospirillium barsilens+fluorescens Pseudomona (B3), Azotobacter chrococum+fluorescens Pseudomona (B4) and B1+B2+Pseudomona fluorescens (B5)}. Minimum days for germination were obtained from B4 (Azotobacter chrococum+fluorescens Pseudomona)+genotype Top yield (4.83 days). The highest percentage of phosphorus, potassium and iron was obtained in B5 treatment with combination bacterial fertilizer with cultivar of Top Yield (0.394%, 3.443% and 377.1mg matter dry-1 respectively). The maximum percentage TSS was observed in B5 treatment with Top Yield (10%). The best significant effect on yield production was obtained in B5 treatment with cultivar of Top Yield (134.93 ton per hector) compared to control treatment with cultivar of Charleston Gray (66.67 ton per hector).

It is widely believed that tropical soils (mainly Oxisols) have excellent physical characteristics such as high infiltration rates, high permeability of water, good and stable soil structure and that consequently, they can support mechanized agriculture. However in the Eastern Plains (Llanos Orientales) of Colombia, when Oxisols are subjected to tillage using disc harrow, soil physical conditions deteriorate rapidly. We report here that change in land use with deep-rooted tropical pastures can enhance soil quality by improving the size and stability of soil aggregates when compared with soils under monocropping. In addition, rates of water infiltration improved by 5 to 10-fold while rainfall acceptance capacity improved by 3 to 5-fold. We suggest that intensive and sustainable use of these Oxisols, could only be possible if an "arable" or "productive layer" (i.e. a layer with improved soil physical, chemical and biological properties) is constructed and maintained. One option to achieve this arable layer is through the use of introduced tropical pastures with deep rooting abilities that can result in increased soil organic matter and associated improvements in soil physical, chemical and biological properties. One land use option that can achieve these soil improvements is agropastoralism whereby pastures and crops are grown in short-term rotations.

Land use change in moist tropical regions can significantly affect soil stability and carbon stocks, particularly with the conversion from primary forests. This study investigated the effects of land-use on soil aggregation and associated carbon stocks. A total of 200 soil samples were collected across five land-use, comprising rubber (RP) and oil palm plantations (OPP), bamboo forests (BF), fallow land (FL), and natural forest (NF). A comprehensive land-use intensity index, encompassing six key dimensions of land-use change, was integrated into robust regression models. The soil analyses revealed that macroaggregates dominated the top 15 cm (51-64 %), followed by meso-(30-39 %) and microaggregates (6-12 %). At deeper depths (15-30 cm), mesoaggregates prevailed (45.3-52.1 %). NF and BF exhibited the highest microaggregate fractions, resulting in lower mean weight diameter (MWD) and potentially lower aggregate stability. In contrast, RP and OPP displayed the highest macroaggregate distribution and MWD. Soil organic carbon generally decreased with land-use change from NF to FL and plantations, except for RP. MWD significantly correlated with silt and clay content, while meso-and micro-aggregates correlated with silt/clay content, MWD, and nitrogen (N). Models revealed that land-use intensity, bulk density, porosity, and N significantly influenced soil aggregate size. Notably, land-use intensity was lower in NF, BF, and FL compared to plantations (RP and OPP). The findings highlight the critical impact of landuse change in moist tropical regions on soil aggregation and carbon stocks, crucial for assessing the environmental consequences of converting natural forests to agricultural plantations. The study advances knowledge by introducing a comprehensive land-use intensity index, providing insights for sustainable land management and climate action. However, the findings are region-specific, and long-term experimentation and monitoring are needed to fully understand the effects of land use change on soil.

Soil surface crusting, a common phenomenon on cultivated soils, has major implications for agriculture and the environment because of its eects on soil hydrological properties, erosion and crop establishment. The objectives of this study were to evaluate land use controls on crust formation and the hydraulic response of soils to crust development for a Patancheru series soil (clayey skeletal, mixed, isohyperthermic Udic Rhodustalf) in south-central India. Soil aggregates, obtained from cultivated (PL) and naturally vegetated fallow (NV) land, were packed into sample trays and subjected to laboratory rain simulation to form crusts. Thin sections and visual observation indicated that crust development reached a more advanced stage in the PL case compared with NV following 90 min of rain at 40±80 mm h 71 intensity. This was re¯ected in a thicker crust layer with fewer voids in the former and a less smooth surface with partially disintegrated aggregates in the latter. The hydraulic response of the soil surface with the progression of crust development indicated a more permeable and less dense crust formed on NV than on PL soil. The results suggested that NV soil aggregates were more stable and that crust formation is more gradual for stable aggregates compared with the less stable PL aggregates. A structural crust-type formed on the Patancheru soil by means of parallel subprocesses involving translocation and illuviation of aggregate disruption by products, and raindrop compaction and particle rearrangement.

Drylands are very susceptible to the effects of climate change due to water stress. One possible climate change adaptation measure is the construction of lakes to increase water availability for drinking and irrigation (food production) and decrease fire risk. These lakes can also increase local biodiversity and human well-being. However, other non-target services such as carbon (C) storage, water purification, and sediment retention might also change. Our main aim was to evaluate the trade-offs on non-targeted ecosystem services due to lakes construction in drylands. This was done using the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) modeling tools, comparing a Mediterranean area located in southwest (SW) Europe, with and without artificial lakes. Results showed that the construction of artificial lakes caused an increase of 9.4% in C storage. However, the consequent increase in agricultural area decreased water purification and sediment retention services. This could diminish the life span of the lakes changing the initial beneficial cost-benefit analysis on lakes as adaptation measures to climate change. As a global measure for mitigation and adaptation to climate change strategy, we consider lake construction in drylands to be positive since it can store C in sediments and reduces the vulnerability to water scarcity. However, as a general recommendation and when built to support or increase agriculture in semi-arid landscapes, we consider that lakes should be complemented with additional measures to reduce soil erosion and nutrient leaching such as (i) locate agricultural areas outside the lakes water basin, (ii) afforestation surrounding the lakes, and (iii) adopt the best local agriculture practices to prevent and control soil erosion and nutrient leaching.

No-tillage (NT) and legume cover crops generally improve the quality of tropical and subtropical soils, but the mechanisms underlying these effects are not well known. We performed a study to investigate the influence of NT and legume cover cropping on microbial cell-wall constituents [glucosamine (GlcN), taken as indicator of fungal cell-wall; muramic acid (MurN), taken as indicator of bacterial cell-wall], and on their relationships with soil aggregation and soil organic carbon (SOC) accumulation in different fractions (light fraction, and sand-, siltand clay-sized fractions) of a subtropical Acrisol in Southern Brazil. The GlcN concentration ranged from 450.5 mg kg -1 in the 0-5 cm soil layer to 20.5 in the 75-100 cm soil layer, approximately 10 times greater than MurN concentrations (53.1-2.7 mg kg -1 for the same soil layers). No-tillage and legume cover crops favoured the accumulation of fungal and bacterial cell-wall constituents in whole soil, especially in the top 5 cm, with a preferential enrichment in GlcN. Legume cover cropping and NT resulted in greater accumulation of C in the light fraction in surface soil, which favoured the fungal community that, in turn, mediated an improvement in soil aggregation. Fungal-derived glucosamine also preferentially accumulated down to 100 cm depth, and more specifically in the clay-sized fraction of soil, suggesting a specific role of fungi in SOC accumulation at depth. Overall, our study provides field-based evidence that the accrual of fungal cell-wall constituents under NT and legume cover cropping is a key process leading to aggregation and SOC accumulation in subtropical soil profiles. Recent models of SOC formation now consider microbial residues as a main source for stable soil organic matter . Moreover, SOC stabilization by mineral-organic association and soil aggregation would be favoured by labile C inputs . More field-based observations are needed to support these concepts. Cell-wall constituents of fungi and bacteria in soil can provide a "fingerprint" for SOC formation . Contents of muramic acid (MurN) and glucosamine (GlcN) have been used to distinguish bacterial and fungal cell wall residues, respectively, mainly in temperate environments (e.g. . Few studies have been performed in subtropical or tropical soils. In these studies, greater amounts of total amino-sugars,

Background: In the century we live in, due to the environmental problems caused by the use of synthetic fertilizers, sustainable solutions are being sought. The use of beneficial microorganisms as biological fertilizers, which are directed in line with these searches, is remarkable. has become a phenomenon. This study aimed to investigate the effect of microbial fertilizer comparing them with synthetic fertilizer in Van ecological conditions. Methods: This research was conducted in summer seasons of 2020 and 2022 to investigate the effects of microbial (Bacillus atrophaeus, Bacillus-GC group and Rhizobium gallicum) and chemical (Control: No fertilizer, NP100: 40 kg N/ha-1 , 60 kg/ha-1 P 2 O 5 and NP50: 20 kg N/ha-1 , 30 kg/ ha-1 P 2 O 5) fertilizer applications on the yield and nutrient content of beans. The experiment was conducted in split plot design and replicated thrice. Result: Experimental results revealed that the use of microbial fertilizers led to a significant improvement in the morphological characteristics of bean plants in comparison to those treated with inorganic fertilizers. Besides, the utilization of microbial fertilizers, particularly when arranged in a consortium, exhibited performance that was nearly indistinguishable from that of synthetic fertilization. The highest grain yield was obtained with NP100 (40 kg N/ha-1 , 60 kg/ ha-1 P 2 O 5) + NR (Bacillus atrophaeus + Rhizobium gallicum) application. Apart from this effect, other microbial applications also played a positive role in plant growth and production. It was therefore concluded that microbial fertilizers can be employed as a suitable alternative to chemical fertilizers in order to establish a sustainable agricultural system in bean cultivation, to enhance productivity, to safeguard and to improve soil properties.

This study examines the role of abiotic (texture, calcium carbonates or iron) and biotic parameters (earthworm and enchytraeid activities) on the initial phases of soil aggregation. Our research focused on humus forms in alluvial soils, which are considered as young and heterogeneous environments. We hypothesized that the soil structure formation is determined by both the nature of the recent alluvial deposits and the soil fauna. For this purpose, six sites were chosen throughout two types of softwood forests (willow and alder forest) representing two stages of vegetation succession. Evidence of soil texture influence on aggregate stability was observed. A dominance of a coarse sand fraction caused a quick colonization of enchytraeids and epigeic earthworms while a silty texture favoured the presence of anecic earthworms, thus increasing the aggregate stabilisation. Iron forms, acting as cementing agents, were observed in the coarse silt, while calcium carbonates were equally distributed among the textural fractions. Active calcium carbonate fraction, binding organic matter with mineral components, was not found in the coarse sand fraction. In conclusion, the tree age cannot alone be used as an indicator of the humus form evolution but biological and physicochemical parameters also influence the initial steps of soil structuration.

The knowledge of soil hydraulic properties and processes leads to better predictions of both agricultural and environment impact. The objectives of this research are to determine, predict and compare the relationship between measured and estimated soil hydraulic properties and also spatially characterize these properties using geostatistics. Mini disc infiltrometer at a suction rate of 2 cm per second was used for the determination of soil hydraulic properties at different points of an alfisol in Nigeria. Soil samples (100, 200 and 300 mm depths) were also analyzed to determine soil bulk density (BD), total porosity (PT) and water holding capacity (WHC). The coefficients of variation (CV) of the textural classes indicate a non-considerable variability of the sand (CV=6%), silt (CV=20%) and clay (CV=3%) contents. From the statistical and spatial analysis for the different parameters, the variability of hydraulic conductivity (48%&gt;33%&gt;31%), cumulative infiltration (40%&gt;26%&gt...

An evaluation of geometrical pore parameters as influenced by rock weathering is helpful in understanding the development of soil. The objective of this study was to investigate three-dimensional (3-D) geometrical pore characteristics in rocks as affected by the degree of weathering. Rock fragments (clasts) from several moraines, ranging in age from 15-ky to 160-ky, were scanned using high-resolution X-ray computed tomography (CT) at 39-42 µm resolution. From each sample a 480×480×580 data block were extracted for analysis with 3-Dimensional Medial Axis Rock (3DMA-Rock) computer software. As weathering increased, samples developed more pores, and these pores were more extensively connected to other pores. Highly weathered samples had pores with the highest coordination numbers and characteristic coordination number constants. These parameters were significantly different from the un-weathered or partially weathered samples. More weathering also resulted in longer path lengths (PLs) and larger path length constants. PLs were < 2 mm for the un-weathered samples while partial and more fully weathered samples had values ranging up to 6 mm. The average tortuosity values decreased from 2.34 to 1.30 with weathering. Results indicated that 3-dimensional analysis of pore geometry can be used to discriminate rock weathering as well as to better understand the spatial variations in pore parameters.

A field experiment was carried out on sugarcane plant-ratoon system to develop nutrient management strategies for sustaining soil health, quality and sugarcane production at Research Farm, Dr. Rajendra Prasad Central Agricultural University, Pusa, Bihar. Trials were conducted to test the efficiency of various fertilizers in sugarcane on solubility of applied inorganic fertilizer during spring season in calcareous soil. The pooled data revealed that number of millable cane (NMC), cane and sugar yield varied significantly due to integrated use of organic and inorganic fertilizer with bio-fertilizer in combination both in plant and ratoon crops. The significant increase in NMC, cane and sugar yield was recorded in the treatments receiving organic and inorganic fertilizer in combination with bio-fertilizer over control. The highest number of NMC (103.0 × 10 3 ha-1), cane yield (85.8 t ha-1) and sugar yield (11.21 t ha-1) was recorded in treatment T9 i.e 75% NPK of RDF + Acetobacter

Soil health refers to the ecological equilibrium and the functionality of a soil and its capacity to maintain a well balanced ecosystem with high biodiversity above and below surface, and productivity. However, feeding seven billion people with environmental sustainability is a challenge for the next generations. Good soil physical health is essential for optimum sustained crop production. Soil tillage has a direct influence on the soil physical health. Tillage exerts impact on the soil purposely to produce crop and consequently affects the environment. An appropriate tillage system needs to be practiced so as to take care of the soil health, plant growth and the environment simultaneously. Therefore, to achieve sustainable food production with minimal impact on the soil and the atmosphere, conservation tillage practices become more important now than ever ensuring sustainable food production and maintaining environmental integrity. This paper aims to review the work done on maintai...

The dynamics of soil structure is driven by hydraulic and mechanical stresses. Hydraulic stress causes soil swelling and shrinkage during natural wetting and drying. Mechanical load results in soil compaction. In this paper we combined the hydraulic and mechanical stresses by considering shrinkage, moisture release and compaction concurrently. The volume of rigid pores compacted by mechanical stress do not alter soil pore shrinkage capacity. Their shrinkage curves are parallel to each other with an identical coefficient of linear extensibility (COLE) and shrinkage slope, although their structural shrinkage phases narrow with an increase in compaction stress. With different shrinkage properties of rigid and non-rigid pores, we proposed numerical methods to illustrate the bundle of the e-ϑ-σ relationship as affected by mechanical stress stemming from tillage management, and to model the loaded soil shrinkage behavior. The similarity of soil shrinkage behavior before and after tillage management can be easily assessed regarding the dynamics of soil structure during natural wetting and drying cycles.

Abstract: There are two types of mycorrhizae: ectomycorrhizae and endomycorrhizae. Ectomycorrhizae form an extensive dense sheath around the roots, called a mantle. Hyphae from the fungi extend from the mantle into the soil, which increases the surface area for water and mineral absorption. This type of mycorrhizae is found in forest trees, especially conifers, birches, and oaks. Endomycorrhizae, also called arbuscular mycorrhizae, do not form a dense sheath over the root. Instead, the fungal mycelium is embedded within the root tissue. Endomycorrhizae are found in the roots of more than 80 percent of terrestrial plants We concluded that The relationship between plants and fungi is symbiotic because the plant obtains phosphate and other minerals through the fungus, while the fungus obtains sugars from the plant root. The long extensions of the fungus, called hyphae, help increase the surface area of the plant root system so that it can extend beyond the area of nutrient depletion. E...

Grassland grazing, driven human activities, represents a prevalent form of land use conversion. While numerous studies have examined the impact of such conversions on soil carbon cycling, they primarily focus on the content and storage of soil organic carbon (SOC). However, research on the turnover dynamics of SOC and the underlying mechanisms triggered by land use conversions remains relatively scarce. In this study, radiocarbon ( 14 C) tracing technology was applied to investigate the effects of grassland grazing on SOC turnover in the Saihanba area of Hebei province, China. The results revealed that the turnover time of SOC in pasture grassland was shortened by approximately 250 years compared to meadow grassland, suggesting that grazing diminishes the ability of topsoil to stabilize SOC. Furthermore, our findings indicate that grazing leads to a decrease in soil CO 2 flux by 0.50 g C m -2 y -1 under aggregates larger than 250 μm and those between 63 and 250 μm. Conversely, the CO 2 flux under aggregates, specifically those between 2 and 63 μm and less than 2 μm, increased by 0.96 g C m -2 y -1 . This shift suggests a significant increase in the contribution of older SOC pools to the overall soil CO 2 flux. Our study provides novel insights into SOC cycling in the context of grassland grazing, highlighting the importance of understanding SOC turnover dynamics for effective land management.

Root exudation contributes to soil carbon allocation and also to microbial C and energy supply, which subsequently impacts soil aggregation around roots. Biologically-driven soil structural formation is an important driver of soil fertility. Plant genetic determinants of exudation and more generally of factors promoting rhizosphere soil aggregation are largely unknown. Here, we characterized rhizosphere aggregation in a panel of 86 pearl millet inbred lines using a ratio of root-adhering soil dry mass per root tissue dry mass (RAS/RT). This ratio showed significant variations between lines, with a roughly 2-fold amplitude between lowest and highest average values. For 9 lines with contrasting aggregation properties, we then compared the bacterial diversity and composition in root-adhering soil. Bacterial α-diversity metrics increased with the &quot;RAS/RT ratio.&quot; Regarding taxonomic composition, the Rhizobiales were stimulated in lines showing high aggregation level whereas Bac...

Abstract. The Georgia P Index was developed as a tool to evaluate the risk of bioavailable P loss in fields under various management practices. We compared the results of the P Index with four years of data from 1.5 m by 4.6 m bermudagrass plots fertilized with poultry litter at ...

In the Fraser River Delta of British Columbia, Canada, one in three farms faces soil problems associated with poor structure and low organic matter content. Surface soil structure usually degrades in early spring due to prolong wet conditions and a lack of surface cover during winter. Rates of change of surface soil aggregation under different overwinter cover crops followed by spring tillage operations were studied on a lowland soil in the Fraser River. Cover cropping treatments were bare control, winter-killed spring barley (Hordeurn vulgare L.) (cv. Virden), fall rye (Secale cereale L.) (cv. Danko) and annual ryegrass (Lo&m multiflorurn Lam.) (cv. Westerwolds). Aggregate stability, expressed as mean weight diameter (MWD) and the 2-6 mm aggregate-size fraction, decreased from fall to spring, then increased again over summer months. This seasonal variation in MWD was much more pronounced in the least stable bare soil than in the more stable cover cropped soils. In spring, overwinter cover crops had significantly higher MWD and the proportion of 2-6 mm water-stable aggregates up to 0.75 mm and 0.27 kg kg-i, respectively, when compared to bare control soil. Improved aggregate stability with cover crops was related to increasing organic carbon in the soil. After the plots were cultivated in spring, winter cropped soils had lower proportion of > 6 mm clods up to 0.28 kg kg-' than did soils left bare over winter. On the other hand, tilled plots had higher MWD and 2-6 mm aggregates for all cover cropping treatments due to lower aggregate water content at sampling, when compared to no-tilled plots. Overall, the greatest improvement in aggregate stability was observed under annual ryegrass, followed by fall rye and winter-killed spring barley. The results suggest that winter cover crops, such as annual ryegrass, may protect aggregate breakdown during winter and result in better structure after spring tillage operations when compared to the bare soil. 0 1997 Elsevier Science B.V.

Because plant absorption of P depends on the desorption of P around soil aggregates Linquist et from soil, understanding P desorption from soils may improve the precision of P diagnosis and fertilization recommendations. Many al., 1997), suggesting that larger soil aggregates with soils with high P retention due to high levels of Fe and Al are also relatively less surface area than small aggregates may highly aggregated. Extractable P is sometimes higher on larger size reduce P fixation and result in increased availability of aggregates, which will probably result in increased P release from recently applied P. With equivalent levels of extractable aggregates. The effects of aggregate size on P availability of three P, one might expect that desorption from larger aggrehighly weathered soils were quantified with a column-leaching study gates may be lower if P diffuses deeply into the agand a pot experiment. Phosphorus desorption by leaching from small gregates. aggregates was greater than that from large aggregates when P had Soil P release may affect both P supply to plants and been added to the bulk soil (Kapaa and Leilehua soils) and a mixture P discharge from watersheds. Desorption of P would, of different-sized aggregates (Leilehua soil). When aggregates were therefore, probably be more pertinent than P sorption separated and then P added, however, P desorption was greater from large aggregates (4-6 mm) than from small aggregates (Ͻ0.5 mm). when evaluating plant-available P and P buffering prop- erties of soil, an observation noted many years ago by expanded Elovich equations suggests that P desorption is probably . Several experimental techcontrolled by diffusion processes. A pot experiment showed that total niques have been used to investigate P desorption. These include extraction of soil P with P-free solution shoots, and the root dry weights of plants grown in the large aggregates (Kafkafi et al., 1967;, addition of materi-(2-6 mm) were higher than for plants grown in the small aggregates als with high capacities to bind P in order to deplete P (Ͻ0.5 mm) after equal amounts of P were added to the separated in soils , and aggregate fractions. Increased P uptake with increased aggregate size leaching of soil columns with P-free solutions (Sawhney, was attributed to increased P release from aggregates because of 1977; van der Zee and Gjaltema, 1992). The soil column reduced P fixation. The results suggest that soil management that favors soil aggregation may, in some cases, increase availability of leaching method was used in our experiments because applied P. Perhaps the distribution of soil aggregates should be consid-it prevented the breakup of soil aggregates resulting ered in making P management decisions.

La geometría fractal permite describir teóricamente estructuras de diversa naturaleza. De esta se obtiene, la dimensión fractal de fragmentación (D), la cual, está relacionada con el particionamiento y escalamiento que presentan las mismas, y que ha sido empleada en la caracterización y estudio de distribución de tamaño de partículas del suelo (DTP). Se planteó aplicar el modelo fractal e investigar sobre el proceso de microestructuración en seis suelos agrícolas de la pradera pampeana con DTP contrastantes. Las DTP y las D se obtuvieron bajo dos pretratamientos, uno sin materia orgánica (SMO), máxima dispersión, y otro con materia orgánica (CMO) conservando así la microestructura. El modelo fractal aplicado a la DTP con el pretratamiento SMO, en los suelos franco limosos, alcanzó a describir en promedio el 98% de la masa analizada; en el suelo franco arenoso ajustó hasta los 50 µm, describiendo el 38% de la masa, mientas que el suelo areno franco no ajustó al modelo fractal. Con lo...

size and density are identified as two of the most impor- tant properties of soil aggregates. Aggregate density is DENSITY BY VOLUME DISPLACEMENT used to estimate inter-aggregate porosity, and, together with aggregate size, influence plant growth (De Freitas IN TWO NON-MIXING LIQUIDS et al., 1996). During the last decade, fractal models of soil structure have been developed that use variations in Guillermo O. Sarli, Roberto R. Filgueira, and Daniel Gime ´nez* aggregate density with aggregate size as a fundamental scaling property related to soil water retention and other Abstract soil properties (Rieu and Sposito, 1991). There is an interest in methods to determine density of soil aggre-Soil aggregate density is an important property influencing soil gates, and several methods have been proposed. biological, chemical, and physical processes. Current methods used Some methods use a group of aggregates to determine to estimate soil aggregate density are based on more or less restrictive assumptions or require specialized equipment. This study was con-an average aggregate density. In this group is the method ducted to develop an alternative method for measuring aggregate proposed by Chepil (1950), which was successfully used density of soil and other porous objects that is both simple and theoretto determine the density of aggregate size fractions sepaically sound. The proposed method solves the balance of forces rerated by sieving dry soil (Eghball et al., 1993; Filgueira sulting when a kerosene-saturated aggregate is immersed in a mix of et al., 1999a, 1999b). The method, however, assumes water and glycerin. We tested the accuracy of the method by measuring that aggregates and sand grains of similar size pack in the volume of 40 aggregates with diameters ranging from 4 to 20 mm the same way. This assumption is likely to introduce and with variable densities. Soil aggregates were saturated in kerosene, error in the determination of the density of irregularlydrained at a tension of Ϫ30 mm, and their volume estimated using a shaped aggregates. Voorhees et al. (1966) circumvented pycnometer. Upon resaturation, aggregates were suspended from a this problem by using a mixture of glass beads and thread and successively weighed in air, in kerosene, and in a mix of water and glycerin. Aggregate volumes and densities varied between aggregates packed to a known volume to determine 1.20 ϫ 10 Ϫ7 and 3.85 ϫ 10 Ϫ6 m 3 and between 1.05 to 1.86 Mg m Ϫ3 , reaggregate density. The same principle was applied by spectively. On average, aggregate volumes estimated with the pycno-

Phosphorous is an essential nutrient in plants required for root establishment. In the soil, it is applied as DAP, TSP or phosphate rocks. In acid soils, aluminium and iron are dominant and tend to “fix” phosphorous, making it unavailable for plant uptake. Phosphorous deficiencies are monitored through soil chemical analysis. There are many methods for the extraction of available forms; however the choice is dependent on several factors among them soil pH. Forty soil samples were collected from three different acid soils in Western Kenya. The samples were air dried, sieved under 2.0 mm sieve and stored in sample bags for subsequent analysis. Phosphorous extraction of was carried out using a basic extractant (Olsen bicarbonate method) and acid extractant (double acid method). The extracts were measured colorimetricaly by the ascorbic acid method at 880 nm wavelength. The methods were compared in terms of extracting efficiency, correlations and soil critical levels. The soils had a pH...

A five-year monitoring study has been carried out to examine the combined effects of grazing and atmospheric nitrogen deposition on water and solute fluxes in dry coastal dune grasslands. Two vegetation types were studied: (a) a short, species-rich stand on calcareous sand (foredune site) and (b) a short, species-poor stand on partly decalcified soil on calcareous sand (innerdune site). In

Microbial soil communities play a fundamental role in soil organic matter mineralization, which is a key process for plant nutrition, growth and production in agro-ecosystems. A number of these microbial processes take place in the rhizosphere: the soil zone influenced by plant roots activity, which is a &quot;hotspot &quot; of biological and physico-chemical activity, transfers and biomass production. The knowledge of rhizosphere processes is however still scanty, especially regarding the interactions between physico-chemical processes occurring there and soil microorganisms. The rhizosphere is a place where soil aggregates are more stable, and where bulk density, porosity, water and nutrients transfer are modified with respect to the bulk soil (e.g. because of production of mucilage, of which exo-polysaccharides (EPS) produced by roots and microorganisms. During a maize field experiment, rhizospheric soil (i.e. soil strongly adhering to maize roots) and bulk soil were sampled twic...

Production of exopolysaccharides (EPS) can be used as a criteria for the isolation of stress tolerant microorganisms. In the present study, EPS-producing fluorescent pseudomonads were isolated from alfisols, vertisols, inseptisols, oxisols, and aridisols of different semiarid millet growing regions of India and were screened in vitro for drought tolerance in trypticase soy broth supplemented with different concentrations of polyethylene glycol (PEG6000). Out of the total 81 isolates, 26 could tolerate maximum level of stress (-0.73 MPa) and were monitored for the amount of EPS produced under maximum level of water stress. The strain GAP-P45, isolated from alfisol of sunflower rhizosphere, showed the highest level of EPS production under water stress conditions, was identified as Pseudomonas putida on the basis of 16S rDNA sequence analysis, and was used as seed treatment to study its effect in alleviating drought stress effects in sunflower seedlings. Inoculation of Pseudomonas sp. strain GAP-P45 increased the survival, plant biomass, and root adhering soil/root tissue ratio of sunflower seedlings subjected to drought stress. The inoculated bacteria could efficiently colonize the root adhering soil and rhizoplane and increase the percentage of stable soil aggregates. Scanning electron microscope studies showed the formation of biofilm of inoculated bacteria on the root surface and this, along with a better soil structure, might have protected the plants from the water stress.

Primeiramente agradeço a minha família: meu pai, por ter me mostrado a geologia, ciência à qual eu não conhecia nos idos de 2004, pela paciência e muito mais; minha mãe, pelo carinho, dedicação e por ser minha base e meu irmão, maior companheiro da minha vida. Agradeço especialmente minhas orientadoras, Prof.ª Dr.ª Helena Polivanov e Prof.ª Drª Andrea Borges pelo projeto e pela ajuda na execução do mesmo. A Prof.ª Dr.ª Helena Polivanov agradeço ainda pelos três anos de estágio, por ter tido paciência quando entrei "cru" no laboratório e por ter me dado força nesses anos. Agradeço ao Prof. Dr. Emílio Barroso pelas sugestões e ensinamentos e a Fátima Seabra e Osório Luiz por toda ajuda dada nos ensaios nos laboratórios de Solos e Via Úmida, respectivamente. Agradeço ao meu braço direito nesse projeto, Matheus Amaral, e pela colaboração de Mário e Kadson. Agradeço aos meus amigos, que me aturaram em toda a faculdade. Sem vocês, com certeza, a faculdade não teria graça alguma. Muito obrigado pelas descontrações, estudos e pelas tantas alegrias por qual passamos nesses cinco anos. Agradeço a Prof.ª Dr.ª Laura Maria Goretti da Motta por ter cedido seu laboratório, a Msc. Mariluce Ubaldo por toda atenção e sugestões dadas e todos os técnicos do Setor de Geotecnia da COPPE/UFRJ. Por fim, agradeço a minha amada Anna Claudia, pelo carinho, pela paciência e pela força que me encorajava a continuar.

Soil disturbance from tillage is a major cause of organic matter depletion and reduction in the number and stability of soil aggregates when native ecosystems are converted to agriculture. No-till (NT) cropping systems usually exhibit increased aggregation and soil organic matter relative to conventional tillage (CT). However, the extent of soil organic matter changes in response to NT management varies between soils and the mechanisms of organic matter stabilization in NT systems are unclear. We evaluated a conceptual model which links the turnover of aggregates to soil organic matter dynamics in NT and CT systems; we argue that the rate of macroaggregate formation and degradation (i.e. aggregate turnover) is reduced under NT compared to CT and leads to a formation of stable microaggregates in which carbon is stabilized and sequestered in the long term. Therefore, the link between macroaggregate turnover, microaggregate formation, and C stabilization within microaggregates partly determines the observed soil organic matter increases under NT.