Silt Loamy Soil Research Articles

Effect of Soil Texture on Soil Nutrient Status and Rice Nutrient Absorption in Paddy Soils

Soil texture affects rice nutrient uptake and yield formation by influencing soil structure, microbial activity, and soil nutrient supply capacity. Analyzing the relationship between soil texture, nutrient content, and rice agronomic traits is of great significance for precise and efficient fertilizer application. The tillage layer (0–20 cm) of 31 paddy fields in China’s main rice-producing areas was collected to perform rice pot experiments, and soil texture characteristics, physicochemical properties, microbial-related indicators, and rice agronomic traits were measured and analyzed. The results showed that these soils could be classified into four types of soil texture: loamy sandy soil, sandy loam soil, silty loam soil, and silty soil. Analysis of variance showed that the available nitrogen (AN), available potassium (AK), and available phosphorus (AP) contents were the highest in silty loam, silty, and sandy loam soils, respectively, and silt loamy soil had the highest CEC. Principal component analysis (PCA) also showed that soil physicochemical properties can be distinguished to a certain extent according to soil texture types. For the relationship of soil texture parameters and soil physicochemical properties, soil organic matter (OM), total nitrogen (TN), AN, ammonium nitrogen (NH4+-N), and microbial carbon (MBC) contents were positively correlated with soil clay content, AK was positively correlated with silt content, and soil phosphorus status was significantly related to pH. Mantel’s test revealed significant correlations between rice N, P, and K nutrient status, dry matter accumulation, and yield, and soil available nutrient content, MBC, pH, and soil texture parameters. Structural equation modeling (SEM) indicated that sand affected soil available nutrients by regulating pH, while clay can positively influence soil available nutrients by affecting soil organic matter mineralization and microbial activity, thus influencing nutrient absorption and yield formation in rice. Overall, in rice production, the silty and silty loam paddy soil with fine texture and higher clay content facilitates the mineralization of soil organic matter and the activity of soil microbes, resulting in more available soil nutrients, which benefits the rice absorption and accumulation of nutrients. Furthermore, a higher content of clay also promotes the distribution of dry matter to the panicle, thereby promoting rice yield formation.

Role of soil texture and earthworm casts on the restoration of soil enzyme activities after exposure to an organophosphorus insecticide

Pesticides exert important effects on the soil fauna and health. However, little is known about the interactions of soil, microorganisms and earthworms in the presence of pesticides and about their respective roles in the soil biological activity. The aim of this study was to evaluate the effect of the soil type on enzyme activities, measured in bulk soil and in casts of two earthworm species, after exposure to the organophosphorus pesticide parathion. To this aim, two endogeic earthworm species (Apporectodea caliginosa and Allolobophora chlorotica) were cross-acclimated in two different soil textures (each representing the most favorable soil environment for that species). Enzyme activities were measured as a soil quality indicator in samples of bulk soil (collected at day 4 and day 7 of exposure to parathion) and in earthworm casts (collected at day 7). A short exposure (4 days) to parathion significantly (ANOVA, p < 0.001) inhibited carboxylesterases (25–43 % of inhibition) and alkaline phosphatase (∼23 % of inhibition). At day 7 of exposure, parathion impact on the overall soil enzyme activities mainly depended on the soil texture. Indeed, activity inhibition was higher (ANOVA, p < 0.001) in silt-clay soil (decrease by 37 %) than in silt-loamy soil (decrease by ∼18 %). Conversely, parathion effect was not influenced by earthworm presence/absence and earthworm species. However, after soil exposure to parathion, earthworms (both species) improved enzyme activity restoration in their casts.

Sorption, Desorption and Mobility of Microencapsulated Chlorpyrifos in Two Typical Soils.

The sorption, desorption, and mobility of microencapsulated chlorpyrifos (CPF-MC) in two typical soils, namely, silt loam and sandy, were investigated in this study. Sorption/desorption experiments were carried out by using the batch equilibration method. Results showed that the sorption isotherms of CPF-MC and emulsifiable concentrate of chlorpyrifos (CPF-EC) in silt loamy soil were similar. However, a considerable difference was observed in the sorption isotherms of two chlorpyrifos (CPF) formulations in sandy soil. The amounts of CPF desorbed from two soils in four desorption steps decreased sequentially in CPF-EC treatments, while the desorbed amounts remained stable in CPF-MC treatments. Hence, the sorption/desorption processes of CPF-EC were mainly controlled by soil affinity to CPF. However, these processes of CPF-MC were affected by the release rate of CPF from capsules. The mobility of two CPF formulations in soil was estimated in vertical columns packed with soils. Results showed that there was leaching of CPF-EC in silt loam column, whereas CPF-MC was not vertically mobile in silt loam column under the same leaching conditions. However, in column with sandy soil, the percentage of CPF-MC leaching from the column was 86.54%, which was higher than the 73.75% that leached from the column in the treatment with CPF-EC.

Leaf nutrient status of some grafted-pear rootstocks influenced by different soil types

Aim of study: Determining leaf nutrient status of some grafted-pear rootstocks grown under different calcareous soil types.Area of study: The Horticultural Research Station of Kamalabad, Karaj, Iran.Material and methods: Leaf mineral element concentrations were determined in 2015, 2016, 2017, and 2018. Leaf sampling was carried out about 90 days after full bloom. The N-content was estimated by the Kjeldahl method. Total concentration of calcium (Ca), magnesium (Mg), iron (Fe), zinc (Zn), and boron (B) were also determined by the atomic absorption spectrophotometry, and phosphorus (P) and potassium (K) were analyzed using the flame photometry. The deviation from optimum percentage (DOP) and its correlation with the ΣDOP of macro- and micro-nutrients were used to determine the nutritional status of the studied plants.Main results: In clay loamy soil pyrodwarf rootstock, which was grafted with 'William Duchess' scion, presented a more suitable balanced nutritional index than other rootstocks/scion combinations. The OHF69 rootstock grafted with 'Daregazi' offered better balanced nutritional values in fairy lime silt-loamy soil, whereas the pyrodwarf rootstock grafted with 'Louise Bonne' scion in less lime silt-loamy soil was found to have higher values than other studied rootstocks/scion combinations in terms of nutrient concentration.Research highlights: The study determined effective solutions to the field problems of calcium carbonate equivalent which distinctly affect the soil properties related to plant growth. It also revealed the most suitable pear rootstock/scion combinations in different calcareous soil types for orchard establishment in arid and semi-arid regions.

Effect of Tillage Systems on Spatial Variation in Soil Chemical Properties and Winter Wheat (Triticum aestivum L.) Performance in Small Fields

To investigate how tillage intensity modifies the small-scale spatial variability of soil and winter wheat parameters, field trials were conducted on small plots (12 m × 35 m) in three temperate environments in the Swiss midlands: Zollikofen in 1999 (loamy silt soil; Gleyic Cambisol) and Schafisheim in 1999 and in 2000 (sandy loam soil; Orthic Luvisol). Total soil nitrogen (Ntot), total carbon (Ctot) and pH were assessed after harvest. A regular nested grid pattern was applied with sampling intervals of 3 m and 1 m at 0–30 cm on a total of nine no-tillage (NT) and nine conventional tillage (CT) plots. At each grid point, wheat biomass, grain yield, N uptake and grain protein concentration were recorded. Small-scale structural variance of soil Ntot, Ctot and pH was slightly larger in NT than in CT in the topsoil in the tillage direction of the field. Wheat traits had a slightly greater small-scale variability in NT than in CT. Spatial relationships between soil and crop parameters were rather weak but more pronounced in NT. Our results suggest limited potential for variable-rate application of N fertilizer and lime for NT soils. Moderate nugget variances in soil parameters were usually higher in CT than in NT, suggesting that differences in spatial patterns between the tillage systems might occur at even smaller scales.

Resolving compactness index of pores and solid phase elements in sandy and silt loamy soils

Soil structure is expressed by the size, shape, and arrangement of structural elements. Shape indices of pores and solid phase elements along with the physical soil parameters allow for thorough evaluation of soil structure. Therefore, the aim of the research was the analysis of properties of an index of shape – a compactness index CMP=(16area)/perimeter2 – of pore (“pore c-s”) and solid phase element cross-sections (“solid c-s”) ≥100pix2 (0.045mm2) of 4 soils. CMP was calculated via image analysis of resin-impregnated soil blocks prepared from intact soil specimens. The morphometric parameters of the objects assigned to selected CMP classes (≤0.2, the lowest compactness; 0.201–0.4; 0.401–0.6; 0.601–0.8; 0.801–1; 1.001–1.2; >1.2, the highest compactness) were compared via 2-way ANOVA for two horizons (A, C) and two textures (sand, silt loam). The usability of CMP in the description of soil structure was then tested. Moreover, the relations of the morphometric parameters of the objects in CMP classes and soil physical and chemical properties (total organic carbon TOC; bulk and particle density; texture; field water capacity FWC; field air capacity FAC; available water capacity AWC; air permeability at −15kPa lgFAP; saturated hydraulic conductivity lgKS) were examined by way of single and multiple linear regressions. For pore and solid c-s of CMP>0.2 their number, area, and average areas in CMP classes decreased with increasing CMP value. The distributions of pore and solid c-s among CMP classes depended on soil texture and structure (aggregate, non-aggregate), allowing for the diagnosis of soil structure status and change. Number and area of objects in CMP classes showed numerous strong relations (R2>0.7) to the soil physical and chemical parameters for the studied soil textures and horizons. The relations differed for pore and solid c-s and depended also on the object shape (spread, compact or very compact). The average areas of the compact and very compact pore and solid c-s increased with the increase of clay and silt content and the decrease of sand content. The number of pore c-s of CMP>0.2 was related to the texture or particle density. On the other hand, the number of solid c-s of CMP>0.2, and the average area of the most spread solid c-s were related to TOC and bulk density. FWC and AWC increased with the decrease of the number of mainly compact and very compact pore c-s by the decrease of the average area of the most spread solid c-s. Both water capacities increased with the increasing average areas of pore c-s of CMP>0.2 and the average areas of the compact and very compact solid c-s. FAC increased with the increase of the number of the compact and very compact pore c-s. lgKS increased with the increase of the number and area of mostly compact and very compact pore c-s. lgFAP increased with the area and the average area of the majority of pore classes and some of the relations were also controlled by the number of pore c-s and the average area of the most spread solid c-s. The study showed moreover that CMP increased with the decreasing size of the objects when measured via computer-aided image analysis. Small cross-sections revealed usually larger CMP values, and large cross-sections were more often classified as irregular or spread. Therefore the analysis of shape of soil structural elements should encompass a wide range of element sizes in relation to the image resolution to obtain the unbiased shape distributions.

Physicochemical Properties of Silt Loamy Soil and Diversity of Diatom Species Under Winter Wheat and Oats

Physicochemical Properties of Silt Loamy Soil and Diversity of Diatom Species Under Winter Wheat and Oats

Field Assessment of Basin Irrigation Performance in Hetao, Inner Mongolia

Hetao irrigation district (Hetao) is located in the upper reaches of Yellow River basin. Surface irrigation is used because there is a high charge of sediments in the irrigation water and is appropriate to leach salts. Basin irrigation is the most used irrigation method. Traditional practices are inadequate for saving water and surface irrigation modernization is needed. A better knowledge of the performance of irrigation systems is required to base that modernization. An experimental research work was developed at Dengkou Experimental Station to assess the irrigation performance in laser land leveled fields. It is located on an irrigation sector supplied in agreement with a rotational delivery scheme managed by the Water Users Association (WUA), which usually practices a total of 7 events and the autumn irrigation. The typical field length is 50 m, with a width between 10 and 50 m, with a silt loamy soil. The irrigation performance was assess from field measurements carried out in several fields, cropped with the main irrigated crops, wheat, maize and sunflower. The irrigation field evaluation was based on observations of advance and recession times, soil moisture, inflow discharges, application time, topographic survey and crop development data. In addition, infiltration curves for typical and seasonal irrigation events were developed, and the Kostiakov infiltration parameters were estimated from field observations using the inverse method with the SIRMOD model. The irrigation operative parameters and the performance indicators were obtained, concluding that the distribution uniformity is very high, between 90 and 96%, and that the cutoff time has a very sensitive effect on beneficial water use fraction. Finally, the results of this study allowed the appropriate knowledge, including the crop irrigation scheduling data, for the irrigation design models aimed at developing irrigation alternatives.

Sorptive affinity of ionic surfactants on silt loamy soil

Due to their broad applications, ionic surfactants have already been released into or utilized in soil and environmental systems. However, current understanding on the sorption behavior of surfactants onto soils is still limited. This work systematically investigated the sorption kinetics and isotherms of one cationic surfactant, cetyltrimethylammonium bromide (CTAB), and one anionic surfactant, sodium dodecyl sulfate (SDS), onto a silt loamy soil to determine the governing sorption mechanisms. The pseudo-second-order rate equation described the sorption kinetics data better than the pseudo-first-order rate equation. Experimental data showed that the sorption equilibrium for CTAB and SDS were reached at 24 and 240 h, respectively. Langmuir equation was better than Freundlich equation in simulating the sorption isotherms of CTAB and SDS on the soil. Soil Langmuir maximum sorption capacity of CTAB was much higher than that to SDS. When the experimental temperature increased, the sorption of CTAB and SDS on the soil decreased. In addition, the sorptive process of the surfactants on the soil was spontaneous and exothermal, as indicated by the absolute values of Gibbs free energy and enthalpy. The results also indicated that physical sorption was the dominant mechanism for the sorption of the two surfactants on the soil. Findings from this work are crucial to understand the environmental behaviors of ionic surfactants.

Pore-size distribution in loamy soils: A comparison between microtomographic and capillarimetric determination methods

Pore-size distribution in a soddy-podzolic silt loamy soil developing from mantle loesslike loam (Eutric Albic Retisol (Loamic, Cutanic)) was calculated from the water retention curve according to Jurin’s equation and directly determined in microtomographic experiments. Rounded macropores with the diameter of their sections from 75 to 1000 μm predominate in horizontal sections if the studied soil samples. A larger part of the soil pores (>30–35%) belongs to micro- and nanopores, and they cannot be quantitatively determined by the tomographic method, because their sizes are smaller than the detection limit of the applied X-ray microtomography (8.75 μm per pixel). This leads to a significantly larger pore volume determined from the water retention curve in comparison with the “tomographic” pore volume. A comparative analysis of pore-size distribution curves obtained by these methods shows that the major regularities of the pore-size distribution in the range from 30 to 5000 μm are similar in both cases. Fine macropores and, partly, mesopores predominate. Common characteristics of the pore-size distribution curves obtained by these methods, including the coincidence of the peaks, attest to the validity of classical approaches, according to which the hydrology of soil pore space can be perceived as a physical model of cylindrical capillaries of different sizes with capillary-sorbed water.

Effect of irrigation and nitrogen fertilization on the production of biogas from maize and sorghum in a water limited environment

Abstract The expansion of biogas production from anaerobic digestion in the Po Valley (Northern Italy) has stimulated the cultivation of dedicated biomass crops, and maize in particular. A mid-term experiment was carried out from 2006 to 2010 on a silt loamy soil in Northern Italy to compare water use and energy efficiency of maize and sorghum cultivation under rain fed and well-watered treatments and at two rates of nitrogen fertilization. The present work hypothesis were: (i) biomass sorghum, for its efficient use of water and nitrogen, could be a valuable alternative to maize for biogas production; (ii) reduction of irrigation level and (iii) application of low nitrogen fertilizer rate increase the efficiency of bioenergy production. Water treatments, a rain fed control (I0) and two irrigation levels (I1 and I2; only one in 2006 and 2009), were compared in a split–split plot design with four replicates. Two fertilizer rates were also tested: low (N1, 60 kg ha−1 of nitrogen; 0 kg ha−1 of nitrogen in 2010) and high (N2, 120 kg ha−1 of nitrogen; 100 kg ha−1 of nitrogen in 2010). Across treatments, sorghum produced more aboveground biomass than maize, respectively 21.6 Mg ha−1 and 16.8 Mg ha−1 (p

Modification of chemical and hydrophysical properties of two texturally differentiated soils due to varying magnitudes of added biochar

The potential benefit of biochar as a soil conditioner to improve crop yield and simultaneously sequester carbon in the soil, is a subject of intense discourse. Biochar amendment of agricultural soils is presumed to improve water holding capacity of the soil, and enhance nutrient retention within the root zone. However, there are very few investigations which provide quantitative data and qualitative descriptions concerning the specific mechanisms driving these improvements in the properties of biochar-amended soils. In this study, the effect of different rates of biochar amendment on some chemical, physical and hydraulic properties of fine-sand and sandy loamy silt soils was investigated by adding 20, 50 and 100g biochar kg−1 (by dry weight). In order to evaluate the additional effects of biochar application, the initial hydrophobicity and rheological properties were also examined. The result showed that biochar amendment improved total carbon and aggregate properties. The available water capacity was significantly higher in the amended substrates, particularly in the amended fine sand. Saturated hydraulic conductivity of the sandy loam silt increased between 25% and 119%, but decreased in the fine-sand between 23 and 82%. Moreover, biochar amendment of the sandy loamy silt improved particle to particle bonding and resulted in the development of weaker (compared with the unamended control) but more resilient aggregates which were better structured. With increasing rate of added biochar (≥50–≤100gkg−1) the added biochar itself now dominated the internal soil strength of the substrate. Adding (≥20gkg−1) biochar, to the fine-sand induced particle rearrangements, which in combination with possible surface oxidation at the biochar-soil particles interphase, improved bonding in this originally non-cohesive soil. Beyond an amendment rate of 50g biochar kg−1 soil, we observed that most of the positive improvements, associated with the biochar treatment of the soils, were no longer significant and the aggregates became brittle and collapsed more easily. Our results therefore provide more detailed insights into the effect of biochar in agricultural soils depending on texture of the soil and the amount of added biochar.

Changes in microstructural behaviour and hydraulic functions of biochar amended soils

Biochar is increasingly used on agricultural soils to enhance productivity and to sequester carbon. However, there is limited research that directly quantifies the underlying mechanisms, particularly those assessing structural changes in amended soils. Also, there is scanty information on the long-term effect of biochar treatment on hydraulic response of soils. Our objective in this study therefore is to determine the effect of biochar treatment on two different soil types and to evaluate the influence on hydrological and mechanical properties that drive aggregate formation and stability. Test substrates were prepared by adding 2, 5 and 10% (by dry mass) of high temperature pyrolysed (HTP) biochar to fine-sand or sandy loamy silt soil material. The repacked cores were exposed to four cycles of wetting and drying in an experiment spanning about 300 days. Changes in the saturated hydraulic conductivity, aggregate sorptivity swelling and shrinkage behaviour, and microstructural stability during desiccation were also investigated. The results indicated that biochar amendment alters the pore structure with the saturated hydraulic conductivity being significantly increased (p<0.05) in the sandy loamy silt. Repeated wetting and drying significantly increased (p< 0.05) the repellency index of the amended substrates. Moreover micro structural stability was enhanced as the amount of biochar was increased and at lower matric potential. The partial loss of inter-particle cementation at a given pore water pressure due to increasing biochar amount was compensated by the noticeable addition of organic carbon. The combined effects of pore re-arrangement, enhanced particles surface area and improved microstructural stability in the amended soils produces better soil–plant–water environment. These findings proof that the effects of biochar amendment on pore structure, aggregation and stabilization will depend on the amount of biochar, the texture of the original soil material and the number of wetting and drying (WD) cycles.

Controlled release urea improved the nitrogen use efficiency, yield and quality of potato (Solanum tuberosum L.) on silt loamy soil

Numerous studies on the traits of controlled release urea in agronomic production and the environmental protection were conducted in various crops system. However, understanding the effect of controlled release urea on potato production and nitrogen use efficiency was currently limited. In the present study, the effect of newly developed controlled release urea (CRU) including polymer coated urea (PCU) and polymer coating of sulfur-coated urea (PSCU) on the N use efficiency, tuber yield and quality of potato (Solanum tuberosum L.) that was grown on silt loamy soil were investigated in a field experiment over 2 yr at different sites. The application rate of polymer-coated urea (PCU) and urea was 150kgNha−1, and polymer sulfur-coated urea (PSCU) was applied at 150kgNha−1 and 225kgNha−1. The N release rates from CRU synchronized the N requirement of potatoes at different stages. The CRU treatments significantly increased total tuber yields by 8.77–19.88% in 2012 and 14.36–26.46% in 2013 in comparison with the urea treatment during the same year. The marketable tuber yield percentage was pronouncedly promoted by the application of PCU and PSCU in both years. N fertilization significantly enhanced the vitamin C, soluble protein and starch content. The significant difference of vitamin C concentration in tuber was only observed in 2013 between PCU and PSCU treatments. The application of PCU and PSCU markedly improved the N agronomic efficiency and apparent N use efficiency, but obviously decreased the N physiological efficiency relative to urea treatment in 2012 and 2013. Furthermore, enhancing dose of PSCU did augment total tuber yield and did not increase the marketable yield percentage, but decreased the apparent N use efficiency compared with PSCU treatment. Consequently, moderate amounts (150kgNha−1) of PSCU and PCU are recommended to replace urea for gaining greater yields of potato and nutrient use efficiency.

Microbial Biomass and PLFA Profile Changes in Rhizosphere of Pakchoi (Brassica chinensis L.) as Affected by External Cadmium Loading

The effects of root activity on microbial response to cadmium (Cd) loading in the rhizosphere are not well understood. A pot experiment in greenhouse was conducted to investigate the effects of low Cd loading and root activity on microbial biomass and community structure in the rhizosphere of pakchoi (Brassica chinensis L.) on silty clay loam and silt loamy soil. Cd was added into soil as Cd(NO3)2 to reach concentrations ranging from 0.00 to 7.00 mg kg−1. The microbial biomass carbon (MBC) and community structure were affected by Cd concentration, root activity, and soil type. Lower Cd loading rates (< 1.00 mg kg−1) stimulated the growth of pakchoi and microorganisms, but higher Cd concentrations inhibited the growth of microorganisms. The content of phospholipid fatty acids (PLFAs) was sensitive to increased Cd levels. MBC was linearly correlated with the total PLFAs. The content of general PLFAs in the fungi was positively correlated with the available Cd in the soil, whereas those in the bacteria and actinomycetes were negatively correlated with the available Cd in the soil. These results indicated that fungi were more resistant to Cd stress than bacteria or actinomycetes, and the latter was the most sensitive to Cd stress. Microbial biomass was more abundant in the rhizosphere than in the bulk soil. Root activity enhanced the growth of microorganisms and stabilized the microbial community structure in the rhizosphere. PLFA analysis was proven to be sensitive in detecting changes in the soil microbial community in response to Cd stress and root activity.

Preparation of Bio-Material Liquid Film and its Function of Reducing Soil Water Evaporation

Surface mulch is regarded as an effective manner to reducing soil water evaporation, but limited with the adverse influence of plastic film mulch on agro-ecosystems. In this paper, liquid films were prepared with the foundation of kelp as a bio-material. The results showed that the films prepared with the mixture of kelp and polyvinyl alcohol (PA) had superimposed layering structure with tiny pores and gaps, and were stable as well as degradable under field water conditions. The results of the simulative experiments with both of aquic sand-loamy soil and yellow silt-loamy soil that mulching with the film of the mixture of kelp and polyvinyl alcohol (PA) could significantly (P&lt;0.01) reduce water evaporation from soil. It was also found that mulching with the liquid films could increase the water retention capacity of the tested soils. As the initial material – kelp is available, the application of the developed liquid film based on kelp for efficient soil moisture management in agricultural production should be recommended.

Quantification of mycorrhizal water uptake via high-resolution on-line water content sensors

The benefits of mycorrhizas for host plants are well known for a large number of species. However, experimental evaluations of the hyphal contribution to the total water uptake and the assessment of the bulk flow velocity in the hyphae are so far contradictory. Barley (Hordeum vulgaris L. Scarlet) with the inoculum Glomus intraradices was grown in a split plant-hyphal chamber with a 5 mm air gap. During the preparation of the chambers with a loamy-silt soil, water content sensors were inserted in each of the plant and the hyphal compartments. These sensors allow non-destructive measurements with high resolution. In total, 8 drying periods with a length of several days were applied with repeated watering following each drying period. A clear decline in water content in the hyphal compartment during each drying period supports the ability of hyphae to transfer water into the plant compartment. The difference between the decline in the hyphal compartment with and without arbuscular mycorrhyzal fungi is significant at the p < 0.000001 level. The direct and indirect hyphal contribution to the total water uptake was estimated to be about 20%. The application of capacitance sensors for water content determination with a special geometry adapted to the plant-hyphal chambers allows the evaluation of the hyphal water flow with high accuracy.

Morphological characteristics of soybean root apexes as indicators of soil compaction

Plant soil compaction poses a serious problem to agriculture because it produces different types of changes in plant characteristics. No method has been implemented to date to use root morphological changes as indicators of soil compaction levels. Therefore, the aim of the present study was to evaluate whether or not the morphological changes in root apexes of soybean (Glycine max (L.) Merrill) can be used as indicators of soil compaction levels. To this end, a silt-loamy soil material (from a Typic Argiudoll, Esperanza series), sieved through a 2 mm mesh was used and the following soil bulk density levels were determined: 1.1, 1.3 and 1.5 g cm³ for which the corresponding mechanical resistances were &lt; 0.1, 0.5 and 3.5 MPa, respectively. The distance from the apex to the first tertiary root and the root diameter at 1.5 cm from the apex were measured on the secondary root apexes. A form factor equal to the quotient between these two variables was subsequently calculated. An inverse relationship between soil mechanical impedance and secondary root length and form factor as well as a direct relationship with the secondary root diameter were observed. Changes in rhizodermis cells were also recorded. The following morphological characteristics were found to evidence the highest sensitivity to soil compaction: i) the form factor, ii) rhizodermis papillose cells, iii) apical malformations in root hairs, and iv) root diameter in expansion areas. Taken together, the morphological characteristics of root apexes could be considered to be indicative of soil compaction.

Effect of pH on the release of soil colloidal phosphorus

Colloid-facilitated phosphorus (P) has been proved as a significant contributor to eutrophication. Release of colloidal phosphorus (Pcoll) depends on the released soil colloids and their P adsorption abilities, both of which are greatly affected by pH. The aim of the study was to assess the effect of pH in a wide range on Pcoll loss of the top silt loamy soil rich in organic matter and P for the successful description and prediction of P transport. In batch experiment, soil samples were shaken with deionized water in a wide range of pH from 1.4 to 9.9 for 24 h. Then water-dispersible colloids (WDCs) were extracted by pre-centrifugation, microfiltration, and ultracentrifugation processes orderly and determined gravimetrically. The Pcoll values at each pH were calculated as the difference between the concentration of total P in non-ultracentrifuged and ultracentrifuged samples. The same method was applied for the released colloidal mineral elements (Al, Fe, Ca, Si, Mg, Mn). Colloid morphology and P distribution on colloid surface were directly illustrated by transmission electron microscope (TEM) and scanning electron microscope-energy-dispersive X-ray spectroscopy (SEM-EDS) mapping scanning analyses. Over pH 4.6–6.0, the released Pcoll was below 5.5 mg kg–1 soil, while up to 66.8 mg kg–1 soil and 28.5 mg kg–1 soil at pH 1.4 and 9.9, respectively, indicating that both high and low pH values enhanced the mobilization of Pcoll. At the low pH, the potential loss of Pcoll mainly resulted from the dissolution of inorganic encasing cement such as Al oxides and clay mineral. However, besides electrostatic repulsion, dissolution of organic coating at high pH enhanced the Pcoll release as revealed by the SEM-EDS results. The P was heterogeneously distributed on the WDCs and might be associated with soil organic matter, Al oxides, Fe oxides (oxyhydroxide), and clay mineral at the low pH, while mainly with Fe oxides and less clay mineral at the high pH. Both high and low pH enhanced colloid and Pcoll releases. This study first visually revealed that the dissolution of organic cement at high pH enhanced the release of WDCs and their facilitated Pcoll release. The exceptional loss risk of Pcoll may be caused by soil acidification due to the dissolution of inorganic cements, especially in Al-rich soils, and by the enhanced high soil pH due to the dissolution of organic coating in the organic matter-rich soils.

Accumulation Properties of Cadmium in a Selected Vegetable-Rotation System of Southeastern China

A rotation experiment was conducted in a greenhouse with three vegetable crops on red yellowish soil (RYS) and silt loamy soil (SLS) to study Cd accumulation in pak choi ( Brassica chinensis L.), tomato ( Lycopersicon esculentum), and radish ( Raphanus sativus L.). Critical Cd concentrations in the two soils were evaluated for these vegetables based on human dietary toxicity. Cadmium was added as Cd(NO 3) 2 at a rate of 0-7.00 mg Cd kg (-1) soil. Shoot growth was not inhibited by Cd except for radish grown on RYS. A small amount of Cd stimulated growth of the vegetables. Cadmium concentration in edible parts of the vegetables generally increased with Cd concentration in soils but was higher in RYS than SLS. The distribution of Cd in pak choi and tomato decreased in the order root > shoot > fruit, but the order was shoot > root for radish. When Cd content in the edible parts reached maximum contaminant levels for safety food standards, the soil total Cd concentrations were 0.327 and 0.120 mg kg (-1) in RYS and 0.456 and 0.368 mg kg (-1) in SLS for pak choi stem and radish, respectively, whereas ammonium acetate-extractable Cd was 0.066 and 0.089 mg kg (-1) in RYS and 0.116 and 0.092 mg kg (-1) in SLS for pak choi leaf and tomato, respectively, based on food safety standards.