Frequent cultivation and overhead irrigation have led to severe surface crusting, erosion and poor irrigation performance on sandy clay loam soils in the Coal River Valley, Tasmania, Australia. This study was established to identify the key soil properties related to aggregate breakdown determined by different methods, and explore options for reducing soil crusting.
Materials and methodsSoil aggregates were collected from 0 to 5 cm depth from 20 sites managed for packet salad and lettuce production. The stability of air-dried 2.00–4.75 mm aggregates was determined by rainfall simulation, wet sieving and clay dispersion. Soil aggregates were analysed for particle size, mineralogy, soluble and exchangeable cations, pH, EC, labile carbon and total carbon. The association between aggregate stability and the measured soil properties was explored using Spearman correlation, linear regression and regression tree analysis.
Result and discussionAggregate stability determined by rainfall simulation was closely associated with soil properties that promote aggregation, including effective cation exchangeable capacity (ECEC) and the proportion of polyvalent cations (Ca2+, Al3+). In contrast, aggregate stability determined by wet sieving was associated with soil properties that promote disaggregation, including quartz and sand content, and to lesser extent, the proportion of monovalent cations (especially K+). Clay dispersion was closely associated with pH, quartz content, soil texture and the sodium adsorption ratio. Soil carbon appeared to have only moderate influence on aggregate stability, but not clay dispersion, while labile carbon was not significantly related to any measure of aggregate stability or clay dispersion. Similarly, the proportion of Na+ ions was not related to either measure of aggregate stability and was only moderately related to clay dispersion.
ConclusionsOptions for improving aggregate stability appear limited as aggregate stability was strongly related to the content of inherent soil properties such as sand/quartz and smectite contents. However, high correlation between exchangeable Ca2+ and aggregate stability determined by rainfall simulation indicates that soil crusting may be reduced through application of products that rich in Ca2+ such as gypsum.
相似文献The majority of biochar studies use soils with only a narrow range of properties making generalizations about the effects of biochar on soils difficult. In this study, we aimed to identify soil properties that determine the performance of biochar produced at high temperature (700 °C) on soil pH, cation exchange capacity (CEC), and exchangeable base cation (Ca2+, K+, and Mg2+) content across a wide range of soil physicochemical properties.
Materials and methodsTen distinct soils with varying physicochemical properties were incubated for 12 weeks with four rates of biochar application (0.5, 2, 4, and 8% w/w). Soil pH, CEC, and exchangeable base cations (Ca2+, K+, and Mg2+) were determined on the 7th and 84th day of incubation.
Results and discussionOur results indicate that the highest biochar application rate (8%) was more effective at altering soil properties than lower biochar rates. Application of 8% biochar increased pH significantly in all incubated soils, with the increment ranging up to 1.17 pH unit. Biochar induced both an increment and a decline in soil CEC ranging up to 35.4 and 7.9%, respectively, at a biochar application rate of 8%. Similarly, biochar induced increments in exchangeable Ca2+ up to 38.6% and declines up to 11.4%, at an 8% biochar application rate. The increment in CEC and exchangeable Ca2+ content was found in soils with lower starting exchangeable Ca2+ contents than the biochar added, while decreases were observed in soils with higher exchangeable Ca2+ contents than the biochar. The original pH, CEC, exchangeable Ca2+, and texture of the soils represented the most crucial factors for determining the amount of change in soil pH, CEC, and exchangeable Ca2+ content.
ConclusionsOur findings clearly demonstrate that application of a uniform biochar to a range of soils under equivalent environmental conditions induced two contradicting effects on soil properties including soil CEC and exchangeable Ca2+ content. Therefore, knowledge of both biochar and soil properties will substantially improve prediction of biochar application efficiency to improve soil properties. Among important soil properties, soil exchangeable Ca2+ content is the primary factor controlling the direction of biochar-induced change in soil CEC and exchangeable Ca2+ content. Generally, biochar can induce changes in soil pH, CEC, and exchangeable Ca2+, K+, and Mg2+ with the effectiveness and magnitude of change closely related to the soil’s original properties.
相似文献Natural sepiolite (SP) has proven effective on the in-situ immobilization remediation of Cd-contaminated soils. But the practical remediation effect may largely influenced by water management and the application of organic manure. The effects of chicken manure (CM) on SP-amended soils were investigated under normal and saturated water conditions using a pot experiment with Brassica campestris L.
Materials and methodsCd-contaminated paddy soils were amended with CM, SP, and CM?+?SP with no amendment as control. The amount of sepiolite was 0.5% (w/w, the same below) either in SP or CM?+?SP amended soils, while the amount of CM was 0.5, 1.0, and 2.0% in CM and CM?+?SP-amended soils. The plant metal contents, fresh weight, and soluble sugar content of plant edible parts were measured on harvest. Soil Cd was extracted by diethylenetriaminepentaacetic acid (DTPA) and HCl to estimate the mobility of heavy metal. Soil pH and dissolved organic matter (DOM) of rhizosphere soil were determined. The electronegative charges of soils were also measured using the zeta potential.
Results and discussionThe application of CM and increasing soil moisture on SP-amended soil increased plant growth to a greater extent than the application of SP alone. The application of CM along with the increase of soil moisture decreased Cd uptake and translocation in plants grown on SP-amended soil compared to the application of SP alone. Cd content of edible plant parts reached a minimum of 0.24 mg kg?1 with the application of 2.0% CM on SP-amended soils under water-saturated conditions, which was approximately 50% lower than the Cd concentration found when applying SP alone.
ConclusionsThe results of this study suggest that the application of sepiolite on Cd contaminated soil can effectively reduce Cd uptake by B. campestris L., and the addition of CM combined with effective water management also appears to further reduce Cd absorption and accumulation.
相似文献The purpose of this study is to determine the critical soil pH, exchangeable aluminum (Al), and Al saturation of the soils derived from different parent materials for maize.
Materials and methodsAn Alfisol derived from loess deposit and three Ultisols derived from Quaternary red earth, granite, and Tertiary red sandstone were used for pot experiment in greenhouse. Ca(OH)2 and Al2(SO4)3 were used to adjust soil pH to target values. The critical soil pH was obtained by two intersected linear lines of maize height, chlorophyll content, and yield of shoot and root dry matter changing with soil pH.
Results and discussionIn low soil pH, Al toxicity significantly decreased plant height, chlorophyll content, and shoot and root dry matter yields of maize crops. The critical values of soil pH, exchangeable Al, and Al saturation varied with soil types. Critical soil pH was 4.46, 4.73, 4.77, and 5.07 for the Alfisol derived from loess deposit and the Ultisol derived from Quaternary red earth, granite, and Tertiary red sandstone, respectively. Critical soil exchangeable Al was 2.74, 1.99, 1.93, and 1.04 cmolckg?1 for the corresponding soils, respectively. Critical Al saturation was 5.63, 12.51, 14.84, and 15.16% for the corresponding soils.
ConclusionsGreater soil cation exchange capacity and exchangeable base cations led to lower critical soil pH and higher critical soil exchangeable Al and Al saturation for maize.
相似文献In the rice-wheat rotation area, Cd contamination affects food safety of rice and wheat. However, there have been conflicting results and different conclusions on the difference in Cd accumulation capacity of rice and wheat, and the factors that led to the difference were not clear.
Materials and methodsA field survey study was conducted by collecting 60 soil and grain samples in pairs during rice and wheat harvest in 30 long-term rice-wheat rotation areas with clean and mild Cd contamination in Jiangsu Province, China. The soil physicochemical properties, total Cd, soil available Cd, and grain Cd were determined, and the factors affecting Cd accumulation in rice and wheat were analyzed.
Results and discussionThe soil pH during wheat season (22 sampling points) was slightly higher than that during rice season; thus, soil available Cd in wheat was generally lower (with an average three times lower) than that in rice soil. The mean Cd content in rice grain was only half of that in wheat grain, and the Cd concentration in rice and bioconcentration factor of rice at 26 sampling points (86.7% of total samples) were lower than those of wheat, indicating that Cd accumulation capacity of wheat was stronger than that of rice. Pearson correlation coefficient and multivariate linear regression models revealed that the main factors affecting the difference of Cd accumulation in rice and wheat were soil pH and available Cd content in soil.
ConclusionsThe Cd accumulation capacity of wheat was higher than that of rice, especially in neutral and alkaline soil, and the Cd contents in rice and wheat grain depended on the soil pH and available Cd content. The food security risk of wheat was more noteworthy than rice in rice-wheat rotation area.
相似文献The aim of this work was to study the level and degree of mobility of heavy metals in the soil–plant system and to perform bioindication observations in the Don River estuarine region and the Russian sector of the Taganrog Bay coast.
Materials and methodsThe objects of the study included samples of zonal soils (chernozem) and intrazonal soils (alluvial meadow and alluvial-stratified soils, Solonchak, sandy primitive soil) from monitoring stations of the Don river estuarine region and the Taganrog Bay coast, as well as their higher plants: Phragmites australis Cav., Typha angustifolia L., Carex riparia Curtis, Cichorium intybus L., Bolboschoenus maritimus L. Palla, and Rumex confertus Willd. The total concentrations of Mn, Ni, Cd, Cu, Zn, Pb, and Cr in the soils were determined by X-ray fluorescent scanning spectrometer. The concentration of heavy metal mobile forms exchangeable, complex compounds, and acid-soluble metal were extracted using the following reagents: 1 N NH4Ac, pH 4.8; 1 % EDTA in NH4Ac, pH 4.8; 1 N HCl, respectively. Heavy metals in plants were prepared for analysis by dry combustion at 450 °C. The heavy metal concentration in extracts from plants and soils was determined by AAS.
Results and discussionThe total contents of heavy metals in the soil may be described with a successively decreasing series: Mn?>?Cr?>?Zn?>?Ni?>?Cu?>?Pb?>?As?>?Cd. The total concentrations of As, Cd, and Zn in the soil exceed the maximum permissible concentrations levels. Contamination of alluvial soils in the estuarine zone with mobile Сu, Zn, Pb, and Cd has been revealed, which is confirmed by the high bioavailability of Cu and Zn and, to a lesser degree, Cd and Pb accumulating in the tissues of macrophytic plants. Data on the translocation of elements to plant organs have showed their predominant accumulation in the roots. Bioindication by the morphofunctional parameters of macrophytic plants (with a Typha L. species as an example) can be used for revealing the existence of impact zones with elevated contents of metals in aquatic ecosystems.
ConclusionsThe results revealed that increased content of Zn, Pb, Cu, Ni, and As in soil have anthropogenic sources. The high content of Cr in the soils is related to the lithogenic factor and, hence, has a natural source.
相似文献The aim of this study is to investigate the abundance, diversity, and distribution of archaea and bacteria as affected by environment parameters in paddy soils, with focus on putative functional microbial groups related to redox processes. Because there is generally a high iron content in the soil, we also want to test a hypothesis that soil iron concentration significantly affects microbial diversity and distribution.
Materials and methodsQuantitative PCR and barcoded pyrosequencing of 16S ribosomal RNA genes were employed to investigate the abundance and community composition of archaeal and bacterial communities in 27 surface paddy soil samples. Pearson’s correlation, analysis of variance, partial least squares regression, principal coordinates analysis, and structural equation models were performed for the analyses of gene copy numbers, α-diversity, β-diversity, and relative abundances of archaea and bacteria and their relationships with environmental factors.
Results and discussionArchaeal abundance was correlated greatest with temperature, but bacterial abundance was affected mainly by soil organic matter and total nitrogen content. Soil pH and concentrations of different ions were associated with archaeal and bacterial β-diversity. The relative abundances of Euryarchaeota and Thaumarchaeota were 61.3 and 13.1% of archaea and correlated with soil pH, which may affect the availability of substrates to methanogens and ammonia oxidizers. Dominant bacterial phyla were Proteobacteria (32.4%), Acidobacteria (17.8%), Bacteroidetes (9.3%), and Verrucomicrobia (6.0%). The relative abundances of putative bacterial reducers of nitrate, Fe(III), sulfate, and sulfur, and oxidizers of ammonia, nitrite, reduced sulfur, and C1 compounds had positive, negative, or non-significant correlations with the concentrations of their substrates. Soil iron concentration was correlated only with the distributions of some putative iron-reducing bacteria.
ConclusionsIn paddy soils characterized by dynamic redox processes, archaea and bacteria differ in relationships of abundance, diversity, and distribution with environmental factors. Especially, the concentrations of electron donors or acceptors can explain the distributions of some but not all the putative functional microbial groups related to redox processes. Depending on pH range, soil pH has a strong impact on microbial ecology in paddy soils.
相似文献To examine the effect of soil acidification on growth and nitrogen (N) uptake by maize in Ultisols.
Materials and methodsA clay Ultisol derived from Quaternary red earth and a sandy Ultisol derived from tertiary red sandstone were used in this study. A pot experiment was conducted with maize growing in the two Ultisols acidified to different pH values. Urea with 15N abundance of 10.11% was used to investigate the distribution of N fertilizer between soil and plant. Total N content and 15N abundance in plant and soil samples were determined by elemental analysis-isotope mass spectrometry.
Results and discussionCritical soil pHs of 4.8 and 5.0 were observed for maize growing in the clay and sandy Ultisols, respectively. Below the critical soil pH, increasing soil pH significantly increased maize height and the yield of maize shoots and roots (both P < 0.05), but changes in soil pH showed no significant effect on maize growth above the critical soil pH in both Ultisols. Maize growing in the sandy Ultisol was more sensitive to changes in soil pH than in the clay Ultisol. Increase in the pH in both Ultisols also increased N accumulation in maize, the N derived from fertilizer in maize, physiological N use efficiency, and N use efficiency (NUE) by maize. Changes in soil pH had a greater effect on these parameters below the critical soil pH, compared to above. The change in soil pH had a greater effect on N accumulation in maize, the N derived from fertilizer in maize, and NUE in the sandy Ultisol than in the clay Ultisol. The NUE increased by 24.4% at pH 6.0, compared with pH 4.0 in the clay Ultisol, while the NUE at pH 5.0 was 4.8 times that at pH 4.0 in the sandy Ultisol. The increase in soil pH increased the ratio of N accumulation in maize/soil residue N and decreased the potential loss of fertilizer N from both Ultisols.
ConclusionsSoil acidification inhibited maize growth, reduced N uptake by maize, and thus, decreased NUE. To maintain soil pH of acidic soils above the critical values for crops is of practical importance for sustainable food production in acidic soils.
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