| 1. |
- Blomquist, Jens, et al.
(author)
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Soil characteristics and tillage can predict the effect of 'structure lime' on soil aggregate stability
- 2022
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In: Soil Research. - 1838-675X .- 1838-6768. ; 60, s. 373-384
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Journal article (peer-reviewed)abstract
- Context. In Sweden, mixtures of 80-85% ground limestone and 15-20% slaked lime (hereafter, 'structure lime') are used in subsidised environmental schemes to improve aggregate stability and mitigate phosphorus losses on clay soils. Aims. This study investigated different rates of structure lime application and soil variables on aggregate stability on clay soils, and whether soil properties can predict aggregate stability following structure liming. Methods, Increasing application rates of 0-16 t ha(-1) of structure lime (SL0, SL4, SL8 and SL16) were tested in 30 field trials in Sweden. Soil aggregates (2-5 mm) were collected 1 year after liming and subjected to two rainfall events in a rain simulator. Key results. Leachate turbidity after the second simulated rainfall event decreased significantly (13% and 20%, respectively, in SL8 and SL16) compared with SLO, indicating improved aggregate stability. There was a near-significant interaction (P = 0.056) between treatment and trial. Grouping by initial pH(()(H2O)()) (range 6.2-8.3), clay content (10-61%), soil organic matter content (SOM, 2.2-7.1) and clay mineralogy (SmV index, 0.2-3.8) revealed different effects on turbidity. Discriminant analysis of soil characteristics and four tillage variables correctly classified the outcome for 27 of the 30 trial sites. Conclusions. Results show that structure liming can improve aggregate stability 1 year after liming, and can thereby prevent particulate P losses from soils with high clay and SOM content, low SmV index and low initial pH. The discriminant analysis also showed the importance of tillage for the outcome of structure liming. Implications. Clay soil characteristics such as SOM and pH significantly affected aggregrate stability after structure liming.
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| 2. |
- Buckley, Scott
(author)
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Predicting nitrogen mineralisation in Australian irrigated cotton cropping systems
- 2019
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In: Soil Research. - 1838-675X .- 1838-6768. ; 57, s. 247-256
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Journal article (peer-reviewed)abstract
- Cotton cropping systems in Australia have poor nitrogen (N) use efficiency, largely due to over-application of N fertiliser. The N mineralisation from soil organic N reserves is often overlooked, or underestimated despite recent studies indicating that it may contribute the majority of N exported with the crop. Predicting N mineralisation is a major challenge for agricultural industries worldwide, as direct measurements are time-consuming and expensive, but there is considerable debate as to the most reliable methods for indirect estimation. Additionally, laboratory incubations assess potential (rather than actual) mineralisation, and may not be representative of N cycling rates in the field. We collected 177 samples from most major Australian cotton growing regions, and assessed their mineralisation potential using ex situ laboratory incubations, along with an assessment of potential indicators routinely measured in soil nutrient tests. Additionally, at three unfertilised sites we conducted in situ assessment of mineralisation by quantifying soil N at the beginning of the growing season, and soil and crop N at the end of the season. We found that Australian cotton cropping soils had substantial mineralisation potential, and that soil total N and total carbon were correlated with mineralisation, and have potential to be used for prediction. Other potential indicators such as carbon dioxide production and ammonium and nitrate concentrations were not correlated with mineralisation. In parallel studies of ex situ and in situ mineralisation, we found ex situ laboratory incubations overestimated mineralisation by 1.7 times on average. We discuss findings in terms of management implications for Australian cotton farming systems.
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| 3. |
- Jämtgård, Sandra, et al.
(author)
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Optimising methods for the recovery and quantification of di- and tripeptides in soil
- 2018
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In: Soil Research. - 1838-675X .- 1838-6768. ; 56, s. 404-412
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Journal article (peer-reviewed)abstract
- Di- and tripeptides are intermediaries in the nitrogen cycle and are likely to have roles in the soil-microbeplant continuum, but they have hitherto been difficult to measure in soils. To lay the base for future studies of oligopeptides in soil, we added 10 known di- and tripeptides with diverse chemical properties to forest and agricultural soils and then recovered the peptides by means of induced diffusive fluxes using microdialysis, a minimally-intrusive soil sampling technique. The concentration of the peptides recovered with the probes was 25-39% (relative recovery) of the concentration in the external solution, and followed the same trend as previously observed for amino acids, with smaller peptides (e.g. Gly-Gly) recovered at a higher rate than larger ones (e.g. Tyr-Phe). After derivatisation with AccQ-Tag (TM), a standard method for amino acids, peptides were analysed by ultra-high-pressure liquid chromatography-triple quadrupole mass spectrometry. Multiple reaction monitoring mass spectrometry was used to quantify specific peptides with a short run time of 15 min and a detection limit of 0.01-0.02 pmol injected (0.005-0.01 pmol mL(-1)) for the different peptides. This methodology allowed successful analysis of all standard di- and tripeptides tested here. We conclude that microdialysis in combination with UHPLC-MS will allow measurement of plant-relevant fluxes of di-and tripeptides in undisturbed soil.
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| 4. |
- Keller, Thomas
(author)
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Changes in soil stress during repeated wheeling: A comparison of measured and simulated values
- 2018
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In: Soil Research. - 1838-675X .- 1838-6768. ; 56, s. 204-214
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Journal article (peer-reviewed)abstract
- Agricultural machinery traffic is one of the main causes of soil compaction in modern agriculture. Soils with weak inherent soil structural stability already have low bearing capacity and, when subjected to intensive tillage with a high frequency of traffic, are susceptible to severe soil compaction. In this study, repeated wheeling experiments were carried out on an Iranian clay soil prepared at two water contents (corresponding to 0.9 and 1.35 x water content at the lower plastic limit), two wheel loads (light and heavy rear wheel loads of a two-wheel-drive tractor) and two vehicle travel speeds (0.5 and 1 ms(-1)). The experiments tested whether the stress variations due to repeated wheeling are mainly due to variations in rut depth with repeated tyre passes and whether traffic at a higher travel speed has a smaller compaction effect. Mean normal stress was measured at three depths (0.15, 0.25 and 0.35 m) beneath the centre of tyres using cylindrical Bolling probes. Rut depth and cone index were measured after each pass. The results showed a linear increase in rut depth with consecutive tractor passes, with a greater increase on wet soil. However, bulk density increased more in dry soil than in wet soil at 0.15 and 0.25 m depth, most likely due to soil water content being close to the optimum Proctor water content. At 0.35 m depth, the bulk density increase was larger for wet soil, with obvious impacts of wheel load and travel speed (greater increase for slower speed and heavier wheel). Cone index generally increased with repeated tractor passes, with the greatest increase at 0.35 m depth in wet soil under heavy rear wheel traffic. Stress generally increased with increasing rut depth due to repeated wheeling. Reduced distance between the soil-tyre interface and the Bolling probes with increasing rut depth was investigated as a potential reason using analytical stress simulations, but could not fully explain the increase in stress with rut depth. Therefore, additional factors (e.g. soil strength) must have contributed to the stress increase with increasing number of tractor passes.
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| 5. |
- Keller, Thomas
(author)
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Plastic limits of agricultural soils as functions of soil texture and organic matter content
- 2012
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In: Soil Research. - 1838-675X .- 1838-6768. ; 50, s. 7-17
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Journal article (peer-reviewed)abstract
- The plastic limits (lower plastic limit, PL; and liquid limit, LL) are important soil properties that can yield information on soil mechanical behaviour. The objective of this paper is to study the plastic limits of agricultural soils as functions of soil texture and organic matter (OM) content. The plastic limits were highly related to the clay content. The LL was more strongly correlated with clay than was PL, but the reasons are unclear. Interestingly, PL was virtually unaffected by clay content for soils with clay contents below similar to 35%. The OM had a strong effect on the plastic limits. This effect was clearly demonstrated when analysing soils of similar texture with a range of OM. We present equations (pedotransfer functions) for estimation of PL, LL, and plasticity index (PI) from soil texture and OM. Finally, we predict that the clay content must be >= 10% for soils without OM to be plastic; however, soils with <10% clay can be plastic if OM is present. More research is needed to investigate OM effects on soil consistency.
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| 6. |
- Poeplau, Christopher, et al.
(author)
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Qualitative and quantitative response of soil organic carbon to 40 years of crop residue incorporation under contrasting nitrogen fertilisation regimes
- 2017
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In: Soil Research. - 1838-675X .- 1838-6768. ; 55, s. 1-9
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Journal article (peer-reviewed)abstract
- Crop residue incorporation (RI) is recommended to increase soil organic carbon (SOC) stocks. However, the positive effect on SOC is often reported to be relatively low and alternative use of crop residues, e.g. as a bioenergy source, may be more climate smart. In this context, it is important to understand: (i) the response of SOC stocks to long-term crop residue incorporation; and (ii) the qualitative SOC change, in order to judge the sustainability of this measure. We investigated the effect of 40 years of RI combined with five different nitrogen (N) fertilisation levels on SOC stocks and five SOC fractions differing in turnover times on a clay loam soil in Padua, Italy. The average increase in SOC stock in the 0-30 cm soil layer was 3.1Mg ha(-1) or 6.8%, with no difference between N fertilisation rates. Retention coefficients of residues did not exceed 4% and decreased significantly with increasing N rate (R-2 = 0.49). The effect of RI was higher after 20 years (4.6 Mg ha(-1)) than after 40 years, indicating that a new equilibrium has been reached and no further gains in SOC can be expected. Most (92%) of the total SOC was stored in the silt and clay fraction and 93% of the accumulated carbon was also found in this fraction, showing the importance of fine mineral particles for SOC storage, stabilisation and sequestration in arable soils. No change was detected in more labile fractions, indicating complete turnover of the annual residue-derived C in these fractions under a warm humid climate and in a highly base-saturated soil. The applied fractionation was thus useful to elucidate drivers and mechanisms of SOC formation and stabilisation. We conclude that residue incorporation is not a significant management practice affecting soil C storage in warm temperate climatic regions.
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| 7. |
- Savadogo, Patrice, et al.
(author)
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Seasonal variation in fire temperature and influence on soil CO2 efflux, root biomass, and soil water properties in a Sudanian savanna-woodland, West Africa
- 2012
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In: Soil Research. - 1838-675X .- 1838-6768. ; 50, s. 195-206
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Journal article (peer-reviewed)abstract
- Savanna ecosystems are shaped mainly by fires, the consequences of which depend on both their intensities and the season in which they occur. The effects of fire disturbance on key soil parameters are still largely unknown, yet the knowledge of those effects are crucial to our understanding and management of savanna ecosystems. This study was aimed at determining seasonal variations in fire temperature and the influence of fire on soil respiration, root biomass, and soil water infiltration. It was conducted on long-term experimental plots established in 2006 in the savanna-woodland of Burkina Faso. Four fire treatments were applied: no fire, early fire, mid dry-season fire, and late dry-season fire. The results indicated that the average maximum temperature and the residence time of the lethal temperature varied significantly (P < 0.05) depending on the season of fire occurrence, the location of the soil probe, and the interaction between these two factors. The duration of heating above the critical temperature threshold was generally longest at ground level. The season in which fire occurred significantly (P <= 0.001) affected soil respiration, soil root biomass, and soil water infiltration. In conclusion, although fire can be used as a management tool in the savanna, the effects of fire on soil should be considered.
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| 8. |
- Wetterlind, Johanna
(author)
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How does grinding affect the mid-infrared spectra of soil and their multivariate calibrations to texture and organic carbon?
- 2015
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In: Soil Research. - 1838-675X .- 1838-6768. ; 53, s. 913-921
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Journal article (peer-reviewed)abstract
- Mid-infrared (mid-IR) diffuse reflectance spectroscopy can be used to effectively analyse soil, but the preparation of soil samples by grinding is time consuming. Soil samples are usually finely ground to a particle size of less than 0.250 mm because the spectrometer's beam aperture is approximately 1-2 mm in diameter. Larger particles can generate specular reflections and spectra that do not adequately represent the soil sample. Grinding soil to small particle sizes enables the diffuse reflectance of light and more representative sample measurements. Here, we report on research that investigates the effect that grinding to different particle sizes have on soil mid-IR spectra. Our aims were to compare the effect of grinding soil to different particle sizes (2.000 mm, 1.000 mm, 0.500 mm, 0.250 mm and 0.106 mm) on the frequencies of mid-IR spectra, and compare the effect of these particle sizes on the accuracy of spectroscopic calibrations to predict organic carbon, sand, silt and clay contents. Using the Commonwealth Scientific and Industrial Research Organisation's (CSIRO) National visible-near infrared database, we selected 227 soil samples from the National Soil Archive for our experiments, and designed an experiment whereby each soil sample was ground in triplicate to the different particle sizes. These ground samples were measured using an FT-IR spectrometer with a spectral range of 4000-600 cm(-1). Grinding to particle sizes that are <= 2.000 mm reduces subsample variability. Smaller particle sizes produce finer and sharper absorption features, which are related to organic carbon, and clay and sand mineralogies. Generally, better predictions for clay, sand and soil organic carbon contents were achieved using soil that is more finely ground, but there were no statistically significant differences between predictions that use soil ground to 1 mm, 0.5 mm, 0.25 mm. Grinding did not affect predictions of silt content. Recommendations on how much grinding is required for mid-IR analysis should also consider the time, cost and effort needed to prepare the soil samples as well as the purpose of the analysis.
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| 9. |
- Barin, Mohsen, et al.
(author)
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Salinity-induced differences in soil microbial communities around the hypersaline Lake Urmia
- 2015
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In: Soil Research. - 1838-675X. ; 53:5, s. 494-504
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Journal article (peer-reviewed)abstract
- Lake Urmia in north-western Iran is one of the largest hypersaline lakes in the world, and agricultural production in the surrounding area is limited by soil salinity. We investigated the effects of salinity on belowground microbial communities in soils collected from fields of cultivated onions (Allium cepa L.) and lucerne (Medicago sativa L.), and sites with the native halophyte samphire (Salicornia europaea L.). We tested the hypotheses that salinity reduces microbial biomass and changes the structure of the microbial community. The physical and chemical properties of soil samples were analysed, and phospholipid fatty acids were identified as signatures for various microbial groups. We found that the organic carbon (OC) content was the dominant determinant of microbial biomass. We also found linear relationships between OC and the biomass of various groups of organisms across the wide salinity gradient studied. Salinity, on the other hand, caused changes in the microbial fatty acid composition that indicated adaptation to stress and favoured saprotrophic fungi over bacteria, and Gram-negative bacteria over Gram-positive. Principal component analysis showed that salinity variables and microbial stress indices formed one group, and OC and microbial biomass another. The importance of OC for high microbial biomass in severely stressed soils indicates that OC amendment may be used to mitigate salt stress and as a method of managing saline soils.
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| 10. |
- Souza e Brito, Betania Guedes, et al.
(author)
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Litter decomposition in wet and dry ecosystems of the Brazilian Cerrado
- 2020
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In: Soil Research. - : CSIRO Publishing. - 1838-675X. ; 58:4, s. 371-378
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Journal article (peer-reviewed)abstract
- Decomposition of plant litter is a crucial process in carbon and nutrient cycling in all ecosystems, but our understanding of drivers of this process in Brazilian Cerrado (savanna) ecosystems is limited. We determined the decomposition rate and the stabilisation factor in areas of cerrado sensu stricto and palm swamp (vereda) in Bonito de Minas, Minas Gerais, south-eastern Brazil. These two major Cerrado ecosystems differ markedly in environmental conditions, but primarily in water and soil conditions. We used the standardised Tea Bag Index method, characterised soil parameters, and microbial activity to evaluate the decomposition process between these ecosystems. We found higher decomposition rates in the palm swamp compared to cerrado sensu stricto, possibly due to higher soil temperature and humidity conditions and higher microbial biomass.
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