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Soil science students are required to apply knowledge from a range of disciplines to unfamiliar scenarios to solve complex problems. To encourage deep learning (with student performance an indicator of learning), a formative assessment exercise was introduced to a second-year soil science subject. For the formative assessment exercise, students were required to prepare a draft of a critical review of a current topic in soil science, and then (following guidance from staff members) provide feedback to each other through a peer assessment exercise. In contrast to expectations, the formative assessment did not appear to improve overall student performance in this task based upon their grades for this task. Furthermore, despite being given an exemplar and attending a workshop where tactics for searching the scientific literature were discussed, this did not increase the likelihood that students would cite studies from the scientific literature when conducting their critical review. Regardless of these observations, the students were positive and appreciated the feedback they received through the exercise. This study demonstrates the need to ensure that feedback is effective and enables students to identify their weaknesses and modify their work accordingly. (Contains 4 tables.)

In the natural environment, soils undergo wetting and drying (WD) cycles due to precipitation and evapotranspiration. The WD cycles have a profound impact on soil physical, chemical, and biological properties and drive the development of structure in soils. Degraded soils are often lacking structure, and the effect of organic amendments and WD cycles on structure formation of these soils is poorly understood. The aim of this study was to evaluate the role of biotic and abiotic factors on aggregate formation and stabilization of sodic soils after the addition of gypsum and organic amendments (feedlot manure, chicken manure, lucerne pallets, and anionic poly acrylamide). Amended soils were incubated at 25 ∘ C over four WD cycles, with assessment of soil microbial respiration, electrical conductivity, pH, sodium adsorption ratio (SAR), aggregate stability in water (ASWAT), aggregate size distribution, and mean weight diameter. Our results demonstrate that WD cycles can improve aggregate stability after the addition of amendments in sodic Vertisols, but this process depends on the type of organic amendment. Lucerne pellets resulted in highest soil microbial respiration, proportions of large macroaggregates (>2000 µ m), and mean weight diameter. In contrast, dispersion was significantly reduced when soils were treated with chicken manure, whilst anionic polyacrylamide only had a transient effect on aggregate stability. When these organic amendments were applied together with gypsum, the stability of aggregates was further enhanced, and dispersion became negligible after the second WD cycle. The formation and stability of small macroaggregates (2000–250 µ m) was less dependent on the type of organic amendments and more dependent on WD cycles as the proportion of small macroaggregates also increased in control soils after four WD cycles, highlighting the role of WD cycles as one of the key factors that improves aggregation and stability of sodic Vertisols. [ABSTRACT FROM AUTHOR]

In the natural environment, soils undergo wetting and drying (WD) cycles due to precipitation and evapotranspiration. The WD cycles have a profound impact on soil physical, chemical, and biological properties and drive the development of structure in soils. Degraded soils are often lacking structure and the effect of organic amendments and WD cycles on structure formation of these soils is poorly understood. The aim of this study was to evaluate the role of biotic and abiotic factors on aggregate formation and stabilisation of sodic soils after the addition of gypsum and organic amendments (feedlot manure, chicken manure, lucerne pallets, and anionic poly acrylamide). Amended soils were incubated at 25 °C over four WD cycles, with assessment of soil microbial respiration, electrical conductivity, pH, sodium adsorption ratio (SAR), aggregate stability in water (ASWAT), aggregate size distribution, and mean weight diameter. Our results demonstrate that WD cycles can improve aggregate stability after the addition of amendments in sodic Vertisols, but this process depends on the type of organic amendment. Lucerne pellets resulted in highest soil microbial respiration, proportions of large macroaggregates, and mean weight diameter. In contrast, dispersion was significantly reduced when soils were treated with chicken manure, whilst PAM only had a transient effect on aggregate stability. When these organic amendments were applied together with gypsum, the stability of aggregates was further enhanced, and dispersion became negligible after the second WD cycle. The formation and stability of small macroaggregates was less dependent on the type of organic amendments and more dependent on WD cycles as the proportion of small macroaggregates also increased in control soils after four WD cycles, highlighting the role of WD cycles as one of the key factors that improves aggregation and stability of sodic Vertisols. [ABSTRACT FROM AUTHOR]

Background and Aims Signal grass (Urochloa decumbens) is a widely used pasture grass in tropical and sub-tropical areas due to its high aluminiun (Al) resistance. However, the underlying mechanisms conferring this resistance are not clearly understood. Methods The Al concentrations of bulk root tissues and the intracellular compartment were examined, including the impact of a metabolic inhibitor, carbonyl cyanide m -chlorophenyl hydrazone (CCCP). Next, we examined changes in the properties of signal grass root tissues following exposure to toxic levels of Al, including the cell wall cation exchange capacity (CEC), degree of methylation and concentrations of cell wall fractions. Key Results Although signal grass was highly resistant to Al, there was a delay of 24–48 h before the expression of this resistance. We found that this delay in the expression of Al resistance was not related to the total Al concentration in the bulk apical root tissues, nor was it related to changes in the Al bound to the cell wall. We also examined changes in other properties of the cell wall, including the CEC, degree of methylation and changes in the concentration of pectin, hemicellulose and cellulose. We noted that concentrations of intracellular Al decreased by approx. 50 % at the same time that the root elongation rate improved after 24–48 h. Using CCCP as a metabolic inhibitor, we found that the intracellular Al concentration increased approx. 14-fold and that the CCCP prevented the subsequent decrease in intracellular Al. Conclusions Our results indicate that the delayed expression of Al resistance was not associated with the Al concentration in the bulk apical root tissues or bound to the cell wall, nor was it associated with changes in other properties of the cell wall. Rather, signal grass has an energy-dependent Al exclusion mechanism, and this mechanism requires 24–48 h to exclude Al from the intracellular compartment. [ABSTRACT FROM AUTHOR]

Modification of cell wall components such as cellulose, hemicellulose and pectin plays an important role in cell expansion. Cell expansion is known to be diminished by cations but it is unknown if this results from cations reacting with pectin or other cell wall components. Autolysis of cell wall material purified from bean root (Phaseolus vulgaris L.) occurred optimally at pH 5.0 and released mainly neutral sugars but very little uronic acid. Autolytic release of neutral sugars and uronic acid was decreased when cell wall material was loaded with Ca, Cu, Sr, Zn, Al or La cations. Results were also extended to a metal–pectate model system, which behaved similarly to cell walls and these cations also inhibited the enzymatic degradation by added polygalacturonase (EC 3.2.1.15). The extent of sugar release from cation-loaded cell wall material and pectate gels was related to the degree of cation saturation of the substrate, but not to the type of cation. The binding strength of the cations was assessed by their influence on the buffer capacity of the cell wall and pectate. The strongly bound cations (Cu, Al or La) resulted in higher cation saturation of the substrate and decreased enzymatic degradability than the weakly held cations (Ca, Sr and Zn). The results indicate that the junction zones between pectin molecules can peel open with weakly held cations, allowing polygalacturonase to cleave the hairy region of pectin, while strongly bound cations or high concentrations of cations force the junction zone closed, minimising enzymatic attack on the pectin backbone. [Copyright &y& Elsevier]

The mechanism of pectin gelation depends on the degree of methoxylation. High methoxyl pectin gels due to hydrophobic interactions and hydrogen bonding between pectin molecules. Low methoxyl pectin forms gels in the presence of di- and polyvalent cations which cross link and neutralise the negative charges of the pectin molecule. Monovalent cations normally do not lead to gel formation with high methoxyl pectin solutions free of divalent cations, especially Ca. The present study found that alkali (NaOH or KOH) added to high methoxyl pectin leads to gel formation in a concentration-depended manner. It was also found that monovalent cations (Na and K) induce gelation of low methoxyl pectin and the time required for gel formation (setting time) depends on the cation concentration. The results indicate that a combined charge neutralisation and ionic strength effect is responsible for the monovalent cation-induced gelation of pectin. [Copyright &y& Elsevier]

The human sperm motility assay was used as a measure of quality control in the IVF laboratory. The effects of albumin supplementation and incubation time on the sensitivity of the human sperm motility assay were investigated. The assay was also compared with mouse embryo development. The human sperm motility assay and mouse embryo development assays were performed on 25 items commonly used in IVF laboratories. Sperm motility assay was conducted after 2, 4, 6, 8, 24 and 48 h incubation intervals under standard embryology conditions. A calculated sperm motility index value <0.75 was used to indicate sperm toxicity. It was found that optimum sensitivity (P < 0.01) of the human sperm motility assay was attained in the absence of albumin after 4, 8 and 48 h incubation periods. Items identified to be sperm toxic within 8 h by the human sperm motility assay were considered to be of clinical significance due to the close concordance of these results with mouse embryo development. [ABSTRACT FROM AUTHOR]