Amelioration of aluminium phytotoxicity with organic matter
Plant-Soil Interactions at Low pH: Principles and Management, 1995
In strongly weathered soils, the activity of AIH in the soil solution can often, but not always, ... more In strongly weathered soils, the activity of AIH in the soil solution can often, but not always, be predicted using gibbsite solubility relationships. Overestimates are common and often attributed to a lack of equilibrium between the solid and the solution phases. Soil organic matter may also be involved because of its strong affinity for aluminium. The main components of the soil organic matter are humic substances and the effect of adding a sample of humic acid on the activity of AIH was investigated. The addition of the humic acid to an Oxisol from Burundi and an Ultisol from Cameroon decreased the activity of aluminium in the pH range 3.2 to 4.6. At pH 4.2, the activity of AIH in the Oxisol was 38 J-tM, but the addition of 2% humic acid decreased it to 11 J-tM. The corresponding values for the Ultisol were 11 J-tM decreasing to 2 J-tM with the addition of humic acid. In both soils, plots of pAIH against pH were linear. The stability lines for the soils treated with the humic acid were mostly parallel to those of the untreated soils. The displacement of the lines was 0.6 pAIH units in the Oxisol and 0.7 pAIH units in the UltisoI. The displacement decreased the [AIH] [OH-] ion activity product for both soils. Dissolution of the soil aluminium was relatively rapid. This suggests that the displacement of the stability line was more likely due to decreased solubility rather than to kinetic restrictions. The humic acid also decreased the exchangeable aluminium saturation of the two soils by decreasing the activity of AIH and increasing the cation exchange capacity of the system. Exchangeable aluminium was held more strongly giving rise to greater selectivity coefficients for (Ca2+ +Mg2+)/AIH exchange in the soil treated with humic acid. In situations where kinetic restrictions limit the control of AIH activity by dissolution, the short term control will be achieved by rapid cation exchange. The decrease in exchangeable aluminium saturation will further ensure lower AIH activities.
A systematic approach to recycling organics for horticulture: comparing emerging and conventional technologies
Acta Horticulturae, 2016
Recycled organics: how best to use this resource? A three-year study took the first steps towards... more Recycled organics: how best to use this resource? A three-year study took the first steps towards an answer by exploring emerging (biochar from pyrolysis) versus conventional (composting) processing technologies for their ability to convert recycled organics-city green waste and farm trash-into usable products that enhance horticultural productivity, with attendant carbon sequestration and environmental benefits. In this study, we compared organic products prepared from one common feedstock using four different technologies: windrow composting; a small mobile pyrolyser for on-farm processing; a medium pyrolyser for community or small business undertakings; and a large pyrolyser for high through-put requirements. The project then determined whether organic products enhance plant performance, are useable for horticulture and outperform or complement composting. This paper summarises some key outcomes from i) physical and chemical characterisation of organic products and ii) annual vegetable (tomato 'Rebel') and perennial fruit (blueberry 'Opi') field trials, thus providing the first step towards an understanding of the system from feedstock source to the farm.
Humic acids (HAs) and fulvic acids (FAs) were isolated by the exhaustive extractions at pH 7, 10.... more Humic acids (HAs) and fulvic acids (FAs) were isolated by the exhaustive extractions at pH 7, 10.6, and 12.6 of a Grey Brown podzol and of a Gley soil, each in long term grassland. A further exhaustive extraction in base + 6 M urea isolated additional HAs and FAs of significantly different compositions. A subsequent sequential extraction with dimethylsulphoxide (DMSO) + 6 M concentrated H 2 SO 4 isolated humin materials. The solvent sequence used is capable of isolating > 90% of the organic matter (OM) in some soils, and at least 70% of the OM in all soils. Solid state CPMAS 13 C NMR spectroscopy s showed readily observable differences between the compositions of the HAs and FAs isolated at the different pH values, and by the base + urea solvent system. Humin has been considered to be the most intractable component of soil organic matter. However, applications of solid state 13 C NMR and of liquid state proton NMR have shown that soil humin is composed largely of biological molecules of plant and of microbial origins and with a degree of resistance to biological degradation. That resistance is enhanced by the protection afforded by close associations with the soil mineral colloids.
Sustainability of nitrogen use in two dryland farming systems
Progress in Nitrogen Cycling Studies, 1996
In the drier environments of rainfed agricultural systems both water and nitrogen are major limit... more In the drier environments of rainfed agricultural systems both water and nitrogen are major limitations to crop productivity. In the Mediterranean region the traditional cereal-fallow system is being replaced by a cereal- legume rotation. An experiment to measure crop N uptake and biological nitrogen fixation in wheat/lentil and wheat/chickpea rotations was conducted in 1991/92. Recovery of 15N-labelled urea fertilizer by wheat was poor. Significant amounts of crop nitrogen came from biological nitrogen fixation in lentil (>50%) and chickpea (ca. 30%).
Mechanisms of protection of soil organic matter under pasture following clearing of rainforest on an Oxisol
Geoderma, 2008
ABSTRACT Vegetation change from rainforest (C3) to pasture (C4) was used to study the nature and ... more ABSTRACT Vegetation change from rainforest (C3) to pasture (C4) was used to study the nature and capacity for organic matter protection in an Oxisol from eastern Australia. As much as 17.1% and 31.0% of the organic carbon in the 0–0.075 and 0.075–0.15m horizons, respectively, derived from C3 rainforest was still present even after 90 years under continuous C4 pasture. A considerable proportion of the organic carbon is therefore protected in the surface horizons of these oxidic soils. High energy uv photo-oxidation was used to determine the nature of the protection. With increased time of photo-oxidation, the relative proportion of C3-derived OC in the < 53 μm fractions increased under the pasture demonstrating that microaggregates had a significant role in protection of the older C3-derived OC against decomposition. Although tannins or tannin-like materials were present within the < 53 μm microaggregates under rainforest and hence were resistant to photo-oxidation, they were not detectable under the pasture using solid-state 13C NMR spectroscopy. The aryl-C components under pasture appear to be derived from lignin rather than tannin but cannot be attributed to the presence of charcoal. Lipids of microbial origin may also contribute considerably to C3-derived OC under pasture through chemical recalcitrance to decomposition rather than physical protection. There is no evidence that a significant proportion of plant-derived lipids survive in these soils and contribute to a stable pool of soil OC. The work presented here demonstrates that protection within microaggregates is the major mechanism for protection of OC in this Oxisol.
Physico-chemical changes in waterlogged soils, II: effect on specific conductance and soil solution, concentrations of iron, manganese, calcium and potassium
The effects of pH and of form and rate of applied iron on micronutrient availability and nutrient uptake by highbush blueberry plants grown in peat or soil
Journal of Horticultural Science
SummaryThe effects of pH (4.5 or 6.5), growing medium (peat or soil) and of two rates of iron as ... more SummaryThe effects of pH (4.5 or 6.5), growing medium (peat or soil) and of two rates of iron as iron sulphate or iron chelate (Fe-EDTA) on the growth and leaf nutrient content of young highbush blueberries were investigated in a greenhouse study. Plant dry matter production was greater at pH 4.5 than at 6.5 in both media, although the difference was more marked in the peat. From the leaf nutrient contents it appears that at pH 4.5 growth in soil was likely to have been limited by Mn and Al toxicities whereas at pH 6.5 growth in peat was possibly limited by deficiencies of Fe and Mn. Dry matter production was unaffected by Fe treatments at pH 4.5, but at pH 6.5 the high rate of chelate addition reduced plant growth in both media. The reduced growth was associated with lowered levels of leaf Mn but levels of other nutrients were unaffected. Extractable micronutrients showed different trends with pH, depending upon the medium, the extractant used and the element being assayed. In general, EDTA did not appea...
The effects of soil acidification (pH values from 6.5 to 3.8), and subsequent leaching, on levels... more The effects of soil acidification (pH values from 6.5 to 3.8), and subsequent leaching, on levels of extractable nutrients in a soil were studied in a laboratory experiment. Below pH 5.5, acidification resulted in large increases in the amounts of exchangeable A1 in the soil. Simultaneously, exchangeable cations were displayed from exchange sites and Ca, Mg, K and Na in soil solution increased markedly. With increasing soil acidification, increasing amounts of cations were leached; the magnitude of leaching loss was in the same order as the cations were present in the soil: Ca 2+ > Mg 2+ > K + > Na +. Soil acidification appeared to inhibit nitrification since in the unleached soils, levels of NO~clearly declined below pH 5.5 and at the same time levels of NH~-increased greatly. Significant amounts of NH + and larger amounts of NOr, were removed from the soil during leaching. Concentrations of NaHCO3-extractable phosphate remained unchanged between pH 4.3 and 6.0 but were raised at higher and lower pH values. No leaching losses of phosphate were detected. For the unleached soils, levels of EDTA-extractable Mn and Zn increased as the soil was acidified whilst levels of extractable Fe were first decreased and then increased greatly and those for Cu were decreased slightly between pH 6.5 and 6.0 and then unaffected by further acidification. Significant leaching losses of Mn and Zn were observed at pH values below 5.5 but losses of Fe were very small and those of Cu were not detectable.
Changes in humic acid composition with molecular weight as detected by 13C-nuclear magnetic resonance spectroscopy
Science of The Total Environment, 1992
... 395-399. Swift, RS, G. DeLisle and RL Leonard, 1987. ... Solid-state nuclear magnetic resonan... more ... 395-399. Swift, RS, G. DeLisle and RL Leonard, 1987. ... Solid-state nuclear magnetic resonance spectroscopy of humic sub-stances: basic concepts and techniques. In: MHB Hayes, P.McCarthy, RL Malcolm and RS Swift (Eds), Humic Substances II, In Search of Structure. ...
The aims and goals behind the paper are commendable and I expect that the paper will ultimately b... more The aims and goals behind the paper are commendable and I expect that the paper will ultimately be publishable because its lofty goals and foresight research perspective. However, I feel that the paper would have benefit from a more early intervention to improve structure, table and figures prior to being available as a discussion paper. The paper clearly needs improvement in the organization of the results section, which currently split in 7 subsections some with only 2-4 lines, this give a very fragmented read of this section. It maybe better to have no subheadings at all this also shave at least 7 lines of the paper. The information in Table 1 to 3 is nearly effective captured as text. Table 2 is nearly already describe in the materials and method section anyhow. Figure 1 can go to supplementary material. For Figure 2 and 3 it be interesting to have
A great variety of homo- and heteronuclear two-dimensional NMR experiments wer made on humic subs... more A great variety of homo- and heteronuclear two-dimensional NMR experiments wer made on humic substances. These provide detailed insight into the structure of humic substances including an identification of exchangeable protons as well as an unprecedented in detail characterisation of the carbon skeleton.
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