Serhiy Marchuk

An alternative index to the exchangeable sodium percentage for an explanation of dispersion occurring in soils

With the introduction of the cation ratio of soil stability (CROSS) to replace the sodium adsorption ratio (SAR) on the basis of differential effects of K and Mg to Na and Ca, respectively, there is a requirement for a similar index involving these cations to replace the exchangeable sodium percentage (ESP). The exchangeable dispersive percentage (EDP) is derived and proposed to replace ESP. This paper uses two datasets, one where exchangeable K concentration is relatively high and exchangeable Na low, and a further dataset where Mg dominates the cation exchange capacity. EDP is validated against these datasets and further mathematical investigation of the contribution of Mg to dispersion is undertaken. Mineralogy appears to affect turbidity results at a given dispersive index, and an improved criterion for assessment of Mg effect on dispersivity is presented.

Possible effects of irrigation with wastewater on the clay mineralogy of some Australian clayey soils: laboratory study

Potassium is common in a wide variety of wastewaters and in some wastewaters is present at several hundred to several thousand mg L–1. Potassium is taken up by expandable clays leading to its fixation and illitisation of smectitic and vermiculitic layers. Hence the addition of wastewaters to soils may lead to mineralogical changes in the soils that affect their physico-chemical properties. Winery wastewater was equilibrated with clay-rich soils from Southern Australia. X-ray diffraction patterns and chemical composition of clays extracted from untreated and treated soils were determined. In three of the four soils, shifts in peak positions occurred towards more illitic components along with increases in K and sometimes also Mg and Na contents of soil clays. Peak decomposition showed trends towards the formation of interstratifications of illite with smectite at the expense of smectite and an alteration of poorly crystallised illite into its more well-ordered forms. The results show that illitisation may occur as a result of the addition of K-rich wastewaters to clayey soils.

Towards incorporation of potassium into the disaggregation model for determination of soil-specific threshold electrolyte concentration

Use of non-traditional irrigation sources will increase with industry water demand, with many industry wastewaters (e.g. agri-industry processes such as milk factories, piggeries, wineries and abattoirs) containing appreciable potassium (K), which is known to result in soil structural decline if the concentration is sufficient. The threshold electrolyte concentration (CTH) is generally understood to represent the electrolyte concentration (directly proportional to electrical conductivity) at which a soil will remain stable when subjected to a solution of given sodium adsorption ratio, without limiting dispersion. However, current approaches to determine CTH do not incorporate K. Hence, this work seeks to investigate incorporation of K into the disaggregation model for CTH and validate this against equivalent sodium (Na) systems using an ionicity approach. A single generalised coefficient of equivalence for K relative to Na did not appropriately describe the system changes; this coefficient was specific to a soil and appeared to vary with the percolating electrolyte concentration. Incorporation of K into the disaggregation model, although not accurate with a universal coefficient of equivalence for K, was considered reasonable where no other approach could be used. This conclusion was drawn on the basis that the model would produce a conservative CTH under such circumstances, which would not cause undue degradation to the soil environment.

Seen as different, soil clays become more important to soils and also beyond soils

ABSTRACT Using data from the literature, we pose the question of the extent to which a knowledge of soils is contributed by that of its clay fraction. In the past, soil characteristics have not related well to mineralogical analyses but we have redefined clays and also used a computer programme to more closely analyse X-ray diffraction (XRD) profiles. It was found that cation exchange capacities and specific surface areas of soil kaolinites almost always exceed those of standard kaolinites. The surfaces of soil clays are often coated by organic matter, which reduces their capacity to adsorb dissolved organic carbon (DOC). Oxidised iron is closely associated with phyllosilicate clays and enhances their capacity to adsorb DOC. Computer-aided decomposition of XRD traces show that phyllosilicates may contain several phases and react dynamically with potassium-containing solutions. Clays should be regarded as natural products with as yet undiscovered applications, including for cancer treatment.

Dissolved organic carbon in leachate after application of granular and liquid N–P–K fertilizers to a sugarcane soil

The progressive decline of soil organic matter (SOM) threatens the sustainability of arable cropping worldwide. Residue removal and burning, destruction of protected microsites, and the acceleration of microbial decomposition are key factors. Desorption of SOM by ammonia-based fertilizers from organomineral complexes in soil may also play a role. A urea- and molasses-based liquid fertilizer formulation and a urea-based granular formulation were applied at recommended and district practice rates, respectively, to soil leaching columns, with unfertilized columns used as controls. The chemistry of leachate collected from the columns, filled with two sandy soils differing in recent cropping history, was monitored over eight successive wet-dry drainage events. The pH, electrical conductivity, and concentration and species of N in leachate was compared with the concentration and aromaticity of dissolved organic C (DOC) to indicate if salt solutions derived from the two fertilizers extracted SOM from clay mineral sites. Cation exchange capacity and exchangeable cations in the soil were monitored at the start and end of the trial. Fertilizer application increased DOC in leachate up to 40 times above the control, but reduced aromaticity (specific ultraviolet light absorbance at 253.7 nm). Dissolved organic C was linearly proportional to leachate NH-N concentration. Exchangeable Ca and Mg in soil from fertilized columns at the end of both trials were significantly lower than in unfertilized soil, indicating that ammonium salt solutions derived from the fertilizers extracted cations and variably charged organic matter from soil mineral exchange sites. Desorption of organic matter and divalent cations from organomineral sites by ammonia-based fertilizers may be implicated in soil acidification.