Evaluation of the influence of sample preparation and extraction technique on soil solution composition

Soil solutions were extracted by immiscible liquid displacement with trichlorotrifluoroethane and by centrifuge drainage from surface and subsoil samples having a wide range of chemical and physical properties. Extractions were performed on field-moist samples and on air-dry samples which were re-wetted to different matric suctions and for different lengths of time. The composition of the soil solution obtained was the same with both methods of extraction when samples had been pre-wet to a matric suction of 0.1 bar. Immiscible liquid displacement extracted solution from a krasnozem surface soil at suctions as great as 15 bar; in contrast, centrifuge drainage failed to extract solution from this soil at > 3 bar. The concentration of ions in solutions extracted by displacement from soils with increasing matric suction rose to a far greater extent than that anticipated if concentration was the only mechanism operating. In re-wet air-dry samples, major cations and anions were at equilibrium levels in solution after incubation for 1 day; longer incubation times resulted in an artificial elevation of ionic strength through mineralization of organic matter in some surface samples. The levels achieved after 1 day were similar to those present in solutions extracted from field-moist samples

A simple positive pressure apparatus for the ultra-filtration of soil solution

A positive pressure filtration apparatus is described which employs compressed gas to provide the differential pressure required to permit the ultrafiltration of soil solution. The apparatus uses low-cost membrane filter elements and is suitable for use with small volume samples, as there is little retention of solution within the filtration cells. Initial flow rates of ~5 and 25 mL/min were achieved through 0.025 and 0.05 pm pore-diameter filter elements, respectively. Compressed nitrogen is the preferred gas source as exposure of solutions of pH 6 or higher to compressed air resulted in a lowering of pH levels

The Use of Total Ionic Strength Adjusting Buffers in Determining Fluoride Concentration in Soil Solutions by Ion Selective Electrometry

Total ionic strength buffers based on citrate at pH 7.5 and cyclohexylenediaminetetra-acetic acid (CDTA) at pH 5.2 were evaluated for use when determining fluoride (F) concentration in soil solutions. Both buffers achieved acceptable recoveries of F added to ultra-filtered (0.025 μm) solutions. Recovery of F added to unfiltered and 0.22 μm filtered solution was low when the CDTA buffer was used. This effect was attributed to the adsorption of F by micro-particulate materials present in these samples. The use of this buffer would need to be restricted to samples in which micro-particulates were not present. The performance of the citrate buffer was not affected by the presence of micro-particulates; however, electrode response times, and departure from Nernstian response at low F concentrations, were greater when this buffer was employed. Fluoride was found to be present at low concentrations in the soil solution of the 60 virgin highly weathered soils tested. The F concentration in 75% of the surface samples wa

Land amendment irrigation Phase III. Final Report. Santos-UQ Large core project.

Intact soil cores from the Roma (QLD) area were irrigated with coal seam water. The soil was amended with gypsum and sulfur an irrigated with up to 100 mm coal seam water per week. Changes in soil solution composition, water infiltration and drainage water composition was investigated after every 100 mm of irrigation. To minimise salt accumulation in the soil, only soils with sufficient permeability (hydraulic conductivity) were suitable for coal seam water irrigation as salt could be leached from the soil during periods of high rainfall. The presence of a vegetation cover (Rhodes grass or lucerne) was necessary for maintaining soil surface structure and infiltration. As Rhodes grass is more salt tolerant, and tolerant of waterlogging, it is a more suitable pasture species for coal seam water

Exchange and solution phase chemistry of acid, highly weathered soils. I. characteristics of soils and the effects of lime and gypsum amendments

Exchange and solution phase characteristics were evaluated on surface and subsoil horizons of 60 acid, highly weathered soils in the unamended state, and on 39 of the surface horizons following addition of CaCC>3 or CaS04.2H20. Soil solutions from unamended surface samples were dominated by Na (median concentration 0-65 mivi), while the other major cations were present at lower levels (median concentrations: Ca, 0-09; Mg, 0T4; K, 0-28 him). This pattern was more pronounced in the subsoil samples where the median concentrations of the nutrient cations wer

Subsoil nitrogen mineralisation and its potential to contribute to NH4 accumulation in a Vertosol

High concentrations of NH4+ (up to 270 kg N/ha) have been observed in a Vertosol below 1 m depth in south-east Queensland. This study examined the possibility that mineralisation associated with the removal of native vegetation (Acacia harpophylla) for cropping was responsible for the production of NH4+. Particularly, the potential contribution of decomposing root material and/or dissolved organic nitrogen (DON) leached into the subsoil after clearing was investigated. The amount of N that was contained within native vegetation root material was determined from an area of native vegetation adjacent to the cleared site containing elevated NH4+ concentrations. In addition, the amount of NH4+ that could be mineralised in the native vegetation soil was determined by monitoring NH4+ concentrations over 360 days in intact cores, and by conducting waterlogged incubations. To determine the rate at which a source of DON leached into the subsoil would mineralise, soil was amended with glutamic acid at a rate of 250 mg N/kg and placed under waterlogged incubation. The possibility that the acidic pH of the subsoil, or the lack of a significant subsoil microbial population, was inhibiting mineralisation was also examined by increasing soil pH from 4.4 to 7.0, and inoculating the subsoil with surface soil microorganisms during waterlogged incubations. Low concentrations of N, approximately 90 kg N/ha between 1.2 and 3 m, were found in the native vegetation root material. In addition, no net N mineralisation was observed in either the extended incubation of intact cores or in the control samples of the waterlogged incubations. Net N mineralisation was also not detected when the subsoil was amended with a source of organic N. Results indicate that this lack of mineralisation is largely due to pH inhibition of the microbial population. It is concluded that the mineralisation of either in situ organic material, or DON transported to the subsoil during leaching events, is unlikely to have significantly contributed to the subsoil NH4 accumulation at the study site

Supplying the nitrogen needs of cereal crops with swine anaerobic lagoon sludge

Swine anaerobic lagoon sludge is a potential source of nutrients for crop production. In order to best utilise nitrogen (N) contained in the sludge, prediction of plant available N is required. This was estimated from two field experiments conducted on contrasting soil types. The sludge was applied as dry stockpiled sludge at rates of 6 and Is t/ha, and wet sludge at rates of 20 and 65 t/ha on a sandy loam soil, or 40 and 120 t/ha on a clay soil. In addition to field measurements anaerobic and aerobic laboratory incubations were conducted to estimate available N.Sludge source and soil type influenced net release of available N. Preplant soil nitrate plus anaerobically mineralizable N were significantly correlated with plant N uptake plus residual soil nitrate, with R-2 values of 0.49 and 0.80 for the clay and sandy soils, respectively. In spite of the level of variation explained by the two variables the inclusion of anaerobically mineralizable N did not greatly improve the relationship on the sandy soil. Measurement of preplant nitrate to 1.5m depth did not explain enough of the variation in field measured plant available N in order to use this single measurement to predict plant available N. Combining anaerobically mineralizable N, as an indicator of potentially mineralizable N for the growing season, with preplant nitrate concentrations was not st useful index to predict the N supply on soils receiving applications of swine anaerobic lagoon sludge