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Abstract Seven surface horizon soils and their sand, silt, and clay fractions were characterised for mineralogy, and K release by extracting samples with 1 mM Ca[Cl.sub.2] solution daily for 10 [...]

A glasshouse experiment was conducted with 41 surface and 8 subsurface soils to measure their potassium (K) supply capacities and K depletion of soils by ryegrass growth for 260 days and harvesting at ~40-day intervals. Dry matter yield ranged from 0.22 g to 25.4 g/kg soil, cumulative K uptake ranged from 0.006 to 1.49 cmol/kg soil, and values of K concentration (%) in the first cut herbage ranged from 0.40% to 5.97%. Some of the light-textured soils were so impoverished in K that symptoms of K deficiency appeared during the first growth period. Water-soluble K + exchangeable K accounted for 43-100% of cumulative K uptake by the ryegrass. Multiple regression analysis indicated that 68% of the variation in dry matter yield and 90% of the variation in K uptake may be predicted by the exchangeable K content of these soils. The 6 harvests of ryegrass extracted only 0.21-12.07% of total K from these soils, which was not sufficient to cause discernible mineralogical changes in most soils. For some soils vermiculite was formed at the expense of illite/mica by K release to plants. For soils containing vermiculite but no other K-bearing clay minerals, vermiculite peaks broadened on K depletion by plants. Major proportions of total K in these soils are present in silicate minerals, yet only minor amounts are released to plants by very slow weathering processes. For soils that do not contain any K bearing clay minerals, very minor amounts of feldspar may have dissolved to release K. Additional keywords: feldspar, vermiculite, illite, exchangeable-K., Introduction Chemical methods are commonly used to predict the potassium (K) fertility of soils, through establishing relationships between the chemical measure and K uptake by plants. Exhaustive cropping techniques combined [...]

Twenty-one lime trial sites in the south-western agricultural region of Western Australia (WA) ranging in duration from 2 to 15 years were sampled in 1995 to a depth of 40 cm in 10-cm increments. In each case, samples were taken from both control plots and those with highest lime rates; additionally, samples were taken from plots with intermediate lime rates at 3 trial locations. Lime had been incorporated at rates of 2-12 t/ha within the top 0-10 cm layer at 20 of the sites, and at 15 t/ha within 0-20 cm at the remaining site. The following measurements were made: all samples, pH (1:5 0.01 M Ca[Cl.sub.2]) and exchangeable cations (1: 10 0.1 M Ba[Cl.sub.2]); selected depths, undissolved carbonate; selected samples, total Ca (1: 10 0.2 M HCl) and exchangeable Ca (1: 10 0.1 M Ba[Cl.sub.2] buffered to pH 8.2). The pH of the unlimed subsurface was between 4.0 and 4.5 at 10-20 cm for 15 sites, at 20-30 cm for 7 sites, and at 30-40 cm for 2 sites. In addition, 3 of the unlimed sites had a pH [is less than or equal to] 4.0 at all of these depths. Where lime had been applied, the pH was significantly (P [is less than] 0.05) higher than in the controls by at least 0.2 units for 13 sites at depths of 10 cm below the depth of lime incorporation. The same significantly elevated pH was found for 5 sites at depths of 20 cm and for 4 sites at depths of 30 cm. At 5 sites that had also been sampled 3 years previously, the subsurface pH had increased within 4-7 years of liming with 2.5-5 t/ha. Where added lime could be accounted for, the amount of lime added explained 65% of the variation in the residual lime effect at a depth of 10-40 cm. Over all of the wheatbelt trials this represented an average downward movement of lime to a maximum depth of 40 cm of at least 8.3 kg/ha.year.t Ca[CO.sub.3] applied (range 0-22.5). Increased exchangeable Ca corresponded with a decrease in other base cations in only 2 trials. Decreases in exchangeable Al corresponded with increases in both pH and exchangeable Ca, but were less than the Ca increases. Precipitation of exchangeable Al represented an average of about one-sixth of the pH buffering capacity. Mass balance for Ca was achieved in 11 out of 20 cases in the wheatbelt, if Ca loss as nitrate was assumed to occur at rates of leaching published for WA. Lime recovery on the basis of pH increase was lower. The quantity of lime accounted for by Ca in the added and the residual undissolved lime, plus the increase in exchangeable Ca, ranged from [is less than] 10% to [is greater than] 90%, with [is less than] 50% in 9 of 19 cases at 15 trials. Non-exchangeable Ca in HCl extracts of a subset of surface samples was from 1% to 60% of Ca not accounted for. In 6 cases the Ca deficit exceeded plausible rates of acidification, and at 2 of these marked decreases of about 1 t/ha undissolved Ca[CO.sub.3] corresponded with episodes of high wind speed and observations of soil erosion. The implications of possible losses of lime by erosion are discussed. Additional keywords: lime requirement, sustainable agriculture, leaching, non-exchangeable Ca, wind erosion., Introduction Agriculturally generated subsurface soil acidity is a potential threat to the sustainability of agriculture on sandy soils (Loss et al. 1993; Dolling and Porter 1994; Dolling et al. 1994; [...]

The B horizon of duplex soils in the wheatbelt of Western Australia is sometimes enriched with potassium (K). K supply from this source is, however, not taken into account in fertiliser recommendations based on soil tests on samples from the 0-10 cm layer. Grain yield responses of wheat to K were measured over 4 years on 10 duplex soils in the medium rainfall (400-600 mm) regions of the West Australian wheatbelt. The depth at which the texture changed markedly ranged from 25 to 75 cm. K was measured through the profile and the concentration was reduced to a single value with a weighting equation that takes account of the distribution of root length. The weights chosen by the fitting procedure discounted the K content of the subsoil severely and provided no evidence that subsoil K was important in determining yield. Furthermore, the improvement obtained by using the weighted K concentration in the 0-1 m layer compared with using the topsoil (0-10 cm) analysis was not statistically significant. K deficiency can be diagnosed in those soils using analysis of the 0-10 cm samples only. Additional keywords: profile, weighting, response, relative yield, seasonal rainfall, deficiency., Introduction Potassium (K) deficiency was first reported in pastures in the wetter regions of the south-west of Western Australia (Fitzpatrick and Dunne 1956) and later extended to pastures grown in [...]

Abstract This investigation was undertaken to determine the potassium (K) status and adsorption behaviour of 227 samples from horizons of 41 representative virgin soil profiles, extending from Geraldton in the [...]

Abstract The incidence of potassium (K) deficiency is increasing in crops, pastures, and forestry in south-western Australia. Although soil K can be measured using soil sampling and analysis, [Gamma]-ray spectrometry [...]

SUMMARY Labelled urea was applied to monolith lysimeters in the 1st year of a 2-year experiment at Onne in south-east Nigeria. On eight lysimeters maize and rice were grown in each of the 2 years. Four lysimeters were similarly cropped in the 2nd year after being uncropped in the 1st year. Measurements were made over the 2-year period of labelled and unlabelled mineral nitrogen in the drainage water, and labelled and unlabelled nitrogen in the crops. At the end of the experiment, weeds and the soil were also analysed for labelled and unlabelled nitrogen. The total recovery of 15N in crop, soil and leachate varied between 70 and 93%. It was lowest when applied to the second season rice crop, which recovered only 15%, and highest when it was leached in the 1st year or was taken up by the maize crop. The highest crop uptake was 31%. The results indicate that, depending on the treatment, between 10 and 30% of the 15N was immobilized in the soil, lysimeters cropped in the 1st year lost between 22 and 29% of the 15N in drainage water, and between 7 and 30% was lost by denitrification. The accuracy of these figures is discussed. [ABSTRACT FROM AUTHOR]

SUMMARY At Onne in South-east Nigeria, drainage water was collected from four monolith lysimeters and analysed for nitrate. The lysimeters contained an acid sandy loam. At the start of the first rainy season two lysimeters received urea labelled with 15NO3- and two received no nitrogen fertilizer; all four were uncropped in the first year. The peak concentrations of 15NO3- and of unlabelled (soil) NO3- were found after 2.5 pore volumes of water had passed through the lysimeters. Using the same soil in the laboratory after fine sieving, the peak concentration of tritiated water was found at 1 pore volume whereas nitrate leaching was retarded. The pattern of nitrate leaching was well described by miscible and immiscible models which included an adsorption coefficient for nitrate. Over the 2 years 81.4% of the 15N added at the start of the first rainy season was recovered in the drainage water. [ABSTRACT FROM AUTHOR]

Managing phosphorus (P) is a global priority for environmental water quality due to P lost from agricultural land through leaching, runoff and subsurface flow. In Western Australia (WA), following decades of P fertiliser application to crops and pastures in low rainfall regions, questions have been raised about this region's contribution to environmental P loss. This study was conducted on the Fitzgerald River catchment in the south Western Australia (WA) with mixed cropping and grazing land uses and a Mediterranean climate with low mean rainfall (~350 mm yr -1 ). Phosphorus forms were monitored continuously over a three-year period in five separate streams, each draining a defined sub-catchment. The P concentrations in streams consistently exceeded Australian and New Zealand Environment Conservation Council (ANZECC) trigger values throughout the monitoring period. Of the measured total P concentration, ~75% was dissolved P (DRP; <0.45 μm) and 80% of that fraction was in the filterable reactive form (FRP). These water quality measurements and other independent soil investigations at this site, suggest that transport of dissolved P rather than erosion of sediment-bound P was dominant in this environment. Based on extractable soil P (Colwell P) and the P buffering index (PBI), predicted concentrations of dissolved reactive P (DRP) in soil solution in topsoils (0-10 cm) across this catchment, generally exceeded ANZECC's values of 0.07 mg PL -1 . The level of exceedance was spatially variable. Streams draining areas with the lowest predicted DRP concentrations also had the lowest measured FRP concentrations. Elsewhere stream water FRP concentrations depended on both DRP concentration and the PBI of the land being drained. Our findings suggest that deployment of practices that physically filter runoff, for example riparian vegetation, would be ineffective in restricting P transport into stream in this environment. This conclusion is consistent with previous findings of the ineffectiveness of riparian buffers on coarse textured sandy soils in higher rainfall areas of southwest WA. A reduction in DRP losses without yield loss could be achieved by following evidence-based fertiliser advice from soil testing to limit losses of legacy P"., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)