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A modified version of the popular agrohydrological model SWAP has been used to evaluate modelling of soil water flow and crop growth at field situations in which water repellency causes preferential flow. The parameter sensitivity in such situations has been studied. Three options to model soil water flow within SWAP are described and compared: uniform flow, the classical mobile-immobile concept, and a recent concept accounting for the dynamics of finger development resulting from unstable infiltration. Data collected from a severely water-repellent affected soil located in Australia were used to compare and evaluate the usefulness of the modelling options for the agricultural management of such soils. The study shows that an assumption of uniform flow in a water-repellent soil profile leads to an underestimation of groundwater recharge and an overestimation of plant transpiration and crop production, The new concept of modelling taking finger dynamics into account provides greater flexibility and can more accurately model the observed effects of preferential flow compared with the classical mobile-immobile concept. The parameter analysis indicates that the most important factor defining the presence and extremity of preferential flow is the critical soil water content. Comparison of the modelling results with the Australian field data showed that without the use of a preferential flow module, the effects of the clay amendments to the soil were insufficiently reproduced in the dry matter production results. This means that the physical characteristics of the soil alone are not sufficient to explain the measured increase in production on clay amended soils. However, modelling with the module accounting for finger dynamics indicated that the preferential flow in water repellent soils that had not been treated with clay caused water stress for the crops, which would explain the decrease in production. Additional keywords: SWAP, preferential flow, water repellence, clay spreading., Introduction Water repellency in soils has been documented in many parts of the world in both arid and humid climates (Jaramillo et al. 2000). It is mostly caused by hydrophobic [...]

Copper is an important micronutrient and trace amounts are essential for crop growth. However, high concentrations of copper will produce toxic effects. Australia is increasingly developing production of crops in water repellent soils. Clay amendment, a common amelioration techniques used in Australia, has demonstrated agronomic benefits in increased crop or pasture production. The sorption and desorption of copper and the effect of clay treatment on copper behaviour in a water repellent soil collected from an experimental farm in South Australia is studied. We found that the water repellent soils amended with clay have an increased adsorption capacity of copper. Also the clay-amended soils had an increased ratio of specific sorption to total sorption of copper. The implications of this study to the sustainable agro-environmental management of water repellent soils is discussed. Additional keywords: copper, sorption, desorption, water repellent soils, clay amendment., Introduction Water repellency is a property of soil that reduces infiltration capacity and crop germination, reduces nutrient and chemical-holding capacity, and promotes erosion (Cann and Lewis 1994). Water repellency is [...]

Australia is a water-stressed nation and demand on potable water supply is increasing. Consequently water conservation and reuse are increasingly becoming important. Irrigation of recycled wastewater on water repellent soils is a technology that is being trialled as a means of improving crop production and conserving potable supply. However, recycled water contains potentially harmful heavy metals. This paper reports the competitive sorption and desorption of several common heavy metals found in soils collected from a farm located in the southeast of South Australia. The soil from this location is severely water repellent, but some sites were amended with kaolinite clay ([Si.sub.4][Al.sub.4][O.sub.10][(OH).sub.8]) about 7 and 15 years ago. The metals studied were Cu, Pb, Cd, Cr, Ni, and Zn. Competitive sorption of the metals was distinctly observed. For all heavy metals, the quantity of metal sorbed was higher in amended soil, and there was a strong correlation between the specific sorption to total sorption ratio and the amount of clay in the soil. The sorption intensities varied with metal, Cr, Pb, and Cu having a high sorption tendencies and Zn, Cd, and Ni having comparatively low sorption tendencies. The total sorption capacity for all metals increased in clay-treated soils compared with non-treated soils. On average, clay-amended water repellent soils had a 20-40% increased capacity to adsorb total metals; however, this increase was largely caused by the increased capacities to adsorb Zn, Cd, and Ni. The effect of clay treatment largely enhanced the sorption capacity of relatively weakly adsorbing heavy metals. The implications for using recycled wastewater on the long-term sustainable agro-environmental management of these soils are discussed. Additional keywords: sorption, desorption, clay, kaolinite, heavy metal, recycled wastewater, cadmium, chromium, copper, lead, nickel, zinc., Introduction In Australia, as in many other parts of the world, increasing regulation covering the delivery and collection of on-farm water and realistic charges being applied for its use are [...]

After an initial evaluation of several solvents, the efficiency of Soxhlet extractions with isopropanol/ammonia (s.g. 0.88) (70:30 v:v; 24 h) in extracting compounds associated with water repellency in sandy soils was examined using a range of repellent and wettable control soils (n = 15 and 4) from Australia, Greece, Portugal, The Netherlands, and the UK. Extraction efficiency and the role of the extracts in causing soil water repellency was examined by determining extract mass, sample organic carbon content and water repellency (after drying at 20°C and 105°C) pre- and post-extraction, and amounts of aliphatic C-H removed using DRIFT, and by assessing the ability of extracts to cause repellency in acid-washed sand (AWS). Key findings are: (i) none of organic carbon content, amount of aliphatic C-H, or amount of material extracted give any significant correlation with repellency for this diverse range of soils; (ii) sample drying at 105°C is not necessarily useful before extraction, but may provide additional information on extraction effectiveness when used after extraction; (iii) the extraction removed repellency completely from 13 of the 15 repellent samples; (iv) extracts from all repellent and wettable control soils were capable of inducing repellency in AWS. The findings suggest that compounds responsible for repellency represent only a fraction of the extract composition and that their presence does not necessarily always cause repellency. Additional keywords: water repellency, water repellence, hydrophobicity, extraction, aliphatic, DRIFT., Introduction It has been proposed that water repellency is caused by the accumulation of hydrophobic organic compounds released from roots (Dekker and Ritsema 1996; Doerr et al. 1998), as fungal [...]

Ponds holding industrial wastewater can quickly develop algal blooms, which in turn results in high pH excursions. Such deterioration in water quality is experienced in Portland Aluminium's retardation pond. A covering of floating aquatic plants, such as Azolla filiculoides and Lemna minor, will reduce the light entering the water body, in turn reducing algal production and lowering pH levels. In the case of Portland Aluminium's retardation pond, the initial installation of such a system has to be established under alkaline conditions and in high fluoride concentrations (up to 10 mg/L). The survival and growth of A. filiculoides and L. minor under alkaline conditions (pH levels of 7-9.5) and under different fluoride concentrations (0-10 mg/L) were assessed in the laboratory and in field conditions. L. minor grew well under alkaline and high fluoride conditions in short-term laboratory tests, but appeared unable to compete with itinerant algae in the field. A. filiculoides survived only in media of pH 7 and 0-mg/L fluoride in the short-term laboratory tests, but grew very well in the long-term field experiments. A. filiculoides was also observed to inhibit algal growth in the field. Both species absorbed fluoride. Fluoride concentrations in the plants rose and fell in relation to the fluoride concentrations in the pond, suggesting that the fluoride was readily desorbed and that the absorption itself was by a passive mechanism.