Of the 13 fly ashes from Australian power stations, all were dominated by both amorphous and crystalline aluminosilicates and quartz, and these were associated with minor amounts of Fe oxides, lesser amounts of Ca, Mg, Na, K, Ti and P oxides, and variable levels of incompletely combusted C. The ashes consisted of particles predominantly in the silt plus fine sand fraction (67-98%), and electron microscopy revealed that ash matrices consisted of glassy spherical particles and less regularly shaped spongy particles. The available water capacity was high and varied from 27 to 105% with 11 of the 13 samples having values > 40%. Twelve of the 13 ashes were alkaline to strongly alkaline (pH range 8.0-12.8). Soluble salt levels were related to the coal source, and electrical conductivity of the saturation extracts (ECse) varied from 0.63 to 7.0 mS cm -1 for 11 of the samples; two ashes produced from brown coal had ECse values of 46.0 and 55.0 mS cm-1. The nutritional status of the ashes was assessed on samples leached with water to reduce the soluble salts to equilibrium levels. The ashes contained negligible amounts of N, but their P status was variable. The amounts of NH4OAc-extractable Ca and Mg were generally high in most samples and were considered more than adequate for most plant species; however, NH4OAc-extractable K values were generally low. Adequate levels of sulfate-S existed in 12 of the 13 samples, and levels of DTPAextractable Cu, Zn, Mn and Fe were high when compared with published critical values. Most of the unleached samples contained potentially toxic levels of B. The results are discussed with reference to the establishment of vegetation on ash dumps and to the use of fly ash in ameliorating the properties of soils.

SUMMARY Waterlogging the soil promotes epinastic growth of tomato petioles and increases the concentration of ethylene which can be extracted from various parts of the shoot. These concentrations exceed those normally required to promote epinasty when applied to the shoots of non‐waterlogged plants. Waterlogging also results in a rapid decline in the concentration of dissolved oxygen in the soil water. Low concentrations of oxygen around the roots of plants growing in nutrient solution promote epinastic growth and also increase ethylene concentration in the leaves. Experiments with detached shoots indicate that the root system is required for the response to low O2concentrations to develop. Ethylene concentrations in the soil can increase during waterlogging to levels which may allow sufficient movement into the shoot to stimulate epinasty. Treatment with substances which can inhibit the action of ethylene, such as carbon dioxide or 7‐chloro‐4‐ethoxycarbonylmethoxy‐5‐methyl‐2, 1,3‐benzothiadiazole also inhibit the epinastic response in waterlogged plants, in plants with low O2 concentrations around the roots and in plants treated with ethylene. The internal level of carbon dioxide in the lower leaves is little affected by waterlogging for up to 96 h.

SUMMARY Epinastic growth by petioles of tomato (Lycopersicon esculentum Mill., cv. Moneymaker) is stimulated by waterlogging the soil and the responding leaves and other shoot parts contain higher concentrations of ethylene than those of non‐waterlogged plants. Waterlogged soil also contains increased amounts of ethylene in solution and the possibility that ethylene from this source can move to the shoots of waterlogged plants has been tested by applying the gas to the roots of plants growing in water culture. When concentrations of 2 ppm and above are supplied in this way, petiole epinasty develops in association with increases in ethylene extracted from the responding petioles. When 100 ppm is applied to the roots, increases in ethylene in the petioles precede the development of epinastic growth. Use of [14C] labelled ethylene indicates that the gas can move rapidly, unchanged from roots to shoots. The movement of ethylene and epinastic growth are both reduced if plants are previously steam‐girdled near the base of the stem, suggesting that much ethylene moves by a route other than the transpiration stream. Ethylene supplied to the roots is shown to promote adventitious rooting and downward rolling of the young leaf laminae and to modify the orientation of shoot growth in the tomato mutant‘diageotropica’. It is proposed that increases in soil ethylene and movement of the gas to the shoot system are factors contributing to the development of epinasty and other responses of the shoots to waterlogging the soil.

No abstract

Fly ash from a coal-fired power station was incorporated with each of a 'fine' (0.2-0.5 mm) and 'coarse' (1.4-2.0 mm) sand fraction to give mixtures containing 0, 10, 20, 30, 40, 50, 75 and 100% fly ash by weight. The addition of 10% by weight of ash increased the available water capacity by factors of 7.2 (1.0-7.2% by weight) and 13.5 (0.4-5.4% by weight) for the 'fine' and 'coarse' sands respectively. Subsequent additional 10% increments of ash increased the capacity by smaller amounts. The saturated hydraulic conductivity of the sands decreased markedly with ash addition. The changes in available water capacity and hydraulic conductivity were associated with an increase in capillary pores at the expense of non-capillary pores. Addition of fly ash to both sand fractions resulted in a bilinear relationship between void ratio (volume voids/volume solids) and fly ash percentage in the mixes which was closely related to that theoretically predicted for binary mixtures. The measured void ratios of the mixes exhibited minimum values at 36% and 20% ash by volume for the 'fine' and 'coarse' sand mixes respectively, which compared with the theoretical void ratios for these mixes of 27% and 23% respectively.

The highly co-ordinated development of root systems in uniform environments implies the existence of complex mechanisms for the regulation of growth. I t suggests t h a t in a heterogeneous environment development of a particular member depends not only upon the conditions in its immediate surroundings but also upon the growth of the remainder of the root system. E x p e r i m e n t s have been carried out in which normal patterns of development were disturbed by the removal or desiccation of parts of the root system or its partition between environments of different temperature. The results demonstrated a clear dependence of the development of any part of the root system upon t h a t of the remainder and indicated that there were a range of possible interactions between members.

Summary Benzyladenine (BA) and gibberellic acid (GA) were applied together as a foliar spray to young tomato plants growing in pots of well drained soil, waterlogged soil or in nutrient solution supplied with air (aerobic), nitrogen gas (anaerobic), or ethylene (20 or 100 ul 1−1 in air) for up to 6 days. BA and GA (10 fig ml−1) lessened the inhibitory effects of waterlogging on stem elongation, transpiration and the increase of fresh and dry wt of the shoots. In absolute terms the promotion of shoot growth by BA and GA was greater in plants growing in non‐waterlogged than in waterlogged soil. Root growth was inhibited by BA and GA. The effect of waterlogging in promoting adventitious rooting at the base of the stem was reduced by BA and GA. Epinastic curvature by petioles was promoted by growing plants in waterlogged soil or anaerobic solution culture in association with an increase in the production of ethylene by the petioles. Applications of BA and of GA inhibited this epinastic growth but they did not lower the rate of ethylene production. However BA and GA diminished the effectiveness of ethylene as a stimulator of epinastic curvature. The application of ethylene to the roots inhibited the accumulation of dry wt by the root system and decreased slightly the growth promoting effects of BA and GA in the shoots. The inhibiting effect of waterlogging the root system on stem elongation could be offset if adventitious roots maintained in well aerated conditions were previously induced on the main stem above the primary roots. Epinastic curvature and ethylene production were not decreased by the presence of an adventitious root system. The extent to which applications of BA and GA may reflect the activity of endogenous hormones produced by aerobic roots is discussed.

Following observations that ethylene can occur in anaerobic or partially anaerobic soils at concentrations which can affect plant growth, shoot and root growth of barley plants, maintained in solution culture, were examined after long-term exposure of the roots to ethylene in air; the subsequent growth on transfer to a similar but ethylene-free environment was also studied. Both root and shoot dry weights were reduced slightly by the ethylene t r e a t m e n t ; seminal root extension was inhibited greatly while lateral root growth was stimulated; absorption of ions and their transport from root to shoot within the plant was not affected. On transfer to an ethylene free environment the extension rate of the seminal axes increased markedly and was the greater the shorter the period of the preceding ethylene t r e a t m e n t ; the extension of laterals initiated during the ethylene t r e a t m e n t was stimulated greatly but the growth of those formed subsequently was inhibited.Split root experiments showed that on any plant only those roots actually exposed to ethylene became modified by the gas while those remaining in an ethylene free environment were typical of roots of untreated plants.