The rôle of aluminium in soil infertility and toxicity

Abstract

1. The main results of soil investigations on the rôle of aluminium in soil infertility are reviewed, with particular regard to the physicochemical principles involved.2. Magistad's conclusion that soils or other nutrient media whose reaction values lie within the range pH 4·7 and pH 8·5 do not contain aluminium in soluble form, and are probably therefore not toxic to plants, is discussed in the light of modern knowledge of the properties of hydrous alumina and its peptisation phenomena.3. Dialysis experiments which have led to this generalisation are criticised on the grounds that they do not take into account the disturbing effect of dialysis on hydrous colloidal systems, and that dialyser membranes do not simulate plant-cell membranes.4. Aluminium may possibly penetrate plant-root cells, and, under certain conditions, may be translocated, within the plant body, in at least four different forms, namely, (a) simple ions, (b) more complex colloidal electrolytes, (c) co-ordinated complex anions, and (d) organo-compounds. These may conceivably be interconvertible.5. Aluminium appears to exert true toxic effect only when presented to plant roots as simple ions, or as the more soluble colloidal electrolytes. Apparently, the degree of toxicity varies for different plant species.6. The reaction conditions of nutrient media and of plant saps doubtless largely decide the form in which aluminium occurs therein. At reactions approaching the isoelectric point of hydrous alumina, toxic effects may never be exerted, although the assignation of a strict reaction-range applicable to all soils or nutrient media, and to all plant species, is probably inadmissible.7. Non-toxic forms of aluminium may apparently accumulate under certain conditions at definite tissue regions of certain plants, and may disturb their metabolic processes, disposing the plants to certain diseases.8. Within the reaction-range at which toxic aluminous solutes cannot exist in soils or other culture media, hydrogen-ions may exert controlling influence on plant growth, and may thus be of major significance in natural plant distribution, and in the behaviour of plants growing in normal agricultural soils.

Influence of Aluminum Ions on Developmental Morphology of Sugarbeet Roots1

“…Entrance might have occurred when the root cap begins to separate due to precipitate accumulation, resulting in breakage of epidermal cells. Our data support the findings of Hardy (9) and Rasmussen (18) who stated that AI penetrates root cells.…”

Differential Responses of Grasses and Legumes to Liming and Phosphorus Fertilization1

“…Burst rum ( 6) has shown that calcium is essential for the elongation of wheat roots, but if calcium could move downward in roots (as demonstrated by Schmehl eta!., 14) lack of calcium should not have limited the growth of fescue and clover roots in the lower layer of soil, at least not where sufficient calcium was available from the upper (limed) layer of soil. The inhibition of root development is one of the first observable symptoms of aluminum toxicity, and the symptoms observed with fescue and clover in the present experiment were similar to the effects of aluminum observed by many other workers (7,8,10,15). It is probable that soluble aluminum was the factor inhibiting the root growth of fescue and clover in the unlimed soil.…”

“…Gilbert and Pember (7) and Hardy (8) showed that there are large differences in the susceptibility of plant species to aluminum toxicity. Blaser and Brady ( 4) have demonstra_ted that nutrient competition between plants is an ecological factor.…”

Aluminum Toxicity

“…It has been asserted by a number of workers (3,5,7,8,10,11,13,15,16,18,19) that aluminum salts are decidedly toxic, and that the toxicity of acid soils is due primarily to this cause (1, 2, 6,7,9,15). Others maintain that aluminum compounds are so insoluble that they cannot occur in solution in a sufficient concentration to cause injury to plant growth (4,12,13).…”