The Relation Between Bulk Density, Available Water Capacity, and Air Capacity of Soils

Abstract

The effect of bulk density on moisture content at 5 0 mb tension in four soils of different textures was studied. The volumetric water content increased linearly with bulk density over a wide range of densities. Depending on texture, a maximum bulk density was reached above which continued compaction decreased the water content. This is shown to be the point at which the air capacity of the soil at this tension approaches zero. Accepting that the gravimetric wilting point depends mainly on texture, the available water capacity varies in a manner similar to the 50 mb water content.If the relationships described are valid in the field, the available water capacity and air capacity may be optimized using cultivation techniques to adjust the bulk density. The available water capacity of coarse-textured droughty soils may be increased by increasing the bulk density providedthat the air capacity remains above acceptable lower l i m i t s (10-15 per cent). Conversely, the air capacity of compacted soils with large available-water capacities could be increased by reducing the bulk density to a value corresponding to an acceptable available-water capacity. In very compacted soils a decrease in bulk density will benefit both available-water capacity and air capacity.

The effect of soil compaction on the water retention characteristics of soils in forest plantations

“…Thus a number of optimum bulk densities were identified, corresponding to maximum A WC providing that aeration was not limiting at these bulk densities. Reeve, Smith & Thomasson (1973) showed the relationship between bulk density and FC, and therefore A WC, to be more complex by considering a wider range of soil textures than those studied by Archer and Smith (1972). Volumetric water content at FC, which for all soils was taken as -5 kPa, was found to decrease with increasing compaction for all soils except' loams and clays where FC increased with increasing bulk density.…”

“…The influence of bulk density on FC, taken as the water content at a matric potential of -5 kPa for a range of British soils, was studied by Archer and Smith (1972) who found that volumetric water content at -5 kPa increased with increasing compaction until a critical bulk density was,reached and then declined rapidly. Archer 'and Smith (1972) suggested that since wilting point is predominantly controlled by texture, available water capacity (A WC) varies in a manner similar to Fe.…”

“…Archer 'and Smith (1972) suggested that since wilting point is predominantly controlled by texture, available water capacity (A WC) varies in a manner similar to Fe. Thus a number of optimum bulk densities were identified, corresponding to maximum A WC providing that aeration was not limiting at these bulk densities.…”

Influência da posição relativa à linha de cultivo sobre a densidade do solo em dois sistemas de manejo do solo

“…A densidade é negativamente relacionada com a porosidade de aeração e positivamente relacionada com a resistência do solo à penetração das raízes (Archer & Smith, 1972;Ehlers et al, 1983;Silva et al, 1994). Os efeitos dos sistemas de preparo na variação da densidade do solo podem ser manifestados de forma diferenciada de acordo com a intensidade de tráfego e a posição relativa à linha de semeadura (Kaspar et al, 1991;Kaspar et al, 1995).…”

Uma classificação físico-hídrica dos solos

“…Outros autores (Archer & Smith, 1972;Thomasson, 1978) denominaram capacidade de ar a diferença entre a porosidade total e a umidade em certo nível de tensão (a 60 ou 50 cm de coluna d'água, normalmente), devendo, porém, tal conceituação ser evitada, uma vez que o processo de drenagem interna tende a se estabilizar no campo num nível de umidade (capacidade de campo) que não coincide com nenhuma tensão de água constante (Salter & Williams, 1965a;Reichardt, 1988;Fabian & Ottoni Filho, 2000). Assim, a capacidade de campo deve, preferencialmente, ser determinada "in situ", pois depende, além da seqüenciação dos horizontes, da lâmina d'água aplicada e da umidade inicial no perfil (Hillel, 1980a;Cassel & Nielsen, 1986;Fabian & Ottoni Filho, 2000).…”