Bulk Density, Porosity, Percolation and Salinity Control in Shallow, Freely Draining, Potting Soils1

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Abstract
Ten mixtures of soil, sphagnum peat moss, pinebark, almond hulls, and sheep manure, and 8 combinations of clay loam and sand, 20cm deep, were examined for relevant physical properties and possible use as greenhouse potting composts under Cypriot greenhouse conditions. There were significant variations of bulk density, porosity, moisture content, air space and percolation rates. Comparison of these data with other workers’ information showed a linear relationship between bulk density and total pore space regardless of specific gravity. The rate of salt removal, as measured by effluent conductivity, was predictable from a knowledge of the starting salinity concentration, regardless of the potting mixture. The higher the percolation rate, the less efficient was salt removal, with the removal rate decreasing as the initial salt concentration decreased. Percolation rate showed an exponential relationship with the ratio of porosity to maximum moisture content, with percolation increasing markedly above a ratio of 1.8. Mixtures in excess of 0.70cm3 cm−3 total porosity showed markedly high percolation rates, requiring large water volumes to reduce salinity. It was the opinion of these authors that very porous potting mixtures would unnecessarily increase water utilization in a semi-arid climate, with problems in controlling salinity with trickle irrigation systems likely to be exacerbated.

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