Physical Properties of Soil Mixes

Laboratory methods for evaluating soil mixes for potting media are proposed, and measurement values from laboratory-compacted smaples are correlated with equivalent ones made under actual use of the mixes in gallon-sized soil containers in greenhouse conditions. Details are given of the materials and methods, and tables are presented which show the particle size distributionof the three soils (used in preparation of the soil mixes), the influence of various amendements on water retention and on saturated water conductivity, and comparison of the bulk-density and water-storage properties measured on laboratory-compacted cores with the same mixes in greenhouse. The study indicates that values of bulk density and hydraulic conductivity for compacted samples appeared to have usefulness in predicting these properties for the mixes in use. Water retention expressed as water released between 0 to 10 cb suction was not significantly correlated with this property by the use of root-extraction techniques. Water released by the soil to the root system over the range from 0 to 30 cb suction appeared to be a good index for evaluating soil mixes in relation to irrigation management. A safe irrigation program for potted plants should be based on irrigating when tensiometer readings reach 30 cb.