Evaluating soil amendments for improvement of soil physical properties

All of the amendments tested lowered the bulk density and greatly improved the water flow rate through the soil mix, thereby reducing management problems. Wetting agents were found of value in management of soil mixes difficult to re-wet after being depleted of water. Water storage capacity of a soil mix was improved most by the addition of such water-absorbing materials as peat moss, redwood shavings, and vermiculite. Amendments that improved all soil properties, except water storage, included pumice and calcined clay. Only slight increases in water storage were obtained from use of larger wood chips, fir bark, or rice hulls.

Evaluations of various amendments to several soils by two different laboratory and greenhouse methods showed agreement in results but the laboratory method required much more equipment. The greenhouse method could easily be used by anyone interested in evaluating his own soil, and amendments. The only equipment needed is a balance and several small tensiometers. The greenhouse method also allows evaluation of the plant grown to extract the water, for its response to the treatment. The laboratory method offers the possibility of evaluating many more mixes over a shorter period of time, however.