Physical properties of media for container-grown crops. II. Peat mixes

The effect of addition of sand, perlite, polystyrene and pumice in half and quarter proportions and in various particle sizes, on physical properties of peat mixes was studied. Coarse sand had no effect on air space (AS), while fine sand reduced AS and at the higher rate the value fell to an unsatisfactory level. At the higher rate of coarse sand addition, easily available water (EAW) fell to an unsatisfactory level. Fine sand increased EAW. Total porosity (TP) and water-buffering capacity (WBC) were generally reduced as a result of sand addition. The addition of coarse perlite at the higher rate increased the AS, while fine perlite at both rates and medium perlite at the high rate reduced AS. The effect of addition of coarse and fine perlite on EAW was similar to sand addition. Total porosity was reduced by coarse perlite and by medium perlite addition at the higher rate. The addition of polystyrene increased AS, but decreased EAW and the value fell to an unacceptable level at the high rate of application. Bulk density, WBC and TP were decreased by the addition of polystyrene. The addition of a standard grade of pumice had no effect on AS, but the EAW, WBC and TP were reduced. However, only in the case of WBC was the reduction below the critical level.