| Samenvatting: | The physical and chemical characteristics of the substrates are important to obtain a nursery plant with adequate morphological characteristics. Three substrates of current use in forest nurseries were characterized: S1: moss peat, vermiculite and perlite; S2: composted bark, peat moss and sawdust and S3: pine sawdust, moss peat and composted bark, all in 3: 1: 1 vol proportion, to which 8 g L-1 of Osmocote® fertilizer of 8 - 9 months of release was added. They were used to produce Pinus greggii var. australis Donahue & Lopez. The porosity, pH, electrical conductivity and carbon/nitrogen ratio were evaluated before and after plant production, while granulometry, retention curves and water release only before production. The initial and final ranges of total porosity, aeration and water retention were 77% - 83%; 19% - 27% and 54% - 63%, respectively. In all substrates the aeration porosity decreased, and the water retention increased at the end. The readily available water varied from 19% to 30%, higher in S3. According to the granulometry, the largest proportion of particles was from 0.26 mm - 0.75 mm in diameter. The initial (4.8-5.3) and final (6.3-6.7) pH values are in the acid range. The initial EC was 0.9 dS - 1.7 dS, lower than the end one of 1.7 dS - 2.4 dS. The C/N ratio was different for the three substrates; S1 presented the lowest value (159), S2 with 537 and S3 the largest (613). The alternative substrates evaluated have suitable characteristics to be used in the production of forest plant and to replace the use of peat moss.
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