The effect of soil compaction, profile disturbance and fertilizer application on the growth of eucalypt seedlings in two glasshouse studies

Soil damage, compaction and displacement, during logging or clearing and cultivation affects both soil physical and chemical properties and reduces growth of regenerated or planted tree seedlings. Understanding the factors involved will aid management and set limits for indicators of sustainable management in eucalypt forests. In the first of two glasshouse studies, three Eucalyptus species were grown for 110 days in soils from six forest sites in Tasmania, Australia. Sites sampled ranged from low rainfall dry forest to very high rainfall wet forest. Soil was collected from three soil depths, in 10 cm increments to 30 cm, each packed in pots to four different bulk densities, ranging from that present in undisturbed field sites to that plus 0.17 g cm^?3. In the second study Eucalyptus globulus Labill. seedlings were grown in soil collected from disturbed and undisturbed sites, packed to two bulk densities, and fertilized with combinations of N and P. Increasing soil compaction, in Study 1, caused a proportional decrease in final mass of seedlings of up to 25%. Growth on soil from lower horizons (10–30 cm) averaged only 41% of that on topsoil, a significantly greater restriction of growth than that achieved through compaction. It was concluded that topsoil displacement and profile disturbance was a more significant form of soil damage than compaction. Above-ground dry weight of seedlings was most strongly correlated with soil total N but poorly correlated with other macronutrients. Growth of E. globulus seedlings grown on disturbed soils, in Study 2, averaged 30% of that on undisturbed sites. With added P and N on undisturbed sites growth averaged seven times that of the unfertilized seedlings indicating a general deficit of available P and N on the three soils tested. On soils from disturbed areas, there was also a response to fertilizing with N and P together but the response varied on the three soils. The effects of profile disturbance were ameliorated with fertilizer applications on only one of the soils. The results highlighted the importance of retaining topsoil in situ during forest operations.