Effects of deep ploughing and superficial disc harrowing on physical and chemical soil properties and biomass in a new plantation of Eucalyptus globulus

Abstract

A field trial was carried out of Portugal on a plantation of Eucalyptus globulus Labill. to compare the effects of minimal (surface disc harrowing) and intensive (deep ploughing) site preparation techniques on various soil properties as well as on biomass production. The results presented cover the first 30 months after planting. Disc harrowing resulted in a significant decrease in bulk density to 30-cm depth, a decrease in soil compaction to 10-cm depth and an increase in aeration porosity in the 0 to 10-cm layer. Deep ploughing induced a decrease in the bulk density between 10- and 80-cm depth, but had no effect on the aeration porosity or the levels of soil compaction. The rate of water infiltration was higher in the former than in the latter type of treatment. In both treatments the chemical properties of the soil were only affected within the top 20 cm. Significant decreases in organic carbon, pH, exchangeable Ca, sum of bases and cation exchange capacity occurred in both treatments. Decreases in all variables except pH were significantly higher in deep ploughed than in disc-harrowed plots. i.e. where the organic matter was concentrated. Biomass production and partitioning, measured 18 and 30 months after planting, were not affected by the treatments. However, roots were concentrated in the 0 to 20-cm layer in the disc-harrowed plots and in the 20 to 75-cm layer in the deep-ploughed plots. The results are discussed with references to currently applied silvicultural techniques for managing E. globulus plantations in Portugal.