Subsoiling and mechanical hole-drilling tillage effects on soil physical properties and initial growth of eucalyptus after eucalyptus on steeplands

Abstract The re-establishment of trees after previous forest harvesting (so-called second rotation) requires soil structure amelioration, since the tree harvest with heavy machinery usually causes soil compaction and deformation, mostly at the surface, but also in deeper layers. Efficient soil tillage methods are necessary to create a physical environment suitable for the next generation of trees to grow and develop successfully. The aim of this study was to evaluate the effect of four different soil tillage methods on soil physical properties and the initial growth of eucalyptus (Eucalyptus saligna) after eucalyptus on a gravelly Ultisol in southern Brazil with a compacted layer in 0.3 m depth. Tree seedlings were planted in randomized blocks in three replications after applying the following soil tillage methods: intermittent (every 4 m) downslope subsoiling (DSS), cross-slope subsoiling after above-ground stump cutting (C + CSS), cross-slope subsoiling plus ridging after above-ground stump cutting (C + CSS + R), and hole drilling (HD). Before as well as 122 and 391 days after planting, undisturbed and disturbed soil samples were collected in each tillage treatment in five layers down to 1.00 m to evaluate soil bulk density, macroporosity, microporosity, plant-available water content, and penetration resistance, along with chemical analyses. Operational costs and, where applicable, product costs of each method were compared, while the initial growth of E. saligna was evaluated by means of tree survival rate and height, diameter at breast height and wood volume 90, 180 and 330 days after planting. The tillage method did not affect soil chemical properties, but positively influenced physical properties by means of lower bulk density and penetration resistance. The most intensive and expensive method C + CSS + R provided the best conditions for tree growth, while HD was the cheapest method, but the least efficient due to low productivity. Per volume of produced wood, DSS was the most efficient method with lowest total costs and the second highest wood production.