EFFECT OF SUBSOIL COMPACTION AND 3 DENSITIES OF SIMULATED ROOT CHANNELS IN THE SUBSOIL ON GROWTH, CARBON GAIN AND WATER-UPTAKE OF PINUS-RADIATA

The experiment investigates effects of subsoil compaction, of three de nsities of simulated root channels through the compacted layer, and of fertiliser addition on growth, carbon gain and water relations of Pin us radiata. Treatments were designed to simulate subsoil compaction pr oduced by a previous tree crop and access to depth through the compact ed layer via old root channels. Comparisons were also made of diurnal carbon assimilation, micro-climate, water potential, and mineral nutri tion of well-exposed foliage. Subsoil compaction was negatively associ ated with growth, plant water potential, foliar nutrient concentration , water uptake and diurnal carbon gain per unit foliage area. All trea tments with compacted subsoil grew more slowly than controls, and an i nteraction between root access to depth and nutrition is indicated. Di urnal carbon gain per unit foliage area of trees growing on unperforat ed, compacted subsoil was about 0.78 that of controls, while stem grow th was about 0.56 that of controls. Root growth of trees on compacted subsoil with the largest number of root channels showed an effect of f ertilisation on growth. Fertilised trees in this compaction treatment had a significantly greater fine root biomass in the upper 0.3 m of th e profile, greater access to water at depth, higher plant water potent ial, higher soil water content below the compacted subsoil layer, and greater growth than unfertilised trees in the same soil compaction tre atment.