Effect of Subsoil Compaction and Three Densities of Simulated Root Channels in the Subsoil on Growth, Carbon Gain and Water Uptake of Pinus radiata

Abstract

The experiment investigates effects of subsoil compaction, of three densities of simulated root channels through the compacted layer, and of fertiliser addition on growth, carbon gain and water relations of Pinus radiata. Treatments were designed to simulate subsoil compaction produced by a previous tree crop and access to depth through the compacted layer via old root channels. Comparisons were also made of diurnal carbon assimilation, micro-climate, water potential, and mineral nutrition of well-exposed foliage. Subsoil compaction was negatively associated with growth, plant water potential, foliar nutrient concentration, water uptake and diurnal carbon gain per unit foliage area. All treatments with compacted subsoil grew more slowly than controls, and an interaction between root access to depth and nutrition is indicated. Diurnal carbon gain per unit foliage area of trees growing on unperforated, compacted subsoil was about 0.78 that of controls, while stem growth 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 fertilisation on growth. Fertilised trees in this compaction treatment had a significantly greater fine root biomass in the upper 0.3 m of the profile, greater access to water at depth, higher plant water potential, higher soil water content below the compacted subsoil layer, and greater growth than unfertilised trees in the same soil compaction treatment.