Coffee root growth in compacted acid soil layer with and without chemical restrictions

Coffea arabica L. Mundo Novo variety was grown for one year in PVC soil. columns, 60 cm high by 30 cm diameter, made up by superposing three rings of 20 cm high each one. Samples of surface layer of an acid Oxisol were divided into two portions : limed to pH 6 and unlimed. The top (0-20 cm) and bottom (40-60 cm) rings had a soil bulk density of 0.8 g/cm(3), while the central ring (20-40 cm) was compacted to 0.8, 1.1. and 1.4 g/cm(3). The rings were bounded by adhesive tape. Total dry weight of the plant tops and leaf nutrient concentrations were not affected by compaction in limed soil, but decreased with increasing bulk density in unlimed soil. Compaction decreased root growth in both limed and unlimed soil, but with greater reduction in unlimed soil. Compaction increased root growth in the overlying (0-20 cm) and underlying (40-60 cm) soil layers only if these soil volumes were limed, which was associated with elevated Ca and reduced Al. The excess Al compounded by low Ca content in unlimed soil were the main causes which restricted root growth even in well structured soil volume above and beneath the compacted layer. These results demonstrated that Al toxicity and Ca nutrition are the chief soil chemical constraints that determine the ability of coffee plants to compensate when part of the root system is subjected to physical impediment by enhancing root growth in volumes of the soil where well structured conditions exist.