Soil physical attributes and citrus root system distribution as indicators of cohesive layers in soils of coastal tablelands in the State of Bahia, Brazil

The physical characterization of two typical Coastal Tableland soils (Yellow Latosol-YL and Gray Argisol-GL) of the State of Bahia, Brazil, was carried out in 2001 and the citrus root system in such soils was evaluated in order to determine attributes that best identify the cohesive layer. The first four horizons in each soil were sampled for analysis of particle size distribution, soil bulk density, total porosity, macroporosity, microporosity, and saturated hydraulic conductivity. Soil resistance to penetration and critical humidity of soil resistance to penetration were determined. Citrus root samples were collected in the same horizons and the results were expressed in cm cm(-3) of soil. The citrus root system density reduced abruptly in the AB, Bw1, BA, and Bt1 horizons, and this was associated to soil cohesion. The best attribute to identify cohesion was soil resistance to penetration, which should be evaluated at soil humidity below the critical level to express cohesion. Saturated hydraulic conductivity was another attribute that proved appropriate to evaluate soil cohesion. It can be substituted by macroporosity, which is equally important to identify cohesion, with less variability besides being easier to measure than saturated hydraulic conductivity. Soil bulk density can be considered an attribute to evaluate the presence of cohesive horizons, but its use is limited mainly by the interference of particle size in its determination. The recommended indicators allow the detection of the presence of cohesive layers, orienting additional soil management practices to overcome the problems that such soils present for deep root growth.