Compressive Behaviour of Soils in Irrigated Agroecosystems of the Semiarid in Ceará, Brazil.

Knowledge of the compressive behaviour and the load bearing capacity of soil can contribute to maintaining the quality of irrigated soils, which have a greater intensity of usage and different hydro-physical dynamics. This study aimed to evaluate the degree of compaction and the effects of usage on the preconsolidation pressure and compression index in irrigated areas under different systems of usage and cultivation. Four irrigated areas were evaluated: banana of 2 and 15 years cultivation (B2 and B15), pasture (P), succession planting of corn and beans (CB) and areas under natural vegetation. Samples were collected at depths of 0.00-0.10 m and 0.20-0.30 m, being collected both in and between the crop rows for B2 and B15. The following were determined: the degree of compaction (DC), maximum density (D_SMax), critical moisture (U_crit), preconsolidation pressure (σ_p), compression index (Cc), total organic carbon (TOC) and light organic matter (C_lom). The t-test was used at 5, 10, 15 and 20% probability. An increase in DC at 0.20-0.30 m for MF (p< 0.15) was noted, showing the effect of conventional tillage employing plowing and scarifying, together with the traffic of heavy machinery on annual crops. Irrigated cultivation promoted a reduction in the Cc, having no effect on the σ_p under the moisture conditions of field capacity (-10 kPa). Use of the irrigated areas with perennial crops was more effective in preserving the physical quality of the soil. The results for Cc and σ_p showed that the soils under evaluation had a high load-bearing capacity and high susceptibility to compaction.