Estudo da compressibilidade e qualidade de um argissolo amarelo cultivado com cana-de-açúcar nos tabuleiros costeiros de Alagoas

Abstract

Brazilian northeast the sugarcane occupies mainly the coastal tablelands ecosystem, where most of the soils are favored by topography as well as for possessing medium texture and appropriate depth. However, due to great amount of mechanized operations to be accomplished, those soils are submitted to excessive pressures in conditions of moisture content that favor the process of physical degradation. The objective of this work was to evaluate alterations of the mechanical behavior, at the structure and the organic content of a cohesive yellow Argisol of Alagoas coastal tablelands, due to sugarcane cultivation. Five sugarcane areas were selected with different times of use and cultivation types: 4 years winter cultivation (4 years W); 14 years winter cultivation (14 years W); 14 years summer cultivation (14 years S); 30 years winter cultivation (30 years W) and 30 years summer cultivation (30 years S). The cultivated areas were compared amongst themselves and with a native forest area (Forest), through the regression analysis, path analysis and nonmetric multidimensional scaling analysis. To evaluate the treatment effects on the physical attributes and organic content of Argisol, deformed and non-deformed samples were collected at 0 to 20cm, 20 to 40cm and 40 to 60 cm depth, representing the horizons A or Ap, AB and Bt, respectively. The results allowed us to conclude that the Ap horizon compaction should not be considered as a limitant factor, considering that their soil penetration resistance is below to the considered as critic for the roots development, even when the soil presents permanent moisture content regarding the wilting point. Therefore, the sugarcane cultivation reduced the porosity and increased the Argisol density studied at 0 to 20 cm depth, resulting in increase of the limiting water screeches (LWS). The cultivation of sugarcane induced the compaction of the subsurface horizons, having the reduction of the compressibility and increase of the soil penetration resistance at critical levels to the roots development, even in close moisture content to the field capacity, what resulted in the reduction of LWS of the horizons AB and Bt of the cultivated areas. In the three studied depths, the compaction degree and the soil density were the attributes that presented bigger relation cause-effect with the pre-consolidation pressure and soil penetration resistance of studied Argisol. The non-metric multidimensional scaling analysis indicated a reduction in the quality of studied Argisol, even with few years of cultivation with sugarcane, mainly, for the horizons Ap and AB. The decrease of the particulate organic content and aggregate stability was the main indicators of the decrease of the quality of horizon Ap, however, for AB horizon the quality loss was attributed to the soil compaction.