Physical attributes. Retention curve. Physical quality of the soil. Modeling.

The sugarcane production system involves the use of numerous operations, as well as different management systems. In studies of soil physical quality, the soil water retention characteristic curve (CCRAS) has been widely used. CCRAS modeling with adjustments via Van Genuchten has been one of the most used. However, due to the complex pore space presented by tropical soils, where there is a great variation in pore sizes, this can be evaluated considering the bimodal arrangement, as suggested by the Dexter model, with the pores classified into two domains: inter- aggregates and intra-aggregates. The objective of the research was to evaluate the behavior of CCRAS, using different mathematical models and its relationship with the distribution of soil pore diameter, in an area cultivated with sugarcane, under different implementation times. The study was carried out at the Carpina Sugarcane Experimental Station (EECAC/UFRPE), where the soil was classified as Argissolo Amarelo distrocoeso. Deformed and undeformed soil samples were collected at 36 points in three subareas, under different sugarcane cultivation seasons (2nd, 5th, and 7th leaf), in the 0-15 cm and 15-30 cm layers. Undeformed samples were collected in soil blocks and volumetric cylinders (@ 100 cm³), with deformed samples obtained from parts of the blocks, and converted to air-dried fine earth (TFSA). From the cylinder samples, data on CCRAS, pore distribution, saturated hydraulic conductivity, soil resistance to root penetration, and soil bulk density were obtained. For the block samples, they were separated into aggregates, and the tensile strength of soil aggregates and soil aggregation indices were determined. The TFSA samples were used in soil solid particle density tests; distribution of particle size fractions and degree of flocculation; in addition to the characterization of chemical attributes. The Dexter model curves presented a bimodal format, possibly due to the existence of two air entry values. Evaluating the subareas through CCRAS via the Van Genuchten model, they showed almost similar behavior for the different sugarcane plantation implementation times, and only in the soils of the subarea under the 7th leaf, it was possible to notice a greater difference between the curves. The CCRAS, modeled using the Dexter model, presented better adjustments to the curves, highlighting the characteristic of tropical soils of presenting more than one inflection point, and the second tension to promote the entry of air into the soil pores is related to the drainage of soil micropores.