Abstract
Water-soluble polymers are characterized as effective flocculating agents due to their molecular features. Their application to soils with horizons with structural problems, e.g, a cohesive character, contributes to improvements in the physical quality and thus to the agricultural suitability of such soils. The purpose of this study was to evaluate the structural quality of soils with cohesive horizons of coastal tablelands in the State of Pernambuco treated with polyacrylamide (PAM) as chemical soil conditioner. To this end, three horizons (one cohesive and two non-cohesive) of a Yellow Argisol (Ultisol) were evaluated and to compare cohesive horizons, the horizon of a Yellow Latosol (Oxisol) was selected. The treatments consisted of aqueous PAM solutions (12.5; 50.0; 100.0 mg kg-1) and distilled water (control). The structural aspects of the horizons were evaluated by the stability (soil mass retained in five diameter classes), aggregate distribution per size class (mean weight diameter- MWD, geometric mean diameter - GMD) and the magnitude of the changes introduced by PAM by measuring the sensitivity index (Si). Aqueous PAM solutions increased aggregate stability in the largest evaluated diameter class of the cohesive and non-cohesive horizons, resulting in higher MWD and GMD, with highest efficiency of the 100 mg kg-1 solution. The cohesive horizon Bt1 in the Ultisol was most sensitive to the action of PAM, where highest Si values were found, but the structural quality of the BA horizon of the Oxisol was better in terms of stability and aggregate size distribution.
Highlights
The agroecosystem of coastal tablelands in Brazil has been discussed in studies on the soil quality in these areas (Barreto et al, 2012; Gomes et al, 2012)
The increased aggregate stability (Table 3) with the application of polymer solutions can be explained by the chemical-physical interactions between the molecules of the hydrophilic polymer and the constituents of the aggregate particles by means of ionic bonds, hydrogen bonds, and Van der Waals forces, which vary according to the aggregate properties as well as the dynamics of the polymer solution (Liu et al, 2009)
There was an increase in mean weight diameter (MWD) and geometric mean diameter (GMD) of the cohesive and non-cohesive horizons treated with PAM solutions
Summary
The agroecosystem of coastal tablelands in Brazil has been discussed in studies on the soil quality in these areas (Barreto et al, 2012; Gomes et al, 2012). These tableland regions are socially relevant due to the great importance for the national livestock and agriculture sector, mainly for citrus and sugar cane production and extensive and semi-extensive livestock (Cintra et al, 2004; Souza et al, 2006; Silva et al, 2007). The positive effects of PAM on soil preservation are related to increased aggregation of soil particles and pore continuity (Green et al, 2004; Caesar-Ton That et al, 2008), stabilization of the surface structure (Dou et al, 2012), increased water infiltration rates, and reduced surface sealing (Sepaskhah & Shahabizad, 2010) and resistance to root penetration (Busscher et al, 2009)
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