Structural quality of polyacrylamide-treated cohesive soils in the coastal tablelands of Pernambuco

Abstract

SUMMARYWater-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 noncohesive) 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.Index terms: anionic polymer, coagulation/flocculation, aggregate stability.( RESUMO: QUALIDADE ESTRUTURAL DE SOLOS COESOS DOS TABULEIROS COSTEIROS DE PERNAMBUCO TRATADOS COM POLIACRILAMIDAPolímeros solúveis em água caracterizam-se como eficientes agentes floculantes relacionados aos seus aspectos moleculares, cuja aplicação em solos com horizontes que apresentam problemas estruturais, como acontece com o caráter coeso, favorece a melhoria da qualidade física e, assim, amplia a aptidão agrícola desses solos. Esta pesquisa teve como objetivo avaliar a qualidade estrutural de solos com horizontes coesos dos Tabuleiros Costeiros de Pernambuco com a aplicação de Poliacrilamida (PAM) como condicionador químico. Para isso, foram avaliados três horizontes (um coeso e dois não coesos) de um Argissolo Amarelo e, para fins comparativos de horizontes coesos, foi selecionado o horizonte de um Latossolo Amarelo. Como tratamentos, foram aplicadas soluções aquosas de PAM (12,5; 50,0; e 100,0 mg kg -1 ) e água destilada (controle). Os aspectos estruturais dos horizontes foram avaliados pela estabilidade (massa de solo retida em cinco classes de diâmetro), distribuição de agregados por classe de tamanho (diâmetro médio ponderado -DMP, diâmetro médio geométrico -DMG) e magnitude das alterações promovidas pela PAM, medindo o índice de sensibilidade (Is). As soluções aquosas de PAM aumentaram a estabilidade de agregados na maior classe de diâmetro avaliada dos...

Aggregate Stability and Water Retention Near Saturation Characteristics as Affected by Soil Texture, Aggregate Size and Polyacrylamide Application

“…Conversely, in small aggregates the pores are probably too small to enable PAM molecules to fully penetrate into the aggregates (Levy & Miller, ); thus, PAM efficacy in stabilizing the small aggregates had probably been limited. The latter explains the observed lack of efficacy of PAM in improving the resistance to slaking of our smallest aggregate size group (0·25–0·50 mm), which was, generally, in agreement with other studies (Busscher et al ., ; Caesar‐Tonthat et al , ; Melo et al ., ).…”

“…It was further noted that differences in the reduction in water turbidity between control and PAM-treated samples were highly correlated with soil texture, mineralogy, and extractable Fe reductions, with most of the differences in flocculation occurring in subsoils with >20% smectite or vermiculite (McLaughlin & Bartholomew, 2007). Melo et al (2014) studied the contribution of different rates of PAM (0-100 mg kg À1 ) on aggregates' mean weight diameter and geometric mean diameter and structural quality of cohesive and non-cohesive soils from five to six horizons of two Brazilian soils. The authors stressed that, although PAM contribution was soil dependent, PAM was effective in stabilizing aggregates in the two larger-size classes (0·25-2·0, >2·0 mm) in both soils (Melo et al, 2014).…”

“…() studied the contribution of different rates of PAM (0–100 mg kg −1 ) on aggregates' mean weight diameter and geometric mean diameter and structural quality of cohesive and non‐cohesive soils from five to six horizons of two Brazilian soils. The authors stressed that, although PAM contribution was soil dependent, PAM was effective in stabilizing aggregates in the two larger‐size classes (0·25–2·0, >2·0 mm) in both soils (Melo et al , ). Caesar‐Tonthat et al .…”

“…Melo et al (2014) studied the contribution of different rates of PAM (0-100 mg kg À1 ) on aggregates' mean weight diameter and geometric mean diameter and structural quality of cohesive and non-cohesive soils from five to six horizons of two Brazilian soils. The authors stressed that, although PAM contribution was soil dependent, PAM was effective in stabilizing aggregates in the two larger-size classes (0·25-2·0, >2·0 mm) in both soils (Melo et al, 2014). Caesar-Tonthat et al (2008) who studied addition of three PAM rates to three aggregate sizes (0·25-0·5, 0·5-1·0 and 1·0-2·0 mm) of a Norfolk loamy sand soil reported that adding PAM (120 mg kg À1 ), with and or without wheat residue, to aggregates (0·5-1·0 and 1·0-2·0 mm) favored the growth and survival of specific fungi and bacterial species functioning as soil aggregators in vitro, and consequently considerably enhanced aggregation, pore continuity and soil physical condition (Busscher et al, 2007;Caesar-Tonthat et al, 2008).…”

Agricultural use and physical-hydric attributes of cohesive soil

“…Os valores de densidade do solo (Ds) dos horizontes Bt1 dos perfis de solo da área sob mata nativa e da área sob cultivo foram altos em relação a solos sem coesão, mas estão dentro da faixa considerada normal para horizontes com caráter coeso, que é de 1,5 a 1,8 g m -3 (Jacomine, 2001). Estes resultados corroboram outras pesquisas utilizando solos coesos (Giarola et al, 2001;Zuffo et al, 2013;Melo et al, 2014). Comparando-se a as duas áreas, os valores de Ds para os solos sob vegetação nativa não apresentaram diferenças aos da área cultivada (Tabela 1), indicando que o manejo não está afetando a condição de coesão inicial do solo, em relação à densidade.…”