Abstract
Irrigation with treated domestic sewage wastewater (TSE) is an agricultural practice to reduce water requirements of agroecossystems and the nutrient load impact on freshwaters, but adverse effects on soil chemical (salinization, sodification, etc.) and soil physical properties (alteration in soil porosity and hydraulic conductivity, etc.) have been reported. This study aimed to define some relationships among these changes in an Oxisol using multivariate analysis. Corn (Zea mays L.) and sunflower (Helianthus annuus L.) were grown for two years, irrigated with TSE. The following soil properties were determined: Ca2+; Mg2+; Na+; K+ and H + Al contents, cationic exchangeable capacity (CEC), sum of bases (SB), base saturation (V), texture (sand, silt and clay), macro-, micro-, and cryptoporosity (V MA, V MI and V CRI), water content at soil saturation (θS) and at field capacity (θFC), residual water content (θR), soil bulk density (d s), water dispersed clay (WDC) and saturated hydraulic conductivity (K SAT). Factor analysis revealed the following six principal factors: Fine Porosity (composed of Na+; K+; WDC, θR, θRFC, and V CRI); Large Porosity (θS, d s, V MA, Vs); Soil CEC (Ca2+; Mg2+; CEC, SB, V); Soil Acidity (H + Al); and Soil Texture (factors 5 and 6). A dual pore structure appears clearly to the factors 1 and 2, with an apparent relationship between fine porosity and the monovalent cations Na+ and K+. The irrigation (with potable sodic tap water or sewage wastewater) only had a significant effect on Fine Porosity and Large Porosity factors, while factors 3 and 4 (Soil CEC and Soil Acidity) were correlated with soil depth. The main conclusion was a shift in pore distribution (large to fine pores) during irrigation with TSE, which induces an increase of water storage and reduces the capacity of drainage of salts.
Highlights
The use of domestic treated wastewater in agriculture is a good alternative of liquid waste recycling and avoids the use of potable water for irrigation, considering that the preservation of water resources is essential for the economical and ecological development of many countries, especially under semiarid climates as in the northeastern region of Brazil
Many studies have already reported the effects of irrigation with wastewater on soil agroecosystems, and Na+ excess is generally indicated as a major problem (Bond, 1998; Jnad et al, 2001a; Gloaguen et al, 2007)
The main objective of the present study was to separate the independent factors associated to the changes in soil quality during irrigation with sewage and sodic tap water
Summary
The use of domestic treated wastewater in agriculture is a good alternative of liquid waste recycling and avoids the use of potable water for irrigation, considering that the preservation of water resources is essential for the economical and ecological development of many countries, especially under semiarid climates as in the northeastern region of Brazil. It is necessary to identify the best sustainable irrigation management due to possible undesirable effects on soil chemistry and physics caused by the specific characteristics of wastewater. With regard to the soil physical properties, the main concerns are the reduction in infiltration (Meenner et al, 2001) and hydraulic conductivity (Magesan et al, 1999; Bagarello et al, 2006; Bhardwaj et al, 2007) as well as the changes in porosity (Jnad et al, 2001b). A significant connection between soil physical and chemical properties would be useful to determine the main effects of this irrigation practice on the soil quality. The main objective of the present study was to separate the independent factors associated to the changes in soil quality during irrigation with sewage and sodic tap water
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