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Research Project: Integrated Field Scale Management Systems for the Use of Degraded Waters

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Title: Effects of the dissolved organic carbon of treated municipal wastewater on soil infiltration as related to sodium adsorption ratio and pH

Author
item Suarez, Donald
item Gonzalez Rubio, Alberto - University Of California

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2017
Publication Date: 6/30/2017
Citation: Suarez, D.L., Gonzalez Rubio, A. 2017. Effects of the dissolved organic carbon of treated municipal wastewater on soil infiltration as related to sodium adsorption ratio and pH. Soil Science Society of America Journal. 81(3):602-611. doi: 10.2136/sssaj2016.09.0310.

Interpretive Summary: Increasing scarcity of fresh water for irrigation in arid and semi arid regions means that we must utilize alternative water supplies if we are to sustain agricultural production. Treated municipal wastewaters are being increasing utilized for irrigation. In general only the salinity level, extent of sodicity and microbial content of the waters are examined. These water generally contain higher concentrations of sodium, higher pH and higher dissolved organic carbon as compared to traditional irrigation water supplies. We thus examined the effect of the dissolved organic carbon in treated waste water on soil physical properties, specifically the infiltration rate, aggregate stability and dispersibility of the soil. We determined that independent of sodium level and pH the treated wastewater always had a reduced infiltration rate into soil, aggregate stability decreased and dispersibility of the soil increased. Increase in the sodium adsorption ratio and increase in pH also resulted in decreased infiltration and aggregate stability. We conclude that the SAR, DOC and pH of typical wastewaters is sufficiently high to cause substantial loss of infiltration and deterioration of soil physical properties. Sustained use of these waters will require amendments to reduce SAR and lower pH. These results are of interest to scientists and of keen interest to producers, irrigation specialists, irrigation districts and any users applying treated wastewater to soils.

Technical Abstract: Increasing scarcity of fresh water in arid and semi arid regions means that we must utilize alternative water supplies for irrigation if we are to sustain agricultural production in these regions. Treated municipal wastewaters are being increasingly utilized for irrigation. In general only the salinity level, SAR (sodium adsorption ratio) and microbial content of the waters are considered when evaluating their use for crop irrigation. These waters generally contain higher concentrations of sodium, thus higher SAR but in addition higher pH and higher dissolved organic carbon (DOC) as compared to traditional irrigation water supplies. We thus examined the effect of the DOC in treated wastewater on soil physical properties, specifically the infiltration rate, aggregate stability and dispersibility of the soil. Our experiment consisted of treatments of wastewater and prepared waters (free of detectable DOC) at SAR 4, 7 and 10 and at pH 7.0 and 8.0 We applied the waters to a sandy loam soil in outdoor containers for 153 days, allowing the soil to dry to -50kPa potential before applying another irrigation. We determined that independent of sodium level and pH the treated wastewater always had a reduced infiltration rate, reduced soil aggregate stability and increased soil dispersibility. The effect of the DOC was equivalent to a increase in SAR of 2-3 units. An increase in the SAR sodium adsorption ratio and increase in pH (from 4 to 7 and from 7 to 8, respectively) also resulted in decreased infiltration and aggregate stability. The increase in pH of the irrigation water from 7.0 to 8.0 reduced infiltration and aggregate stability, with and without DOC and for all three SAR values examined. We conclude that the SAR, DOC and pH of typical wastewaters is sufficiently high to cause substantial loss of infiltration and deterioration of soil physical properties. Both the pH and DOC of the water, in addition to salinity and SAR have to be considered when evaluating suitability for irrigation.