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Deep subsurface drip irrigation using coal-bed sodic water: part II. geochemistry

Agricultural Water Management

By:
, , , and
DOI: 10.1016/j.agwat.2012.11.013

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Abstract

Waters with low salinity and high sodium adsorption ratios (SARs) present a challenge to irrigation because they degrade soil structure and infiltration capacity. In the Powder River Basin of Wyoming, such low salinity (electrical conductivity, EC 2.1 mS cm-1) and high-SAR (54) waters are co-produced with coal-bed methane and some are used for subsurface drip irrigation(SDI). The SDI system studied mixes sulfuric acid with irrigation water and applies water year-round via drip tubing buried 92 cm deep. After six years of irrigation, SAR values between 0 and 30 cm depth (0.5-1.2) are only slightly increased over non-irrigated soils (0.1-0.5). Only 8-15% of added Na has accumulated above the drip tubing. Sodicity has increased in soil surrounding the drip tubing, and geochemical simulations show that two pathways can generate sodic conditions. In soil between 45-cm depth and the drip tubing, Na from the irrigation water accumulates as evapotranspiration concentrates solutes. SAR values >12, measured by 1:1 water-soil extracts, are caused by concentration of solutes by factors up to 13. Low-EC (<0.7 mS cm-1) is caused by rain and snowmelt flushing the soil and displacing ions in soil solution. Soil below the drip tubing experiences lower solute concentration factors (1-1.65) due to excess irrigation water and also contains relatively abundant native gypsum (2.4 ± 1.7 wt.%). Geochemical simulations show gypsum dissolution decreases soil-water SAR to <7 and increases the EC to around 4.1 mS cm-1, thus limiting negative impacts from sodicity. With sustained irrigation, however, downward flow of excess irrigation water depletes gypsum, increasing soil-water SAR to >14 and decreasing EC in soil water to 3.2 mS cm-1. Increased sodicity in the subsurface, rather than the surface, indicates that deep SDI can be a viable means of irrigating with sodic waters.

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Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Deep subsurface drip irrigation using coal-bed sodic water: part II. geochemistry
Series title:
Agricultural Water Management
DOI:
10.1016/j.agwat.2012.11.013
Volume
118
Year Published:
2013
Language:
English
Publisher:
Elsevier
Contributing office(s):
Denver Federal Center
Description:
15 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Agricultural Water Management
First page:
135
Last page:
149
Country:
United States
State:
Wyoming
Other Geospatial:
Powder River Basin