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Saline Cooling Tower Water for Irrigation in Minnesota: I. Crop and Soil Effects¹

ABSTRACT

Saline cooling tower water (CTW) from the Northern States Power coal-fired plant in Sherburne County, MN was used to irrigate a Hubbard loamy sand (Udorthentic Haploboroll). The objectives of this study were to determine the changes in soil solution salinity, to measure salt accumulations in the soil profile (0- to 240-cm), and to assess the impact of CTW on crop production.

In a 3-yr field study, CTW (2.2 dS m^–1) was applied at two rates to alfalfa (Medicago sativa L.), corn (Zea mays L.), and fallow areas. Analysis of the soil water for electrical conductivity (EC_sw) at 75 cm indicated that an increase in salt concentration occurred over the growing season. Maximum seasonal EC_sw at 75 cm in the cropped areas (3.0–4.0 dS m^–1) were higher than in the fallow areas (2.0–2.5 dS m^–1). Rainfall between the growing seasons, however, was adequate to leach the upper 75 cm of this coarse-textured soil and prevent a stepwise buildup of salts from one year to the next. After an initial buildup, EC_sw at 225 cm was relatively stable. For the last 2 yr, EC_sw at 225 cm was consistently higher under alfalfa than corn or fallow areas.

A seasonal buildup of SO₄ occurred during the growing season. In the fall, SO₄ accumulations in the 0- to 60-cm soil layer were highest under corn. By the following spring, there was no difference between the three cropping systems. Rainfall was very effective in leaching seasonal accumulations of SO₄ from the soil. A lower Ca/Mg ratio in the CTW, as compared with the soil, resulted in increased concentration of Mg in the 0- to 60- and 60- to 150-cm soil layers.

Corn grain and alfalfa production averaged 8440 and 8230 kg ha^–1 for the last two seasons, respectively, and were not adversely affected by salinity produced from the CTW application.

Key Words: sprinkler irrigation • salt • soil solution • alfalfa • corn • fallow

¹ Journal paper no. 13 580, Univ. of Minnesota Agric. Exp. Stn., St. Paul, MN 55108. Contribution from the Dep. of Soil Sci. and Agri. Eng.

² Former graduate research assistant, currently assistant professor of soil science, Southern Agric. Res. Center, Montana State Univ., Huntley, MT 59037; associate professor of soil science, Soil Sci. Dep.; and professor and head of agricultural engineering, Dep. of Agric. Eng., Univ. of Minnesota, St. Paul, MN.

Received for publication October 7, 1983.