IRRIGATION WATER EFFECTS ON INFILTRATION RATE IN THE NORTHERN GREAT PLAINS

Abstract

Supplemental irrigation is expanding in the Northern Great Plains. Limited access to water of suitable quality for sustained irrigation and uncertainty about the impact of the use of marginal water on the soil resource will limit adoption of this practice. The objectives of this study were to determine the effect of irrigation water quality and amount on the infiltration rate, Q, at 50, 100, and 150 mm tensions, (h), and to relate the change in Q to changes in soil salinity and sodicity caused by irrigation. Tension infiltrometers were used to determine Q for soils at two sites in central North Dakota. Each site had 18 nonweighing lysimeters supporting alfalfa (Medicago sativa L.) that had been irrigated at three levels of irrigation (1ET, 2ET, and 3ET) for at least 10 years with either good quality surface water [electrical conductivity (EC) 0.1 S m -1 , sodium adsorption ratio (SAR) 4] or poor quality simulated groundwater (EC 0.34 S m -1 , SAR 16). At the site having sandy soils, Q, averaged over irrigation levels, was greater [Q(50) = 5.34 μm s -1 , Q(100) = 3.74 μm s -1 , Q(150) = 2.96 μm s -1 ] in soils irrigated with good quality water than in soils irrigated with poor quality water [Q(50) = 3.06 μm s -1 , Q(100) = 2.31 μm s -1 , Q(150) = 2.01 μm s -1 ]. Level of irrigation had no effect. At the site having loam textured soils Q was lower under the two higher irrigation levels than under the 1ET level, likely the result of greater replacement of divalent cations with Na + at the higher leaching rates. At this site Q, averaged over irrigation levels, were greater [Q(50) = 3.08 μm s -1 , Q(100) = 2.55 μm s -1 , Q(150) = 2.02 μm s -1 ] in soils irrigated with good quality water than in soils irrigated with poor quality water [K(50) = 2.05 μm s -1 , K(100) = 1.63 μm s -1 , K(150) = 1.28 μm s -1 ]. Reductions in Q were directly related to increases in soil SAR (e.g., at the 1ET level of irrigation, SAR = 3 in soil irrigated with good quality water and SAR = 6 in soil irrigated with poor quality water) resulting from irrigation. These results suggest that these sulfatic soils are sensitive to Na + -induced deterioration. Soil physical deterioration was apparent at SARs much lower than the SAR 13 used to describe soils as sodic. Soil water compatibility in these soils is critical for sustainable irrigation.