The Effects of Long-Term Irrigation Management on Soil Properties

Abstract

Irrigation management has been practiced in Saskatchewan since 1885. Few studies on irrigation and soil quality expand beyond examining the potential for salinization under poor irrigation conditions. The objectives of this study were to determine the effects of long-term irrigation management (= 20 years)on soil chemical, physical and microbiological properties at a field level. Non-saline soils were specifically chosen to assess the effects of irrigation on soil properties excluding salinization. The results of an experiment conducted on soils sampled from the South Saskatchewan River Irrigation District #1 compare soil properties of irrigated and dryland treatments. The bulk density of the irrigated treatment was not significantly different from the dryland treatment. The electrical conductivity (EC) of the irrigated treatment was significantly greater than the dryland treatment (P<0.05), however, the soil was not considered saline. The irrigated soil was reaching equilibrium with the conductivity of the irrigation water. The pHof the irrigated and dryland treatments was not significantly different, suggesting the increased, yearly fertilizer application to irrigated land did not decrease soil pH.Wet aggregate stability (WAS) of the dryland treatment was greater (P<0.05) than the irrigated treatment. The reduction in WAS may have been a result of yearly applications of irrigation water causing aggregate destabilization,or may have been reflecting the previous year's management. The nitrate-nitrogen (N03-N) content of the irrigated treatment was greater (P<O.OOl) than the dryland treatment. The level of N03-Nmay bea reflection of the fertilizer practices involved in irrigation and dryland management. The mineralization of organic Nwas greater in the irrigated treatment (P<O.05) than the dryland treatment. The percent organicmatter (OM), however,was not significantly different between irrigated and dryland treatment. The N supply rate (as measured by an anion exchange membrane) was greater for the irrigated treatment. These results suggest the ability of the irrigated treatment to supply N to the crop was improved under irrigation management. Coefficient of determination (R2)values indicate initial N03-N is an adequate indicator of N uptake. The available phosphorous (P) level of the irrigated treatment was greater (P<O.05) than the dryland treatment. The P level may have been a reflection of the fertilizer practices involved in irrigation management. The sulfate-sulfur (S04-S) and potassium (K)content did not significantly differ between the irrigated and dryland treatments. No significant difference was detected between the irrigated and dryland treatments for algal biomass.