Heavy manure application to agricultural land has long lasting effects on soil properties. A study was initiated at the Lethbridge Research Centre to investigate the residual effect of 14 annual (1973 to 1986) cattle manure applications at rate of 90 Mg ha^-1 yr^-1 (R90) under non-irrigated and 180 Mg ha^-1 yr^-1 (R180) under irrigated conditions (three times the recommended agronomy rate for non-irrigated and irrigated crop production at that time) on soil chemical properties. The years need to return to pre-manure treatment level for soil N and P (recovery time) were investigated using data collected in the next 16 years (1987 to 2003) when no manure were applied with a 2-paramter exponential decay model (y = a * e^-bx). The recovery time for soil NO₃-N content (0 – 150 cm) is 90 yr for R90 (non-irrigated) and 17 yr for R180 (irrigated), respectively. The recovery time for surface soil total N is 24-33 yr and drops to 18 for sub-surface soil (15-30 cm). Similarly, total P recovery time is also longer (37 – 52 yr) for surface than for subsurface soil (25-29 yr). In contract, soil test P (STP) had similar recovery time for both surface and subsurface soil (37-44 yr). Although twice as much amount of manure was applied under irrigation, there are little differences in the number of years needed for the soil to return to pre-manure treatment levels. The shorter recovery time under irrigation resulted from greater leaching, crop uptake and denitrification for NO₃ losses. The higher crop yield and greater N and P crop uptakes were also responsible for the faster rate of TN, TP and AP depletion under irrigation. The long-lasting residual effect of cattle manure application on soil properties is well demonstrated by this project.