The method of irrigating (drip, flood, sprinkler, micro-sprinkler, etc) affects irrigation and nitrogen fertilizer recommendations in several ways. First, the distribution uniformity of the irrigation method will affect the volume of water recommended. A higher application uniformity will reduce the volume of water recommended. Drip usually has a higher distribution uniformity than sprinklers. If 100% is a perfect uniformity, then a new well designed and operated drip system used in commercial fields should provide a distribution uniformity between 85% and 90%. Depending on maintenance, operation, and design, the distribution uniformity of most sprinkler systems in closer to 70 to 80%. If crop ET is 1 inch over a week then a recommended amount of water would be 1 inch/0.85, or 1.18 inches. In comparison, the recommended amount of water for sprinklers would be 1 inch/0.7 or 1.43 inches.
Another way the irrigation method affects the recommendations is when converting from the volume or inches to apply to hours to operate an irrigation system. Sprinklers for example typically apply water at a higher rate than drip systems. If the field application rate of sprinklers is 0.25 inches per hour irrigating for 4 hours would apply 1 inch of water. In contrast, if irrigating with a drip system that applies 0.1 inches per hour, one would need to irrigate 10 hours to apply one inch of water to a field.
Another effect of the irrigation method is on the estimate of crop evapotranspiration. Irrigation practices that wet more soil surface, such as flood and sprinklers, lead to higher rates of evaporation from the soil.
An indirect effect of irrigation method is on the nitrogen credit that CropManage calculates from nitrate in the water when adding a new fertilizer N event. Because the crop ET is higher when irrigating with sprinklers than with drip, more N credit is given for sprinkler irrigation than for drip.