I just got done reading an article about new technology to improve irrigation practices. It was amazing to me that there was no mention of having a good permeable soil with organic matter in it to retain the water. If a lawn or turf area has poor soil to start with you must use more water to sustain it simply because the water just lays on the top of the ground and evaporates. This can also lead to a shallow root system that is dependent on that surface water. Just stop irrigating for a couple of weeks and see what happens. Most likely it will be brown grass. Any plant whether it is turf or tomatoes needs good living soil to survive and produce. Topressing with compost or compost blends and proper aeration are the key to good soils.