It's called hydroseeding. Hydroseeding is a popular means of planting grass due to its relative ease of use and effectiveness. Hydroseeding is a process by which seed, water, fertilizer, fiber mulch, and sometimes lime are blended together in a tank and applied onto a prepared lawn area through a spraying hose. Once sprayed, the wet fiber mulch will help create a bond to the soil and provide the seeds with a water retaining blanketing-coat while protecting it from sunlight, wind, and erosion. As the grass seeds begin to germinate, the fiber mulch will slowly decompose adding nutrients to the soil.Advantages of Hydroseeding 1. If you are planting a relatively large area, hydroseeding can be completed in a very short period of time. 2. Hydroseeding can be very effective for hillsides and sloping lawns to help with erosion control and quick planting. 3. Hydroseeding will typically cost less than planting with sod, but more than regular seeding. 4. Results are often quick with high germination rates producing grass growth in about a week and mowing maintenance beginning around 3-4 weeks from the date of application. Fiber mulch accelerates the growing process by maintaining moisture around the seeds thereby increasing the rate of germination.Disadvantage of Hydroseeding as opposed to sodding the area.1. It will take longer to thicken.2. It will will be more susceptible to disease in NEO August as it will be humid at night. Watch out for Pythium blight.3. Water water water. Get a good automated watering system.4. Root system will not be as strong within one year, two years, etc...5. One strong thunderstorm within a week or two of planting on a hillside will wipe it out. Please take note of this one UA groundskeeper, this happen to me last year and the top highest part of my lawn has still not recovered. But the bottom of the hill looks awesome.