A division of Walker Aero Environmental LLC / J-V Dirt + Loam
Do you have to keep your lawn drenched to keep it half alive? Is your lawn yellow even if you water? Does it green up, just to die back? Compost can help fix that.
If you bought your house new in Austin, you probably noticed that the builder installed your sod just a day or two before closing and advised you to "water the hell out of it." Why? Austin area builders spread the least amount of the cheapest soil they can get, since it is hidden, and in one day the yard will no longer be their problem: it will be your problem. The soil they use is not much better than infield dirt, and is not conducive to healthy turf. It is practically devoid of organic matter, which means it cannot retain water: water either sheets right off of it, or runs right through it.
Compost can reduce or eliminate your use of synthetic fertilizers:
The frequency and intensity of irrigation needed to keep plants healthy may be reduced because of the drought resistance and efficient water use characteristics of compost.2
Sustained plant growth requires slow release of water into the soil. Healthy plants in a moist bed rich in organic material need watering less frequently.3 But how much water you use is linked to the percentage of organic matter in the soil. Organic matter holds a lot of water, thus, the amount of organic matter in a soil directly influences the availability of water to a crop over time. Soil scientists report that for every 1 percent of organic matter content, the soil can hold roughly 1.5 quarts of water per cubic foot of soil. Increasing the organic matter content from 1 to 2 percent would increase the volume of water to 3 quarts per cubic foot of soil. However, organic matter in droughty soils breaks down so rapidly that getting above 2 or 3 percent is difficult to do, but getting to 2 to 3 percent have major positive impacts.4
In addition to supplying the soils with beneficial microorganisms, compost also provides important structural component to gardens. Compost reduces soil crusting, which helps with water absorption and penetration into the soil.5 In clay soils, water tends to run off the surface, and in sandy soil the water runs straight through. However, compost retains the water in micro-aggregates composed of soil and clay particles held together by "glues" produced by bacteria and fungi. In turn, these micro-aggregates are bound into larger aggregates by root hairs and fugal hyphae. Water is trapped in these aggregates and released slowly to surrounding plants.6 The addition of compost in sandy soils can facilitate moisture dispersion by allowing water to more readily move laterally from point of application.7 In short, compost encourages the formation of soil clusters that soak up water and hold it like a sponge.8 The sponge-like nature of compost means that rain or irrigation water will be absorbed and stay in your soil -- where your plants need it -- instead of trickling off int the gutter.9
A 1994 study by A. Maynard found that a 3 inch layer of leaf compost rototilled to a 6 inch depth increased water holing capacity 2.5 times that of a native sandy soil and provided almost a 7 day supply of plant available water. In a 2000 study, Maynard found that increasing the water holding capacity of the soil by adding compost helped all crops during summer droughts by reducing periods of capacity of water stress.
A test in in Colorado showed that one hundred pounds of average Denver soil, which is a 1- by 10-foot row tilled 6 inches deep, mixed with one pound of compost will hold an additional 33 pounds, or four gallons, of water. Add five pounds of compost to that soil, and it will hold nearly 200 pounds, or 25 gallons, of water.  http://www.denverwater.org/Conservation/TipsTools/Outdoor/UsingCompost/
Different soils benefit differently from compost. The table below, published by the Denver Water Utility, shows the relationship between the percent of compost and the amount of water that can be retained by four soil types.