The Texas demonstrations have also shown the benefit of compost for vegetation establishment in the harshest of climatic and soil conditions. Probably it is the latter benefit of compost that makes it the most attractive to Texas contractors. Current practice is for the state to withhold five percent of the payment for highway projects until vegetation is established on 70 percent of the disturbed area. Compost is being applied to the soil surface as a top dressing as well as being applied and tilled into the soil in the Texas demonstrations. Applications range from inch to two inches deep, with most all studies show the maximum benefit of compost is limited to one inch in depth.
Additional depth adds cost without increasing benefits as noted in the Connecticut study as well.
Application of the compost to the soil surface will prolong the longevity of treatment, but without the dramatic soil changes in the first years after application. The Texas specification, like its counterpart in other states, sets minimum requirements for the quality of material and construction methods. With the specification in place, it will be easier for the statewide use of compost to develop. Particle sizes for the erosion control compost are two to three times that of the other two compost classes. As previously mentioned, current TxDOT policy provides an economic incentive for the rapid establishment of vegetation in disturbed areas.