Compost can be added to lower-quality soils to enhance plant growth
Has the ability to transform damaged soil, making it viable for growth
Potentially eliminates need for any extra fertilizers
Retains water, reducing irrigation needs
Compost can be added to the root zone of soil to encourage plant growth on compacted, disturbed, un-irrigated, low-maintenance sites. This use of compost can be critical, as it can not only drastically improve plant growth, but may also be able to transform soil that has been considered unusable or damaged. The compost-soil mixture allows for nutrients to be saved and employed to their best ability, and for water to be retained and saved, meaning that expending resources on extra fertilizer and water would not be necessary.
To use compost to upgrade marginal soils, the area in question should be covered with 1 to 3 inches of compost. In the case of salt-sensitive plants, or native-plant species, a lesser amount of the compost can be used. In the case of sandy soils, and where the aim is to use less water, more compost can be used, so long as the nutrient level is at a lower density.
The process of using compost for upgrading marginal soil involves a handful of factors. First, in order to get the most out of the compost, the soil involved must have an optimal level of water density, meaning that soil cannot be excessively wet or completely barren. If using fertilizer or a pH adjusting chemical, a pre-plant and compost mix can be used to soil the ground.
Some of the information in this article came from the Compost Research & Education Foundation's Compost Use Applications - A Return on Investment (ROI) factsheets. The full set of factsheets can be found here.