In a relatively short amount of time, usually within a couple of months, the buried organics will decompose and enrich the surrounding soil. You can then rotate a planting into that area, and select a new location for your next trench.
<---- Compostable organic materials in the trench,
ready to be covered with soil.
Extra tip: mulch it too! After you've buried the organic materials, don't leave exposed soil on top; cover with a layer of mulch. Over time, that adds even more organic matter to your garden soil. And, if you dig the trench in advance, keep it covered with mulch to prevent erosion by wind and rain.
If you had concerns about neighbors seeing or smelling your compost, try this stealth alternative. No odor, out of sight, and out of mind … keep that valuable organic matter out of the landfill, and start enriching your garden soil by trench composting.
blog entry by Mark Murphy, CMG