When organic fertilizers are used (or very little chemical ferilizers) the mix will retain its quality.
All organic nitrogen sources, such as blood meal, fish meal, feather meal, earthworm castings, chicken manure, and canola meal are effective only for a single outdoor growing season.
Phosphorous needs to be replenished each year. Bonemeal and rock phosphate work well independently or as a combination.
Mineral potash sources, such as greensand and crushed granite, extend their usefulness beyond a single season. The minerals will break down slowly over time, releasing potash to the roots. Fast-acting potash, good for a single season, is available in kelp meal and wood ashes.
Kelp meal also provides most of the necessary trace minerals for the plant, but should be added for each new crop.