Answer: I suspect what you've found are common puff-balls (Lycoperdon pyriforme). These are fungi and, in youth, are edible. As they age the spores inside become powdery. Puff-balls are often found in clusters on stumps and sections of wood, and are very common.
Instead of tilling the fungi into the soil, collect and remove them from the garden prior to preparing the soil for planting. While they're harmless in the garden, spreading the spores will only encourage more puff-balls to grow.
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