Definition of "leached"

[T]he very wet winter will have washed much of the goodness out of the soil. Homemade compost and the load of manure we get from a friendly farmer may not be enough to compensate for what has leached from the ground.

2014 April 21, Mary Keen, “You can still teach an old gardener new tricks: Even the hardiest of us gardeners occasionally learn useful new techniques ”, in The Daily Telegraph (Gardening)‎, page G7