In a mature ecosytem you will lose some minerals to leaching. If your soil is worn down the nutrient levels will increase with the organic matter leveland fixed compounds until a peak level is reached. This level will be found when the natural mineral additions from decay of your soil equal the leaching loses. Nitrogen levels willequalize when the content of the losses from organic matter is equal to additions from lightening and nitrogen fixing bacteria.

Quick answer; you'll have a gain until the soil is close to it's original fertility.

Dan O.