My husband is planning to aerate and fertilize our yard. This is our first year with chickens. We plan to fence off an area that we will NOT fertilize for them to be able to roam in. About how long after fertilizing will we have to keep them in the pen? We usually watch the weather and fertilize before a good rain, and also run the sprinkler lots to soak it in. I am sure fertilizer is not healthy for chickens, so how long before they can safely roam the whole yard again?