Actually, you can do it when turf is present. In fact IFAS (Institute for Food and Agricultural Studies) recommends broadcasting over all other methods. When you deep root or use spikes you are only fertilizing small areas of the root system and with deep rooting you run the risk of missing the majority of the roots in the upper region of the soil. I am sure that you all know that the majority of all roots on mature trees are in the first three feet of the soil. That is why broadcast spreading is the best method.