HORSE PADDOCK: We are maintaining a paddock on a thin layer of soil over a crushed fill rock. Are there any particular problems we should anticipate? Palm Beach County

ANSWER: My immediate concerns for the site you have described are irrigation and soil pH. With a relatively shallow soil, and necessarily distant irrigation heads, it will be challenging to maintain soil moisture, without some areas being either too wet or too dry. The irrigation should be tested with catchment cups, to determine actual precipitation rate. The coefficient of uniformity can then be calculated; this will tell whether to install backup sprinklers in dry areas. The precipitation rate can be used along with daily experience (which should be recorded in an irrigation log), to adjust the times and durations of future irrigations.

The presence of limestone fill rock suggests a high soil pH (alkaline), typical of south Florida disturbed soils, and this is worsened by liming from calcium carbonate groundwater. The high soil pH will contribute to micronutrient deficiencies, most likely manganese, and possibly also iron. Symptoms will be interveinal chlorosis (yellowing) which will be barely noticeable in a hand lens; from a distance, there may be patchy yellowing in areas close to rock and maybe near sprinkler heads. The potentially high soil pH is another reason to throttle the irrigation, to use acid-forming fertilizers (e.g., ammonium sulfate which, unfortunately, is highly water soluble), and to experiment on a spot basis with foliar treatment using micronutrients, e.g., manganese sulfate. There are numerous other problems you might run into, which are specific to the needs of your client. Nevertheless, a healthy turf is one of the best ways to insure useability and safety.