But there's a long answer. It's important to build the soil. Fifteen years ago the only decent soil on the farm was under the big trees. The accumulation of more than fifty years of falling leaves and fruit became an important part of each tree's ecosystem. Unfortunately we had to plant all our new fruit trees in sand. Even weeds couldn't grow in some places. Our solution to help the trees establish was to use mulch from tree-trimming companies. Over the years we have used hundreds of truckloads of mulch (wood and leaves) and our soil is much better. Mulch also helped cool the tender surface roots and was an important part of our low-volume irrigation.
In addition to building soil, retaining moisture and cooling the ground, mulch provides virtually all the nitrogen we give to our trees. To provide other necessary nutrients, we use modest amounts of Gypsum (calcium sulfate), Ironite, Sulfate of Potash Magnesia, Triple Super-Phosphate, Rare Fruit Council 'Fruitilizer' (8-3-9 with minor nutrients), 0-0-6 Minors Mix, and seaweed. Also, from time to time we spray specific trees for specific reasons. Products we use include Sulfur, Copper and Zerotol for molds, various soaps for insect problems. (These products are OMRI approved.) Most of these sprays also provide some nutrition for the plants.
Also of note, we're starting to try composted horse manure in several situations. It seems to be a great product for our type of operation.