Have soil tested, by a lab that gives organic recommendations, to learn the total and available levels of organic matter, nitrogen, calcium, magnesium, sulfur, phosphate, potassium, sodium, chloride, boron, iron, manganese, copper and zinc. Tissue sample tests are important to see what nutrients are being taken up by the plants. Check for life by counting the earthworms in a square foot of soil - should be at least ten.  The best lab for organic recommendations is Texas Plant and Soil Lab in Edinburg Texas.  They may be reached at 956-383-0739.