Soil pH Range for Optimum Commercial Vegetable Production1

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A&M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Thomas A. Obreza, Interim Dean Introduction Soil pH is a measure of soil acidity or basicity, and it is defined as the negative logarithm of the proton (H+) activity. The pH ranges from 0 to 14. A pH of 7.0 is defined as neutral, while a pH of less than 7.0 is described as acidic, and a pH of greater than 7.0 is described as basic (Figure 1). According to the USDA Natural Resources Conservation Service (1993), soil pH ranges roughly from acidic (pH < 3.5) to very strongly alkaline (pH > 9.0). Soil pH is a master characteristic in soil chemical properties because it governs many chemical processes. The pH specifically affects nutrient bioavailability by controlling the chemical forms of nutrients. For example, ferrous iron is a bioavailable form of iron for most crop species, but ferric iron is not. At a relatively high pH, ferric iron is the primary form of the nutrient, and crop plants may experience iron deficiency. As one of the most important soil chemical properties for optimal crop production, soil pH determines nutrient sufficiency, deficiency, toxicity, and need for liming (Fageria and Zimmermann 1998) or addition of sulfur. The pH range of most of the Florida’s soils is approximately between 4.0 and 9.0 (Figure 1; Tables 1–4). Because nutrient solubility is highly pH dependent, soil pH near 4.0 or 9.0 is usually not suitable for commercial vegetable production. A pH range from 5.5 to 7.0 is suitable for most vegetable crops (Figure 2). This pH range can assure high bioavailability of most nutrients essential for vegetable growth and development (Ronen 2007). For example, at soil pH 8.0 or higher, iron and/or manganese bioavailability can’t satisfy most vegetable crops’ requirements. However, when soil pH reaches 5.0 or lower, aluminum, iron, manganese, and/ or zinc solubility in soil solution becomes toxic to most vegetable crops (Osakia, Watanabe, and Tadano 1997).