100 Principles of Food Science fruit loss. Before applying fertilizer, growers need to perform a soil pH test to determine if the pH is adequate for nutrient availability. Local extension agents help growers take regular soil samples for analysis through the state’s land grant university however, private laboratories perform similar analyses. When the analysis returns, a summary of the soil’s pH and the current amounts of organic matter and nutrients are provided to the grower. This information provides the framework for growers to modify their pH to meet the appropriate levels. If the pH is too high, growers usually add sulfur to the soil. If the pH is too low, lime (calcium carbonate) is added. Plant growers know that one of the keys to plant health and optimum growth is to regularly monitor and address the soil or growing media’s pH. If growers want to harvest lemons from their orchards, they must ensure that the pH of the soil is near 6.5 and that sufficient nutrients and organic matter are present in the soil. Farm Futures The Impact of pH on Nutrient Availability in Soils When you bite into a lemon wedge, you immediately experience the intense sour sensation from the juice. The white part of the peel, on the other hand, will taste bitter. The lemon juice tastes sour because it is acidic, and the peel tastes bitter because it is alkaline. Just as the ability to taste is related to pH, the success of the lemon plant relies on the appropriate pH in its growing environment. The nutrients that plants need for optimum growth are most available in a slightly acidic environment. When the soil, also known as growing medium, has a pH of about 6.5, the plant can thrive. Most plants’ roots absorb nutrients in an acidic pH range. Nutrients such as nitrogen and iron are not as available to the plant when the pH dips below 5.5 or rises above 7.0. Imagine a refrigerator full of food with doors that can only open under certain conditions. This is very much like how pH impacts nutrient availability in the root zone of plants. When the plant is in a highly acidic or alkaline environment, it may begin to exhibit signs of nutrient deficiencies. Plants often show symptoms of yellowing, known as chlorosis tip burn stunted growth curling of leaves and even flower or pH versus Availability of Nutrients in Soil 4.5 5.5 6.5 7.5 8.5 9.5 4.0 5.0 6.0 7.0 8.0 9.0 10.0 Strong acid Medium acid Slightly acid Very slightly acid Slightly alkaline Very slightly alkaline Medium alkaline Strongly alkaline Nitrogen Phosphorus Potassium Sulphur Calcium Magnesium Iron Manganese Boron Copper & zinc Molybdenum Copyright Goodheart-Willcox Co., Inc.