Answer: First you'll need to have the soil tested to see what the pH actually is. The you can take steps to improve it. The soil pH (whether a soil is acid or alkaline) affects the availability of nutrients, and also the activity of microbes and other tiny creatures in the soil.
In general, the best soil pH for citrus trees is between 5.5 and 6.5. If the pH falls below 5.0, aluminum toxicity and manganese toxicity often occur in citrus roots. A low pH also causes a deficiency of nutrients such as calcium, magnesium, and phosphorus (which are easily fixed by soil particles), and molybdenum.
Liming with limestone or dolomite is the usual action taken to reclaim soil with such problems. Growers should also avoid applying too much ammonium, in the form of nitrogen fertilizers such as urea or ammonium sulfate. This is because there is a danger of making the soil more acid.
If citrus trees are growing in soils with a pH higher than 7.5, they often suffer from a deficiency of micronutrients such as iron, manganese, copper and zinc. A foliar spray of fertilizer can be applied to supplement the micronutrients. Sulfur can be applied to modify the soil pH to 6.5.
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