How does soil pH affect micronutrient availability?

Soil pH is the gatekeeper for micronutrients that plants utilize. Acidic soils below 6.0 will release iron and manganese while also "trapping" molybdenum. Alkaline soils above 7.0 will do the opposite- iron will be lost and molybdenum will "flood" the roots. An excellent example is that I've witnessed blueberries flourishing and tolerant to pH 4.5 but very shortly after I found them to be iron starving at 6.5.

Iron chlorosis caused the soybeans and pin oak trees to perform poorly when growing in alkaline soils. A client reported a 40% loss in yield from their orchard until we injected iron EDDHA into the drip irrigation lines. The soil test indicated that although there was enough iron, the pH of 7.8 had made it unavailable to use. They later attempted to recover the yield with foliar sprays, but this only offered short-term relief. Soil amendments eventually paid off.

Increase pH very gradually. An application of 2 tons/acre of lime will take 6 months to increase soil pH by 0.5 units. A tomato farm in Michigan over-limited and spiked pH to 7.3 which caused zinc deficiency. So, we banded 5 lb/acre of zinc sulfate and in 3 weeks the new growth started to green up. Testing the soil every 2 years will keep you updated.

Alkaline soils foster molybdenum, but above 2 ppm, molybdenum is toxic. A lima bean field had 5 ppm molybdenum after excessive liming that curled its leaves and killed the rhizobia. Flushing it with 12 inches of water reduced it to 1.8 ppm. Balance is better than extremes.

Read the full article: 7 Essential Micronutrients for Plants: Complete Guide