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A collaborative blog by UC farm advisors and specialists in subtropical horticulture in California.
Bush Poppy
by Greg Alder
on June 15, 2017 at 5:14 PM
I am curious whether micronutrient deficiencies show up on trees NOT given inorganic fertilizer. What I'm wondering is if a tree that lives in a soil where the micro-organisms are fed well with compost and/or wood-chip mulches, for example, will ever have these problems.
by Ben Faber
on June 15, 2017 at 5:31 PM
Yes micronutrient deficiencies can show up on orchards that use solely organic production methods. It's quite common to see iron deficiency. It's interesting that for years zinc deficiency was not seen in citrus grown in California when manures were regularly used as a fertilizer. When synthetic sources of nitrogen started to be used in the 50s, "little leaf" became more common and it was identified as a zinc deficiency. When manure was being used, zinc was applied as a constituent. When manure was stopped, zinc and the other nutrients in the manure were not longer applied. Any zinc was then found to be an essential element to citrus growth.
by Greg Alder
on June 15, 2017 at 9:18 PM
Thank you, Ben.  
Is there a common correlation between iron deficiency in avocados or citrus and soil pH, or perhaps an excess of another specific nutrient?
by Ben Faber
on June 22, 2017 at 7:12 AM
Yep, Greg you are right in both cases. Soil pH controls availability of lots of nutrients, especially the micros like iron, zinc, copper, manganese. The nutrient may be there, but the plant cant get it. Taking the pH down to neutral or a bit lower like pH 6.5 can often relieve a deficiency. This is a better long term approach for correcting these deficiencies rather than applying a foliar or soil-applied iron or zinc. Knock the pH down and the deficiency goes away. Also these deficiencies can be induced by improper application of another nutrient. The classic is applying a phosphate fertilizer thinking there is a P deficiency and inducing an iron deficiency by precipitating available iron with the phosphate fertilizer. The unintended consequences of good actions.
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