nutrient deficiency in citrus trees

None of the citrus trees in the garden have ever done well here, except for the cumquat tree during the first couple of years since moving in, which was many many years ago. That said, no one had really looked after it. Now, we also have 2 orange trees in the garden, and a lemon tree in a pot. 

The larger orange tree is still quite small and hasn't had any fruit before. Back in March, the bigger orange tree was fraught with leaf miners, while the cumquat had green stinkbugs all over it (causing the fruits to drop off prematurely and taste pretty mediocre). I had painstakingly eliminated the little pests on these trees and added compost as mulch for a boost of nutrients.

The cumquat tree is look good, after a lot of the overly tall branches and leaves have been pruned. Little health-looking leaves are emerging now too. 

The orange, though, isn't doing as well. From the look of the leaves, there's clearly some micronutrient deficiencies: 

• The nutrient deficiencies are in the newer leaves, indicating that the deficient element(s) is/are immobile.
• There is chlorosis (yellowing) between veins, and occurs evenly between the tip and the base of the leaf. Mild mottling (yellow blotches) is also visible in newer leaves. The shape of newer leaves are also smaller, longer, and narrower. 
• The inter-veinal chlorosis in younger leaves suggest a deficiency in iron (Fe), while the narrower and mottled leaves suggest a deficiency in zinc (Zn). 
• Deficiencies in Fe or Zn are more pronounced in alkaline soils because even though these elements may indeed be present in the soil, they become unavailable to plants in higher pH levels. However, in this case, given that the soil is slightly acidic (pH 6), the soil is likely to have an insufficient quantity of Zn and Fe.

I had added a lot of compost and blood and bone fertiliser around the base of the orange tree last month, and more recently, I have been watering the tree on a daily basis. Perhaps this was excessive, especially during the winter months. 

A foliar spray of zinc sulphate should be sprayed to the tree, particularly during the spring flush of leaves, and this should be done annually. Because deficiencies in zinc and iron are aggravated in waterlogged soils, overwatering is to be avoided. 

(the above text was used in a Science of Gardening assignment) 

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I've applied a foliar spray of zinc and manganese sulfate to the leaves today - they were already combined in the product, and I couldn't find them sold separately. I'll see how effective this is in a couple of weeks.