The carbonates do not dissociate readily and therefore are harder for the leaves to absorb. Phosphates applied topically can result in phytotoxicity and leaf burning. The nitrate conjugated micronutrients will obviously supply additional nitrogen, and this is usually something that is usually not preferred when the plants are receiving an otherwise known amount of nitrogen. There are also chelated micronutrients and they would be even less appropriate for a foliar spray. Sulfate bonded elements are readily available, cheaper, and less toxic to the leaves.

This is mainly because chlorides or more toxic to plants compared sulfates. The toxic limit of chlorides is far below than sulfates. 

Sulfates dissolve easier than oxides

The aim of foliar feeding is not to replemish soil fertilization. Supplying a plant’s major nutrient needs (N,P,K) is most effective and economical via soil application. However, foliar application has proven to be an excellent method of supplying plant requirements for secondary nutrients (calcium, magnesium, sulfur) and micronutrients (zinc, manganese, iron, copper, boron, and molybdenum), while supplementing N-P-K needs for short and/or critical growth stage periods. Primarily, foliar feeding is intended to delay natural senescence processes shortly after the end of reproductive growth stages. Foliar feeding targets the growth stages where declining rates of photosynthesis and leveling off of root growth and nutrient absorption occur, in attempts to aid translocation of nutrients into seed, fruit, tuber or vegetative production. Secondarily, foliar feeding can be an effective management tool to favorably influence pre-reproductive growth stages by compensating for environmentally induced stresses of adverse growing conditions and/or poor nutrient availability. Early foliar applications can make an already good crop better, either by stimulating more vigorous regrowth or maximizing the yield potential growth stage period. The advantages of foliar feeding in accomplishing the desired crop responses are two-fold

1. It is a highly efficient and timely method of applying needed and/or critical plant nutrients.

2. It is a means of compensating for soil or environmentally induced nutrient deficiencies.

Dear All,

Find several review studies about foliar and micronutrients on our website:

http://www.vfrc.org/Research/VFRC_Reports

The Virtual Fertilizer Research Center (VFRC) is a research initiative that fosters the creation of the next generation of fertilizers and production technologies to help feed the world’s growing population and provide sustainable increases in global food production, and this global issue requires a global solution. Want to join our network? Would be great to collaborate with a growing body of scientists.

Foliar spray resulted the maximum availability and absorption and have no losses and direct effect on the crop growth as compared to soil applied fertilizer.  

Dear Colleagues,

It looks as if you have been doing lots of trials with foliar fertilization as compared to soil applied. We are exactly trying to work on this type of comparisons. Would there interest in sharing our knowledge and end up drafting a scientific paper about this topic?

Dear Bindraban 

Definitely we can bring out a good scientific paper on this particular aspect