Question
I have been researching for a while, and I have come to know that produce grown with organic fertilizers have more vitamin C than produce grown with synthetic fertilizers. I was wondering why this happened?

Answer
I don't have an answer for you.

I can tell you, however, that there is no biological explanation why this should be.

Nutrients (nitrogen, phosphores, potassium, calcium, magnesium, boron, magnenese, etc) are taken up by plants by the roots. To facilitate this, the nutrients must be dissolved in water after which the cells of the plant roots take up nutrients by a process called osmosis which is simply the diffusion of water across a (cell) membrane.

The only molecules these cell membranes allow to pass are very small molecules, like water molecules (H20) and small molecules of individual fertilizer nutrients such as Calcium (Ca), Magnesium (Mg), Nitrate (NO3), etc.

The way it works is very simple. Take table salt as example. Sodium chloride (table salt) NaCI, consist of two molecules, Na (sodium) and CI (Chloride). Together they form the well known white chrystalized form we see in the salt shaker. When placed into water, the two negatively charged hydrogen atoms of the water molecules will surround the positively charged Sodium (Na) molecule and literally pull it apart from the Negatively charged Chloride (CI) molecule which will attach itself to the positively charged Oxygen molecules found in water (Water = H20, e.g. 1 oxygen + 2 hydrogen molecules).

What you end up with is two individual compounds: Na and Ci each sourrounded by water molecules. These molecules can now pass through the cell membrances and into the roots. In it's complex form NaCI the sodium chloride molecule could not be taken up by the roots, but as Sodium and Chloride seperately they are taken up by the roots.

In similar manner, the plants can not use organic fertilizers (NH2) as the molecules are too large and complex and further, these molecules are not easily dissolved in water (e.g. their composition do not lend themselves to be seperated by the hydrogen and oxygen molecules of water).

Thus be able to pass into the plants via the cell membranes, first the microbacterial life (microbes) in the soil must convert the organic nitrogen into inorganic nitrogen (ammonium, or NH4). Ammonium (NH4+) can be taken up by the plants, and a fair amount does, but other microbes in the soil continue to decomposition process and convert ammonium (NH4+) into nitrates (NO3-) which are also taken up by the roots.

Synthetic fertilizers typically have the nitrogen in the ammonium and/or nitrates forms. If a fair amount is in nitrate forms, the uptake into the plant is rapid, even in cold soils. In warmer soil, the level of nitrates are less critical and ammonium form fertilizers are quite acceptable.

The key point to understand here: organic fertilizer is never taken up by the plants. organic fertilizers are first converted into inorganic fertilizer by the microbes in the soil and it is these inorganic fertilizer nutrients which are then taken up by the roots after being dissolved in water.

One could theorize that plants grown primarily with organic fertilizers are also grown in better soil ?

E.g. say the organic fertilizer was composted manure, adding this as fertilizer would also act as soil improvement at the same time. This alone could improve the quality of some plants especially those liking a soil with high organic matter (OM). Soil with good organic matter often have a higher CEC (caption exchange capacity) which is an important factor when you consider fertilization. High CEC soils can hold on to - and exchange - individual fertilizer nutrients with plants more easily and thus is capable of feeding the plants more consistently over a long period of time. Water holding capacity of soil with good organic content is often higher, too, which improves the final product.

Soil can be improved with organic matter by mixing in peatmoss sphagnum, compost, vermicompost, etc and then continue to use synthetic fertilizers.

You could theorize that the adding of an organic fertilizer, like composted manure, actually improved the organic matter content (OM) of the soil and this, not the organic vs synthetic fertilizer, improved the result ?

Another thing which could the reason.. adding an organic fertilizer would result in a gradual feeding of the plants as the organic nitrogen was gradually converted to synthetic nitrogen. You can further theorize that the organic fertilizer (which is converted faster in warm soil and slower in cool soil) may have suited the growth habit of the produce . If this is the case, and the inorganic fertilizer was not added gradually and in doses which suited the plants, then it is the feeding process itself (e.g. the dosing amount) which is the cause of the change .. not the type of fertilizer used.

An experienced grower would use a high nitrate fertilizer in cool whether (when microbacterial life is limited) and switch to an ammonium based fertilizer as the weather warms up. If an inexperienced grower fed the plants with high ammonium early in the season this could lead to ammonium toxicity which could explain a difference in result. For example, popular home growers choices like osmocote 14-14-14  and miracle grow 15-30-15 contain a very high percentage of the nitrogen in ammonium (and urea which is converted into ammonium) form.

To say for sure if there IS truly any difference in the choice of organic vs inorganic fertilizer you would have to provide the two types of fertilizers to two test groups: experienced as well as inexperienced growers and have them run dual tests using both fertilizer types.

In my opinion, there is no difference feeding produce or any other plant with organic vs inorganic fertilizer.

The organic fertilizer may meet recycling goals and also meet individual ethical goals of grower. They may also provide for automatic addition of organic matter to the soil (would require a fertilizer like manure used and not just liquid fish fertilizer for example). The organic fertilizers may also make dosing easier, feeding more gradual and thus meet specific plant preferences.

Inorganic fertilizers are often cheaper, they contain  nutrients which are readily available and which work in poor soils, in low temperatures, and which does not require microbacterial life to convert them. Some people prefer inorganic fertilizers to hauling manure in their private cars, and the same people may appreciate buying inorganic factory produced fertilizers which has created local jobs as opposed to organic kelp fertilizers which may have been harvested using techniques which destoyed marine life...

it is impossible to give the explanation for preferences. it is almost certain, however, that the plants don't care much. they can only take up inorganic nutrients to begin with.

Note: the most common organic fertilizer in the world: UREA is often considered 'inorganic' or 'artificial' (chemical) by the organic community. This is often because it is produced in factories as opposed to being 'recycled' from plant or animal matter. However, it does contain carbon and thus is organic according to the true definition of organic.


I hope this answered your question.
Thanks.

Kenneth