How to use iron sulfate in agriculture


Despite the existence of a large number of iron chelates that protect this ion from degradation in the soil, especially in limestone soils, iron sulfate continues to be of great importance in agriculture. It has simply adapted to new technologies and “got used” to other uses. Let’s talk a little more about this great product that is iron sulfate .


One of the great problems that we find in many Spanish soils is their rich limestone content and, therefore, high pH. This causes some mixtures, such as iron sulfate , to become insolubilized and precipitate quickly.

You just have to see this table where you can see how the assimilation or availability of iron decreases depending on the increase in pH. From pH it begins to be a limiting factor, and at pH close to 8, quite common in southern soils, its precipitation is quite high.


One thing to keep in mind is that anything that is applied foliarly has a faster assimilation. It does not interact with the edaphic environment and the possibility of it interacting (both positively and negatively) with the rest of the cations and anions in the soil is practically nil.

However, it is necessary to differentiate between complexes and chelates , since they are not the same. In foliar applications, it is advisable to use complex-based products. On the other hand, via the root canal, the choice of chelates is better.

One of the biggest problems with iron is that it is photosensitive and easily degrades in contact with light. Used as a deficiency corrector (an iron chelate), it can be applied in the early hours of the morning, at doses that vary between 200-300 cc / hl for most products, which have a wealth of iron that varies between 6 and 7.5%.


It is very common, and in many cases it is done this way, for convenience, the application in fertigation or the “gimmick” of using iron chelate or iron sulfate only in the plants or trees that require it.

A variable dose per plant is usually applied to correct an iron chlorosis with visual symptoms . In this link you can see what this deficiency consists of and how it can be identified in the leaves.

An example dosage for a common iron chelate :

Iron chelate 7%

  • 30-50 grams / foot for developing trees
  • 50-100 grams / foot for large and highly developed trees.

A visual example, to see the importance of iron in crops, demonstrated in this essay.


First of all, as we always recommend at Gardenprue , is to do a prior soil analysis to find out what we have in the soil, what we are going to use and what we have to replace.

The application of iron sulfate, in this sense, offers several benefits.

On the one hand, the application of large amounts, between 400 and 600 kg / ha of iron sulfate , helps to lower the pH of the soil, if we are dealing with very limestone soils that have great problems to mobilize micronutrients.

Another recommended dose can also be between 35 and 50 grams / m2 , with the interest of applying iron to the soil in a simple and cheap way.

By simply taking a look at the above table of mobility of nutrients (macro and micronutrients) as a function of pH, we make a day of what we could gain by acidifying or alkalizing a soil.

Although, as we have already repeated a few times, the soil has a great buffer capacity, and only large amounts can help to modify the pH.

Therefore, in limestone soils , the application of iron sulfate not only helps to lower the pH of the soil, provide iron in large percentages and sulfur, but also highlights its ability to mobilize and improve the assimilation by the plant of other nutrients that they are only mobile in acidic pH.


One of the major drawbacks of iron sulfate applied in agriculture is its great potential to degrade.

It is one of the best known sources of iron, but once it is applied to the soil, sulfur and iron dissociate, so that each will go their own way.

In different situations, pH, type of soil, luminosity, etc. iron is easily degraded from ferrous sulfate (FeSO4), with a content between 20 and 25% of iron, to Fe 3+ , an insoluble , solid compound and a precipitate.

However, plants are very intelligent and have developed many strategies that are still being studied today.

These plants are capable of secreting substances that acidify the soil (with a high energy cost). They release a high charge of H + protons to try to solubilize Fe3 + which, as we have said, is insoluble at neutral or basic pH.

On the other hand, there are the siderophore microorganisms , which are capable of  transforming the Fe 3+ to  the Fe 2+   state , which is soluble and assimilable by plants.

Do you use iron sulfate regularly?

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