The effectiveness of PeptonĀ® replacing chelates in citrus production

Line of biostimulants with highly bioavailable iron

A recent study carried out on mandarin trees grown in calcareous soils in the town of Massafra, in the province of Taranto (Italy), has proven the positive impact of Pepton biostimulants on citrus production. Under these conditions, iron deficiency can lead to problems such as iron chlorosis. The results obtained in the study are encouraging, showing a significant increase in fruit weight, higher juice production and an increase in calcium pectate content, an important indicator of fruit quality and resistance. All this supports the use of APC Agro biostimulants as an effective solution to improve citrus production and quality in calcareous soils.


Iron is an essential nutrient for plants as it is a key component of several proteins and enzymes, including chlorophyll. The mechanism of action of iron in plants is complex and is related to its ability to act as a cofactor for several enzymatic reactions. Iron is required for chlorophyll production and in the synthesis of proteins and enzymes participating in respiration, DNA synthesis and defence against abiotic stress.

Plants have evolved iron uptake mechanisms, including the reduction of ferric iron (Fe3+) to ferrous iron (Fe2+) in the rhizosphere, which increases the solubility of iron in the soil and its uptake by the roots. Iron is absorbed by the plant roots in the form of iron ions and transported through the xylem to the leaves and other plant tissues. For uptake, iron must be in soluble form, which can be a challenge in some soils, especially in calcareous soils with an alkaline pH.

Citrus require an adequate amount of iron to produce good quality fruit and maintain optimal tree health. The amount of iron required varies depending on the citrus variety, soil conditions and other environmental factors. However, in general, the level of iron in soil recommended for citrus crops should range between 2 and 6 ppm (parts per million). In the Mediterranean basin, the usual doses of iron chelate for citrus are usually in the range of 50-100 g per tree.

Lack of iron in the soil can result in a condition known as iron chlorosis, which is characterised by yellow leaves with green veins. This can reduce fruit production and affect citrus quality. It is therefore important to ensure that citrus crops have access to an adequate amount of iron in the soil. This can be achieved by applying iron-containing fertilisers, as well as by improving soil quality through appropriate management practices such as crop rotation and adding organic matter to the soil.

Iron chelate is usually applied by drip irrigation, as this ensures a uniform distribution of the nutrient in the soil and its uptake by the tree roots. The frequency of application will depend on the iron demand of the tree and the capacity of the soil to retain the nutrient.

Chelated irons are commonly used for citrus fertilisation, but the most appropriate ones will depend on the soil characteristics and the specific needs of the citrus variety. Ethylenediamine-N,N'-bis(2-hydroxyphenyl) acetic acid (EDDHA) is one of the most effective chelates in alkaline and calcareous soils, which are common in the Mediterranean basin. EDDHA has a high stability and is able to keep iron available to the roots of citrus trees for a prolonged period of time. Diethylenetriamine-pentaacetic acid (DTPA) is particularly effective in slightly acidic or neutral soils. It is less stable than EDDHA, but can be used in a wide range of soils.

In general, the use of iron chelate in the form of EDDHA is more suitable for alkaline and calcareous soils, whereas DTPA can be used in a larger number of soil types. It is important to note that the choice of chelate form should be based on soil analysis and recommendations from a fertiliser expert to maximise effectiveness.

Pepton (Image 1) is a line of biostimulants of natural and organic origin according to European regulations, available in microgranulated form, highly soluble in water and produced by enzymatic hydrolysis of animal protein (APC Europe S.L., Spain). They contain high amounts of L-α  amino acids (min. 84.83%), free amino acids (min. 16.52%) and organic nitrogen content (min. 12%), medium potassium concentration (min. 4.45%) and a high amount of haem iron (max. 3000 ppm). This is a perfectly chelated haemic iron and the one that is best absorbed by plants as it is bound with peptide and amino acid residues that act as a transporter while absorbed by plant roots. Due to this high iron absorption, we decided to carry out a study to check whether one of the products in the line could replace the use of EDDHA iron chelate in mandarin trees in production.

Development of the study

The study was carried out in cooperation with CRO Agricola 2000, on a plantation in the town of Massafra,  province of Taranto, southern Italy. The plantation featured a calcareous soil with a carbonate content of 79 g/kg and pH of 8, according to the pre-treatment analysis carried out on 72 six-year-old mandarin trees, distributed in 18 plots with four trees each. A total of six plots (24 trees) were used for each treatment: a control, where Fe-EDDHA iron chelate (6% iron) from a well-known leading brand was used, added at a dose of 2.5 kg/ha; a combination of EDDHA iron chelate and the biostimulant, at a dose of 1.25 kg/ha of each; and a treatment in which all the iron was provided by the biostimulant, added at a dose of 2.5 kg/ha per application.

 A total of six applications of each treatment were made, i.e. 15 kg of each product or combination in total, in accordance with the manufacturer's recommendation for chelated iron for calcareous soils. The applications were made at the end of April (before flowering); ten days later, with early flowering; ten days later, in mid-May, with late flowering; at the end of May, after petal fall and the beginning of fruit set; at the end of June, with fruit development; the last application was made at the end of July to coincide with fruit fattening. The mandarins were harvested at the beginning of November.

The parameters analysed were SPAD indices, fruit diameter, fruit weight (all mandarins from four trees per plot), juice content (in weight or volume) and juice quality parameters such as Brix degrees, citric acid milliequivalents and pH. The total calcium and calcium pectate content of the mandarins was also analysed, as well as the iron content of the leaves.

Results obtained

The study led to surprising results, given that, in terms of plant development there were no differences in SPAD levels between treatments, nor in the diameter of the mandarins. However, a significant (P<0.05) increase in the weight of mandarins harvested with the treatments containing the biostimulant was detected (as shown in Image 2, Figure 1).

The higher fruit weight showed a correlation with an increase in the amount of juice, both in terms of weight and volume (as shown in Image 2, Figure 2). It is important to note that the higher fruit and juice production was not detrimental to any parameter related to fruit or juice quality, given the Brix content, citric acid content or pH, which were not affected by the higher production in the biostimulant treatments. On the other hand, a significant increase in the amount of calcium pectate in fruit was observed in the treatment combining biostimulant and EDDHA iron chelate (as shown in Image 3, Figure 3).

There were no differences regarding the content of any macronutrients (nitrogen, potassium, phosphorus, calcium, magnesium or sulphur) or micronutrients (iron, manganese, copper, zinc, boron or molybdenum) in leaves between treatments at the end of harvest. It is important to note that the content of total iron and active iron (Fe2+) in leaves did not differ between treatments, although the values for active iron were slightly higher in the treatments using the biostimulant (as shown in the graphs in Image 3, Figures 4 and 5).

Conclusions of the study

Based on these results, we can conclude that Pepton can be combined with or replace Fe-EDDHA application at the same rate, and that its biostimulant effect offers several production benefits, including an improvement in the weight of mandarins per tree and a higher juice production without a detrimental impact on quality. It was also found that the combination of Fe-EDDHA with the biostimulant improved the calcium pectate content, which several studies have correlated with being a form of calcium bound to proteins and one of the main indicators of fruit quality and shelf life. Calcium pectate within the plant is related to the fruit's resistance to natural degradation or damage by pathogen attack, which allows for high quality harvestable products with a longer shelf life.

The conclusion is that the haemic iron contained in all the biostimulants of the Pepton line, despite its relatively low value (max. 0.3% or 3000 ppm), is highly absorbable and capable of replacing Fe-EDDHA, which has 22 times more iron. Moreover, being an organic biostimulant, it offers the production advantages associated with the use of this type of product.

The application of biostimulants with proven and scientifically verified effectiveness is a good strategy that seeks to help farmers tap the genetic potential of plants, ensure good productivity and reduce the eventual negative effects of different types of abiotic stress.



Javier Polo(1), Giacomo Scatolino(2)Lorenzo Palanga(2), Giulio Giovannetti(1) 

(1)APC Europe, S.L., Granollers, Spain; (2) Agricola 2000 S.c.p.A. Milan, Italy

Original article published in Phytoma (Spain)

Tell us about your background in the agricultural sector. How did you get started, and where does your vocation come from?

There has always been a farm in my family, and ever since I was a little girl, I have helped manage it. My vocation comes from those moments that I have spent in the fields, both working and having good times eating altogether.

While growing up, I felt responsible for having the capacity and knowledge to solve the different problems generated on our farm.

Also, this is a beautiful sector in which you are continually learning.

Did you have any moment of indecision when wanting to enter a predominantly male profession?

Before starting in this profession, I did not think that this was a male sector since everyone contributed equally in my family. During my studies, there were a greater number of male students than female students, but inequality was not noticeable either.

When I started working as a technical advisor in the field, I became aware of this inequality. The owners of the farms are mostly men, are used to receiving opinions and advice from men. I have always had to make more efforts than my male peers to make my voice heard.

Do you think it is important to have mixed teams in the sector?

Yes, the profession must become more modernized. By having mixed teams, the farmers' vision will be changed, and the value of our words will be heard as equal to our male counterparts.

Has there been any woman in your life that have influenced you to be where you are at today?

I cannot choose just one; my grandmothers Paquita and Teresa have always been fighters and have transmitted their strength to me.

What would you say to a young lady who wants to work in the agricultural sector?

Be brave, and together we will be able to change perspectives. It is essential to trust yourself, be ready with your education and documentation. This way, no one will make you doubt your knowledge.



When plants are challenged by temperature and nutrient stress, their root growth can be affected.

Pepton helps promoting longitudinal and lateral root growth and therefore increasing belowground vegetative growth, which may in turn lead to improved aboveground vegetative growth and increased yields.

The publication at Frontiers in Plant Science shows how Pepton can help tomato plants under stress conditions.

Read the full study HERE.

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APC-Europe SLU has been beneficiary of an aid of 125,000€ from the European Regional Development Fund of the European Union under the FEDER Operational Programme of Catalonia 2014-2020 in the project R17-1-0096 to be carried out between February 2018 and August 2020. The project will have a total estimated cost of 867,731.51€ and is titled:

 “Desenvolupament d’hidrolitzats de sang pel seu ús com a bioestimulants de creixement vegetal i recerca del mecanismo d’acció a nivel fisiològic en la planta”

(“Development of blood hydrolysates to be used as plant-growing biostimulants and research into the physiological-level mechanisms of action of the plant”)

The main objective of the project is the research and development of new hydrolyzed animal blood products that can be used as biostimulants, i.e. products that improve the availability and absorption of nutrients, and/or increase tolerance to abiotic stress, and/or improve the quality aspects of the harvest. Within this framework, extensive studies are being carried out in cooperation with the University of Barcelona and IRTA, on the mechanisms of action at the physiological level of the plant. More specifically, an integral investigation is carrying out at both, laboratory and pilot plant levels, as well as on the ground, in order to give response to a gap of scientific knowledge in the field of the biostimulants offering, additionally, innovative products with unique features. Therefore, through the realization of this project, the company seeks to increase its know-how in Agro and obtain non-existent products in the current market, so it will be more competitive both nationally and internationally.