Fertilization in Carob Tree
Carob is a tree that is traditionally hardly fertilized, as it can grow even on poor soils. However, studies show that nitrogen in particular can increase fruit production in older gardens. What is interesting is this: Although carob is a legume, it does not form nodules on its roots and cannot bind nitrogen from the air.
In this article, we discuss the nutritional needs of carob, the common misconception about nitrogen fixation, the recommended fertilizer amounts and timing in the sources, the role of organic fertilizer and mycorrhizal partnerships, in the light of official guidelines and scientific studies in Turkey.
Does Carob Require Fertilizer?
Carob is known as a contented tree that can grow in nutrient-poor soils. According to the monograph published by IPGRI, carob orchards have traditionally been almost never fertilized. The species has always been considered highly adaptable to very poor soils and has only been given some stable manure when it can be found locally. However, in recent years, with the re-appreciation of the crop, some farmers have started to use mineral or organic fertilizers (Batlle and Tous, 1997).
Julia Morton also states that most of the growers consider fertilization unnecessary, whereas fertilization is supported in Cyprus (Morton, 1987). In the investor guide of the Ministry of Agriculture and Forestry, it is stated that carob does not like mineral-rich soils and that soils with low mineral content are ideal for the development of the plant.
This information indicates that carob can live without fertilizer. However, "being able to live" is not the same as "giving the best yield". Many of the sources cited in the monograph highlight the utility of nitrogen in increasing fruit production in older carob orchards.
Legume But Nitrogen Doesn't Bind: Nodule Debate
One of the most well-known features of the legume family is that it can bind nitrogen from the air thanks to the bacteria living in the nodules formed on its roots. Plants such as chickpeas, beans and clover enrich the soil with nitrogen due to these properties. Since carob is also from the legume family, it is often assumed that it has the same feature. However, scientific studies show that this is not true.
According to the IPGRI monograph, although carob is a legume, it does not form nodules like most members of the Caesalpinioideae subfamily and therefore cannot fix nitrogen. In the monograph, it is stated that this determination is based on studies conducted in Portugal in the 1980s (Batlle and Tous, 1997).
This was also tested by a field study in Italy. Natural isotope ratios of nitrogen were measured in the leaves of adult carob trees in six orchards in Sicily and Sardinia and the results were compared with known nitrogen-fixing trees (mule and false acacia) and non-nitrogen-fixing trees (olive, arbutus, and gum tree). The leaves of nitrogen-fixing trees had different values as expected, while the values of carob leaves were similar to those of non-nitrogen-fixing control trees. The researchers concluded that the data do not support the hypothesis that field-grown carob uses symbiotically bound nitrogen (La Malfa et al., 2010).
In the same study, it was stated that only about 5 percent of the species in the subfamily Caesalpinioideae establish nitrogen-fixing partnerships and nodules are rarely found in carob in nature. For this reason, one should not act on the assumption that nitrogen will be met by the plant itself in the carob garden.
Mycorrhizal Partnerships and Nutrition
Although carob cannot fix nitrogen, it has another commonality that helps it feed. According to the IPGRI monograph, arbuscular mycorrhizal fungi can settle in carob roots; an ectomycorrhizal partnership has not been found. Mycorrhizal colonization can increase the plant's nitrogen uptake. Because carob often grows in soils deficient in nitrogen and phosphorus, these fungi can improve nutrition (Batlle and Tous, 1997).
In a study conducted with young carob trees in Morocco, the combined application of local mycorrhizal fungi and green waste compost increased phosphorus uptake by 75 percent, nitrogen uptake by 46 percent, potassium uptake by 35 percent, and calcium uptake by 40 percent at the end of eight months in plants under drought stress compared to the control (Boutasknit et al., 2021). While these results belong to controlled trials, they point to the importance of organic matter and soil vitality in carob nutrition.
Recommended Fertilizer Amounts in Sources
Sources show different approaches to fertilization in carob. This difference is due to the targeted production method (traditional, intensive or organic).
Proposal of the IPGRI Monograph
The IPGRI monograph states that 50 kg of nitrogen (N), 20 kg of phosphorus (P₂O₅) and 50 kg of potassium (K₂O) can be applied per hectare for conventional orchards with 50 trees per hectare and an average yield of 2,500–3,000 kg/ha (Batlle and Tous, 1997). This recommendation is given according to a specific type of garden; in gardens with different tree density, soil structure and yield, it needs to be adapted by soil and leaf analysis.
| Nutrient | Amount per hectare | Time of application |
|---|---|---|
| Phosphorus (P₂O₅) | 20 kg | In autumn, after harvest |
| Potassium (K₂O) | 50 kg | In autumn, after harvest |
| Nitrogen (N), 25 percent | A quarter of 50 kg | In autumn, after harvest |
| Nitrogen (N), the remaining part | Three-quarters of 50 kg | In February, as ammonium sulfate |
Source: Batlle and Tous, 1997. It is a proposal for 50 trees per hectare and a yield of 2,500–3,000 kg/ha.
In the monograph, it is also stated that nitrogen and potassium can be given in gardens with some irrigation in May and June, which coincide with the rapid growth phase of the pods.
Fertilizer Irrigation Trial
In a study conducted on mature 'Mulata' trees in Portugal, three irrigation levels (0, 50 and 100 percent of evaporation) and two nitrogen doses (21 and 63 kg per hectare per year, as ammonium nitrate) were tested together. It was observed that vegetative growth and fruit production increased as the amount of fertilizer irrigation increased (Correia and Martins-Loução, 1995). In the IPGRI monograph, it is stated that these results indicate that nitrogen applications can be effective even without irrigation under standard conditions in the Mediterranean region.
Organic Fertilizer
In carob fertilization, organic matter is the common thread of the vast majority of sources. The IPGRI monograph emphasizes the benefit of applying organic matter in carob, as in all other fruit and bark fruit trees, and recommends introducing 30–40 kg of stable manure per tree every 3–4 years during autumn tillage.
Organic fertilizer also stands out in the sources in Turkey:
| Ministry of Agriculture and Forestry | It recommends the use of animal manure or carob pulp as fertilizer in the first planting of saplings; It specifies filling the empty places in the planting pit with a mixture of stable manure and soil. |
| Western Mediterranean Development Agency | Since organic production is generally recommended in carob farming, he recommends approximately 1 ton of burnt farm manure per decare to be used in planting pits (Erbaş, 2024). |
| Alanya Carob geographical indication certificate | It recommends applying well-burned animal manure (preferably ovine and goat) and base fertilizer to the soil during planting (Turkish Patent and Trademark Office, 2025). |
It is important that the organic manure is well burned (ripe). Sources specifically speak of "burnt" or "well-burned" manure, as fresh manure can have undesirable effects in the root zone.
Fertilization in Saplings and Young Trees
The nutrient requirement of young trees is different from that of adult trees. According to the IPGRI monograph, regular fertilization should be applied after the second irrigation after planting the saplings, and nitrogen should be given mainly in the form of ammonium instead of nitrate, as it can be taken more easily.
In the Alanya Carob geographical indication certificate, it is stated that NPK and organic matter are applied in the nutrition of the saplings, and NPK, trace element and organic matter needs should be met throughout development in the first years after planting. Thus, the root and crown development of the tree is supported and the fruiting time can be shortened. We discuss the planting phase in detail in our article "How to Plant Carob Saplings?".
Organic Production and Fertilization
Some Turkish sources recommend limiting fertilizer to the first planting in carob cultivation. In the ministry guide, it is stated that animal manure or fruit pulp will be used in the first planting, and fertilization is not recommended in other years in order not to affect the organic formation of the carob fruit. In the guide, it is also emphasized that carob is a plant that does not have many diseases and pests, and that it can be grown for many years without spraying, especially in areas with wild populations.
In the feasibility model of the Western Mediterranean Development Agency, fertilization was calculated only for the first year, and fertilization was not foreseen in the following years (Erbaş, 2024).
There is a tension between this approach and the finding in international sources that "nitrogen increases yield in aged orchards". In fact, the two approaches serve different goals: One aims to produce low-input, near-natural and organic quality; the other aims to maximize yield. Which one is preferred depends on the grower's production target, market and organic certification conditions, if any. It should also be noted that the fertilizers to be used in organic production must comply with the relevant legislation.
Things to Consider When Fertilization
When we bring together the principles in the sources, the following points come to the fore for fertilization in carob:
- The decision to fertilize should be based on soil analysis; The ministry guide also recommends that the necessary analyzes be carried out before establishing the garden.
- It should not be assumed that carob will meet its nitrogen needs itself because it is a legume.
- Some of the nitrogen with phosphorus and potassium can be given in the fall, after harvest; the remaining part of the nitrogen can be given in February.
- In irrigated gardens, nitrogen and potassium can be coincided with May-June when pods grow rapidly.
- Organic matter should be given at regular intervals as well-burned manure.
- In young saplings, nitrogen can be preferred in the form of ammonium.
Fertilization alone does not determine yield. In the IPGRI monograph, the common causes of periodicity in carob include deficiencies in garden management such as fertilization and pruning, as well as rainfall irregularity, frost and lack of pollination. Therefore, fertilization; It should be considered together with irrigation, pruning and pollination management.
Frequently Asked Questions
Should the carob tree be fertilized? Carob can live without fertilizer and has traditionally been very little fertilized. However, international sources report that nitrogen in particular can increase fruit production in older gardens.
Does carob bind nitrogen because it is a legume? Although carob is a legume, it does not form root nodules and cannot bind nitrogen from the air. An isotope study conducted in Italy also found no evidence that carob trees in the field use bound nitrogen.
What fertilizer to give to carob? Sources recommend well-burned barnyard manure as the basic organic fertilizer. If mineral fertilizer is to be used, the IPGRI monograph recommends 50 kg of N, 20 kg of P₂O₅ and 50 kg of K₂O per hectare for a conventional garden.
When to fertilize carob? Some of the phosphorus, potassium and nitrogen can be given in autumn after harvest; the remaining part of nitrogen can be given in February. Organic fertilizer can be applied every 3-4 years during autumn tillage.
From Balanced Fed Tree to Quality Product with Carob Türkiye
Carob is an agricultural product close to nature with its structure that can be grown with little input. Nutrition in the right amount and at the right time contributes to the tree to produce balanced and quality products for many years.
At Carob Türkiye, we supply carob fruit, crumbs, flour/powder, seeds, and extracts. Our Products Carob Fruit and Our Products For general information about carob What is Carob? You can read our article. For your wholesale and export requests Contact Now You can contact us on our page.
Domestic resources
Republic of Turkey Ministry of Agriculture and Forestry, General Directorate of Forestry, "Carob Orchard Facility Project Feasibility Report and Investor Guide", Ankara, 2020. Eskisehir.
agriculture. gov. en/ DocumentsArchive/ Yat%C4%B1r%C4%B... Erbaş, S., "Carob Agriculture and Industry Feasibility Report", Western Mediterranean Development Agency, Publication No: 153, ISBN 978-605-4752-49-2, 2024. DEVELOPMENT LIBRARY.
gov. en/ assets/ upload/ files/ Keciboy... Turkish Patent and Trademark Office, "Alanya Carob / Alanya Carob – Mahreç Sign, Registration No: 1705", 2025. ci.
turkpatent. gov. en/ Files/ GeographicalSigns/ 7bbe4a8b- 399… Foreign sources
Batlle, I., Tous, J., "Carob tree. Ceratonia siliqua L. Promoting the conservation and use of underutilized and neglected crops. 17", Institute of Plant Genetics and Crop Plant Research, Gatersleben / International Plant Genetic Resources Institute, Rome, 1997. ISBN 92-9043-328-X. hdl.
handle. net/ 10568/ 104277 La Malfa, S., Tribulato, E., Gentile, A., Ventura, M., Gioacchini, P., Tagliavini, M., "15N natural abundance technique does not reveal the presence of nitrogen from biological fixation in field grown carob (Ceratonia siliqua L.) trees", Acta Horticulturae, 868, 191–196, 2010. doi.
org/ 10. 17660/ ActaHortic. 2010. 868. 22 Correia, P. J., Martins-Loução, M. A., "Seasonal variations of leaf water potential and growth in fertigated carob-trees (Ceratonia siliqua L.)", Plant and Soil, 172(2), 199–206, 1995. sapientia.
ualg. pt/ entities/ publication/ 29bd966c- 4312- 406f... Boutasknit, A., Baslam, M., Ait-El-Mokhtar, M., Anli, M., Ben-Laouane, R., Ait-Rahou, Y., Mitsui, T., Douira, A., El Modafar, C., Wahbi, S., Meddich, A., "Assemblage of indigenous arbuscular mycorrhizal fungi and green waste compost enhance drought stress tolerance in carob (Ceratonia siliqua L.) trees", Scientific Reports, 11, 2021. doi.
org/ 10. 1038/ S41598- 021- 02018- 3 Morton, J. F., "Carob", Fruits of Warm Climates, Miami, 1987. Growables.
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