Nutrient needs and Fertilization of Lemon trees

Nutrient Dynamics in Lemon Tree Fertilization

Lemon trees (Citrus limon (L.)) are esteemed members of the Rutaceae family, cultivated for their vibrant fruits rich in vitamin C and versatile applications in culinary and medicinal domains. Achieving optimal growth and fruit production requires a good understanding of the plant’s nutrient needs and adopting a balanced and suitable fertilization plan. In this article, we delve into the key elements contributing to the nourishment of lemon trees, shedding light on the intricate roles of nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), and sulfur (S).

How to determine the fertilization needs of lemon trees? 

Determining fertilization requirements is commonly executed through foliar diagnostics (leaf analysis), a diagnostic methodology employed to assess the nutritional status of individual trees. Insights derived from these analyses serve as a basis for extrapolating the nutritional condition of entire trees and, by extension, the overall fruit production. The farmer should also perform a soil analysis to obtain information regarding the soil characteristics and nutrient availability.

How to create a fertilization program for commercially cultivated lemon crops? 

Several critical factors necessitate consideration in formulating a comprehensive fertilization program for a commercial lemon orchard. The efficacy of such a program lies in a systematic analysis of soil characteristics, climatic conditions, nutritional demands of trees, suitable fertilizers, and the prevailing irrigation system.

What is the role of Nitrogen (N) in lemon trees? 

• Chlorophyll Synthesis
• Amino Acid and Protein Synthesis
• Enzyme Activation
• Nucleic Acid Production
• Carbohydrate Metabolism
• Vegetative Growth and Resilience
• Fruit Development

When should nitrogen (N) be applied as part of lemon tree fertilization? 

Nitrogen plays a pivotal role in the development of lemons, with specific periods demanding strategic fertilization to meet the trees’ requirements effectively.

1. Early Spring Nitrogen Application (February to April, for the north hemisphere): The demand for nitrogen in lemons peaks from February to April, coinciding with crucial stages like bud differentiation, spring vegetation initiation, flowering, and early fruiting. Approximately 40 to 50% of the annual nitrogen requirement is needed during this period. To meet this demand, it is important to apply nitrogenous fertilizers in a timely manner (different doses), ideally between mid-January and late February, ensuring it precedes bud swelling.
2. Critical Fruit Growth Periods: 

a. First Stage (May-June, for the north hemisphere): As lemons undergo initial growth marked by cell division, a modest increase in size occurs. Nitrogen application during this period should be gradual and measured.

b. Second Stage (July Onwards, for the north hemisphere): The subsequent phase sees a significant and rapid increase in fruit size due to cell enlargement. From fruit set onward, it is advisable to administer nitrogen in small, intermittent doses to prevent excessive vegetative growth, which could lead to abnormal fruit drop post-setting and during the summer months (June-July).

Moderation of Nitrogen Application: To avoid complications like heightened vegetative growth and increased fruit drop, nitrogen applications should be decreased from mid to the end of September. Colder areas may necessitate an earlier reduction of nitrogen application by mid to late August.

What is the role of Phosphorous (P) in lemon trees? 

• Energy Transfer in Photosynthesis
• Root Development
• ATP & DNA Synthesis
• Cell Division and Growth
• Early Growth Stages
• Foundation for Fruit Production
• Flowering and Fruiting

When to apply Phosphorous (P) as part of lemon tree fertilization? 

Phosphorus is a vital element for the optimal development of lemon trees, and its demand peaks during the spring when crucial growth activities such as root system renewal, bud development, flowering, and fruiting take place.

1. Early Spring Phosphorus Application (January-February): To ensure that phosphorus is readily available during the pivotal spring period, it is advisable to apply it much earlier, usually in January or February. This application should constitute 70-100% of the annual phosphorus dose. Given its limited mobility in the soil, this early application facilitates its incorporation into the root zone, supporting the tree’s nutritional needs during the subsequent stages of growth.
2. Winter Surface Application with Irrigation (When Possible): 

a. Surface Application (Winter): In situations where irrigation is possible, a beneficial practice is applying 70% of the phosphorus on the soil surface during winter.

b. Partial Irrigation Application (May to September): The remaining 30% of the phosphorus can be applied partially through irrigation from May to September. This phased approach ensures a sustained and balanced supply of phosphorus, catering to the evolving nutritional requirements of the lemon trees.

What is the role of Potassium (K) in lemon trees?

• Osmotic Regulation
• Stomatal Function
• Enzyme Activation
• Fruit Size and Weight
• Vitamin C Concentration
• Skin Thickness
• Ripening Index

When should potassium (K) be applied as part of lemon tree fertilization? 

1. Early Application for Spring Vitality (January- February): It is essential to apply potassium earlier, typically in January or February, to meet the potassium demands during bud differentiation, spring vegetation initiation, flowering, and fruiting (March-April). Lemon trees absorb a significant portion (30-40%) of their annual potassium requirement during this crucial period.
2. High demand for potassium from Fruit Setting to First Growth Stage (June): From the fruit set until the first stage of fruit growth (June), the potassium requirements remain notably high, ranging between 30-50%. Sufficient potassium supply during this phase is crucial for robust fruit development.
3. Continued Requirement Until Ripening (July to Fruit Ripening): Substantial potassium amounts (30-40%) are essential from July until the fruits ripen to ensure the production of high-quality fruits.
4. Nutrient Ratio Considerations: 

a. General Ratio for Fully Productive Lemon Trees (N:P: K, 1:0.3:1): As a standard, a nutrient ratio of N:P:K at 1:0.3:1 is adhered to when fertilizing adult, fully productive (mature) lemon trees.

b. Adjustments for Specific Soil Conditions: In cases of sandy soils or when leaf diagnostics reveal persistently low potassium levels despite repeated applications, a 25% increase in the amount of K₂O relative to N is recommended. Conversely, if potassium levels in the leaves are excessively high, the fertilization regimen should be adjusted by limiting applied potassium amounts.

Table 1: Indicative quantities of elements (grams/tree) applied annually, divided into 3-4 equal doses, to the young lemon trees before they enter the fruiting (stage)

Table 2: Indicative quantities of inorganic elements required per year and per hectare of cultivation of fully productive adult lemon trees over 8 years old with a yield of 2.5 tons of fruit per hectare and a planting density of 30-40 trees per hectare planted in 3-4 equal doses, in the young lemon trees, before they enter into fruiting

The Role of Macronutrients in the growth and fruiting of lemon trees

In addition to the 3 basic elements, N, P, and K, magnesium (Mg) and sulfur (S) play pivotal roles in lemon trees’ optimal growth and development. Ensuring adequate levels of Mg and S in soil management practices is vital for sustaining lemon trees’ overall health and productivity.

Magnesium (Mg) 

Magnesium (Mg) is a critical element in lemon tree nutrition and has multiple crucial roles in the overall health and productivity of the lemon orchard.

1. Structural Component of Chlorophyll: Magnesium is essential to the composition of chlorophyll, the pigment responsible for the green color in leaves and unripe fruits. As a result, magnesium is also essential for photosynthesis.
2. Involvement in Photosynthesis: Magnesium activates the enzymes essential for converting light energy into chemical energy. This function directly influences the tree’s energy production and overall metabolic processes.
3. Activation of Enzymes: Magnesium’s involvement extends beyond photosynthesis; it activates numerous enzymes within the lemon tree. This enzymatic activation is crucial for regulating various biochemical reactions vital for plant growth and development.
4. Impact on Nucleic Acid Synthesis: Magnesium influences the synthesis of nucleic acids, contributing to the genetic material essential for the lemon tree’s growth and reproduction. This role positions magnesium as a critical player in the tree’s long-term developmental processes.
5. Effect on Carbohydrate Metabolism and Transport: Magnesium exerts influence over carbohydrate metabolism and transport mechanisms within the lemon tree. Its impact on these processes is integral to efficiently allocating energy and resources for growth and fruit development.
6. Slight Improvement in Ripening Index: Magnesium, while modestly affecting the ripening index, plays a role in facilitating timely and coordinated fruit maturation, contributing to efficient harvesting practices.
7. Enhanced Cold and Drought Resistance: Lemon trees with sufficient amounts of magnesium exhibit increased tolerance to cold and drought conditions, mitigating potential damage and improving the tree’s adaptability to challenging environmental stressors.

As a result, magnesium (Mg) improves the productivity of lemon trees and increases their vegetation. It also positively influences the size and weight of the lemons while reducing the thickness of the fruit’s skin. Lastly, it slightly improves the ripening index, thus promoting the maturation of lemons while increasing the resistance of trees to cold and drought. 

Sulfur (S) 

Sulfur (S) is a crucial element in the nutrition of lemon trees since it plays a diverse and indispensable role in supporting their growth and resilience.

1. Enhancement of Nitrogen Use Efficiency: Sulfur operates as a facilitator, elevating the efficiency of nitrogen utilization by lemon trees. This collaborative relationship ensures optimal nitrogen uptake, promoting robust vegetative growth.
2. Essential for Amino Acid and Protein Synthesis: Sulfur is a fundamental component in the synthesis of amino acids (pivotal building blocks for proteins), supporting the structural and functional aspects of the lemon tree’s cellular machinery.
3. Activation of Enzymes in Fatty Acid Metabolism: Sulfur’s involvement extends to activating enzymes in fatty acid metabolism. This biochemical role contributes to the energy dynamics of the lemon tree, influencing lipid utilization for growth and metabolic processes.
4. Crucial for Aromatic Oils and Flavor Compounds: Sulfur participates prominently in the synthesis of aromatic oils and other compounds that intricately shape the aroma and taste of lemons. This chemical fingerprint is a key determinant of the fruit’s sensory profile.
5. Contributor to Plant Resistance Mechanisms: Sulfur’s influence is not limited to biochemical pathways; it actively participates in the synthesis of substances crucial for enhancing the tolerance and resistance of lemon trees to various environmental stressors, including pests, diseases, and abiotic factors.

Conclusion

The fertilization of lemon trees is a meticulous science, with each chemical compound playing a distinct and indispensable role in sustaining their health and productivity. By understanding the nuanced interactions between nitrogen, phosphorus, potassium, and macronutrients, cultivators can tailor their fertilizer regimens to meet the specific needs of lemon trees at different stages of growth. A suitable fertilization program ensures not only the resilience of lemon trees but also the production of high-quality fruits that delight the senses and contribute to the rich tapestry of horticultural diversity.

References

Ferguson, J. J. “Fertilization of young citrus trees with controlled release fertilizers.” Proceedings of the Florida State Horticultural Society. Vol. 108. 1995.

Quaggio, J. A., et al. “Lemon yield and fruit quality affected by NPK fertilization.” Scientia Horticulturae 96.1-4 (2002): 151-162.

Ennab, H. “Effect of Organic Manures, Biofertilizers and NPK on Vegetative Growth, Yield, Fruit Quality and Soil Fertility of Eureka Lemon Trees (Citrus limon (L.) Burm).” Journal of Soil Sciences and Agricultural Engineering 7.10 (2016): 767-774.

 Tuzcu, Ö., et al. “Influence of different irrigation methods on nutrient uptake of lemon trees.” Influence of different irrigation methods on nutrient uptake of lemon trees (1988): 1000-1005.

Further reading

Fruit-tree related terminology and categorization – Pomology

The most Popular Lemon Tree Varieties

Lemon Tree Pruning for Optimal Growth and Yield

Nutrient needs and Fertilization of Lemon trees

Important Citrus Diseases caused by Fungi

Important Virus Diseases in Citrus trees

Bacterial Citrus Diseases: Identification and Control