Dissertation – Foliar Nutrition

Maintaining high yields and consistent quality in coffee production requires careful nutrient management, as the crop is highly responsive to both macro- and micronutrient availability throughout its growth cycle. Traditional soil fertilization practices often face limitations due to factors such as nutrient leaching, mineralization requirements in the soil, soil fixation, individual nutrient mobility, and varying root uptake efficiency. In this context, foliar nutrition - the direct application of nutrients to plant leaves - is an underutilized complementary strategy to enhance nutrient use efficiency, correct deficiencies rapidly, and support critical physiological processes during key growth stages. This is especially important for nutrients that are less mobile in the soil and plant tissues (i.e. Boron, Manganese, Zink, etc.). Foliar feeding can play an important role in overcoming soil-related constraints - particularly in coffee-growing regions where soil fertility may decline over time. Targeted foliar applications can help optimize growth, flowering, fruit set, and seed development, directly impacting both yield and cup quality.

The Poma Foliar Feeding System®

The Poma Foliar Feeding System® is a structured foliar nutrition protocol designed to optimize both the productivity and quality of coffee production. This system recognizes that soil fertility alone often cannot fully meet the dynamic nutrient demands of coffee plants, especially during critical growth stages and under the challenging conditions typical of coffee-growing regions. This is especially due to immobility of micronutrients and availability status of nutrients in the soil.

The Poma Foliar Feeding System is built around three core principles: continuous leaf analysis, target nutrient levels, and responsive corrective action based on both laboratory data and field observations. Regular leaf sampling is conducted throughout the crop cycle to monitor nutrient concentrations and compare them to well-defined optimal ranges. When deviations are detected — or when visible deficiency symptoms appear in the field — targeted foliar applications are carried out to address imbalances swiftly and efficiently.

The system’s standard foliar feeding schedule includes the following stages:

1. Before Flowering: Two foliar applications of nitrogen (N), zinc (Zn), boron (B), and manganese (Mn) are applied to stimulate healthy flower bud development and enhance pollination.

2. After Flowering / Before Fruit Set: Two additional applications with focus on nitrogen (N), manganese (Mn), and magnesium (Mg) to support early fruit development and maximize bean filling potential.

3. During Visible Deficiency Symptoms: Additional targeted foliar sprays are applied as needed, depending on the specific nutrient deficiency identified through leaf analysis or visual diagnosis.
   
   

The Poma system uses the following indicative target ranges (based on our climate-controlled research) for leaf nutrient concentrations in mature coffee leaves, sampled from 80-100 fully expanded leaves on plagiotropic branches (random selection) over the entire plot that needs investigation:

By combining proactive monitoring with timely foliar nutrition, The Poma Foliar Feeding System aims to minimize nutrient stress, improve flowering and fruiting, and enhance cup quality — while supporting more sustainable and cost-effective fertilizer use. Overall, this system represents Poma Coffee’s commitment to data-driven, responsive crop management that helps farmers achieve higher yields and consistent seed quality, even under variable environmental conditions.

Experiment

An experiment was conducted over one production cycle (12 months) to evaluate the effectiveness of The Poma Foliar Feeding System on an Ethiopian Heirloom variety grown in our climate-controlled greenhouse in Denmark, simulating an Ethiopian climate and an elevation of 1,800 meters. The trial compared two plots of equal size (20 trees each):

• Control Lot: Standard soil fertilization/fertigation only, no foliar feeding.

• Treated Lot: Standard soil fertilization/fertigation plus four foliar sprays according to The Poma Foliar Feeding System® protocol (2 sprays before flowering with N, Zn, B, Mn; 2 sprays after flowering/before fruit set with N, Mn, Mg).
  

The results of this study demonstrate that implementing The Poma Foliar Feeding System had a clear positive impact on the performance of an Ethiopian Heirloom variety under controlled conditions. The treated lot showed improvements across all key parameters measured, including fruit set ratio, leaf chlorophyll content, yield per tree, bean density, and cupping score.


The 11% increase in fruit set suggests that timely foliar applications of nitrogen, zinc, boron, and manganese before flowering effectively supported flower fertility and retention. Similarly, the observed 10% higher leaf chlorophyll content in treated trees indicates improved leaf nutrition and photosynthetic activity, which likely contributed to better fruit filling and overall plant vigor.


Yield per tree increased by approximately 9%, aligning with the improvements seen in fruit set and leaf health. In addition, the treated lot produced beans with slightly higher density (740 g/L vs. 714 g/L), pointing to better bean filling and uniformity — factors that directly contribute to higher physical quality grades.


Notably, the treated lot also achieved a small but meaningful improvement in cup quality, with an average cupping score of 86.5 compared to 85.5 in the control. This supports the idea that balanced foliar nutrition can enhance both the physical and sensory attributes of coffee.


Overall, these results highlight the value of integrating continuous leaf analysis with stage-specific foliar feeding as a practical way to close nutrient gaps during key growth phases. The findings suggest that adopting The Poma Foliar Feeding System can help coffee producers optimize both productivity and quality in a sustainable, targeted manner.

When to Apply Foliar Nutrition 

The timing of foliar feeding is crucial because it directly affects how well the plant absorbs and utilize the nutrients.

1. Before Flowering: 2x (N, Zn, B, Mn)

2. After Flowering / Before Fruit Set: 2x (N, Mn, Mg)

3. During Visible Deficiency Symptoms: Depends on deficiency

It’s good practice to integrate foliar feeding with routine pest or disease control sprays, when possible, to save time and labor — but only if the chemicals are compatible. Consult with your advisor before mixing or reach out to rama@pomacoffee.com.

Challenges in Application

Foliar feeding has clear benefits, but it also comes with practical and agronomic challenges.


Firstly, leaves can only absorb a certain amount of nutrients at a time. Large nutrient demands, especially for macronutrients like nitrogen (N), phosphorus (P), or potassium (K), often can’t be met fully through foliar feeding alone but should be seen as a highly effective supplement for soil fertilization. Foliar application is far more effective for micronutrients that plants require in smaller quantities.


Weather strongly influences foliar application success. Unforeseen rainfall soon after application can wash nutrients off before they’re absorbed, reducing effectiveness and wasting inputs. On the other hand, high temperatures or low humidity can cause the spray to evaporate too quickly, or lead to leaf burn if concentrations are too high. Excessive concentrations or inappropriate mixing of foliar fertilizers can damage leaf tissue, causing leaf burn or defoliation (phytotoxicity). This is particularly a risk when combining foliar sprays with pesticides or when conditions favor rapid drying.


Foliar spraying also requires good equipment, skilled labor, and careful timing. In regions with smallholder coffee farmers and challenging terrain, uniformly covering plants can be difficult. Poor application technique can lead to uneven nutrient distribution, phytotoxicity, or wasted inputs.

Conclusion


This study demonstrates that foliar nutrition, when applied strategically and based on continuous monitoring, is a highly effective complement to traditional soil fertilization in coffee cultivation. The Poma Foliar Feeding System® provides a clear framework for integrating targeted foliar applications with regular leaf analysis and field observations, allowing farmers to respond quickly to nutrient deficiencies and optimize plant performance during critical growth stages.