Innovative nutrition for Latin American avocado crops

CROP NUTRITION

Innovative nutrition for Latin American avocado crops

Correct fertilizer usage at each crop stage can helps avocado growers improve their yield, quality and profitability. ICL’s Mateo Martinez and Alveiro Salamanca-Jimenez explain how growers can supply crop nutrients to avocado trees, efficiently and effectively, using economically- and environmentally-sustainable principles.

Avocado (genus Persea, family Lauracea) is a stone fruit that grows in tropical and Mediterranean climates. Uniquely, avocado fruit is high in ‘healthy’ monounsaturated fats, compared to other more carbohydrate- and sugar-rich fruit types.

Avocados have surged in popularity in recent years with their global market value expected to hit $23 billion by 2027. Global demand has seen crop production double during the past decade – especially in Mexico, the world’s largest avocado producer and exporter.

Mexico produced 2.39 million tonnes of avocados in 2020, valued at $2.8 billion. Mexico is currently responsible for around 60 percent of the global avocado harvest. Chile, Dominican Republic, Indonesia, Peru, Colombia, Brazil and the US are also major avocado producers.

Inside Mexico, Michoacán is by far the country’s largest avocado producing state, accounting for three-quarters of total domestic output in 2020. Four other states – Jalisco, Mexico, Nayarit, and Morelos – also contributed another 20 percent to national production.

Nutrient requirements

There is a great opportunity to improve avocado yields in Latin America, by improving nutrient management and adopting agricultural technologies, given the region’s relatively low average yield (<12 t/ha).

The nutrient requirements of avocado crops will typically vary according to:

• Soil and climate conditions
• Cultivar type
• Growth stage.

4Rs nutrient stewardship – applying fertilizers at the right dose, right source, right time, right place – is another major consideration. This approach ensures that nutrient supply meets crop demand efficiently and also helps to reduce fertilizer leaching and the negative environmental impacts caused by nutrient losses.

The right dosage (application rate) can be estimated by combining nutrient analyses (soil, foliar and sap) with information on seasonal growth, crop demand and yield potential. The ultimate aim being to enhance nutrient uptake and maximise fruit yield and quality as well as crop profitability. Nutrient removal rates for different avocado varieties grown in different countries are shown in Table 1.

Main soil requirements

The following soil properties have a major impact on avocado cultivation:

• Organic matter: greater than three percent ideal
• pH: ideally 5.5-6.5
• Electrical conductivity (EC): below 0.5 dS/m preferred

Avocado crops grow better in soils with organic matter higher than three percent. Organic matter contributes to soil productivity in three different ways by providing:

• Physical benefits. Improves soil aeration, water infiltration, water holding capacity and reduces runoff.
• Chemical benefits. Increases cation exchange capacity (CEC) – an indicator of the soil’s ability to hold and supply essential nutrients, such as calcium, magnesium, and potassium. Organic matter also improves soil buffering capacity (the ability to resist pH change) and accelerates mineral decomposition making nutrients more available for plant uptake.
• Biological Benefits. Provides food for the living organisms. Organic matter also helps suppress diseases and pests by improving the biodiversity of soil microbes and boosting microbial activity.

Table 1: Nutrients removal (kg) by avocado crops for every 10 tonnes of fruit yielded

Avocado roots in an organic-rich soil.

PHOTO: ICL

An optimum soil pH of 5.5-6.5 is ideal for avocado growing. Plants are very sensitive to alkaline soils, as a pH greater than 7 can cause nutrient deficiencies by inhibiting the uptake of phosphorus, manganese, iron and zinc.

Soil acidity is also detrimental. Some growing areas in Mexico and Colombia, for example, exhibit a soil pH below 5.5 and therefore require liming to raise this. In contrast, the application of elemental sulphur before planting, or the supply of acid via fertigation, is required to reduce soil alkalinity (>pH 7) in other areas. The management of high pH is, however, generally more problematic in areas without an irrigation system.

Table 2: Desirable soil nutrient concentrations for avocado

Controlled-release fertilizer applied on a young avocado tree.

PHOTO: ICL

Avocado nutrition from ICL Innovative Solutions

Avocado trees are highly sensitive to salinity. The negative effects of salinity are particularly pernicious in young trees as their new roots easily suffer from fertilizer burn when standard commodity products are used. To avoid this risk, innovative technologies such as slow- and controlled-release fertilizers (SRFs/CRFs) are recommended.

CRFs release nutrients in a controlled manner to match and satisfy the nutrient uptake of any crop. Consequently, they are able to:

• Increase crop production
• Reduce plant toxicity and stress
• Cut soil, water and atmospheric pollution.

Indeed, CRFs have been proven to eliminate the problem of avocado root burn and reduce nutrient losses by leaching and runoff1 .

ICL is a leading global manufacturer of CRFs, supplying suitable products such as Osmocote, Agrocote Emax, Agrocote Poly-S, plus smart blends such as Agroblen, Agromaster etc.

Polysulphate is another innovative ICL product that is well-suited to avocado. This natural fertilizer is approved for organic agriculture and has a very low carbon footprint. It prolongs nutrient availability, improves nutrient use efficiency (NUE) and nurtures and sustains plant roots. Composed of the natural mineral polyhalite, this product contains four of the six essential macronutrients (K, Mg, Ca alongside sulphur) in the flowing proportions:

• 14 percent K2 O
• 6 percent MgO
• 17 percent CaO
• 58 percent SO4 .

Table 3: Suggested fertilization plan for avocado tree establishment

Electrical Conductivity (EC) is another important property that deserves consideration – since avocados prefer soils with EC below 0.5 dS/m. High EC levels damage root systems and limit plant growth, especially when associated with high soil sodium (Na) levels.

In general, soil nutrient concentrations need to be within an optimum range to ensure balanced nutrition and proper yields in avocado crops (Table 2). This includes a sodium concentration in the soil CEC of less than three percent.

New Plantations

For new avocado plantations, combining the CRF Osmocote Plus with Polysulphate (see box) allows growers to supply a complete and efficient nutrition plan for their avocado trees (Table 3):

• Complete because Osmocote Plus contains N, P, K, Mg, S, Fe, Mn, Zn, Cu and B and Polysulphate provides K, Ca, Mg and S – supplying the entire nutrient requirements for this growth stage.
• Efficient because Osmocote Plus release nutrients in a precise manner according to the longevity selected. That can be any period from between one and 12 months. Polysulphate, in contrast, releases its nutrients gradually for 2-3 months.

Furthermore, the combination of Osmocote CRF technology and natural Polysulphate offers growers a promising nutrient management alternative. Used together, these two products improve nutrient supply and decrease environmental pollution, while maintaining high crop yields and benefitting crop quality. Both technologies deliver higher yield, quality and/or profitability when compared with conventional fertilizers, as has been thoroughly demonstrated in trials on many crops.

The fertilization programme in Table 3 provides avocado plantations with a well-balanced first year nutrition plan that is also safe for new roots. However, the application frequency and rate can be varied – depending on soil and water analyses and plant size. Uniformly spreading fertilizer at three different depths in the planting hole is also recommended to improve nutrient uptake:

• One third at 5-10 cm above the hole bottom
• One third in the middle of the plant hole
• One third at 5-10 cm below soil top.

Young avocado tree.

PHOTO: ICL

Young Avocado Trees

Similarly, young avocado trees also require a complete and balanced nutrition programme. More macronutrients are demanded at this stage. This includes more nitrogen and potassium to promote new growth and stronger branches, as well as more phosphorus and calcium to produce abundant root growth.

ICL has designed and developed Special Agroblen CRF formulations to supply avocado trees with an optimal amount of nutrients. These contain N, P and K combined in different ratios to match each phenological stage. Agroblen contains a blend of Agrocote Emax and Agrocote Poly-S. Encapsulated granules provide all of the essential nutrients for young avocado trees at precise grades.

The addition of Polysulphate to the fertilization programme is also recommended to supplement nutrients provided by Agroblen, as shown in Table 4. This programme is designed to fertilize plants at high nutrient use efficiency. The recommendation is to spread fertilizer granules around tree stems and then cover/incorporate these beneath the soil at a depth of 2-5 cm. The programme is flexible and application rate and frequency can be adjusted in response to soil and water analyses, plant size and rainfall.

Table 4: Nutrition programme for young avocado trees

Adult avocado tree.

PHOTO: ICL

Adult avocado trees

Fertilizer demand in adult trees (> 3 years old) increases due to higher nutrient removal by fruits. Crop nutrition plans can also vary greatly due to multiple factors such as:

• Plantation density
• Tree age
• Soil fertility
• Whether the crop management system is irrigated or rainfed.

In Mexico, most farmers have an avocado fertilization programme that combines the application of granulated fertilizers during the rainy season (summer-autumn) with water-soluble fertilizers during the dry season (winter-spring). Depending on local circumstances, the total NPK application rates used by farmers (N, P2 O5 and K2 O) may range between:

• 60-120 kg/ha/year
• 150-250 kg/ha/year
• 200-350 kg/ha/year.

Table 5: Nutrition programme for adult avocado trees using two applications of CRF* and Polysulphate blends

Table 6: ICL Fertigation programme for avovado

Case study: Agroblen trials for Hass avocados, Periban, Mexico

Hass avocados produced using Agroblen.

The use of the CRF Agrocote for the fertilization of Hass variety avocados was validated at Periban, Michoacan (19°26’16.5″N 102°26’02.9″W) in 2016-2018. Different CRF formulations and application rates were compared with conventional fertilizers, all using standard growers practice (Table 7). The evaluation was on 10-15 years old rainfed avocado trees grown in a loamy soil with the following characteristics:

• pH of 6.5
• EC of 13.1
• Major elements – Ca 9.7, Mg 1.3, K 1.8, Na 0.15 (cmol/kg)
• Minor elements – Fe 39, Mn 6, Cu 4, Zn 4.1, B 1.3, P 43, S 19 (ppm).
• The plant density was 200 trees/hectare.

Trials involved seven treatments (Table 7) on four replication plots of 20 avocado trees each. The resulting 28 experimental units were distributed according to a completely randomised design. Six avocado trees in each replication plot were monitored at harvest to determine the crop yield. The trial period covered four harvests in total.

Fig. 1: Hass avocado trials at Periban, Michoacan, Mexico, 2016-2018: average annual avocado yields for six CRF treatments at different N and K applications rates vs control. See Table 7 and main article for details

The accumulated yields at harvest during the first two years were recorded. This information was averaged and converted to tonnes of fresh fruit per hectare per year.

Results demonstrated that all CRF treatments increased yields by 10-26 percent, versus the control, with treatment five (T5, 40% N-CRF) producing the highest yield (Figure 1). Results also confirm that avocado growers – by adopting Agroblen – can potentially reduce their N and K application rates by 15-30 percent, and still obtain better yields. This is due to the higher nutrient use efficiency delivered by Agroblen and the consequent reduction in both nutrient losses and negative environmental impacts.

Table 7: Hass avocado trials at Periban, Michoacan, Mexico, 2016-2018: six CRF treatments vs one control

Table 8: ICL’s complete nutrition recommendation for avocado

Granular fertilizers are supplied via three split soil applications during the growing season:

• June. The first application of granular fertilizers takes place at the beginning of the rainy season, with farmers mainly focusing on supplying phosphorus at an NPK ratio of 1-2-1 or similar.
• August. The second application is more balanced at an NPK ratio of 2-1-2.
• September. The last application mainly focusses on supplying potassium at an NPK ratio of 2-1-3.

“Nowadays, however, the adoption of drip systems has become more common in response to water shortages.”

Traditionally, farmers have formulated their NPK blends by combining fertilizers such as urea, ammonium sulphate, ammonium nitrate, monoammonium phosphate, diammonium phosphate, potassium sulphate etc.

Innovative and responsible farmers are, however, looking to optimise their fertilizer consumption and improve nutrient use efficiency, as well as reduce the groundwater pollution caused by intense runoff during periods of high rainfall. These farmers are therefore starting to adopt slow- and controlled-release fertilizers (SRFs and CRFs) instead – substituting these for standard commodity products – to obtain the best balance between efficiency and economic viability.

ICL has successfully demonstrated the advantages of adding CRFs and Polysulphate in avocado nutrition programmes through trials and commercial plots. The use of Agrocote Emax N, Agrocote P and Agrocote K can, respectively, supply 30-50 percent of the nitrogen (N), 5-10 percent of the phosphorus (P2 O5 ) and 25-40 percent of the potassium (K2 O) nutritional needs of plants. These CRFs allow growers to supply properly formulated blends at the correct NPK ratios (Table 5).

Another advantage of using CRFs and Polysulphate is that they allow growers to cut the number of fertilizer applications. These are reduced to just two during the rainy season instead of the three applications usually necessary.

Fertigation and foliar nutrition for avocado

Many avocado growers have introduced fertigation as part of their irrigation systems. Previously, sprinkler systems were largely favoured by growers. Nowadays, however, the adoption of drip systems has become more common in response to water shortages – and due to their ability to deliver precise crop nutrition via fertigation, especially during the dry season.

ICL has developed a unique range of water-soluble products designed to work well in fertigation systems and via foliar application to plant leaves. These treatments complement soil fertilization and provide excellent results.

Water-soluble fertilizers (e.g., Agrolution, Pekacid and HiPeak fertigation products, the Nutrivant foliar fertilizer range and the surfactant agent H2Flo) are an ideal source of plant nutrients, especially where growth-limiting conditions apply (hard water, nutrient deficiencies, light soil texture etc.). An example fertigation programme for avocado featuring ICL’s product range is shown in Table 6.

This is a generic fertigation plan and adjustments are typically necessary based on plant nutrient status, as determined from soil and foliar analyses. ICL’s technical teams are available to help with local implementation, make suitable fertilizer recommendations and define the correct application rates.

Conclusions

ICL’s complete nutrition plan for avocado (Table 8) is being implemented by more avocado growers. Adopting the correct fertilizer sources for each crop stage allows growers to improve avocado crop yield, quality and/or profitability. This plan also benefits agriculture and nature by delivering crop nutrients using economically and environmentally sustainable principles.

About the authors

Mateo Martinez is a sales and technical specialist at ICL Mexico. Alveiro Salamanca-Jimenez is the agronomic leader for Latin America at ICL/ASJ Agroservices.

References

1. Rajan, M., et al. 2021. Controlled release of fertilizers – concept, reality, and mechanism. In: Lewu, F., et al (Eds) Controlled Release Fertilizers for Sustainable Agriculture. Academic Press, pages 41-56.