Nutritional Needs for Cashew Trees

Cashew (Anacardium occidentale L.) is often planted on marginal soils and treated as a low-maintenance crop – but that approach costs farmers dearly in yield and nut quality. The reality is that cashew responds exceptionally well to proper nutrition. Research from India’s All India Coordinated Research Project on Cashew found that adequate nutrient management can increase nut yield by 50 to 100%. Getting the nutrition right – with the correct nutrients, the right amounts, and proper timing – is one of the most impactful decisions a cashew grower can make.

Why nutrition matters so much in cashew 🔗

Cashew trees have a dual production demand that most fruit crops don’t. They must simultaneously develop vegetative structure, produce a fleshy cashew apple, and form the true nut – all from the same nutrient pool. According to FAO’s integrated production guidelines for cashew in India, the light sandy and laterite soils where cashew is predominantly grown are naturally low in organic matter and key nutrients, making external fertilization essential for commercial productivity.

Without adequate nutrition, you’ll see slow canopy development, poor or erratic flowering, low nut set, and nuts with inferior oil content and kernel weight. A structured nutrition program addresses all of these issues systematically.

The three core macronutrients for cashew 🔗

Nitrogen, phosphorus, and potassium (NPK) are the foundation of any cashew fertilization program. Each plays a specific and irreplaceable role in the tree’s growth and productivity cycle.

Nitrogen – the growth driver 🔗

Nitrogen is the primary nutrient responsible for vegetative growth. It drives the development of new flushes, leaves, and shoots, and is essential for chlorophyll synthesis. As noted by AgriFarming, the light sandy coastal soils where cashew is commonly cultivated are naturally deficient in organic matter and nitrogen, making external nitrogen supply critical. Deficiency symptoms appear first in older leaves – they become pale, the stem becomes thin, and overall growth stalls.

However, nitrogen needs to be balanced carefully. Excess nitrogen at the wrong stage can promote excessive leaf and shoot growth at the expense of flowering and nut production. The recommended dose for a mature cashew tree is 500 g of nitrogen per tree per year, typically supplied through straight fertilizers like urea.

Phosphorus – root development and fruit formation 🔗

Phosphorus plays a critical role in energy transfer within the plant, making it especially important during flowering and early nut development. According to Matix Fertilizers, phosphatic fertilizers such as single superphosphate (SSP) or diammonium phosphate (DAP) are commonly applied to meet the phosphorus demands of cashew trees. Without sufficient phosphorus, trees show poor root systems, delayed flowering, and reduced fruit set.

The standard recommendation is 125 g of phosphorus (P₂O₅) per tree per year. Since cashew root systems can spread up to 2 meters from the trunk, strong root development directly determines how efficiently the tree absorbs water and all other nutrients from the soil.

Potassium – quality and resilience 🔗

Potassium is closely linked to the final quality of the cashew nut. Research on cashew nutrient management shows that a potassium shortage leads to poor nut development and low oil content, while adequate potassium improves kernel quality and crop resilience. Potassium also facilitates the movement of water and photosynthates through the plant, keeping the tree’s internal systems functioning efficiently – particularly during the critical flowering and fruit fill stages.

The recommended dose is 125 g of potassium (K₂O) per tree per year, commonly supplied through muriate of potash (MOP). Trees with adequate potassium produce nuts with better oil content, longer shelf life, and improved pest resistance.

The role of organic manure 🔗

Organic manure is not just a supplementary input – it forms the foundation of a sustainable cashew nutrition program. The standard recommendation is 10-15 kg of well-decomposed farmyard manure (FYM) per tree per year. This can be substituted with poultry manure at 10 kg per tree where available, or with vermicompost and oil cakes in organic production systems.

Organic matter improves soil structure, increases water retention capacity, and feeds beneficial soil microorganisms that enhance nutrient uptake by cashew roots. A four-year integrated nutrient management study on cashew found that combining 100% recommended NPK with FYM produced the highest cumulative nut yield compared to inorganic fertilizers alone. Organic matter also acts as a slow-release nutrient buffer, complementing the faster-acting inorganic fertilizers.

It is important to use fully decomposed manure only. Partially composted material can burn roots and attract soil pests. Application should ideally be done at pit-filling time during planting and then annually as a top dressing around the tree basin.

Fertilizer schedule: starting from year one 🔗

Young cashew trees cannot handle the full recommended dose of fertilizers immediately after planting. Applying too much too soon causes fertilizer burn, damages the root system, and can set back plant establishment. The correct approach is a phased schedule that gradually increases inputs as the tree grows.

India’s National Coordinated Cashew Research trials established the following phased application schedule based on full adult dose targets of 500 g N, 125 g P₂O₅, and 125 g K₂O per tree per year:

Year 1 – establishment phase (25% of full dose) 🔗

In the first year after planting, apply approximately 25% of the recommended dose. The focus at this stage is on root establishment rather than flowering or nut production. Organic manure should be incorporated into the planting pit at the time of planting to provide a slow-release nutrient base. Keeping nitrogen levels modest prevents excessive shoot growth before an adequate root system has developed.

Year 2 – growth phase (50% of full dose) 🔗

In the second year, increase fertilizer application to around 50% of the full recommended dose. By this time, the tree has established its root system and canopy is expanding. The increased nutrient supply supports accelerated vegetative development in preparation for the first productive flowering cycles.

Year 3 onwards – full dose 🔗

From the third year, the tree should receive the complete adult dose: 500 g N + 125 g P₂O₅ + 125 g K₂O per tree per year, along with 10-15 kg of organic manure. Long-term NPK trials at AICRP Cashew Research Station, Karnataka confirmed that this dose level produced the highest cumulative nut yield and the most favorable benefit-to-cost ratio over 10 years.

How and when to apply fertilizers 🔗

Timing and method of application are just as important as the quantities used. Fertilizers applied at the wrong time or in the wrong way result in nutrient losses through leaching or surface runoff, with no benefit to the tree.

Timing of application 🔗

Cashew fertilizers should be applied in two split doses per year – the first during pre-monsoon (May-June) and the second during post-monsoon (September-October). Applying immediately after the cessation of heavy rains, when the soil still has adequate moisture, ensures better nutrient uptake. AgriFarming recommends that fertilizers always be applied after weeding and clearing the area around individual tree basins to reduce competition and improve absorption.

Method of application 🔗

The application method depends on soil type and terrain. On flat red loamy soils – common on the east coast – fertilizers can be broadcast in circular bands along the drip line of the canopy and raked into the soil. On laterite soils and sloping land on the west coast, the FAO cashew production guide recommends placing fertilizers in circular trenches about 25 cm wide along the drip line, then filling and mulching the trench to retain moisture and prevent runoff.

Since around 72% of active cashew roots are within 2 meters of the trunk, the drip-line zone is where fertilizer placement delivers the most efficient uptake. Applying directly at the base of the trunk bypasses most of the feeder roots and is far less effective.

Choosing the right fertilizer form 🔗

Straight fertilizers are preferable to complex (compound) fertilizers for cashew. The reason is practical: the NPK ratio recommended for cashew (500:125:125) doesn’t match the fixed ratios available in most compound fertilizers. Using straight sources – urea for nitrogen, single superphosphate for phosphorus, and muriate of potash for potassium – allows precise and independent adjustment of each nutrient.

Micronutrients and soil testing 🔗

While NPK gets most of the attention, cashew trees also require micronutrients for complete nutrition. Zinc and boron deficiencies are known to cause misshapen nuts and poor fruit set in cashew. Zinc is involved in enzyme function and leaf development, while boron directly influences flower and nut formation. Copper plays a supporting role in enabling the tree to utilize other nutrients more effectively.

Soil testing every two to three years is essential to identify any nutrient imbalances, pH issues that may be locking up nutrients, or emerging micronutrient deficiencies before they become yield-limiting. In acid soils, lime or dolomite should be applied two weeks before fertilizer application to correct pH and improve nutrient availability. Site-specific fertilizer management based on soil test results is always more precise – and more cost-effective – than blanket application of standard doses.

What do you think? Given how significantly nutrition affects both yield and nut quality, do you think phased fertilizer scheduling from year one is common practice among cashew growers in your region? And considering the clear benefits of combining organic manure with inorganic NPK, what factors might prevent smallholder farmers from adopting an integrated nutrient management approach?

References

1. https://ishs.org/ishs-article/1080_37/
2. https://www.fao.org/4/ac451e/ac451e04.htm
3. https://www.agrifarming.in/best-fertilizer-for-cashew-tree-organic-npk-compost-manure-and-how-to-apply
4. https://matixgroup.com/crop/cashew/
5. https://www.fertilizertrelfey.com/cashew/
6. https://www.researchgate.net/publication/269518305_Integrated_nutrient_management_in_cashew_for_increasing_production_with_sustainability