Cashew care: weeding, pruning, creating canopy, watering, fertilizing, renovating old gardens

Fig 1. Weeding in cashew garden

Mulching the basin

Mulching with fallen leaves and dry grass helps to improve soil nutrient, conserve soil moisture, inhibit weed growth, reduce surface evaporation and also regulates the soil temperature in the cashew-planting area.

Irrigation

In areas with long dry seasons, because water levels are too low, it is necessary to apply additional water to cashew plants by watering them once a week. The average amount of irrigation water is 20, 50, 100 and 200 liters per graft, respectively in the first, second, third and fourth years. In general, according to the soil moisture condition, decide whether to water regularly or not. Cashew does not withstand water stagnation and it should be ensured that there is proper drainage after each heavy rain.

Fig 2. Watering trunk for cashew tree gardens

Intercropping

The soil in the cashew garden should not be left bare, without any plants growing, or exposed to direct sunlight because it will cause soil moisture to evaporate and nutrients in the soil to be washed away due to sun and rain. Therefore, it is necessary to intercrop short-term crops of the legume family such as peanuts, cowpeas, green beans, etc. to protect the soil and increase income in the first years of newly cashew orchards. Leguminous cover crops such as ghost beans (Centrosema pubescens) and hairy beans (Calapagonium muconoides) enrich the soil with the plant nutrients, add organic matter, prevent soil erosion and conserve moisture. The seeds of these cover crops may be sown in the beginning of the rainy season with a seed rate of 7-8 kg per ha.

Besides, cashew is grown in combination with casuarina and coconut. Casuarina is also a tree inter-crop planted at a spacing of  1x1m or 1.5 m×1.5 m in cashew orchards in Andhra Pradesh and Orissa. In Goa, cashew is grown in combination with eucalyptus and teak in the first few years successfully.

In general, intercropping is only necessary in the first few years of growing cashews. Intercropping must be stopped before the cashews bear flowers and fruits, when the canopy of cashew trees has covered the planting area.

Fig 3. Model of inter cultivating cocoa in the cashew garden

Pruning - creating canopy

If a cashew tree grows naturally, it will produce many branches close to the ground, turning the tree into a shrub. Crisscross branches of cashew trees planted close together diminishes the yield of trees. Therefore, branches and canopies should be pruned properly right from the first two years after planting, which helps make farming and intercropping easier. Besides, as cashew trees begin to bear fruit in the third year, this also helps facilitate harvesting cashew nuts.

Any branches that begin to grow from the trunk less than 60 cm (if pruned manually) or less than 1m (if pruned mechanically) from the ground must be removed. For each tree, only 3-5 branches with all evenly sides should be selected.

It should be noted that once the tree has been properly shaped, it is no longer necessary to prune branches regularly and on a fixed schedule. Still, diseased and withered branches should be cut off, which also serves as protection for the growing area while also increasing tree yields.

For cashew trees with high yields, pruning large branches will weaken the tree due to latex leaking from the cuts. Therefore, this should not be done. 

According to many assays on the pruning time and intensity for grafted cashew trees at Directorate of Cashew Research in S.K.Karnataka (India), it has been shown that pruning main branches with an 50% intensity 50% of tree height in July and August has significantly increased seed yield per tree. In particular, while pruned trees yield 9.22 - 9.36 kg of seeds per tree, non-pruned trees only yield 4.32 kg of seeds/tree (average data for 2 years 1985 and 1986, E. Mohan and Room Singh).

Fig 4. Laborers are pruning cashew branches

Thinning

The first thinning is done on a 1-year-old tree when the tree height reaches about 120cm. This is also the way to clear each hole to leave a healthy and best-developed tree.

Subsequent thinnings will depend on requirements of planting spacing when the tree is fully mature.

As a general rule, the distance between trees should be about 2 times the width of the tree canopy. In fact, thinning should be done when the canopies begin to get close together, to prevent them from overlapping and the branches from crossing each other.

For instance, in Nachingwea (Tanzania), cashew is planted at an initial spacing of 6 m x 6 m. After 3 harvests, when the trees are 5 years old, cashew canopy is thinned to reach a spacing of 9m x 9m. In West Africa, with an initial planting spacing of 5 m x 5 m, 6 m x 6 m, 7 m x 7 m, arrange the trees in a square shape, the first pruning is done in the fifth year of the tree and the second time is done in the ninth year of the tree to get the final spacings: 10 m x 10 m, 12 m x 12 m and 14 m x 14 m.

Fertilizing

For a long time, it had been said that cashew was a wildland tree that was easy to grow and could tolerate drought conditions and still grow well without  fertilization and care. However, like other tropical fruit-bearing trees, the cashew tree also requires careful fertilization and care in order to live, grow and produce high yields especially in areas with a lack of nutrients. Symptoms of mineral deficiency and their effects on the life process of young cashew trees as described by Ohler and Coester (1973) can be divided into three groups: 

1. Dangerous deficiencies that are lethal; in order of seriousness: Fe, Mg, K, N and Mo.
2. Deficiencies that developed early but were not lethal. In order of severity: S, Ca, Mn and Zn. 
3. Deficiencies that developed slowly and did not cause severe effects; in order of importance: P, B and Cu.

Only through soil analysis can specifically determine nutrients that are lacking to supply  cashew trees with these  substances.

Results of  experiments conducted at some research  stations such as I.F.A.C Research Stations (Malagasy), Nachingwea Southern Research Station (Tanzania), Research Stations (India) and Pacajus (Brazil) showed that cashew plants respond well to fertilizer application, especially with Nitrogen and Phosphorus treatment but no response and less response with Potassium. On the other hand, calcium has a negative impact on the plant because this plant prefers soil with weak acidity.

Due to the root system of the cashew tree and its downward growth, applying mineral fertilizer at the time of planting or applying it to the root zone is more effective than applying it on the surface.

According to Mathew Thomas M. (1982), in order for cashew trees to produce continuously with fully mature trees, 250 g N, 125 g P2O5 and 125 g K2O must be applied to young trees, specifically 84 g N, 42 g K2O in the first year and double in the second year. Trees with higher yield can increase up to 500 g N per plant.

De Geus J.G. (1967) stated that for  10-year-old cashew trees, the present fertilizer recommendation is to apply 250 g N, 150 g P2O5, 100 g K2O (equivalent to 2 kg of compound fertilizer with a grade of 12:8:8).

For a 1-year-old cashew tree, the recommendation is to apply 250 g Super phosphate, 250 g ammonium sulfate. After 3 months of planting, and in the second year, this amount of fertilizer is doubled plus 150 g of Potassium Chloride.

According to Mohapatra and Vijaya Kumare Bhat (1973), a mature tree with high yield annually consumes 2.84 kg N, 0.752 kg P2O5 and 1.265 kg K2O. On this basis, it is possible to calculate the amount of fertilizer needed for cashew plants at different ages.

Fig 5. Fertilizing the cashew plant

According to "Package of Practices for cashew"-ICAR (1982), the specific fertilization schedule for a cashew plant is as follows:

Table 1. Fertilizer Schedule for cashew trees in the first 3 years and subsequent years (g/tree)

In the first few years of a cashew tree, fertilizers should be applied in a circular trench of  about 20 cm depth according to the projected circumference of the foliage, then cover it with soil. When the tree is mature, apply fertilizers in a  circular trench of 1.5 m radius around the tree basin, then cover it with soil. It is necessary to clean weeds around the basin before fertilizing.

There is also a fertilizer schedule that can be  applied as follows:

Table 2. Fertilizers recommendation for cashew (according to "Cashew production and processing" - 1989)

The above amount of fertilizer is applied twice a year, divided equally into 2 times:

- The first time is before the rainy season, around May to June.

- The second time is after the rainy season, around September to October.

According to the "Technical Instructions for Cashew Cultivation" table issued by the science and technology council of The Ministry of Agriculture and Rural Development in 2000, fertilization for cashew trees is divided into two periods: the basic construction period (seedling stage) and exploitation period (fruit-bearing stage).

Table 3. Fertilizers recommendation for cashew during the fresh planting period

Table 4. Fertilizers recommendation for cashew during exploitation period

In a summary, the care and management of cashew orchards can be carried out according to the schedule and the tasks below. 

This schedule is applicable to cashew growing areas with climatic conditions as follows:

- Winter with dry conditions: from December to March of the following year.

- The beginning of the rainy season: from April to May.

- The rainy season: from June to September.

- The end of the rainy season: from October to November.

* December - January: cashew trees bear flowers from December to January. To-do lists include:

- Spraying insecticide Endosulfan or Quinaphos to prevent mosquito teas, thrips and some other pests.

- Weeding

*February - April: harvest season. To-do lists:

- Harvesting and collecting fallen fruits (nuts) periodically (with cashew trees that have been selected as mother trees, when harvested, the nuts are kept aside as seedlings).

- Layering branches in February - March to transplant in June - July.

* May:

- Carrying out the first round of fertilizing for cashew tree before the start of the rainy season (quantity: 1/2 amount of plant fertilizer/year).

- As the first rains of the season begin, preparing soil for the new planting area includes: weeding, digging holes, and building stairs on a slope. It should be sure that everything must be finished before heavy rains of the rainy season begin.

- Sowing seeds in soil pots under cover when heavy rains begin.

* June - July:

- Transplanting seeds directly to the field (for trees grown from seeds) and transplanting seedlings and vegetative seedlings to the field.

-  After removing diseased branches, spraying Bordeaux 1% to prevent die-back disease.

- The cashew nursery should be well-drained to prevent root rot in seedlings.

- If infected with collar-rot disease, after it rains, cashew seedlings should be sprayed with Bordeaux 1%.

* August - September: after the rains subside, applying fertilizer in the second round (the remaining amount of fertilizer). After the rains stop,  manure from cattle or green manure can be applied to cashew plants.

* October - November: the tree begins to sprout new shoots. Flowering plants may begin blooming soon. Spraying Endosulfan to prevent mosquito teas, leaf borers, leaf and flower webbers and other pests.

Renovating the old cashew garden

Old cashew trees (from 8 to 15 years old) that have a slow growth, poor productivity and nut quality need to be renovated to improve productivity and quality, which helps improve their economic efficiency and prolong exploitation time. There are two widely-used methods to renovate old cashew gardens: caring for the tree more frequently and cutting the tree.

Fig 6. Renovating the old cashew garden

- Caring more frequently

After the harvest season, cleaning the garden. Next, sawing old and diseased branches off, then repairing the irrigation system and weeding.

Applying fertilizers twice a year: the first application is after harvest season (June - July), fertilizing each tree with 1 kg of urea + 1.5 kg of super phosphate + 0.5 kg of potassium chloride. The second application is in October, which helps the tree bloom and prepare for flowering and fruiting.

Watering the tree thoroughly during the dry season, continuously once a week until the tree bears fruit (at the beginning of the rainy season).

Also, preventing pests such as borers, anthracnose and other pests actively.

- Cutting method:

At the beginning of the rainy season, about 0.5 m-0.7 m of the height from the ground, sawing the tree trunk. After sawing, many shoots sprouted from the tree basin when it rains. Pruning away weak shoots, leaving 8 - 10 of the strongest shoots in each basin (shoots evenly distributed around the basin). These shoots are used as rootstocks using the softwood wedge method. About 60 to 70 days of grafting, selecting 4 - 5 best grafted buds. Because the cut surface of the tree trunk is susceptible to fungi infection, it is necessary to water it with Bordeaux solution to eliminate the fungus, and at the same time use beef tallow, tar or water-resistant paint to prevent stem rot. The surface of positions of removed young shoots need to be sprayed with pesticides to prevent stem borers. Taking care of the grafted buds. As a result, the new cashew garden has been successfully renovated.

REFERENCE

Thanh P. D. Cashew nuts - Production and Processing (2003).