Soursop (Annona muricata L.), also known as graviola, guyabano, guayabano guanabano and babana, is a shrub or small tree 3-10 meters in height. It is adapted to warm, humid tropical climate, and can tolerate both drought conditions and partial shade.
This fruit crop grows in any kind of soil but prefers loose, fairly rich, deep loam and well drained soil with pH ranging from 6.1 to 6.5. It thrives well from sea level up to 300 meters above sea level although it is known to grow up to 1000 m.
It has numerous uses. The young green fruits with seeds that are still soft can be cooked as vegetable. When ripe, the flesh can be eaten off hand or as dessert, or processed into candies, jams and jelly. Its juice is used for flavoring or packaged into refreshing guyabano drinks. The leaves are used as herbal medicine. Because the tree is small and tolerant of partial shade, it can be intercropped with coconut or with large fruit trees like mango, durian, avocado and jackfruit.
The fruit consists of about 67.5% edible white pulp with a pleasing fragrance and flavor. It is a good source of vitamins B and C with some calcium and phosphorus.
This plant is relatively safe from grazing animals. Actual observation revealed that even goats do not feed on them. However, just like other crops, they can be damaged by trampling of large animals.
The plant also has a short juvenile phase. It starts flowering 2 to
4 years from seed. But old, bare-root transplants were observed to start flowering from as early as 6 months after transplanting.
To grow soursop in commercial scale, the following farming methods are recommended:
1. Variety Selection.
Choose either of the two types: sweet or sour. The sweet type is preferred for eating, the sour type for processing into guyabano juice. The sweet type has generally small and few seeded fruits with a sub-acid flavor.
2. Plant Propagation. Soursop is commonly raised from seeds. However, it can also be propagated using bareroot transplants and asexually by marcotting (air layering), budding and grafting. The seeds to be used for seedling production should be obtained from hardy and prolific plants with medium to large-sized fruits of desirable qualities. After extracting from the fruit, the seeds should be washed in tap water and air-dried. They may be stored temporarily but it is better to plant immediately.
The seeds are sown in seedboxes or seedbed with sandy soil. Sow the seeds about 2.5 cm apart and 1 cm deep. Provide shade and keep the seedbed moist by regular watering. About 85 to 90 percent of the seeds will have germinated in 20 to 30 days.
The seedlings are ready for potting into individual containers when the first set of leaves mature. Black plastic bags with a size of 7 in x 10 in (about 18 cm x 25 cm) or thereabout can be used as potting containers. Punch 4 to 6 holes close to the bottom and fill with sandy soil. Poke a piece of wood at the center of the pot and insert the basal part of the seedling into the hole. Water immediately and keep under partial shade.
The seedlings can be outplanted 6 to 8 months later. To prevent transplanting shock, they should be prepared first for the prevailing field conditions by hardening. This involves gradual exposure of the seedlings to full sun and reduction in the frequency of watering.
3. Land Preparation and Planting. Soursop may be planted at a distance of 4 m x 4 m to 7m x 7 m in square, rectangular or triangular pattern. The number of trees that a one-hectare farm can accommodate will range from about 204 to 625 in square system and 235 to 719 in the triangular system. The exact number can be determined by preparing a planting layout plan.
The land is prepared for planting by following the usual plowing-harrowing tillage system, especially in large farms. However, for small farmers with limited capital and where planting is on staggered basis, land preparation may be done by slashing of the thick vegetation followed by clearing of the immediate periphery of the marked hills. Dig holes about 50 cm wide and 50 cm deep. Refill with top soil when the seedlings are set in and water immediately.
4. Fertilizing. To ensure vigorous growth, apply fertilizers regularly at the onset and end of the rainy season or every 6 months. Fertilizer application can be started a month after planting using ammonium sulfate (21-0-0) at the rate of 100-150 grams per tree. The rate is increased every year until the start of the fruiting stage at which time 250-300 grams of complete fertilizer (14-14-14) is applied. This amount is also increased every year from 1.5 to 3 kg plus 200-300 kg of muriate of potash (0-0-60). To ensure supply of micronutrients, organic fertilizers can be incorporated in the fertilization plan.
5. Watering. The soursop can tolerate dry conditions and in fact requires a dry climate to induce synchronous flowering. However, prolonged drought will cause excessive leaf shedding. In that situation, supplementary water will be beneficial.
6. Weeding and Mulching. Ring weeding should be done regularly. This can be accomplished by shallow cultivation of the immediate periphery of the tree. Weeds can be piled around the bases of the trees to serve as mulch.
7. Pruning. Branch pruning should be done to disperse the remaining branches and to promote air movement and light penetration. Water sprouts, diseased and decaying branches and twigs should be removed also.
8. Intercropping. To maximize utilization of the land and help suppress the growth of weeds, annual crops such as cereals, pulses, root and tuber crops and vegetables may be grown between the soursop trees while still young. It can be intercropped also with perennial crops like banana, citrus and black pepper.
9. Insect Pest and Disease Control. Although soursop is more resistant compared to other fruit crops, it is not entirely safe from insect pests. Insect pests that attack this crop include root grubs, mealy bugs, carpenter moth larva, scale insects and oriental fruit fly. The major diseases are root rot, pink disease and anthracnose.
A crop protection plan should be formulated and incorporated into the overall farm management system. It may include both prevention (e.g. sanitation, burning of diseased plant parts, disposal of fallen fruits, removal of alternate hosts) and control measures (chemical, organic or biological). Livestock may also be raised as a component of crop-livestock integrated farming system (click to read how this has benefited mango).
10. Harvesting. Soursop continues flowering year round but the peak is May to June. The fruits are harvested when fully developed and still green. They are considered mature when their spines are set far apart and the shiny green color turns dull-green or yellowish green. Selective harvesting is practiced because the fruits on a tree do not mature at the same time.
A cost and return analysis prepared by the Bureau of Plant Industry for guyabano planted at 5m x 5 m spacing shows a progressive increase in yield starting 4 years after planting with a fruit yield of 4.8 tons per hectare and a net profit cost ratio of 47.56% in the seventh year. In the 10th year, net profit cost ratio is about 200% with a projected yield of 11.8 tons per hectare. Data obtained from Hawaii, however, disclosed that with 215 trees per hectare fruit yield in the 6th year was 18 tons per hectare (Verheij and Coronel, 1992).
Verheij, E.W.M. and R.E. Coronel (eds.). 1992. Edible fruits and nuts. Plant Resources of South-East Asia No. 2. Bogor, Indonesia: Prosea Foundation. pp. 75-78.
Bureau of Plant Industry. undated. Production guide on guayabano. Retrieved September 29, 2010 from http://www.bpi.da.gov.ph/Publications/productionguides/guayabano.htm.
(Ben G. Bareja. 2010)