|Soils, Crops and Fertilizer Use: A Field Manual for Development Workers (Peace Corps, 1986, 338 p.)|
|Chapter 10: Fertilizer guidelines for specific crops|
(Banana, Mango, Papaya)
Fruit crops are often a very casual or neglected part of agriculture but can play several useful roles on small fares and in gardening projects:
· Nutrition: Fruits can be valuable sources of energy, vitamin, and minerals. Some like mango and papaya are rich sources of vitamin A (as carotene) and vitamin C. Citrus fruits and guava are high in vitamin C. Nearly all fruits provide large amounts of potassium, an important body electrolyte. Even the leaves of some types like jujube and papaya are eaten and provide vitamins A and C, 8 vitamins such as folic acid, and minerals such as calcium and iron.
· Income: Fruit crops can be a good income producer and merit inclusion in most gardening projects.
· Other functions: Some like cashew and jujube (Zyziphus mauritiana) can be part of a living fence or windbreak.
Basic Facts on Bananas
An average size banana has about 100 calories and is about 70% water. Bananas are a fair source of vitamin C and are very high in potassium; they are excellent as a carbohydrate source but are low in protein.
Bananas vs. Plantains: Plantains are close relatives of bananas but larger and with a much lower sugar content when ripe. They should be cooked before eating.
The banana plant's stem is called a pseudostem, since it's really formed from rolled-up leaves growing out of a true stem located underground in the con (i.e. a core is an underground stem). A new feat appears every 10 days until the terminal bud (flower) emerges at 7-8 months; harvest follows in about 80-90 days.
Most of the plant's roots are found in the top 15 OD of soil, though some penetrate 60 to 90 c.. The roots may grow out laterally as far as 5 meters. Lateral roots grow out fro. the main roots and are the only ones that absorb nutrients and water. Since these feeder roots are scarce close to the stalk, fertilizer should be applied about 60 cm or more out from the base.
Established plantings regenerate themselves by producing several "suckers" per mother plant; the mother plant produces just one crop. In establishing new plantings, either corms from suckers or the suckers themselves are used. "Sword" suckers which have slim narrow leaves are preferred for propagation; "water" suckers (broad, wide leaves) are considered to be inferior, due to smaller corms.
Adaptation: Bananas prefer a warm, moist climate with about 1500-2500 mm of rainfall fairly well distributed. The, prefer full sun but have a slight tolerance to shade. Good drainage is important; the plants can tolerate only a da' or two of flooding. HiBh winds (above 65 km/hr) cause considerable damage by tearing leaves and uprooting plants. Although tolerant of a soil pH ranging from 4.5-8.0, bananas do beet at about 6.0-7.5. Very low pH can promote Panama disease (a soil-borne fungus; Fusarium oxysporum).
Yields: A good bunch will contain 8 hands (fruit clusters) with 15 fingers (fruits) each and weigh about 20 kg. Yields range from about 10,000-30,000 kg/ha when planted as the sole crop.
Fertilizer Needs of Bananas
Bananas use high amounts of N and K, though their P needs are moderate. Bananas benefit from high levels of soil organic matter. The planting hole can be partially filled with rotted manure or compost. Locating a compost pile adjacent to banana trees will provide shade, and any leached nutrients from the pile will benefit the plants. Mulching around the plants is very beneficial.
Feasibility of Chemical Fertilizers: When bananas are grown in the back yard or as part of a mixed garden (see Chapter 8), there is seldom any need for applying chemical fertilizers. Compost and manure can easily satisfy the nutrient needs of the plants.
Nitrogen: N-deficient plants have a pale yellowish-green color. N stimulates faster growth, earlier flower emergence and maturity, greater leaf area, and increased fruit size. N recommendations range from about 150-350 kg/ha applied in 3-10 applications, depending on leaching potential. About 80 grams actual N per plant is considered the minimum for commercial plantings, and often 100-200 grams actual N is used. All the N should be applied before flowering, since it's important to stimulate early rapid growth. Research has shown a good correlation between the area of the third leaf and total bunch weight. Later N applications seem to promote ''openhandedness" of the bunch. Where regular spraying with fungicides is done, N can be supplied foliarly using urea (600 grams urea per 100 liters water for plants 1-2 months old and up to 3 kg/100 liters on older plants. One study showed that 65% of the urea was absorbed through the leaves in just 25 minutes.
Phosphorus: P needs are relatively low compared with N and K. Most recommendations are in the range of 50-85 kg/ha of P2O5 or about 50-100 grams P2O5 per plant. P can be applied in one application at or near planting or at various times as part of an NPK fertilizer. P deficiency causes a premature drying of the lower leaves.
Potassium: Where deficient, added K greatly increases yields and pseudostem growth, improves fruit quality and storage life, and promotes disease resistance. Moderate K deficiencies cause yellowing around the outer edges of the leaves; more severe hunger causes the leaf tips to turn reddish-brown and die. K hunger is also associated with the disorder called "premature yellowing" of the leaven. Most recommendations range from 80250 grams of KsO per plant or about 110-380 kg/ha of K2O. K can be applied in 3 or more applications, depending on leaching potential.
Magnesium: Deficiencies are common in acid soils, especially where high amounts of K are used. Applying 200250 grams of dolomitic limestone per plant will cure deficiencies. Mg hunger produces a broad bend of yellowing along the edges of the lower leaves.
Iron. Zinc. and Manganese deficiencies can occur at soil pH's above 6.8.
Molybdenum deficiency has occurred in Honduras on highly-lesched acid soils. Raising the pH is often effective at controlling Mo deficiency if the soil is very acid; otherwise, Mo should be applied.
Application Methods for Chemical Fertilizers: Young plants should have the fertilizer applied in a 30-50 co wide band around the plant, starting about 30-40 cm from the stem. The band can be moved out to about 60-90 cm fro. the stem as the plants grow. Cover the fertilizer with about 3-5 co of soil, but be careful not to injure the shallow roots.
Associated Growing Practices for Bananas
Much banana growing by small farmers is done on a very casual basis. Diseases, nematodes, insects, and overcrowding are co. on. Don't count on fertilizer alone to boost yields under such conditions. Some possibly appropriate improved practicer are listed below:
Proper selection and preparation of planting materials. Trimming the cores and sterilizing then with hot water or chlorox and water will help control neeatodes and diseases and prevent their spread to new ground.
· Mulching to suppress weeds, conserve water, and add organic matter.
· Pruning out the excess suckers.
· A spray program for insects and diseases.
· Cutting off the terminal bud and dipping the cut in a fungicide solution to prevent decay. This can add about a kilogram to bunch weight.
· Covering maturing fruits with clear polythene baga with air holes; it can speed up maturity by 2 weeks and increase yield up to 20%.
Mango is a widely-adapted tropical and subtropical evergreen tree that can grow as tall as 15-25 m with a spread of up to 15 m or more (smaller dwarf varieties are also available). It is related to cashew, pistachio nut, and poison ivy. Mango does well on a variety of soils as long au drainage is good. It prefers an annual rainfall of at least 450-1000 mm distributed over at least 6 months but likes a pronounced dry season for flowering and fruiting. It does well within a pH range of 5.5-7.5. Mango has fair drought-resistance, thanks to a very deep taproot.
One medium mango (200 grams) supplies more than twice the daily adult requirement of vitamins A and C along with about 150 calories of energy. The fruit can be eaten fresh, juiced, or made into preserves and chutney
Most of the world's mangos are grown from aced, but the fruit tends to be stringy and variable in quality. The best varieties are produced by budding or grafting to diseaseresistant rootstocks. Grafted varieties begin bearing at 4-5 years of age (seedling mangos take longer), and the fruit is ready for harvest about 100-140 days after flowering. They have an economic life as long as 40-80 years. An average yield under good management is about 400-ff00 fruits/tree.
Fertilizer Needs of Mango
Mango responds well to organic or chemical fertilizers. Mulching around the trees is a very beneficial practice. Nitrogen helps stimulate flowering and vegetative growth and lessens the tendency of alternate bearing (fruiting every other year).
Where chemical fertilizer is used, yearly rates per tree run about 0.5-1.6 kg N, 1.5-3.2 kg P2O5, and 0.5-1.0 kg K2O. The N should be split into 4-8 applications depending on rainfall; K should also be split where leaching potential is high (sandy soils, high rainfall). If more convenient, an NPK fertilizer can be applied in split applications. Micronutrient sprays of copper, zinc, iron, and manganese are applied where needed.
Application method: For young trees, chemical fertilizer is spread uniformly over the root area from near the trunk to 60-90 cm beyond the edge of the leaf canopy (called the drip line). To avoid root damage, work it on no deeper than 3-4 cm, and apply it evenly. P is utilized fairly well with this method. Unlike uniform broadcasting over the entire soil surface, this method confines it to a small area, somewhat like a localized placement method (see Chapter 9).
Papaya is a short-lived, fast-growing perennial tree about 4-6 meters tall. It does well on most soils as long as drainage is good; it won't tolerate flooding for more than 48 hours. Papaya needs a minimum of 1000-2500 mm annual rainfall fairly well distributed; otherwise, supplemental watering is needed. It has a weak, hollow stem which makes it susceptible to wind damage. Papaya prefers a soil pH of about 6.0-7.0. It is susceptible to nematodes.
There are 3 kinds of papaya trees: male, female, and hermaphroditic, but flowers may change fro. female to male under stress. Male trees seldom produce, and their fruit is misshapen and of poor quality. Fruit production on female trees requires the presence of a male tree for pollination. Hermaphroditic varieties such as the Solo group are selfpollinating. (Solo papayas produce grapefruit-size fruit and are popular for the export market; however, all Solos except the Cariflora variety are very susceptible to ring spot disease and several other viruses which are co on in Central America and the Caribbean. Cucurbits such as squash and cucumber are an alternate host for these viruses.)
Papaya is propagated from seeds which sprout in about 10-15 days and can be sown in pots or directly in the ground. Flowering occurs about 5 months later, and fruit is ready to harvest at about 9-11 months of age. Yield per tree is about 60-90 kg/year. Trees have an economic life of about 3-4 years.
Papaya fruits vary in size, shape, and color; the most co "on flesh colors are yellow or reddish. The outside shin ripens to a golden color, starting from the stem. One medium papaya (300 grams) supplies 100% of the daily adult requirement of vitamin A and 3-5 fold the daily vitamin C needs. It can be eaten raw or preserved. The leaves and the pulp of unripe fruit contain a good amount of an enzyme called papain, useful as a meat tenderizer and digestive aid. The leaves can also be eaten and have all the benefits of other dark green leafy vegetables, being rich in vitamins and minerals (including calcium) and also in protein. In some areas, papaya leaves are used as a diarrhea remedy.
Like most crops, papaya will respond well to organic fertilizers. However, farm manure shouldn't be mixed with the soil in the planting hole since it is known to favor the development of Pythium root rot. Papaya responds well to a continuous supply of nitrogen; P and K help promote rapid growth and early flowering; K is especially important after flowering.
In Australia, 8-12-6 fertilizer is recommended at 700 grams/tree the first year and 9001350 grams/tree in the following years. The dosage is split into 4 applications per year. In South Africa, 100 grams actual N is recommended per tree the first year and 200 grams per year after that; P2O5, is applied once at about 100 grams per tree (about 450 grams of 0-20-0).
Application method: The fertilizer should be broadcast in a wide band from near the trunk outward about 60-90 cm during the first 6 months, expanding to 1.5 meters as trees grow. Work it in shallowly 2-3 cm to avoid root damage. The P applied in this manner isn't subject to as much tie-up as with regular broadcasting, because it's still confined to a relatively small area.
Some hunger signs in papaya: Yellowing of the bottom. leaves may indicate N deficiency. P deficiency produces dark-green leaves with a reddish-purple discoloration of the leaf veins and leaf stalks.