Banana planting material, spacing and fertilizer plan for a new 0.5 ha block
A farmer in Sonitpur wants to plant 0.5 ha (5,000 m2) of banana cv. Grand Naine. He has 500 tissue-culture plantlets and can buy more, or use suckers from his old plantation where about 10% of mats show dark green, narrow, bunched leaves and stunted growth. The planned planting distance is 1.8 m × 1.8 m. The field is on a gentle slope with sandy loam, pH 5.5, and irrigation is available only once a week. He plans to intercrop cowpea in the first four months and to apply 100 g urea per plant per month as the sole fertilizer.
1. Calculate the plant population for 0.5 ha at 1.8 m × 1.8 m. Decide whether the 500 plantlets plus suckers from the old plantation are enough, and advise on the planting material.
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Population. Area per plant = 1.8 × 1.8 = 3.24 m2. For 5,000 m2: 5,000 ÷ 3.24 = 1,543 plants, rounded to about 1,540. The farmer therefore needs roughly 1,540 plants, not 500.
Planting material. The 500 tissue-culture plantlets cover only about one-third of the area. He needs about 1,040 more. Using suckers from the old plantation is risky: the description of dark green, narrow, bunched leaves and stunting is consistent with banana bunchy top virus, which is transmitted by aphids and spread through infected suckers. About 10% of the old mats showing symptoms means the source is not clean. Cutting suckers from that field would introduce the virus into the new block, and there is no cure once it is established.
Advice. Buy additional certified tissue-culture plantlets of the same variety, or reduce the planted area to match the clean planting material available. Do not use suckers from the affected plantation, even from apparently healthy mats, unless they have been indexed and certified. Inspect the new block every two weeks and remove any plant showing bunchy top symptoms immediately, together with its suckers, to prevent spread.
2. Assess his fertilizer and irrigation plan. What would you change for the first four months, and how does the cowpea intercrop affect the nitrogen programme?
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Fertilizer assessment. 100 g urea per plant per month supplies 46 g N per month, or about 552 g N per plant per year. At 1,540 plants this is about 850 kg N/ha per year, which is excessive and expensive. It also ignores potassium, the nutrient banana removes in large quantities, and provides no phosphorus or organic matter. Applying urea as the sole fertilizer is therefore unbalanced and likely to leach on a sandy loam, especially with weekly irrigation.
What to change. Apply well-rotted farmyard manure or compost at about 10-15 kg per plant before planting. Split the nitrogen into 6-8 doses rather than one large monthly dose, and include potassium, for example as muriate of potash, along with a basal phosphorus application. Place fertilizer in a ring around the plant, not against the pseudostem. The cowpea intercrop will fix some nitrogen and cover the soil; incorporate the cowpea after four months as green manure rather than removing it. Reduce the banana N dose slightly to account for the incorporated legume, but do not omit K.
Irrigation. Once-a-week irrigation may be insufficient on a sandy loam during dry spells. Banana needs a relatively steady moisture supply. Basin or drip irrigation with more frequent, smaller applications would be better than a weekly flood, and mulching will reduce evaporation.
3. If bunchy top appears in 5% of the new planting despite using tissue-culture plants, what would you do and why?
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Action. Rogue out every affected plant immediately, including the pseudostem and suckers, and destroy the material away from the field. Do not leave the cut pieces at the field edge. Mark the gap and monitor surrounding plants for at least the next few weeks. Control aphids, especially the banana aphid, which spreads the virus, but do not rely on insecticide alone. Avoid taking suckers from the affected block for replanting. Report the incidence to the local extension office so that the source of the planting material can be checked.
Reasoning. Banana bunchy top virus is systemic and there is no cure. A 5% incidence is low enough that early roguing can still reduce spread, but only if the infected plants are removed before aphids move the virus to neighbouring plants. Because the initial planting material was tissue-culture, the appearance of the disease suggests either a failure in the certification chain or spread from an external source. The response should therefore combine roguing, vector monitoring and a review of the nursery source, rather than simply spraying and hoping the plants recover.