High salt levels in the soil or irrigation water cause plant stress resulting in marginal leaf chlorosis, stunted growth and thin, deformed fruit.
When the level of total soluble salt in soils exceeds an EC of 4 in the soil solution, plants and fruit are visibly affected. Salinity levels above this result in plant stunting and senescence. Even in the absence of visual stress symptoms, salinity restricts root and above ground plant growth (Figures 4 and 5). Plant height, circumference and leaf area, can all be adversely affected by higher levels of salinity.
Excessive potassium, sodium and magnesium levels also create nutrient imbalances, reducing uptake of other nutrients. At high sodium levels, contents in roots can rise to 1.5% - around three times the normal level - especially when potassium is deficient.
Bananas seem to be more sensitive to sodium than to chlorine. For example, crops will still grow where there is excessive, sucker growth and fruit fill is restricted. AAA type bananas (e.g. Cavendish) are more sensitive than plantains (AAB/ABB types) to both aluminum toxicity and salinity stress. Where possible, growers should irrigate to leach out salts and hence minimize salinity damage.
Crops respond to mulching which returns organic matter, improves soil fertility as well as water and nutrient retention and availability. A range of materials is used including old leaf and pseudostem remains, grass and legume cover crops, brought in organic material such as compost, straw, and wood chips. In the tropics, up to four applications (commonly one or two) of mulch may be applied every year, unless a cover crop is grown.
Nutrients from plant material are very quickly mineralized in high temperature, high moisture conditions.
Mulching is particularly important in low input plantain production as means of recycling nutrients, and has increased yields by up to 40%. Other practical benefits of mulching include:
- Reduction of surface water evaporation.
- Increased winter soil temperatures.
- Reduced summer soil temperatures.
- Suppressed weed growth.
- Reduced soil erosion.
- Improved soil fertility where little or no fertilizer is applied.
Intercropping with maize, cassava, rice, yam, beans, sugarcane, or coffee is quite common in African and Central American plantain plantations.