Thus, it is best to avoid heavy clays and highly leachable sands or gravels. Rooting depth depends on soil condition and the height of the water table. Crops generally root to 5-10m depth, but in practice up to 85% of roots occur within the top 30cm of the soil due to physical or chemical restrictions to growth.
Roots usually spread around 1.5m out from the pseudostem, but with most active roots located some 30-60cm out from the pseudostem, most fertilizer is directed to this narrower zone in order to maximize uptake.
Bananas have a high water demand and 25mm/week is regarded as the minimum for satisfactory growth. Tropical crops can utilize 900-1800mm of water in the ten months leading up to harvest.
|pH and Yield|
|Banana - Guinea|
|4.5 - 5.0||16.9|
|5.0 - 5.5||25.7|
|5.5 - 6.0||30.7|
|Ref: Oschatz - 1962|
If this is not available, then irrigation is essential. Growers need to take into account the very high evapotranspiration rates that can occur in high temperature conditions. Equally important is the need for good drainage in very wet regions, especially where annual rainfall is in excess of 2500mm. Significant yield loss occurs as a result of root dieback where soils are saturated for 24 to 48 hours or more.
Optimum soil pH is between 6.0 to 6.5, however crops are grown on soils with a wide range of pHs from 4.5 – 8.0, with a range of different yield responses. Soil pH has a direct effect on nutrient availability. Aluminum toxicity symptoms can occur below pH 5.0 and become most severe with decreasing pH values below 4.5. Free aluminum in the soil solution affects uptake of water and nutrients. In trials, with nutrient solutions containing 2.2ppm Al in solution, water uptake was halved after 40 days compared to controls. At the same time, calcium, magnesium, potassium, phosphorus and nitrogen uptake was reduced by around 50%.
Lime is incorporated pre-planting and applied to the surface at regular intervals throughout the season, to reduce toxicity and increase nutrient availability.