Better drainage for banana plantations
Jeff Daniells, Department of Primary Industries and Fishereies.
Darryl Evans, Department of Natural
Resources and Mines
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Poor drainage is a major cause of reduction in yield and quality of bananas grown in north Queensland. This is particularly so on alluvial soils. In many cases its effects are not recognised, it goes untreated, and consequently high yields are not achieved. Bananas must have good surface and internal drainage for good yields. This article outlines some effects of poor drainage and how drainage can be improved.
Effects of poor drainage
A poorly drained site does not allow for the rapid disposal of surface water, resulting in ponding, nor for the rapid movement of water through the soil profile. The water table often rises into the banana root zone in such situations particularly during the wet season. Essentially the soil in such a site becomes waterlogged. This refers to the air spaces in the soil being displaced by water.
Waterlogging can also come about by inundation with flood waters and from sustained heavy rain maintaining the soil in a saturated state. Air (specifically oxygen) in the soil is essential for healthy root growth of plants. Poor drainage thus causes a decrease in production because plant roots become stunted or killed and can no longer supply the plant with the necessary water, nutrients and anchorage.
Because of the damage to the root system plants can suffer from water stress and nutrient deficiencies despite adequate quantities being present because of the damage to the root system.
Poor drainage is indicated by:
- shallow root systems
- small plants and bunches
- choking
- pseudostem breakage
- yellowing, reddening or scorching of leaves (Fig. 1)
- reduced finger length
Damage to roots due to burrowing nematodes is also believed to be worse in poorly drained soils. Certainly the impact of nematodes would be worse in a poorly drained situation because of the poorer root growth due to waterlogging.
Sub-soil colouring can indicate past waterlogging if a water table is not present when inspecting a site. An orange and black mottling of the soil is caused by ferric and manganic ions and indicates periodic water saturation. Blue or grey coloured soil indicates prolonged water saturation.
Drainage strategies
The type of drainage system required depends largely upon the soil type and situation. Alluvial soils are generally those in most need of drainage works but even soils in sloping situations can suffer from waterlogging where there are changes in soil type, impermeable layers and springs.
Specialists in drainage are necessary to determine your exact requirements. To minimise the effects of poor drainage both surface and sub-surface drainage are required.
Fig. 2. Veeing out of interrows greatly
improves surface drainage
Fig. 3. Delver plough used for
surface drainage
Surface drainage
Before planting it is advantageous to implement a drainage plan for your property to ensure runoff water is efficiently controlled and disposed of. This may first involve a grid survey to determine the best planting direction. Where possible land should be shaped to allow the ready movement of water off the block and into a system of grassed waterways (shallow drains) or into natural drainage lines. This may involve land-planing to ensure a continuous steady fall. Rows should be aligned so that water can move along the interrow passageways.
Rows of bananas should be mounded up either before or after planting (Figure 2). In double rows it is particularly preferable to do so before planting so that water does not pond between the two rows of the double row causing waterlogging. When mounding it is also important to ensure that there is still sufficient fall at the outlet to avoid ponding at the ends of rows. This means that headlands may have to be lowered to provide a good outlet.
The mound should peak between the 2 rows of the double row. Mounds may be formed with graders or special delving ploughs (Figure 3). Mounding of banana rows is an important strategy for reducing the effects of waterlogging.
Subsurface drainage
Deep ripping of land before planting greatly improves plant growth and the movement of water through the soil profile so improving the internal drainage of the soil. Deep drains are necessary to take excess surface water away from the plantation to water courses. They can also assist in lowering the water table of the soil so that more of the soil profile is aerated allowing for root growth.
Fluctuating water tables are particularly damaging to banana root systems. If the water table rises into the root zone for 24 hours or longer many roots are killed.
Water tables should be maintained below 1m. The level of the water table can be assessed by digging observation holes. Deep drains can also act as part of the drainage network for taking excess surface water away.
In overseas countries where bananas are produced for export very elaborate drainage systems are utilised within the plantations. The frequency of drains depends upon a number of factors including the duration and intensity of rainfall and the rate of water movement in the soil.
The design of drainage systems is usually left to drainage engineering specialists.
The effectiveness of a drainage system can be assessed during periods of heavy rainfall. Standing surface water should not be present for more than two hours following the cessation of heavy rain. Water should be moving freely towards the main drains.
Other considerations
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Plantation access can be badly impeded by poor drainage or too many drains. This makes it difficult to spray the crops for pests and diseases as required and to get the fruit to the packing shed.
The latter can lead to additional mechanical damage of fruit due to the uneven road surface.
Waterlogging problems can also be induced by overirrigating. Generally bananas require from 20-50mm of water per week. Applying more than this will cause the soil in the root zone to be saturated for longer than is necessary.
Special attention should be paid with drip irrigation to ensure the correct spacing of drip emitters (approx. 80cm will be good in most situations) to limit the extent of the saturated zone which occurs for extended periods directly below the emitter.
Some marginal soils have naturally low water infiltration rates. Even with alteration to surface and sub-surface drainage the bananas growing on them will still suffer major problems with waterlogging. Soil ameliorants such as fly ash (from sugarmills), organic matter (from various sources) and gypsum may prove beneficial for some of these problem soils.
Licensing
Any 'works' involving the bed or banks of a watercourse require a licence to be obtained BEFORE the works are installed. Drainage outlets into creeks generally require licences.
You should check with an officer from the Department of Natural Resources and Mines to arrange an inspection. Some Local authorities may also require drainage works to be approved under their local bylaws.
Acknowledgement
This DPI&F Note was first published as a Technical feature in the Queensland Fruit and Vegetable News, July 9, 1992.
Further Information
Agrilink Tropical Banana Information Kit provides information on all aspects of growing and marketing tropical bananas in Queensland. It is available from the Agrilink office (phone 1800 677 640) or website (www.dpi.qld.gov.au/agrilink) or the DPI&FShop On-Line (www.dpi.qld.gov.au/shop)
DPI&F Call Centre on 13 25 23 - local call 8 am to 6 pm Monday to Friday (non-Queensland residents phone 07 3404 6999). E-mail: callweb@dpi.qld.gov.au
Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries and Fisheries, Queensland has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.
Last reviewed 21 April 2005
