Water management is a very important aspect of oil palm cultivation. Deficit or surplus of water would create stress to oil palm and adversely affect yield of the crop. To realize full oil palm yield potential, focus should thus be given to ensuring adequate water and moisture in the soil throughout the year in tandem with other agronomic practices.

Water management is aimed at achieving the following goals.

1. Minimizing impact of drought and floods.
2. Optimizing utilization of rainwater and fresh water from streams.
3. Maximizing utilization of effluent and EFB from the oil mill.
4. Minimizing impact of salt-water incursion and acidity level.

Water management is basically divided into three main categories according to the nature of the problem. These are management of fresh water, management of tidal water and moisture conservation on undulating and hilly areas.

Management of fresh water in flat and coastal soils is aimed at maintaining water of good quality for oil palm growth, i.e., water with pH more than 4.5 and salinity level lower than 1000µs/cm. This is obtained by minimizing the effect of floods, water-logging and in certain instances to reduce hyper-acidity conditions in acid sulphate soils.

In flat areas with a high water table, drainage is very important to remove excess water in order for oil palm roots to proliferate the entire soil profile rather than being restricted to the upper layer as otherwise roots may be unable to supply the needs of the palms during sustained dry weather. In non-acid sulphate soils, the water table is retained between 60 cm – 90 cm below ground surface at all times as long as possible, whereas in acid sulphate soil the water table should be maintained above the pyretic layer. In order to achieve the desired water-level, the minimum drain intensity required is at least one drain to every eight rows of palm and in the intensity could be further increased to one in very four or one in every two rows of palms depending on the need.

Another practice to conserve water and avoid/reduce flash floods in flat coastal areas is through creation of water bodies. Water bodies can be either in the form of silt pits or close-ended trenches. The trenches would store water during wet seasons and is connected to collection drains by polypipes for discharging excess water. The polypipes are installed 45 cm below ground level in acid sulphate soils and 60 cm in non-acid sulphate soils.

Fresh water retention in drains will reduce saline water incursion due to the driving force of hydraulic gradient from the water. Installing drain blocks or sluice gates at strategic points would achieve efficient water retention. This is particularly important on acid sulphate soils where periodic flushing to reduce the salinity and acid concentration in the drain water is essential. During the wet season, all drain blocks and sluice gates are opened at intervals to allow flushing of poor quality water. It is thus important for drain blocks and sluice gates to be set in place well before the dry season to retain the fresh water to a required level. Proper maintenance of the block and gates thus needs no further emphasis.

In areas where bunds are constructed to keep out tidal water, bund side drains are also constructed to act as a catchment and thus buffer to avoid saline water incursion. Such drains are constructed about 4m away from the bund to catch saline water if bund leakages occur. Such buffer drains are directly connected to the bund outlet without any link to field drains.

Silt-pits are constructed to trap water sediments from surface runoff. These pits are dug near the roadside or mechanical terrace path and placed at 20 m to 30 m intervals depending on the degree of slopes and seriousness of the erosion. The depth of the pits should not be more than 1m to enable the conserved water to be fully utilized by the palms.

Foothill drains are a form of trench constructed at the fringes of hills where the slope or gradient changes abruptly. Water from surface runoff will be trapped in the drains during the rainy days. This drain acts as a breaker for surface runoff as well as conserving moisture.

Leguminous cover crops (LCC) assist soil conservation and moisture retention by:

1. Interception of rainfall by absorbing the energy of the raindrops and thus reducing runoff.
2. Retarding erosion by decreasing surface velocity.
3. Physically restraining soil movement.
4. Improvement of soil aggregation and porosity.
5. Increasing biological activity in the soil.

Normally, LCC is established during land preparation for replanting. The common LCC established in estates include Mucunabracteata,Pueraria phaseoloides and Calopogonium cearuleum. Mucuna bracteata was introduced and planted in estates in view of its desirable characteristics of very vigorous and dense cover, deep rooting system and superior total biomass production.

In steep terraced areas, deep rooting Vetiver grass is used for soil and moisture retention.