Cocoa: Nursery Practices

Nursery practices should be geared to produce really well grown and vigorous seedlings free from major pests and diseases. There is really no substitutes for starting off with really well nursed planting materials. Cutting corners in the nursery such as overcrowding the seedlings to save space and planting out small undersized seedlings usually only ends up more costly in the fields. Small seedlings are more difficult to look after in the field. They cannot withstand adverse growing conditions as well as the well grown seedlings and also come into bearing much later. Longer immature period means higher cost and poorer cash flows.

Major nursery operations and the recommended practices are briefly outlined below:-

Ordering cocoa seeds

Seeds must be ordered well in advance from several reputable sources particularly where large plantings are involved.

Essentially, one must ensure that adequate quantities of the desired crosses are available for planting at the correct time.

The number of seeds that must be ordered depend on the planting density, expected losses in the nursery from non-germination, runts, poor growth, pests/disease damage and losses in the field after planting.

For example if	:-	the number of planting points	=	A,
		the number of non-germination	=	x %
		the number of nursery losses	=	y %
		the number of field losses	=	z %
The number of seeds that must be ordered

Under normal circumstances, about 40% extra seeds must be ordered to allow for non germination, nursery culling and supplying.

Nursery site/space/shade

Nursery site should be well drained, close to cheap sources of adequate and reliable water supply and good top soil (potting media) and to the area to be planted; well protected from animals and theft and within easy reach for supervision.

The allotted area should allow for spacing of polybags and also for drainage, paths and transport access. For good growth and to avoid etiolation, the seedlings should be spaced depending on the nursery period (Table 2).

Table 2 : Nursery spacing and polybag size

The ideal shade for nursery is one that can be adjusted to transmit the required amount of light for optimal growth. At sowing, the shade should be about 80%. The shade regime should be gradually reduced to about 50% at field planting, usually at 5-7 months.

Potting media/polybag filling

Only good top soil, preferably from the top 75 mm of soil should be used for filling the bags. The soil medium should allow good drainage and root growth and should not disintegrate when the bag is removed at transplanting. Recommended textures are sandy clay loam to clay loam.

If heavy clay has to be used, coarse river sand in the ratio of 1:4 should be added to improve drainage and aeration. A homogeneous mix may be achieved with the aid of a rotavator/cement mixer.

Basal fertilizers if recommended should be mixed thoroughly with the potting medium. This can be satisfactorily done in convenient heaps with the aid of a changkul/spade. However, it is important that the soil to fertilizer ratio should be correctly calibrated.

pH of soil, if not already known, should be checked and corrected to 5.5 to 6.5 unit.

Bag filling is more efficient if a hopper and funnel is used. Bag bottoms should be folded in so that bags sit better.

The soil should be allowed to settle in the bags before planting of seeds. However, bags should not be filled more than 2 to 3 weeks in advance of planting and should not be filled when the soil is wet.

The bags should be spaced out at the suggested spacings prior to planting. Spacing at a later stage is undesirable as the growth of cocoa seedlings are adversely affected if shifted. At the same time, double handling of large numbers of bags is labour intensive and expensive. Delay in spacing out is also not uncommon, resulting in etiolation of the seedlings. This is extremely undesirable. Etiolated seedlings are difficult to establish and grow poorly in the field. In extreme cases, the seedlings have to be supported to remain erect.

Planting seed

On receipt, the bags holding the seeds should be opened and spread out immediately by a responsible person for airing and checking.

This is important as cocoa seeds though properly processed and cleaned can still generate a fair amount of heat in transit. Excessive heat build up can kill the seeds.

Seeds may be planted as soon as they are received. Alternatively, they can be pregerminated prior to planting. The latter method is preferred if non-germination is expected to be high.

Deep planting should be avoided. As cocoa seed germination is epigeal, the cotyledons are pushed above the ground in the process of germination. Hence one should not attempt to cover up the seeds with soil as the cotyledons emerge from the soil during germination.

Watering

Watering is perhaps the most important single requirement in a polybag nursery. Adequate water should be supplied for good growth. However, over-watering especially in the first 2-3 months should be avoided as the young cocoa seedling is extremely sensitive to water-logging.

Watering once a day with ½ to ¾ litre of water per seedling is generally enough. However, the correct rates may be determined by checking the moisture content of the potting media. It should be moist at the top and bottom of the bag. Increase the rate if the soil is dry and withdraw/decrease the rate if it is too wet. During unusually long spells of dry weather, it may be necessary to water the seedlings twice a day.

An overhead sprinkler irrigation system if feasible is advantageous. Sprinkler output will determine the length of sprinkling. An equivalent of 6 mm rain/day is generally adequate. However, the rates should be checked by examining the moisture content of the potting media. Distribution of the sprinkler system should be regularly checked to ensure even watering.

Pests and Diseases

The most likely nursery pests are the leaf eaters, particularly cockchafers. Cockchafer damage is normally higher along the road sides and in the more open areas where there are less vegetative barriers. As even moderate loss of leaves can set back the growth of seedlings severely, appropriate control measures such as regular insecticide spraying or erecting vegetative barriers of fronds along the perimeter should be carried out.

Common nursery diseases are Phytophthora blight, Collectotrichum leaf disease and Vascular Streak Dieback. All the 3 diseases can cause considerable losses if not controlled in time. Disease monitoring and control is therefore important in the nursery. A combination of cultural practices (reducing inoculum/humidity and improving drainage) and fungicide spraying usually provide adequate control.

Manuring/records

Nutrient requirements by cocoa seedlings in the nursery stage are not high. Small quantities of balanced nutrient applications are generally adequate to ensure good growth. However, it is important to use good potting media mixed with rock phosphate. The pH of media should also be adjusted to 5.5 to 6.5 with calcium limestone if they are too acidic.

Reference 
Ooi L.H. and Chew P.S. 1985. Some important agronomic and agricultural practices in cocoa estates. TDMB Plantation Management Seminar, Kuala Trengganu

Note: The full list of references quoted in this article is available from the above paper.