Abstract

The effect of four different cover crop species ( Flemingia congesta (Roxb), Arachis pintoi .L, Pueraria phaseoloides (Roxb) Benth and Desmodium ovalifolium Wall) on early oil palm growth was evaluated. Oil palm growth as affected by the leguminous cover crops ranked as follows from best to poorest after 450 days: F. congesta , P. phaseoloides , Tester, D. ovalifolium and A. pintoi . The magnitude of the differences on oil palm growth under these intercropping system will be the subject of future research.

Introduction

Oil palm ( Elaeis guineensis Jacq.) is an important crop in Costa Rica. Traditionally, kudzu ( Pueraria phaseoloides (Roxb) Benth L.) has been the most commonly used cover crop in oil palm, in Costa Rica. Leguminous cover crops are planted to protect the soil surface from erosion, help control weeds and obtain organic N from biological fixation. Agamuthu and Broughton (1985) found that the total benefits of leguminous covers intercropped with oil palm amount to 239 kg N ha -1 year -1 .

Turner and Gillbanks (1974) indicated that some desirable cover crop characteristics are:

1. Vigorous growth.
2. Easy to maintain.
3. Strong root system.
4. Low competition with oil palm.
5. Low lying.
6. Beneficial to soil nutrient content.

Bourgoing (1990) pointed out that the longevity of a cover crop and its positive effect on coconut yield will depend on proper soil preparation and the right choice of the cover crop species. Oil palm growth and yield vary under different types of cover crops (Turner and Gillbanks, 1974). The purpose of this study was to evaluate the effect of four different cover crops on early oil palm growth on the southern Pacific coast of Costa Rica.

Material and Methods

A field experiment was conducted using one-year-old oil palm (Deli x Calabar) nursery palms field planted in June 1990. A completely randomized design with four replications and five treatments was used.

Treatments were:

1. Tester (bare soil)
2. Pueraria phaseoloides (Roxb.) Benth
3. Flemingia congesta Roxb
4. Desmodium ovalifolium Wall
5. Arachis pintoi L.

Each leguminous cover crop was planted between the oil palm rows which were set apart 9.0 m on an equilateral triangular pattern. Treatments were randomly allocated in 20 plots. Each plot covered an area of 0.14 ha and contained 20 palms.

Growth measurements (Corley and Breure, 1981) were taken at 180, 270, 360, and 450 days after cover crop planting (DAP). Due to its high vegetative growth, F. congesta was pruned to 100 cm height and D. ovalifolium to 40 cm one year after cover crop planting. The vegetative material originated from such pruning was applied to the palm weeded circles.

Results and Discussions

Growth measurements up to 450 DAP are shown in Table 1 . Cover crops had a major influence on the rachis length and petiole cross section (PXS). The F. congesta treatment rachis length was higher as compared to all other treatments, but similar to P. phaseoloides from 180 to 360 DAP. No statistical differences were found 450 DAP, but a trend similar to previous measurements was observed.

The F. congesta treatment showed the highest PxS values as compared to the other treatments 360 and 450 DAP. These values were statistically similar to P. phaseoloides and the tester (bare soil) and greater than the D. ovalifolium and A. pintoi treatments. Similar behavior was observed for total number of leaves and leaf length 450 DAP. In general, the opposite effect was found for number of leaflets per rachis meter from 180 to 360 DAP. All this indicated that the oil palm suffered from etiolation due to the F. congesta competition.

Oil palm growth measurements showed the following results for most variables: F. congesta P. phaseoloides Tester D. ovalifolium and A. pintoi . There was a slight trend showing better oil palm growth in D. ovalifolium treatment as compared to A. pintoi .

These results suggested that F. congesta as a cover crop leads to improved palm growth in spite of a deleterious effect of slight etiolation due to competition for light. The magnitude of the potential beneficial effects are not known, but will be the subject of future research. Similarly, the mechanisms for the apparent negative effects of D. ovalifolium and A. pintoi on oil palm growth need to be identified.

References

Agamuthu, P. and Broughton, W. J. 1985. Nutrient cycling within the developing oil palm-legume ecosystem. Agriculture Ecosystems and Environment 13:111-123.

Bourgoing, R. 1990. Elección de la planta de cobertura y de un método para establecerla, en el cultivo de cocoteros híbridos, en un medio campesino. Oléagineux 45(1):29-30.

Corley, R. H. V. and Breure, C. J. 1981. Measurements in oil palm experiments (Internal report). Unilever Plantations Group, London. 35p.

Turner, P. D. and Gillbanks, R. A. 1974. Oil palm cultivation and management. The Incorporated Society of Planters, Kuala Lumpur, Malaysia, 671 p.