Abstract

Soil compaction is an important problem in soils planted with oil palm ( Elaeis guineensis Jacq.). Harvesting and cultural practices using heavy machinery result in soil compaction and cause soil degradation. An experiment was carried out to evaluate the effect of different tillage systems that reduce soil compaction, before replanting the oil palm. The experiment was started in May, 1991 in an Aeric Tropaquept and Fluvaquentic Eutropept Complex in the Palma Tica company oil palm plantation in Coto 52, Costa Rica. A completely randomized block design with four replications was used. Treatments were: subsoiling to 60 cm depth, disking to 30 cm depth (2 passes), subsoiling plus one disking pass, and a no-tillage tester. Growth measurements of the petiole cross section area (PxS), rachis length , and leaf area were recorded every 6 months. Results after two years showed that all growth variables were lowest in the no-tillage treatment as compared to the tillage treatments in all dates. To improve initial palm growth, tillage practices should be implemented in some of these alluvial soils of Coto before replanting.

Introduction

Soil tillage practices can have a profound effect on the soil's physical environment, influencing water dynamics and plant growth. A new oil palm crop is planted every 20 to 25 years. Soil compaction from the wheel traffic of heavy farm equipment used in harvesting and cultural practices contributes to the gradual deterioration of the physical condition of soils. Consequently, a decrease in the potential yield occurs.

Subsoiling during land preparation helps to reduce soil density and hardness, increase the volume of macropores which promote aeration, internal drainage, and a more rapid infiltration (Cassel, 1979). Caliman et al . (1990b) found that using subsoiling to loosen compacted areas caused by the farm equipment had a positive effect on oil palm root development in the Ivory Coast. After subsoiling in an oil palm plantation, Caliman (1990a) recommended terminating the use of heavy machinery. This experiment was conducted to evaluate the effect on initial oil palm growth of different tillage systems, used before replanting.

Materials and Methods

The experiment was carried out in an oil palm plantation of the Palma Tica Company in Corredores, Costa Rica. Treatments consisted of subsoiling to 60 cm depth, disking to 30 cm depth (2 passes), subsoiling plus one disking, and a no-tillage tester, evaluated in a completely randomized block design with four replications. Treatments were applied on a Fluvaquentic Eutropept and Aeric Tropaquept Complex before replanting with Deli x Calabar palms in March 1991. Each experimental plot was 1.0 hectare in size and the experiment had a total area of 16 hectares. Determinations of soil resistance to penetration, bulk density, total porosity and texture were made to a depth of 60 cm at intervals of 10 cm depth after 18 months. The overall soil texture of the experimental plots at 0-60 cm depth was silty clay. Oil palm growth measurements from the petiole cross section area (PxS), rachis length, and leaf area were recorded every 6 months for 24 months. A Fisher Protected Least Significant Test was used for means separations.

Results and Discussion

Petiole cross section, rachis length, and leaf area were lowest in the no-tillage treatment ( Table 1 ). All other treatments were (or tended to be) higher than the no-tillage in all dates. Tillage practices should be implemented in some of these alluvial soils of Coto before replanting where compaction problems occur as a result of machinery traffic from harvesting and cultural practices.

No differences between treatments were found for any of the soil variables tested, except for resistance to penetration ( Table 2 ). Subsoiling plus disking showed the lowest resistance to penetration at all depths ( Table 2 ). This was in accordance with the slight trend for better palm growth with this treatment. All other tillage treatments showed very similar results. This was also in accordance with the slight trend for a better palm growth with these treatments.

In general, it appeared that the combined tillage practices of subsoiling plus disking gave the most positive influence on young palm growth. This may have occurred because subsoiling breaks down compaction layers to a depth of 60 cm and improves water infiltration; whereas the disking operation helps to provide a proper bed for early root growth after transplanting. The combination of these two tillage operations may have a synergistic effect on young oil palm growth.

Acknowledgment

The authors wish to acknowledge Sytze de Bruin for his cooperation in the establishment of the experiment and Dr. D.L. Richardson for his advice and review of the manuscript. We appreciate the computer data processing of Guido Monge and the field support of Olman Fernández, Ricardo Jiménez, Arles Álvarez, Félix Gómez, and Félix Vallejos.

References

CALIMAN, J.P.; CONCARET, J; AUBRY, M. 1990a. Subsoiling in oil palm plantations. Description of andapted tool and conditions for its use. Oleagineaux, 45(8-9):391-392.

CALIMAN, J.P.; CONCARET, J.; OLIVIN, J.; DUFOUR, F. 1990b. Maintenance of physical soil fertility under oil palm in humid tropical regions. Oleagineaux, 45(3):109-110.

CASSEL, D.K. 1979. Subsoiling. Crops and Soils. American Society of Agronomy. Madison, WI. p. 7-9.