Abstract

Field experiments were conducted in 1989 and 1990 to determine the effect of empty fruit bunches (EFB), and palm shell (PS) mulches and fertilizer (21-3-16-5-1) (F) on soil nutrient content, oil palm ( Elaeis guineensis Jacq.) growth, midday relative water content (RWC) and abaxial stomatal conductance (C ab ). A honeycomb experimental design with seven treatments, including EFB, PS and F applications and a tester, were used. The EFB increased soil P, K, and pH, improved soil moisture, and produced higher midday RWC and C ab values. Single and double layers of EFB plus F and the PS mulch increased oil palm growth during the rainy season. The EFB did not carry its beneficial water conservation effects to the second dry season, whereas PS maintained its effects through 1991.

Introduction

T he use of mulch has extensively proven to preserve soil moisture, reducing the soil temperature and increasing nutrient uptake and crop productivity (Simpson and Gumbs, 1986; Gallaher, 1977; Hartley, 1981). With the increasing cost of inorganic fertilizers, the use of oil palm by-products as mulch and sources of nutrients is an important alternative. Arokiasani (1969) evaluated methods of using EFB as fertilizer in oil palm. The application of EFB has been practiced as a mulch in oil palm field nurseries (Gunn, et al ., 1961) and has shown beneficial effects on oil palm growth and yield increases in mature palms under different soils and rainfall regimes in Malaysia (Loong et al ., 1987; Chan et al ., 1980; Singh et al ., 1976; and Khoo and Chew, 1969). Chiew and Weng (1989) reported increases in fresh fruit bunch (FFB) yield when EFB was applied at the time of field planting. These authors also indicated that EFB must be applied at planting to fully exploit its agronomic benefits as compared to EFB applied at the onset of maturity.

Palm shell is another by-product that can be used for mulch purposes. Approximately five tons of shell are obtained from sixty-six tons of FFB (Chan et al ., 1980). Palm shell is often used as a mulch in nursery polybags. Its beneficial effect is mainly due to better weed control and avoiding soil surface crusting.

Mulch and fertilizer applications may help improve the oil palm water status and its stomatal conductance during periods of water shortage. Villalobos et al . (1990) showed that the use of K fertilizer improved water status of mature oil palms under conditions of water stress. The purpose of this study was to evaluate the effect of oil palm empty fruit bunches, palm shell, and fertilizer on the soil nutrient content, oil palm growth and water conservation in juvenile oil palm plants.

Materials and Methods

The experiment was started in Nicoya Farm, Quepos, Costa Rica in December 1989 on an Aquic Eutropept. A honeycomb statistical design with 28 replications was used. Seven treatments on the weeding circle were tested:

1. Tester, bare soil
2. Palm shell (PS)
3. Palm shell plus fertilizer (PS+F)
4. Fertilizer alone (F)
5. Empty fruit bunches (EFB)
6. EFB plus fertilizer (EFB+F)
7. Double EFB layer plus fertilizer (DEFB+F)

The fertilizer formula used was 21-3-16-5-1, applied at 85, 117, and 123 kg ha -1 . Applications took place 0, 150, and 240 days after the experiment was started on seven-month-old field palms. The PS and EFB were applied on the weeded circle, leaving a clear radius of 0.5 m of the inner circle for fertilizer application.

Empty fruit bunches were distributed in one layer around the plant for treatment 5 and 6 and two layers for the DEFB treatment. Palm shell was applied in a 5 cm thick layer. Soil sampling at 0-5, 5-10, 10-15, and 15-30 cm depth was made 0 and 120 days after treatment application (DAT). Palm growth measurements were taken from leaf number 1 at 0, 60, 120, 240, and 360 DAT. Mulch was applied at the beginning of the dry season in December 1989. A mean statistical analysis was carried out using a T test (P<0.05).

Abaxial stomatal conductance (C ab ) measurements were taken at midday from the midsection of the leaflets on the central part of leaf 9, using a diffusion phorometer LI-700. Ten to fifteen readings were obtained from each plant. Five leaflets were used to determine the relative water content (RWC).

To determine the RWC the central portions of the leaflets were placed in sealed plastic bags (Zip-lock R ) and kept in an ice chest. Later on the same day, twelve discs (25 mm in diameter, including the central vein) were obtained from each leaf sample. Fresh weight (FW) of the disc sample was recorded. The discs were then placed in a pan between a double layer of cheese cloth saturated with water. After two hours, the discs were superficially dried with paper towel and the sample turgid weight (TW) was recorded. The dry weight (DW) was obtained by drying the tissue for two days at 65°C in a forced convection oven. The RWC was calculated using the formula:

RWC = [(FW-DW) / (TW-DW)] x 100

Soil moisture was determined using the gravimetric procedure by drying soil samples for two days at 65°C in a convection oven.

Results and Discussion

Soil nutrient content and pH

pH

Higher pH values (0.11-0.7 units) were observed at 0-5 cm soil depth when EFB was applied as compared to the other treatments. A similar trend was observed at 5-10 and 10-15 cm depth ( Fig.1 ). No differences were found at 15-30 cm depth.

Phosphorus

Soil P content increased (0.35-5.5 mg kg -1 ) at 0-5 cm depth when EFB was applied, as compared to the other treatments where little or no increase was observed ( Fig. 2 ). Increases in soil P content were obtained at 5-10 and 10-15 cm depth for the treatments including EFB and/or fertilizer. No differences were found at 15-30 cm depth.

Potassium

A substantial increase in K content was observed at all soil depths when EFB was applied ( Fig. 3 ). These results were similar to those of Arokiasani (1969) and Singh et al ., (1976); who reported high K content in EFB. Uribe and Bernal (1973) determined that the EFB ash contained 30 to 35 per cent of K 2 O. High amounts of K could be available for oil palm uptake 120 days after the application of EFB.

Calcium

Soil Ca content decreased in all treatments. However, a greater dicrease was observed for the EFB treatments at 0-5 cm depth, where K content was highest. This indicated a possible inverse relationship between soil Ca and K supplied through EFB application. However, the reason why Ca content decreased is unknown.

Oil palm growth

The highest petiole cross section (PxS) values were found for DEFB+F, followed by EFB+F, PS, and EFB treatments, 120 DAT (Table 1). Similar results were observed for rachis length, Petiole corss section, and leaf area 120 DAT.

Petiole cross section tended to be greater when mulch was applied 240 DAT. PXS and leaf emission rate were lower in the tester as compared to all the other treatments. Rachis length was shorter and leaf area lower for treatments EFB+F and DEFB+F at the same date ( Table 1 ).

The application of DEFB+F showed highest PXS and rachis length values as compared to other treatments 360 DAT (Table 1). In general, DEFB+F showed the highest values for oil palm growth variables. It was closely followed by EFB+F and PS application treatments. Basically, all mulch and fertilizer treatments were better than the tester.

The application of EFB showed a slightly higher overall PxS value as compared to PS and was greater than the tester. However, PS application showed a greater overall leaf area and leaf emission rate as compared to the application of EFB and the tester, respectively (Table 2). Simultaneously, higher oil palm growth was observed when fertilizer was applied, regardless of the mulching treatments, as compared to treatments where fertilizer was not applied (Table 2). Visual observations indicated that PS was still present in the weeding circle 360 DAT, whereas most of the EFB were already decomposed after the first rainy season.

Water relations

The EFB application improved soil moisture during the first dry spell similarly to what has been observed with the use of other mulch types (Daisley et al ., 1988; Simpson and Gumbs, 1986) (Table 3). However, EFB material decomposed during the following rainy season and did not carry its beneficial effect on soil moisture content to the next dry season. On the other hand, the application of palm shell slightly improved soil moisture in 1990 and maintained its effectiveness through 1991 (Table 3).

The overall values of RWC in the treated palms during the period in which soil water became limiting were greater than those in the plants that did not receive EFB (Fig. 4). The application of fertilizer improved the plant RWC, but to a lesser extent than the EFB mulch application (Fig. 5). However, the C ab values were not affected by the fertilizer treatment, in agreement with what was found in adult palms by Villalobos et al ., (1990). The C ab was improved by the mulching treatments except at the time of greater water shortage (Fig. 4).

Conclusions

Oil palm EFB supplied high amounts of K to the soil. Soil P and pH increased with the application of EFB. The application of a double layer of EFB+F increased oil palm growth 360 DAT. A similar result was observed when EFB+F and PS mulch were applied.

Overall plant growth was greater when PS was applied, as compared to EFB and no applications. The fertilizer application (overall) showed a positive effect on oil palm growth.

The use of EFB and PS as weeding circle mulch improved soil moisture. Relative water content values in oil palm should be interpreted with caution, since a stomatal control of the plant's water status under conditions of water stress has been recently demonstrated (Villalobos et al ., 1991). This implies that the stomatal closure may induce a high RWC value. However, since the greater values of RWC corresponded to greater C ab values (palms with EFB mulch), it can be concluded that the increase in turgor was a response to the application of EFB mulch. Fertilizer applications induced higher RWC but showed no differences in C ab .

The application of EFB mulch is recommended to alleviate the problem of water stress and to increase soil nutrient content in areas exposed to water deficit, at least during the first dry season after field transplanting, when the palms are more susceptible to water deficit.

Acknowledgments

The authors wish to thank Dr. D. L. Richardson for his advice in the design of this experiment and the manuscript review. We also thank Mr. Herbert León and Mr. Luis García of Palma Tica Co., Quepos Division for their cooperation throughout the experiment and Mr. Guido Monge for the data processing.

References

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