Factors affecting the development of the rooting system in young oil palms (Elaeis guineensis JACQ.)

Agriculture, Ecosystems and Environment, 17 (1986) 173--179

173

Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

FACTORS AFFECTING THE DEVELOPMENT OF THE ROOTING SYSTEM IN YOUNG OIL PALMS (ELAEIS GUINEENSIS JACQ.)

P. AGAMUTHU and W.J. BROUGHTON'

Department of Genetics and Cellular Biology, University of Malaya, Kuala Lumpur (Malaysia) (Accepted for publication 11 April 1986)

ABSTRACT Agamuthu, P. and Broughton, W.J., 1986. Factors affecting the development of the rooting system in young oil palms (Elaeis guineensis Jacq.). Agric. Ecosystems Environ., 17: 173--179.

Oil palms established together with leguminous cover crops yield more fresh-fruit bunches than can be attained by any other means of planting. One explanation for this observation is that legumes stimulate rooting in the developing palms. Accordingly, two unique characteristicsof legumes (their high nitrogen content and their enhanced ability to physically protect the soil) were examined as factors likely to affect growth of palm roots. Seedlings of Elaeis guineensis Jacq. cultivar D × P were grown either in soil held in polyethylene bags or in flowing nutrient solution. The effects of various types and levels of nitrogenous fertillsers were studied in both bags and hydroponics, the effects of different types and levels of phosphate fertillsers only in soil, and the effect of temperature only in hydroponics. Factors most likely to be influenced by legumes in the field, i.e. increased soil nitrogen levels and reduced soil surface temperatures, strongly affected the development of the oil palm rooting system. It seems possible, therefore, that amongst others, these factors contribute to an optimal environment for the development of oil palm feeder roots.

INTRODUCTION

Oil palms (Elaeis guineensis Jacq.) are normally planted into fields stripped of all other vegetation. Leguminous cover crops (e.g. Centrosema pubsecens and Pueraria phaseoloides) are planted simultaneously with the off palms to provide other, less tangible benefits. These include: (a) contributing nitrogen to the ecosystem through nitrogen fixation; (b) absorbing nitrogen and other minerals from the soil during the initial stages of plantation establishment; (c) reducing leaching losses; and (d) releasing accumulated

~Present address: Laboratoire de biologie mol~culaire des plantes sup~rieurs, Universit~ de Gen~ve, 1, ch. de l'Imperatrice, CH-1292 Chambesy/Gen~ve, Switzerland.

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© 1986 Elsevier Science Publishers B.V.

174 nutrients to the developing oil palm rooting system as the leguminous cover crop slowly dies back (Agamuthu and Broughton, 1985). As a result, palms planted concomitantly with legumes produce higher fruit yields throughout their commercial life (Broughton, 1976). One possible way of explaining this post-legume effect is that oil palms raised together with legumes have better developed rooting systems (Broughton, 1976). As legume cover crops have no marked effect on soil structure in oil palm plantations (Agamuthu and Broughton, 1985), changes within the soil environment seem more likely to influence rooting of the oil palms. Factors that may be different in the vicinity of legume roots as opposed to naturally regenerated covers or bare soil include higher soil nitrogen levels and reduced soil temperatures under the denser legume vegetation. Accordingly, the effect of rate of nitrogen fertiliser application (as well as the type of nitrogenous fertiliser) and temperature were measured on the roots of young oil palm seedlings. Similar measurements were also made with respect to phosphate fertilisers as legumes have no direct effect on phosphorus. MATERIALS AND METHODS Ten-day-old oil palm seedlings (Elaeis guineensis cv. D × P) were planted in large polyethylene bags (flat dimensions 46 X 38 cm) and watered daily (Agamuthu, 1979). Nitrogenous fertilisers [(NH4)2SO4, NH~NO3, KNO3 and urea] or phosphate fertilisers [Christmas Island rock phosphate (CIRP), triple superphosphate and KH2PO4] were applied to the seedlings at a level which approximated that applied to palms of comparable age under normal estate practice ( " N " or " P " level) as follows: one m o n t h after planting 0.012 moles N or P (as (NH4)2SO4, NH4NO3 etc. or as CIRP, triple superphosphate etc.) per palm; 3 months after planting -- 0.18 moles N or P per palm. Additionally, treatments representing 1/2, 2 and 4 times " N " or " P " levels per palm were also applied. Control palms were not fertilised and all treatments were replicated 6 times. After 7 months growth, the palms were harvested, divided into shoots and roots and the length, weight, area and (for roots) type determined. The effects of nitrate concentration and temperature on r o o t growth of the oil palms were also studied. Ten-day-old seedlings (cv D X P) were planted into 100 1 of a flowing nutrient solution (based on that of Broughton and Dilworth, 1971) contained in a rectangular chamber measuring 75 X 45 X 30 cm deep (see Agamuthu, 1979 for full details). Either different temperatures were employed (27.5, 30, 35 and 40°C) with the nitrate concentration held constant (1 mM KNO3) or the temperature was maintained at 30°C and the nitrate concentration varied (0, 1.25, 2.5 and 5 mM). Light, aeration of the roots and pH of the nutrient solution (6.8) were held constant throughout a nine-week growth period. Twenty seedlings were used per treatment, and they were analysed as described above.

175

RE$ULTS As expected, nitrogenous fertilisers stimulated shoot growth of the oil palms (Figs. 1 and 2). Ammonium sulphate was most efficacious in the experiments conducted in the soil while potassium nitrate was best in hydroponic culture. In both cases, the optimum level of nitrogen application was about twice the normal level of nitrogenous fertiliser application under estate management and about 2.5 mM nitrate in hydroponic experiments. Since nitrogenous fertilisers often inhibit root growth, it was surprising to find that comparable levels of nitrogen application were optimal for both root and shoot growth. On the other hand, ammonium nitrate and urea had the greatest stimulatory effect on root growth while increasing concen90-

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trations of ammonium sulphate reduced growth of roots (Fig. 1). Additionally, some nitrogenous fertilisers modified the pattern of root growth, e.g. ammonium nitrate and urea stimulated production of the primary roots. Only CIRP consistently stimulated shoot growth of the oil palms (Fig. 3). Even then the level of CIRP application had little effect suggesting that phosphate supply is not limiting to the growth of palms. There is some evidence that single and triple superphosphate also have an effect on modifying the pattern of root growth, but the intrinsic variance associated with phosphate application was so large that these effects were not statistically significant. Temperature had by far the greatest influence on the oil palm rooting system (Fig. 4). Optimum root temperatures for both shoot and root growth

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were between 30 and 35°C. Over the range 27 -- 35°C, shoot growth increased by over 50%, r o o t growth more than doubled, the number o f secondary roots increased by a b o u t 25% and the surface area o f the primary roots increased four-fold. As these experiments were of much shorter duration than those in soft, it is difficult to predict the long-term effects o f temperature on rooting of the oil palm, b u t it appears that temperature has a modifying effect on the pattern of r o o t growth. DISCUSSION

The levels of nitrogenous fertiliser application and the temperature of the rooting medium influence both shoot and r o o t growth of oil palm seedlings as well as the pattern o f r o o t growth. As leguminous covers must affect the distribution of oil palm feeder roots, this is an important finding.

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Fig. 4. R o o t number, weight, surface area and shoot weight of y o u n g oil palms grown at various temperatures in flowing nutrient solution 9 weeks after planting (i m M K N O 3 ).

TABLE

I

Daily m e a n m a x i m u m

Atmosphere (30 cm above ground)

32.4±0.1

soil temperature at different depths under various covers

Natural

Bare

Legume'

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10 c m below surface

Soil surface

10 c m below surface

Soil surface

10 c m below surface

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27.0+- 0.1

* M e a s u r e d u n d e r l e g u m e s e s t a b l i s h e d using " o x y f l u o r f e n " h a - ' ) (See A g a m u t h u et al., 1 9 8 0 , 1 9 8 1 ) .

(0.25 kg active i n g r e d i e n t

179

Legumes are rich in nitrogen and their rapid and dense shoot growth quickly protects the soil surface from solar radiation. Thus, the higher soil nitrogen levels in oil palm plantations raised together with legumes is probably the basis for the increases in tertiary and quarternary oil palm feeder roots observed by Tailliez {1971). Undoubtedly temperature modifies this effect, and the present data suggest that slightly higher temperatures 10 cm below the soil surface may be beneficial to rooting of the oil palms (Table I, Fig. 4). However, phosphate fertiliser application has only a small and unpredictable effect on rooting of oil palms. ACKNOWLEDGEMENTS

We wish to thank Han Siew King, Roll Jesinger, S. Jodhy, Khoo Khee Ming and Ramadevi for their help with many aspects of this work. Financial assistance was provided by Sime Darby Plantations Sdn. Bhd., Rohm and Haas Asia Inc., and the University of Malaya.

REFERENCES Agamuthu, P., 1979. Factors affecting the development of oil palm (Elaeis guineensis) seedlings. M.Sc. Thesis, University of Malaya, Kuala Lumpur, 202 pp. Agamuthu, P. and Broughton, W.J., 1985. Nutrient cycling within the developing oil palm-legume ecosystem. Agric. Ecosystems Environ., 13: 111--123. Agarnuthu, P., Chan, Y.K., Jesinger, R., Khoo, K.M. and Broughton, W.J., 1980. Effect of diphenyl ether pre-emergence herbicides on legume cover establishment under oil palm (EIaeis guineensis Jacq.). Agro-Ecosystems, 6: 193--208. Agamuthu, P., Chart, Y.K., Jesinger, R., Khoo, K.M. and Broughton, W.J., 1981. Effect of differently managed legumes on the early development of oil palms (Elaeis guineensis Jacq.). Agro-Ecosystems, 6: 315--323. Broughton, W.J., 1976. Effect of various covers on the performance of Elaeis guineensis (Jacq.) on different soils. In: D.A. Earp and W. Newall (Editors), International Oil Palm Developments. Inc. Soc. of Planters, Kuala Lumpur, pp. 501--525. Broughton, W.J. and Dilworth, M.J., 1971. Control of leghaemoglobin synthesis in snake beans. Biochem. J., 125: 1075--1080. Tailliez, B., 1971. The oil palm root system on the San Alberto plantations, Columbia. Oleagineux, 26(7): 435--447.