Changes in Soil Properties: References

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Chew P.S. and Pushparajah E. (1996). Nitrogen management and fertilization of tropical plantation tree crops. In: Bacon, P.E. (ed). Nitrogen Fertilization in the Environment. Marcel Drekker Inc., New York : 225 – 294.

Goh, K.J. and Chew P.S. (1995a). Managing soils for plantation tree crops I: General soil management. In: Paramanathan, S (ed). Course on Soil Survey and Managing Tropical Soils. MSSS and PASS, Kuala Lumpur : 228-245.

Goh K.J. and Chew P.S. (1995b). Direct application of phosphate rocks to plantation tree crops in Malaysia . In: Dahanayake, K., Van Kauwenbergh, S.J. and Hellums, D.T. (eds). Proc. Int. Workshop on Direct Application of Phosphate Rock and Appropriate Technology Fertilisers in Asia : What Hinders Acceptance and Growth. International Fertiliser Development Center , U.S.A. and Institute of Fundamental Studies, Sri Lanka , Kandy , Sri Lanka : 59 – 76.

Goh K.J . and Kee K.K. (2000) The oil palm sector in Southeast Asia : Changing requirements for fertilizers, particularly P and K. In: Workshop on Improving Soil Fertility Management in Southeast Asia . 21-23 November 2000, Bogor , Indonesia . IBSRAM, Thailand : Preprint.

Hartemink A.E. (2003). Perennial Crop Plantation . In Soil fertility decline in the tropics with case studies on plantations. Publs. CABI Publishing 2003.

Hashim M, Teoh C.H., Kamaruzaman A. and Ali M. (1993). Zero burning – an environmentally friendly replanting technique. In Proc. of the 1993 Porim International Palm Oil Congress. PORIM: Kuala Lumpur . pp 185-195.

Haynes R.J. (1990). Active ion uptake and maintenance of cation-anion balance: A critical examination of their role in regulating rhizosphere pH. In Plant and Soil. Publs. Kluver Academic Publishers, Netherlands . Vol. 126, pp 247 – 261.

Henson I.E. (1999). Comparative ecophysiology of oil palm and tropical rain forest. In: Oil Palm and the Environment: A Malaysian Perspective. Gurmit, S., Lim, K.H., Teo, L. and Lee, K. (eds). Malaysian Oil Palm Growers’ Council, Kuala Lumpur : 9-39.

Kee K.K., Goh K.J and Chew P.S. (1995). Effects of NK fertilizer on soil pH and exchangeable K status on acid soils in an oil palm plantation in Malaysia . In: Plant Soil Interactions at low pH. R. A. Date et al . (eds). Publs. Kluwer Academic Publishers 1995, Netherlands . pp 809-915.

Khalid K, Zin Z.Z. and Anderson J.M. (2000). Soil nutrient dynamics and palm growth performance in relation to residue management practices following replanting of oil palm plantations. In: Journal of Oil Palm Research Vol. 12 No. 1, June 2000. pp 25-45.

Law W.M. and Tan M.M. (1973). Chemical properties of some Peninsular Malaysian soil series. In: Proc. Conf. Chemistry and Fertility of Tropical Soils, MSSS, Kuala Lumpur : 180-191.

Ling A.H., Tan K.Y., Tan P.Y. and Syed Sofi (1979). Preliminary observation on some possible post clearing changes in soil properties. Seminar on Fertilizer and Management of deforested land. K.K Sabah (1979).

McCulloch G.C. (1982). A method of clearing oil palms for replanting. In The Oil Palm in Agriculture in the eighties. E. Pushparajah and Chew P. S. (eds). The Incorporated Society of Planters: Kuala Lumpur . pp 653-665.

Moris N. and Mohinder S.S. (1980). Manual of laboratory methods of chemical soil analysis. RRIM, Kuala Lumpur : 121 pp.

Ng H. C. P., Chew P.S., Goh K.J., Kee K.K. (1999). Nutrients requirements and sustainability in mature oil palms – an assessment. The Planter 75:331-345.

Ng S. K. (1969). Soils of south Johore and manuring oil palms. The Planter 45: 348-358.

Poon Y.C. (1983). The management of acid sulphate soils – HMPB experience. In: Seminar on Acid Sulphate Soils. MSSS, Kuala Lumpur : Preprint.

Sly J.M.A. and Tinker P.B. (1962). An assessment of burning in the establishment of oil palm plantations in southern Nigeria . Trop. Agri., Trinidad , 39. pp. 271-280.

Steel R.G.D. and Torrie J.H. (1981). Principles and Procedures of Statistics: A Biometrical Approach, 2 nd edition. Tokyo : McGraw-Hill, Inc., pp 633.

Tinker P. B. (1993). The Demand for Sustainability. In: International Conference in Cambridge , December 1993.

Zaharah A.R. (1979). Phosphate adsorption by some Malaysian soils. Pertanika 2(2):78-83.

Changes in Soil Properties: Appendix

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Appendix 1a: Descriptive statistics for the initial values (x₁) of soil chemical property at two sites

Appendix 1b: Descriptive statistics for the initial values (x₁) of soil chemical property at two depths

Appendix 1c: Descriptive statistics for the rates of change (%) of soil chemical property at two sites

Appendix 1d: Descriptive statistics for the rates of change (%) of soil chemical property at two depths

Changes in Soil Properties: Conclusions

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This study indicates that soil pH, organic C and total N tended to decrease with time in the oil palm agro-ecosystem. However, the decline in soil pH was slight whereas those related to organic C and total N corresponded to the period where the oil palm biomass was burnt or partially burnt at replanting. The large increases in soil organic C with the current norm of zero burnt replanting technique were favourable in regards to sustainability and land degradation.

There were large positive changes in soil P and exchangeable K, which might be attributed to the applications of higher rates of phosphate rocks and K fertilizer especially from the 1990s following the results of fertilizer response trials. However, excessive build-up of soil nutrients on the highly weathered tropical soils of Ultisols should be avoided due to their generally low nutrient holding capacity, which may increase the risk of pollution. On the other hand, nutrient depletion should also be prevented as they commonly lead to lower production in the long-term. Thus, close monitoring of the changes in soil nutrients in the oil palm estates is essential.

This study shows explicitly that the soil fertility status of the Ultisols under oil palm in Johor was enhanced through sound fertilizer management practices and zero burnt replanting technique.

Changes in Soil Properties: Results and Discussion

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The changes, Δ, to pH, organic C, total N, total P, Bray-2 P, exchangeable K and exchangeable Mg were discussed from the following aspects:

• Site: The different sites where sampling was carried out i.e. in IR and PC
• Depth: Comparison of rates of change in soil nutrients between the two depths i.e. 0 – 15 cm and 15 – 45 cm
• Initial value: The initial value, x ₁
• Time / period: The soil sampling data were grouped into 3 main periods i.e. 1982 and earlier (coinciding with burning as the main land clearing method), 1983 to 1994 (where partial burning was generally carried out) and post 1994 (where zero burning was the main land clearing method). The lag time for all 3 periods are not the same.

Site, Depth and Initial Value

Table 2 summarizes the sample size for the data used as well as the median initial value of each parameter for both sites (IR and PC) and depths (0 – 15 cm and 15 – 45 cm) while Table 3 summarizes the % change of each parameter.

Table 2 : Sample size and median initial value of each soil chemical property (parameter)

Soil pH

Most crops grow best at a certain range of soil pH as soil acidity affects plant growth in many ways. However, the oil palm is tolerant to high acidity and is able to grow well under a broad range of soil pH (Goh and Chew, 1995a), from 4.0 to 5.5. Hyperacidity symptoms could be observed when soil pH is below 3.5 as the low pH is deleterious to normal root growth and function (Poon, 1983).

In general, there was a slight decline in soil pH of less than 3.2 % for both micro-sites and depths (Table 3). The declines in soil pH might be mainly attributed to nitrification process, which oxidizes NH₄ + to NO₃^– and releasing H⁺ ions as follows:

Therefore, N sources from applied fertilizers, organic manure and legumes containing or forming NH₄⁺ increases soil acidity.

The change in soil pH (Table 3) was more pronounced in the IR (pH lower by 3.2%) compared with the PC and this could have been attributed to the higher initial value of pH in the IR (Table 2), which was more susceptible to change due to the sigmoidal pH buffering curve. Moreover, the lower exchangeable bases in the IR (Table 2) would reduce its buffering capacity against the H⁺ produced from the nitrification process resulting in a larger decline in soil pH.

The lower initial value of pH in the PC (pH = 4.26) could be due to the prolonged concentrated application of N fertilizers in its limited space compared with the IR (Kee et al ., 1995). Most experimental evidence also supports the view that the electrical potential gradient maintained by the H⁺ efflux pump provides the driving force for active uptake of K⁺ across the plasma membrane (Haynes, 1990). Therefore, with more rooting activity for K uptake in the PC (Kee et al ., 1995), higher extrusion of H⁺ would occur resulting in low soil pH. The same would also be expected to occur to Ca₂⁺ and Mg₂⁺ uptake. The NO₃^– is also leachable to lower depths along with the basic ions of K⁺, Ca₂⁺ and Mg₂⁺. As these bases were removed and replaced by more H⁺, soils at lower depths (2^nd depth of 15 – 45 cm) became slightly more acidic, which was evident from the results in Table 3.

This acidifying effect has also been reported in established oil palm plantations (Chew and Pushparajah, 1996), whereby fertilizer applications have been carried out as a routine. From our data, the magnitude of decline in pH also appeared to be larger with a longer lag time in sampling (Figures 2a and 2b) i.e. % drop in pH greater when the two samples were taken at longer interval. Kee et al . (1995) working on Musang series soil (Typic Paleudult) showed that the surface soil pH after 7 years of applying fertilizers at the highest rate within a circle of about 2 m radius around the palm base declined markedly to 3.8 compared with control plots of 4.2, a drop of almost 10% compared with the approximately 3% obtained via our data (extrapolated for 7 years from Figure 2b). All in all, the drop in pH although noted, was generally small and probably negligible to the oil palm, which is tolerant to such conditions.

Nevertheless, we should still take necessary measures to prevent soil pH from going lower as it is usually used as a criterion of land degradation. Some measures to minimize the reduction of soil pH include the following:

• Broadcasting of fertilizers instead of applying them in a band or concentrating them only to the PC
• Use of ammonium nitrate or urea will have lower acidifying effect. However, urea application should be restricted to clayey soils and properly timed to reduce volatilization losses whereas ammonium nitrate should be avoided in sandy soils due to its higher leaching potential
• Application of alkaline fertilizers e.g. magnesium carbonate and empty fruit bunches
• Maintain proper water-table over acid sulphate layers in acid sulphate soils to prevent or reduce the oxidation of sulphite that results in sulphuric acid build-up

Soil Organic Carbon

Managing the soil organic carbon (organic C) would go hand in hand with the management of soil organic matter (SOM) and in oil palm plantations, soil fertility is mainly determined by the management of SOM including soil biological activity, soil nutrient management etc. Soil fertility management on the other hand is a keystone of sustainable agriculture. As the oil palm plantations have many sources of SOM, most of them are produced daily by the living oil palm itself such as pruned fronds, male inflorescences, shed leaf bases and roots as well as palm bio-products of empty fruit bunches (EFB), palm oil mill effluent (POME), decanter sludge, shell and fibre, natural vegetation and legumes, efficient management of SOM and the soil organic C would then ensure soil fertility, hence sustainability (Figure 3).

Soil organic C decreased at both depths (0-15 cm and 15-45 cm) with the lower depth dropping at a greater magnitude of 15.76% (Table 3). Although this decrease in soil organic C was substantial, it was localized and may not represent a decline in organic carbon on an agro-ecosystem basis as exemplified by a simplified oil palm “Carbon Cycle” (Table 4). The carbon supply from the oil palm ecosystem was computed from data of pruned fronds only without considering the following where data are unavailable:

• How much is lost as CO₂
• How much is the net return from other palm organic sources e.g. palm bio-products (EFB, POME etc.), male inflorescence, frond buds and root turnover
• How much is the contribution of ground vegetation

Table 4 : Simplified oil palm “Carbon Cycle”

Source 1: Henson (1999)
Note 2: Weighted age from data of Table 3

The 9.7 % and 15.8% reduction in organic C resulted in a total of 710 kg/ha/yr loss in organic C. Nevertheless, annually more than 4000 kg/ha (Table 4) of carbon can be potentially replenished by the palm’s pruned fronds alone. However, no data is currently available to determine the conversion efficiency of pruned fronds to organic C in oil palm agro-ecosystem in the long-term.

Chew and Pushparajah (1996) reported that organic C increase was not noted in oil palms due mainly to the uneven redistribution of recycled fronds, which could also explain the reduction of organic C obtained by our data set. In general, the IR, where soil sampling is carried out are kept relatively free of pruned fronds and hence no addition of organic matter to this micro-site would occur except from the low density of light vegetation kept by cultural practices, if any. Therefore, the practice of stacking pruned fronds in neat, narrow rows should probably be changed to wider placement covering as much of the IR as possible in view of the above. Establishing vigorous shade tolerant perennial leguminous cover crops such as Mucuna bracteata may offer another option to build up the SOM.

Total N

The Ultisols in Johor have low total N contents with a median value of 0.12 % in the top soil and 0.09 % in the lower depth (Table 2). Total N decreased in both soil depths in tandem with their soil organic C. This implies that most of the total N in the soils is in the organic form. The declines in total N contents contradicted the work of Chew and Pushparajah (1996) and Ling et al . (1979) who reported a lack of changes in soil N under oil palm cultivation.

The drop in total N in the first soil depth was not as accentuated as the second depth (Table 3). This might be ascribed to the higher rooting activity and root turn-over of oil palm in the upper soil depth, which may contribute substantially to the organic C balance (Henson, 1999). Similarly, the higher biological activity of the topsoil and potential addition of organic matter from the oil palm such as pruned fronds, EFB and POME, and the leguminous cover crops during the palm’s immaturity phase might have mitigated the decrease in soil organic C in the first depth and therefore, total N content also compared with the lower depth (Table 3). Nonetheless, the approaches to enhance SOM as suggested earlier are also appropriate to sustain total N content of the soils.

Total and Bray-2 P

The Ultisols in Johor were also generally marginal in P status (Table 2). Phosphate rocks have been used to supplement the P requirement of the oil palm and positive P responses have been obtained (Goh and Chew, 1995b). Despite the regular applications of phosphate rocks in the oil palm estates, total P and Bray-2 P posted increases in the IR only with slight declines in the PC (Table 3). This might be attributed to the policy of applying phosphate rocks in the interrow of mature palms and onto the legumes in immature palms. These results were agreeable with Hartemink (2003) who detected much higher soil P levels in soils under perennial crops compared with natural forest and Ling et al . (1979) who found a build-up of P even when the fields were burned for planting.

The higher increase in Bray-2 P compared with total P following phosphate rock applications corresponded well to the findings of Zaharah (1979). Bray 2-P extracted substantial amount of phosphate rocks apart from the dissolved P, which accentuated the P increase in particular when the initial P values were low (Table 2).

Build-up of both total and Bray-2P was also noted in the upper layer due to surface applications of P fertilizers, the low dissolution of phosphate rocks and slow migration of dissolved P into the lower soil depth due to P fixation or adsorption by sesquioxide. Thus, most of the dissolved P accumulated in the top 30 cm of tropical soils (Zaharah, 1979).

Exchangeable Kand Mg

Most Ultisols also have low exchangeable cations of K and Mg and those in Johor are no exception (Table 2). Even if complete recycling of EFB and POME produced from the FFB yield is to be carried out, the nutrients required by the palms for high yield levels are still higher than the nutrient supply from the oil palm agro-ecosystem (Ng et al ., 1999). Therefore, they need to be augmented by inorganic fertilizers to maintain the yield levels.

This resulted in positive changes to exchangeable K in the IR and both soil depths (Table 3). Slight increase in exchangeable K was also reported by Ling et al . (1979) when improvement in the legume coverage was obtained. Kee et al ., (1995) also noted a four-fold increase in exchangeable K, which were evident to a depth of 60 cm. The build-up of exchangeable K in the IR compared with the PC (Table 3) could be due to the applications of K fertilizers in the former micro-site for mature palms in particular with the wider use of fertilizer spreaders. In addition, pruned fronds and EFB, both containing high amounts of K are also normally applied in the IR.

Exchangeable Mg was noted to decrease for both micro-sites and depths (Table 3) due mainly to the generally high rates of NH₄⁺ fertilizer and KCl fertilizer used, which were known to cause the soil Mg to leach down due to the ionic exchange between the above cations at the soil complex. The magnitude of drop in exchangeable Mg in the PC although not statistically significant, was lower compared with the IR. This might be ascribed to the practice of applying Mg fertilizer, Kieserite, in the former micro-site. The negative soil Mg balance should be arrested with closer monitoring of the soil Mg status and the applications of ground magnesium limestone and/or kieserite where appropriate.

Time / Period

The data were also summarized to coincide approximately with the 3 different practices of land preparation for oil palm planting i.e. burning, which was generally the case in 1982 and earlier, partial burning (1983 to 1993) and the zero burn technique (McCulloch, 1982; Hashim et al ., 1993) which is the most common method from 1994 onwards. We shall discuss the two extreme periods only i.e. the burnt and zero burnt to avoid complication in the interpretation since the partial burnt period might include some fields that were fully burnt or zero burnt.

Burning of the organic palm biomass at replanting had little effect on the long-term soil pH (Table 5) although short-term increase in soil pH had been reported (Ling et al ., 1979), which was attributed to the addition of exchangeable bases in the ash. These two results probably indicated that the ash effect on soil pH was temporary and easily nullified by the applications of acidifying fertilizers to the palms.

With the zero burn technique, soil organic C improved in the IR and in both depths (Table 5). Sly and Tinker (1962) also concurred that slight depression of organic C would be obtained if burning was carried out during land clearing. Similarly, Ling et al . (1979) reported reduction of soil organic C by burning in a jungle clearing although slight increase in the topsoil organic C was noted twelve months after the land clearing. Khalidet al . (2000) also found that different replanting policies of partial burning, stacking and pulverizing resulted in varied increases in soil organic C with the latter two methods yielding the highest increases.

Table 5 : % change for each soil chemical property (parameter) based on median for different periods

In general all the major soil nutrients of total N, total P, Bray-2 P and exchangeable Mg improved during the zero burnt period. Soil exchangeable K on the other hand appeared to yield better results when burning was carried out. This was agreeable with the observations made by Sly and Tinker (1962) that burning depressed nitrogen and decreased soil magnesium and calcium but gave larger exchangeable K. The increase in total N during the zero burnt period corresponded with the build up in soil organic C, which implied a large return of N from the previous palm biomass. On the other hand, the large positive changes in Bray 2-P and exchangeable K in the PC could be attributed to the increased P and K fertilizer rates to the palms following the higher yield responses to these nutrients (Goh et al ., 2000). The build-up of soil exchangeable Mg with zero burnt replanting technique will require further work to ascertain.

Extreme Soil Nutrient Changes

Although the median values of soil nutrient changes in the Ultisols under oil palm in Johor were favourable in the light of sustainability, land degradation and the environment, there were extreme values for all the soil chemical properties (Appendices 1c and 1d). These extreme values could be outliers due to sampling or analytical errors but nevertheless it is still prudent to scrutinize them because excessive soil nutrient depletion (negative values) and build-up (positive values) are both detrimental to the oil palm agro-ecosystem. Long-term nutrient depletion is known to cause yield declines in many agricultural crops (Hartemink, 2003) whereas excessive build-up of N and P can cause ground water pollution and eutrophication, respectively. In general, the data showed that build-up of soil nutrients was dominant compared with soil nutrient depletion in the Ultisols under oil palm in Johor (Appendices 1 c and 1 d).

Changes in Soil Properties: Materials and Methods

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The data used in this paper were extracted from long-term soil analysis results of samples collected from 21 estates from 1967 to 2000. The estates were located from northern to southern Johor along the central belt (Figure 1). They covered over 37,000 ha, of which data from approximately 13,000 ha were used. Only analysis data of Ultisols from Johor were reported in this paper and they encompassed 26 soil series, which were mostly developed over igneous rocks, sedimentary rocks and riverine alluvium. Examples of soils in the study area would include Rengam series (deep coarse sandy clay soil derived from granite), Bungor series (deep fine sandy clay soil derived from sandstone/shale) and Holyrood series (deep coarse sandy clay loam soil derived from sub-recent alluvium).

Sampling Method

36 soil-sampling sites were randomly located in a representative area of each field. At each sampling site, soil samples were collected from two micro-sites of palm circles (PC) and interrows (IR) using a 2.5 cm diameter screw auger. At each micro-site, soil samples from two depths of 0 – 15 cm and 15 – 45 cm were extracted. This gave four distinct soil samples (two micro-sites x two depths) for each field, which were each bulked from the soil samples taken from the 36 sampling sites.

Chemical Analysis

Each soil sample was analyzed for some or all of the soil chemical properties listed in Table 1. We also restricted the data set to soil samples where they were collected and analyzed at the same time for two different soil depths and/or sites in each field. Thus, the number of samples available varied among the soil chemical properties (Table 1).

Soil pH was determined in the supernatent suspension of 1:2.5 soil: water. Organic carbon was analysed by the Walkey-Black procedure while total N was extracted using micro-Kjeldahl method. Total P was extracted using 6M HCl whereas available P followed Bray No. 2 procedure. Exchangeable K, Mg and Ca were extracted by leaching the soil sample with 1 M ammonium acetate solution at pH 7.0. K was then determined using flame photometer while Mg and Ca were determined using atomic absorption spectrophotometer. Details of the above analytical methods can be found in Moris and Mohinder (1980).

Table 1: Number of soil samples analyzed for each soil chemical property

Soil Nutrient Changes

Quantifying the rates of change in soil chemical properties for different soils and climate is necessary to reckon if any, the soil fertility decline as very few studies have been conducted in which these rates were calculated (Hartemink, 2003). In this paper, the rate of change was calculated for each soil chemical property as follows (Hartemink, 2003):

where Δ = the rate of change in %
x ₁ = the initial value of the variable at sampling time t ₁
x ₂ = the final value of the variable at sampling time t ₂

The soil samples where x ₁ and x ₂ were determined came from the same field. The period between the soil samplings t ₂– t ₁varied from one to 13 years.

Statistical Analysis

The main descriptive statistics such as mean, median, minimum, maximum, standard deviation, standard error of mean were calculated to examine the means and distributions of the initial value (x ₁) and change (%) for each soil chemical property (Appendices 1a to 1d).

Since the rate of change (%) for each soil chemical property was not normally distributed, non-parametric statistics and median were used to analyze the data. Wilcoxon’s signed rank test (Steel and Torrie, 1981) was used to investigate the differences in the rate of change (%) of each soil chemical property between the two sites of IR and PC, and between the two soil depths (0-15 cm vs. 15-45 cm).

In the Wilcoxon’s signed rank test, the sample size (Table 2) did not equal to half the number of soil samples collected (Table 1). This was because in calculating the rate of change (%), we took two soil samples (x ₁ and x ₂) that were collected from the same field but at different sampling periods (t₁ and t₂). This implied that if a field was sampled twice at two different sampling periods, then the sample size equaled to one. On the other hand, if a field was sampled three times, then the sample size equaled to three, i.e. the rates of change (%) were calculated fromx ₁ and x ₂, x ₂ and x ₃ as well as x ₁ and x ₃. The same applies for other soil samples taken at different periods from the same fields i.e. four sampling periods would yield a sample size of four.

Changes in Soil Properties: Introduction

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The oil palm requires large amount of nutrients to sustain its growth and production so that high yield levels of 30 tons/ha/yr (Ng et al ., 1999) or more could be achieved and maintained. This is mainly due to the low soil fertility in most Malaysian soils (Law and Tan, 1973) in particular the Ultisols of Johor (Ng, 1969). High fertilizer rates are also essential to prevent negative soil nutrient balance and in many instances, to build-up the soil fertility to ensure sufficient nutrients are present in the soil solution for maximum uptake by the roots (Goh and Chew, 1995a).

Traditionally, soil samples are taken on a regular basis for nutrient analysis and are commonly used in the diagnosis of fertilizer requirements in oil palms, monitoring soil fertility and ensuring that fertilizers recommended have been applied. Thus, large long-term data set on soil nutrients are available from most big plantation houses. Despite this, changes in soil nutrients under oil palm as influenced by agro-management practices have not been reported. This is particularly important as the issues of soil nutrient changes have since gone beyond their traditional uses and are nowadays frequently regarded as one of the most important measures of sustainability and impact on the environment. Tinker (1993) pointed out that for an agriculture crop to be sustainable, one of the criteria should include preserving the resource base on which it rests upon whereas Hartemink (2003) has also argued that a drop in world food production might be attributed to the decline of soil nutrients. Soil nutrient changes with regards to the impact on the environment would normally be scrutinized from the point of land degradation and potential pollution, which should be avoided in order to be sustainable.

This paper studies the soil nutrient changes of pH, organic carbon, total nitrogen, total and Bray-2 phosphate and exchangeable potassium and magnesium in different micro-sites (palm circles and interrows) and depths under oil palms. The effects of time and the different replanting practices from previously on soil nutrient changes were also investigated.

Soil Management: Changes in Soil Properties

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Abstract

The soil nutrient changes under oil palm need to be examined to ensure agro-management practices go along the lines of sustainability and not harm the resource base on which the oil palm rests upon. As most large plantation houses carry out regular soil sampling of their fields for the diagnosis of fertilizer requirements and monitoring soil fertility, long-term data are available to study the soil nutrient changes of pH, organic carbon, total nitrogen, total and Bray-2 phosphate and exchangeable potassium and magnesium in different micro-sites (palm circles and interrows) and depths. The effects of time and different replanting practices on soil nutrient changes were also investigated. This study was restricted to the Ultisols in Johor.

Results indicated that soil pH, organic C and total N tended to decrease with time in the oil palm agro-ecosystem. However, the decline in soil pH was slight whereas those related to organic C and total N corresponded to the period where the oil palm biomass was burnt or partially burnt at replanting. The large increases in soil organic C with the current norm of zero burn replanting technique were favourable with regard to sustainability and land degradation. There were large positive changes in soil P and exchangeable K, which might be attributed to the applications of higher rates of phosphate rocks and K fertilizer especially from the 1990s following the results of fertilizer response trials. Exchangeable Mg tended to decrease with burn or partial burn replanting techniques but showed large increases in both micro-sites and soil depths with zero burn techniques. Excessive build-up of soil nutrients on the highly weathered tropical soils of Ultisols should be avoided due to their generally low nutrient holding capacity, which may increase the risk of pollution. On the other hand, nutrient depletion should also be prevented as they commonly lead to lower production in the long-term.

This study shows explicitly that the soil fertility status of the Ultisols under oil palm in Johor has been enhanced through current fertilizer management practices and zero burn replanting technique.

Reference
Ng PHC, Gan HH and Goh KJ (2004) Soil nutrient changes in Utisols under oil palm in Johor, Malaysia. In: Oils and Fats International Congress (OFIC) 2004 in module on Agriculture, Biotechnology and Sustainability (AB), 29-9 to 2/10 2004, PWTC, Kuala Lumpur: Preprint.

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