Fadly 60 68

Fadly H. Yusran

AgroscientiaeISSN 0854- 233360

THE ROLE OF ORGANIC CARBON IN PHOSPHORUS AVAILABILITYOF LATERITIC SOILS

PERANAN KARBON ORGAN IK DALAM KETERSEDIAA N FOSFORPADA TANAH LATERITIK

Fadly Hairannoor YusranSoil Department, Faculty of Agriculture, Lambung Mangkurat University,

Jl. Jend. A. Yani Km.36 PO Box 1028 Banjarbaru 70714e - mail: [email protected]

ABSTRACT

The loss of organic - C has been neglected; especially in lateritic soils which are usually exist in very highrainfall tropical areas. As a highly influential and mobile substance, its occurrence is very important in bio-availability of nutrients. Not only in the decomposition process of soil organic matter - which is the mainprocess of nutrient availability- , but also in sorption- desorption process of P in solid- liquid phases of soils. Inaddition, ligand exchange is another process which occurs due to the existence of organic- C in Ptransformat ion. Another important factor is the role of soil micro- organisms in mediation of P dynamics in thesoil. In this role, soluble P immobilisation and its mineralisation due to phosphatase enzyme are anotherimportant biochemical processes related to organic - C. Therefore, investigation to quantification of C and itsmobility in soils, either horizontally or vertically, is really crucial in lateritic soils, especially when thesemarginal soils are going to convert to agricultural land.Key words: Lateritic soils, organic - C, organic matter persistence, P mobility and availability.

ABSTRAK

Hilangnya C - organik selama ini tidak banyak mendapat perhatian, terutama pada tanah- tanah lateritik yangbanyak terdapat di wilayah tropika. Sebagai substansi dengan mobilitas tinggi dan sangat berpengaruh,keberadaaanya menjadi sangat penting dalam siklus ketersediaan unsur hara. Tidak hanya dalam prosesdekomposisi bahan organik yang merupakan proses utama ketersediaan hara, tapi juga dalam prosessorpsi- desorpsi pada fase padat dan fase cair (larutan) tanah. Demikian pula halnya pada prosespertukaran ligan dalam transformasi P. Faktor lainnya adalah peranan mikro- organisma yang menjadimediator dinamika P. Pada mekanisme ini, immobilisasi P dan mineralisasinya dengan enzim fosfatase jugamempunyai pengaruh dalam reaksi biokimia C- organik. Oleh karena ini, penelitian tentang C- organik danmobilitasnya, baik secara horizontal maupun vertikal, sangat penting dilakukan di tanah- tanah lateritik.Apalagi mengingat banyakn ya lahan marginal ini dipilih sebagai lahan pertanian alternatif di masa depan.Kata kunci: Tanah laterik, C - organik, bahan organic, mobilitas dan ketersediaan P.

INTRODUCTIONThe loss of soil organic matter in agricultural

lands, usually by erosion and/or rapid mineralisation,is often considered to be the most serious factor incausing soil degradation (Craswell and Lefroy, 2001;Katyal et al. , 2001; Paustian et al., 1997). T his losscan have detrimental effects on soil physical,chemical, and biological properties. Indeed,maintaining and improving soil organic mattercontent is generally accepted as being an importantobjective of any sustainable system of agriculture.In most developing countries, extending the area ofagricultural land is a major problem becauseagricultural areas are under the pressure of highrates of population growth and the expansion ofurban areas into productive agricultural soils.

Consequently, s oils with low fertility tend to be themost likely alternative for expanding agriculturaldevelopment. However, in many developingcountries, the knowledge required for exploitingthese soils is far behind that of existing agriculturalsoils.

Lateritic so ils such as Ultisols and Oxisols, whichare commonly low in soil organic matter, are acidic,have limited cation exchange capacity, and have lownutrient status could become more suitable for foodcrops if levels of soil organic matter are raised. Thiscould be achieved by amending soil with varioussources of organic matter. More specifically, thetransformation of soil organic carbon during thedecomposition of organic matter allows soil toprovide nutrients for plants, especially P. In thisrespect, s oil organic carbon (C) has been known to

The Role of Organic Carbon in & &

Agroscientiae Volume 19 Nomor 1 April 2012 61

influence phosphate adsorption (Brennan et al.,1994; Erich et al., 2002; Leytem et al., 2002) and tobe positively correlated with phosphatase activity(Baligar et al., 1999).

Processes involved in interactions b etween soilsolutes and the soil solution such as ligandexchange, sorption, and desorption, may beconsidered as being directly involved in Ptransformation in association with organic matter.Some soil micro- organisms play an important role inmediating P dynamics in soils, especially where Pinput from fertilisers is limited (Beck and Sanchez,1994; Yao et al., 2002). Immobilisation of solublephosphate and the promotion of P mineralisation byproduction of phosphatase are among thebiochemical processes involving soil organic matterwhich affect P transformation.

In forest soils, C leaching contributes between 6-46% of total- C loss as DOC (Cronan, 1985; Magilland Aber 2000). Investigations of C balance havefocused on the effect of temperature on Cmineralisation (Liechty et al., 1995; Tate et al., 1993;Zogg et al., 1997), which is only effective in surfacesoil (MacDonald et al., 1999). The leaching of DOCfrom soil may return to the atmosphere as CO

2 lossfrom streams, lakes, or oceans (Kling et al., 1991).For soils in the tropics, the balance between upward(respiration) and downward (DOC leaching) losscould be important, especially for lateritic soils if theeffectiveness of SOM application is to beunderstood. Hence, heavy rainfall may be anadditional factor in increasing OC loss from soil, notonly in erosion but also in infiltration of water throughthe soil profile.

Several studies have concluded that the C lossas dissolved organic - C via leaching could reach 50% of the total C loss from s oil (Cronan, 1985; Magilland Aber , 2000). However, these studies mainlyconcern C loss at the soil surface. Investigation of Cleaching within the soil profile is crucial, especially inareas with very high annual rainfall. Carbon transferdue to leaching through the soil profile is importantbecause soluble organic - C may affect soil chemicalproperties such as sesquioxide concentrations. Forlateritic soils in tropical areas, heavy rainfall not onlycauses nutrient leaching (Duwi g et al ., 2000 ; Less aand Anderson, 1996) but also removes organicsubstances (Haberhauer et al., 2002) which mayaffect sorption and desorption of nutrients such asphosphate.

Soil organic matter can change the phosphatefixing capacity of some soils (Eric h et al., 2002;Iyamuremye and Dick , 1996; Kwabiah et al., 2003;Ohno and Crannel, 1996). Several mechanismshave been proposed to explain how soil organicmatter affects phosphate adsorption, either due tobiotic or abiotic processes (Iyameremye and Dick,1996). In biotic processes, soil organic matter

affects P mineralisation and transformation(Frossar d et al., 2000; Magid et al ., 1996), andabiotic processes affect P dynamics via mechanismssuch as organic ligand exchange (Hinsinger , 2001;Violante and Gianfreda, 1993), dissolution (MacKa yet al., 1986; Traina et al . , 1986), and desorption(Burkitt et al., 2002 ; Rhue and Harris , 1999).

Organic - C leaching may lead to loss of appliedorganic matter and, at the same time, may affect Pdynamics throughout the soil profile. Interactionsbetween soil solutes and the soil solution where theprocess of P sorption and desorption occur need tobe investigated, especially when lateritic soils areused being used. This is not only because of higherrainfall in the tropics where lateritic soils arecommon, but also due to high phosphate sorbingcapacity of the soils. Any novel information withinthe frame of limiting factors of these soils is neededto be repeatedly investigated for the final results inthe applied knowledge according to the specificareas.

LATERITIC SOILSLateritic soils can be low in phosphorus (P)

availability for plant growth due to their high contentof aluminium (Al) and iron (Fe) - oxides which areable to adsorb phosphate from added fertilisers(Buol and Eswaran, 2000). Soil organic matter candecrease the affinity of Al and Fe- oxides forphosphate and provide biochemical conditionssuited for making P more soluble (Dubus andBecquer, 2001; Haynes and Mokolobate, 2001;Maguire and Sims , 2002; Yusran, 2010a). However,the persistence of organic matter in soil is animportant issue as artificial sources of organic matterof agricultural origin often decompose rapidly,especially in tropical areas (Chuyong et al., 2000;Silva and Cook, 20 03). Furthermore, theeffectiveness of newly applied organic matter inalleviating P deficiency is limited, as earlydecomposition processes are not necessarilyfavourable for P to be mineralised or transformedfrom organic - P to inorganic - P (Iyamuremye andDick, 1996).

Lateritic soils are very common in tropical regions(Eswaran, 1993). Those in high rainfall areas arehighly weathered with inorganic colloids beingmainly kaolinitic with significant amounts of(hydr)oxides, especially those of iron (Fe) a ndaluminium (Al) (Buol and Eswaran, 2000; Eswaran,1993; West et al., 1998). Because of the highambient temperatures throughout the year and theabundance of water, the turnover of soil organicmatter is rapid (Rezende et al., 1999; Silva andCook, 2003; Silver, 1998), with a half life of 9- 33days (Rezende et al ., 1999). However, soil organicmatter associated with inorganic colloids in these

Fadly H. Yusran


soil environments appears to have a considerableturnover time in soil environments, ranging from 14-275 years (Monreal et al ., 1997). This kind of soilorganic matter may have an important role in thereactivities of the soil colloidal component and in soilfertility, especially in lateritic soils in the tropics.

Ultisols are part of a group of soils with an argillicand/or kandic horizon that have developed in ahumid climate (West et al., 1998). Importantfeatures of these soils are: (1) the parent materialcontains minerals which weather to form silicateclays, and (2) the climate during soil developmentchar acteristically has more precipitation thanevapotranspiration. Ultisols are common in tropicaland subtropical areas between 40 N and 40 S(Eswaran, 1993).

The main characteristic of Ultisols thatdifferentiate them from other soils is that they musthave 35 % or less base saturation in the lower partof the subsoil (Soil Survey Staff, 1999). Thisdefining characteristic is related to other propertiessuch as low pH, low cation exchange capacity, andhigh Al saturation, resulting in negative effects of theability of these soils to sustain agricultural plantgrowth. Therefore, chemical properties are the mostcommonly discussed limiting factors in managingUltisols for plant production.

With regards to cation exchange capacity,Ultisols have permanent negative charges fromisomorphic substitution of cations within the clay, butthey also have variable charges (Barnhisel andBertsch, 1989; Wada and Wada, 1985), which arepositive at low pH. Consequently, most Ultisols areexpected to have very limited net negative chargeand this influences on nutrient retention, especiallyfor cations.

Oxisols are characterised by the existence of oxichorizons which usually have a minimum of 15% clay(Buol and Eswaran, 2000; El Swaify, 1980).Physical properties of Oxisols are determined bytheir sesquioxides and kaolinite mineralogy. Thefine and very fine granular structure is very porousand leads to low bulk density which is generallybetween 1.0- 1.3 Mg m - 3 (El Swaify, 1980). Oxicmaterial with high oxide content is generally notsticky, and can be hydrophobic to some extent.Water moves rapidly through the large poresbetween aggregates. The combination of highporosity (Tejedor et al., 2003) and low wettability(Scott, 2000) can make these soils susceptible toerosion (El Swaify, 1980; Scott, 2000; Tejedor et al.,2003), leading to loss of organic matter.

Oxisols have a low capacity to retain cations(Buol and Eswaran, 2000; Krishnaswamy andRichter, 2002). Cation exchange capacity for thesesoils arises from kaolinitic clays and organic matter,it is pH dependent, and effective cation exchangecapacity values are less than cation exchange

capacity at pH 7. Oxisols with substantial content ofFe- oxides have a high fixation capacity forphosphate applied from fertilizers (Haynes andMokolobate, 2001; Leytem et al., 2002). Oxisolsalso have low quantities of essential elements forplant growth (Melgar et al., 1992; Moraghan andMascagni, 1991). As a consequence, Oxisols andUltisols are usually the next optio ns in thereclamation program for agricultural development formany countries in tropical regions. Managing thesesoils requires comprehensive knowledge in order togain profits from their management, not only foragricultural products but also for sustainability of thesoil resource.

SOIL ORGANIC MATTERThe term soil organic matter has been widely

used to describe the organic components in soils.The initial concept of soil organic matter refers to thewhole of the organic material in soils, including litter,light fraction, microbial biomass, water solubleorganics, and stabilised organic matter (humus)(Baldock and Nelson, 1998; Stevenson, 1994). Soilorganic matter is defined as the total of all organicmaterials contained within and on soils (Baldock andNelson, 1998), as well as non- decayed plant andanimal tissues, their partial decomposition productsand the living soil biomass (MacCarthy et al., 1990).

Soil organic matter investigations, have beenestablished for decades. The importance of soilorganic matter as a source and sink of C has alsobeen known (Lal, 1999; Lal, 2001). Considerablerecent research on soil organic matter has beenfocused on the dynamics of dissolved organic- C,ranging from description and chemical composition(Kaiser et al., 2001; Strobel et al., 2001),quantification and its role in soil chemistry andpedogenesis (Jansen et al., 2003; Kaiser and Zech,1998), and the availability of dissolved organic - C tosoil micro-flora (Kalbitz et al., 2003; Yano et al .,2000). More over, knowledge of dissolved organicmatter, as well as dissolved organic nitrogen (N), iswell documented (McDowell, 2003). However, therelationship between these processes and soilphosphorus (P) is less well understood, especiallydissolved organic - P. In agricultural soils wherefertiliser input was regular, dissolved organic - P wasabout 70% of total- P in solution (Chardon et al.,1997), and dissolved organic matter was responsiblefor redistribution and loss of P in forest soils (Donaldet al., 1993). Dissolved organic - C is in close contactwith soil particles that adsorb phosphate so it isexpected that this pool is important in controlling Pdynamics in soil solid and soil solution interactions.

In lateritic soils, soil organic matter is a majorcontributor to the soil exchange capacity (Buol andEswaran, 2000; Pushparajah, 1998; West et al.,



1998). Since the clays in lateritic soils are mainlykaolinitic (Allen an d Fanning, 1983; Wes t et al.,1998), soil organic matter is a major contributor tothe negatively charged colloids and plays animportant role in soil chemical (Pushparajah, 1998;Schnitzer , 2000) and biological properties (Marinar iet al., 2000). However, the content is generally low(Buol and Eswaran, 2000; Pushparajah, 1998; Westet al., 1998). Critical factors include: climate, wherewarmer temperature and high rainfall create the fastbreakdown of organic residues, and erosion wheresoil organ ic matter is lost (West et al., 1998).Erosion may also lead to leaching of some forms oforganic matter. In this case, there must be anexcess of precipitation in relation to the capacity ofthe soil to retain water, so that water will alsopercolates through the solum (Miller, 1983). As aconsequence, highly weathered soils commonlyoccur in warm areas from the humid tropics to humidwarm temperate climates.

The application of organic matter to soil toimprove soil physical, chemical, and biologicalproperties (Anikwe and Nwobodo, 2002; Khalilian etal., 2002; Larbi et al., 2002) has been a practicesince prehistoric time (Kleber et al., 2003). In thepast, the types of organic matter applied weregenerally manure, green manure, compost, cropresidues , and to some extent sewage sludge andbiosolids. Today, the term organic amendment hasbecome broader in meaning and includes materialsfrom various terrestrial and marine sources such asfish bone meal and crab meal. The use of organicamendments is increasing with the development oforganic farming and the increase is even higheramong conventional farmers (Hart z et al., 2000).This is not only because of social pressure forhealthy food under conditions that protect theenvironment, but also as a result of pressure forrecycling organic resources (Thuries et al ., 2001).

Among physical properties, organic matterenhances soil particle aggregation for better waterpermeability and gas exchange (Poch et al., 2000).Organic matter increases water retention bypreventing shrinking and drying (Hajnos et al ., 2003;Stehouwer, 2003). The black colour of organicmatter may facilitate soil warming in temperateregions by balancing the radiative heat (Schmidt andNoack, 2000). In relation to chemical character -ristics, organic matter increases cation exchangecapacity and buffering capacity to minimise changesin solute concentrations and pH. Soil organic mattercan also adsorb and buffer trace soil components(Barancikova et al., 2004; Burt et al., 2003; Minkinaet al., 2000). In addition, an improved biologicalenvironment in soil results from organic matteraddition increasing microbial activity, leading tomineralisation and enhanced availability of nutrientssuch us N, P, potassium (K), and sulphur (S) for

plant growth (Fortuna et al., 2003; Krishna, 2002;Williamson and Wardle, 2003).

Organic matter affects nutrient availability forplants directly and indirectly (Stevenson, 1994).Organic matter is a source of N for plants whenmineralised (Parfitt et al., 1998; Russell and Fillery,1999), a process which also supplies P (Parfitt et al.,1998) and S (Blair et al., 1994; Eriksen et al ., 1995).The amounts of each element released duringmineralisation, and the rate of release, depend onthe content of the element and elemental ratios inthe biomass, which reflects the origin of the organicmatter. Indirectly, organic matter contributes to themineral nutrition of plants in soils throughincorporation of N and S into humic substancesduring decomposition, or by complexation of calcium(Ca), Al, and Fe from their respective phosphates byhumic substances to increase concentrations ofsoluble phosphate (Stevenson, 1994).

Incorporation of N (Kelley and Stevenson, 1995)and S (Brown, 1986; Xia et al., 1998) int o humicsubstances, as well as P (Cooper et al., 1998; Singhand Amberger, 1990) keeps the nutrients fromvolatilising (except P) and leaching and alsoprovides those nutrients to plants for longer periodsof time. Furthermore, there is a relationshipbet ween those nutrients within organic matter whichhas been described as a definite ratio. The C:Nratio of organic matter has been used as an indicatorfor the maturity of compost (Contreras- Ramos et al.,2004; Priya and Garg, 2004) and the stage of Csequestration in soils (Tan et al ., 2004). Theaverage C/N/P/S ratio of 140:10:1.3:1.3 was claimedto be an optimum for those nutrients to sustain plantgrowth (Stevenson, 1994).

Another key reason why organic matter canparticipate in a wide range of chemical reactions insoils is due to the presence of oxygen- containingfunctional groups (- CO

2H, - OH, C=O). Thesefunctional groups are capable of enhancingdissolution of soil minerals by complexing anddissolving metals, transporting them throughout thesoil solution, and making them available for plantsand microbes (Schnitzer, 2000). Interactionsbetween soil organic matter and metal ions includeion exchange, surface adsorption, chelation,peptisation, and coagulation reactions.

PHOSPHORUS CYCLE IN RELATI ON TO SOILORGANIC MATTER

Phosphorus is an essential nutrient for livingorganisms due to its vital role in life processesincluding photosynthesis in green plants andtransformation of energy in all forms of life (Sanyaland De Datta, 1991). Compared with other essentialnutrients, P is by far the least mobile and leastavailable to plants under most soil conditions

Fadly H. Yusran


(Hinsinger, 2001). Therefore, P often becomes amajor limiting factor for plant growth.

In the soil solution, P usually occurs at fairly lowconcentration as orthophosphate or organicphosphate, while a large proportion is more or lessstrongly held by soil minerals (Frossard et al., 2000).Some phosphate ions can be adsorbed toaluminosilicate clays and/or Fe and Al oxides.Phosphate ions can also form a range of minerals incombination with metal cations such as Ca2+ , Fe3+ ,and Al3+ . These sorption- desorption andprecipitation- dissolution equilibria control phosphateconcentration and the same time both the chemicalmobility and bioavailability. According to Hinsinger(2001) the major factors that determine thoseequilibria are: (1) soil pH, (2) the concentration ofanions that compete with phosphate ions for ligandexchange reactions. Including in these anions isphosphate ion itself, and; (3) the concentration ofmetals (Ca, Fe, and Al) that can precipitate withphosphate ions.

Other factors affecting phosphate availability arethe amount and type of adsorbing phases, such asdominant clay mineral and various oxides (Hue,1991; Wahba et al., 2002). Therefore, byconsidering these factors, the effect of organicmatter on phosphate ions must relate to the secondfactor due to organic ligands such as carboxyl. Ingeneral, the effect of soil organic matter on the Pcycle is related to the effect of biotic processes thatcontrol P release to soil solution (Frossard et al.,2000). In this process, P turnover from organicmatter plays an important role despite the fact thatorganic matter also contributes via abiotic processessuch as adsorption- desorption and dissolution-precipitation. In biotic processes, soil organic matterplays the central role in mineralisation andimmobilisation.

Considering phosphate rock as a non- renewableresource and the availability of P is relatively low insoils, P supply to plant growth must be rationalised.This is true especially for Oxisols and Ultisols thathave Fe and Al- oxides which strongly adsorb solublephosphate from fertilisers. To improve the efficiencyof P supply in soils, it is imperative to maximise Precycling from crop residues or even from organicand mineral fertilisers.

The P cycle is very dynamic and involves bothgeochemical and biochemical reactions (Figure 1).The cycle of P is different from that of C, N, and S.This is because P has no pathways to atmosphericpools. The overall cycle ranges from solubilisationand fixation at clays and oxide surfaces in the soilsolution to mineralisation- immobilisation processesmediated by micro- organisms. The roles of soilorganic m atter and soil micro- organisms are verysignificant in the P cycle. Microbial activity is anagent that functions as a reversible sink for P,

continuously consuming and releasing P to the soilsolution (Stewart, 1981).

In highly weathered soils, which are commonlyacidic (Eswaran, 1993; West et al., 1998),phosphate is usually adsorbed to Al and Fe oxidesor precipitated as insoluble Al- and Fe- phosphates(Iyamuremye and Dick, 1996; Lindsay et al., 1989;Stevenson and Cole, 1999; Yusran, 2005; Yusran,2010 b). Both forms are poor sources of P for plantsand P deficiency is common in soils rich in Fe andAl, such as Oxisols and Ultisols of the tropics andsub tropics. The application of organic matter tothose soils may complex Al and Fe, in either ionicform or as oxides. Furthermore, in many soils, theavailability of P may depend more on the turnover ofeasily decomposable soil organic matter than on therelease of adsorbed phosphate.Dissolution and precipitation

The beginning of the P cycle involves parentmaterials, climate, and time as factors affecting theexistence and amount of P in soils. Dissolution of Pfrom its origin can usually be explained asdissolution from apatite [Ca

10X 2(PO 4) 6, where X =OH - or F - ; Ca may also be substituted with Na or Mg,and PO

4 with CO 3] which are the most commonprimary phosphate minerals.

Precipitation of phosphate with Ca carbonatesand its adsorption on Al and Fe hydrous oxides hasbeen known since the mid- nineteenth century.Calcium phosphate is formed following phosphateadsorption to calcite (Syers and Curtin, 1989). Asphosphate is adsorbed to the surface of calcite,monocalcium phosphate [Ca(H

2PO 4) 2] precipitatesand transforms to become dicalcium phosphatedihydrate (CaHPO

4.2H2 O), to octocalcium[Ca

8H 2(PO 4) 6.5H 2O] and finally to hydroxyapatite[Ca

10(PO 4) 6(OH) 2]. Adsorption of phosphate with Aland Fe oxides resulted in the formation ofamorphous Al- phosphate and Fe- phosphate whichmay later transform to variscite (AlPO

4.2H 2O) andstrengite (FePO

4.2H 2O) af ter prolonged aging(Lindsay et al., 1989). Phosphate adsorption is notonly attributed to the hydrous oxides of Al and Fe,but also to 1:1 lattice clay such as kaolinite,especially in acid tropical soils (Dubus and Becquer,2001; Sanya l et al., 1993; Uehara, Gillman, 1981).

Apatite dissolution requires a source of H+ , whichoriginates from plant roots, micro- organisms, or fromthe soil itself (MacKay et al., 1986; Smillie et al.,1987). Dissolution from precipitated P (with Ca, Al,and Fe) is also possible (Iyamuremye and Dick,1996), and can make P more available when organicresidues are added to soils. Dissolution of bothgroups of solid phases relies on organic acids suchas citrate and formic acid (Traina et al ., 1986) as thesource of H+ . The process is the replacement of



phosphate sorbed on metal hydroxides (Fox et al.,1990).Sorption and desorption

The term sorption is used to describe the surfaceaccumulation of phosphate on soil componentswhich can be accompanied by penetration ofadsorbed P by diffusion into the adsorbent body,resulting in further adsorption of the adsorbedspecies (Sanyal and De Datta, 1991). These twoprocesses take place simultaneously. Desorption isdefined as the adsorbed phosphate ions beingreleased as a reciprocal action of sorption. Thesorption of phosphate ions has been interpreted as abiphasic reaction (Rhue and Harris, 1999), i.e. theinitial and rapid sorption which is believed to last inthe order of minutes or hours. The second sorptionis slo w reaction lasting weeks or months. There aretwo mechanisms responsible for the process:1. Ion exchange, mechanism from the electrostatic

attraction of phosphate anions to positivelycharged sites exist on variable- charge surfacesbelow the zero point char ge, and

2. Ligand exchange, mechanism by which aphosphate anion replaces a surface hydroxyl thatis coordinated with a metal cation in a solidphase (Rhue and Harris, 1999).The last mechanism, ligand exchange, is also

referred as specific adsorption and is characterisedby: a) adsorption is accompanied by the release ofOH - ; b) ligand exchange shows a high degree ofspecificity; c) adsorption step often occurs muchmore rapidly than the desorption step, leading toapparent hysteresis in the isotherm, and; d)adsorption is accompanied by an increase in surfacenegative charge (McBride, 1994).

The second sorption or the slow phase is thoughtto have two mechanisms, i.e. diffusion (either intosoil particles or to surface sites of limitedaccessibility), and pr ecipitation (either by directheterogenous nucleation or following the dissolutionof the host solid, following an initial adsorptionreaction) (Rhue and Harris, 1999). Phosphorussorption and desorption are important mechanismscontrolling soil phosphate partitioning between thesorbed and solution phases (Burkitt et al., 2002) andhave crucial implication for P management. Thismechanism is commonly referred to phosphatebuffering capacity, which describes a soil s capacityto moderate changes in phosphate solutionconcentration when P is added or removed from thesoil (Ozanne, 1980).

In relation to soil organic matter, the release ofphosphate by mineralisation may be difficult toseparate from the sorption mechanisms, especiallyin soils with high sorbing capacity such as lateriticsoils. This is not only because of the high content ofsesquioxides and 1:1 clay content in these soils, butalso due to negligible amounts of soil organic matter.However, by observing the net release ofextractable- P and determining phosphate adsorptionisotherms, the two processes can be separated asmore and less important in releasing phosphates tothe soil solution. Furthermore, as Afif et al . (1995)found that the effect of soluble organic matter onphosphate release from Oxisols to be transient, thisleads to the question of whether peat would have alonger - term effect on P adsorption due to itsresistance to decomposition. At the same time peatcan possibly slowly release soluble organic ligandswhich compete for adsorption sites with phosphate.This also could be determined by analysingphosphate adsorption isotherms.

Figure 1 . Soil phosphorus cycle, its components and measurable fractions (adapted from Stewart and Sharpley (1987) .Arrows represent fluxes between reservoirs.





















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CONCLUSIONSThere are two main processes are governing P

transformation, i.e. biotic and abiotic processes.The biotic process is mainly responsible formineralisation and immobilisation of P. Thisprocesses involve the role of a wide range of soilmicro- organisms. While abiotic process isresponsible for maintaining the equilibrium ofsorption- desorption with precipitation andsolubilisation mechanisms. In this process, either inrapid or slow sorption, ion and ligand exchanges areresponsible with their typical characteristics inrelation to other available factors in lateritic soils.Above all, organic - C role in P availability in lateriticsoils is diverse, ranging from very rapid to very slowreactions which taking hundred years in the process.All processes have many implications inmanagement of the soils.

REFERENCESAfif, E., V. Barron, and J. Torrent. 1995. Organic

matter delays but does not prevent phosphatesorption by cerrado soils from Brazil. SoilScience Society of America Proceedings159:207- 211.

Allen, B.L., and D.S. Fanning. 1983. Compositionand soil genesis, p. 141- 192, In L. P. Wilding,et al ., eds. Pedogenesis and Soil Taxonomy, I.Concept and Interactions. Elsevier,Amsterdam.

Baligar, V.C., R.J. Wright, N.K. Fageria, and G.V.E.Pitta. 1999. Enzyme activities in cerrado soilsof Brazil. Communications in Soil Science &Plant Analysis 30:1551- 1560.

Beck, M.A., and P.A. Sanchez. 199 4. Soilphosphorus fraction dynamics during 18 yearsof cultivation on a Typic Paleudult. Soil ScienceSociety of America Journal 58:1424- 1431.

Brennan, R.F., M.D.A. Bolland, R.C. Jeffery, andD.G. Allen. 1994. Phosphorus adsorption by arange of Western Australian soils related to soilproperties. Communications in Soil Science &Plant Analysis 25:2768- 2795.

Buol, S.W., and H. Eswaran. 2000. Oxisols, p. 151 -195, In D. L. Sparks, ed. Advances inAgronomy, Vol. 68. Academic Press, SanDiego, USA.

Burkitt, L.L., P.W. Moody, C.J.P. Gourley, and M.C.Hannah. 2002. A simple phosphorus bufferingindex for Australian soils. Australian Journal ofSoil Research 40:497- 513.

Chuyong, G.B., D.M. Newbery, and N.C. Songwe.2000. Litter nutrients and retranslocation in acentral African rain forest dominated byectomycorrhizal trees. New Phytologist148:493- 510.

Contreras - Ramos, S.M., D. Alvarez- Bernal, N.Trujillo- Tapia, and L. Dendooven. 2004.Composting of tannery effluent with cowmanure and wheat straw. BioresourceTechnology 94:223- 228.

Craswell, E.T., and R.D.B. Lefroy. 2001. The roleand function of organic matter in tropical soils.Nutrient Cycling in Agroecosystems 61:7- 18.

Cronan, C.S. 1985. Comparative effects ofprecipitation acidity on three forest soils:carbon cycling responses. Plant & Soil 88:101-112.

da Silva, S.H.S.A., and H.F. Cook. 2003. Soilphysical conditions and physiologicalperformance of cowpea following organicmatter amelioration of sandy substrates.Communic ations in Soil Science & PlantAnalysis 34:1039- 1058.

Dubus, I.G., and T. Becquer. 2001. Phosphorussorption and desorption in oxide- rich Ferralsolsof New Caledonia. Australian Journal of SoilResearch 39:403- 414.

Duwig, C., T. Becquer, I. Vogeler, M. Vauclin, andB.E. Clothier. 2000. Water dynamics andnutrient leaching through a cropped Ferralsol inthe Loyalty Islands (New Caledonia). Journal ofEnvironmental Quality 29:1010- 1019.

El Swaify, S.A. 1980. Physical and mechanicalproperties of Oxisols, p. 303- 324, In B. K. G.Theng, ed. Soils With Variable Charge. SoilBureau, DSIR, New Zealand.

Erich, M.S., C.B. Fitzgerald, and G.A. Porter. 2002.The effect of organic amendments onphosphorus chemistry in a potato croppingsystem. Agriculture Ecosystems & Environment88:79- 88.

Eswaran, H. 1993. Assessment of global resources:Current status and future needs. Pedologie43:19- 39.

Frossard, E., L.M. Condron, A. Oberson, S. Sinaj,and J.C. Fardeau. 2000. Processes governingphosphorus availability in temperate soils.Journal of Environmental Quality 29:15- 23.



Gregorich, E.G., M.R. Carter, D.A. Angers, C.M.Monreal, and B.H. Ellert. 1994. Toward aminimum data set to assess soil organic matterquality in agricultural soils. Canadian Journal ofSoil Science 74:367- 385.

Haberhauer, G., B. Temmel, and M.H. Gerzabek.2002. Influence of dissolved humic substanceson the leaching of MCPA in a soil columnexperiment. Chemosphere 46:495- 499.

Haynes, R.J., and M.S. Mokolobate. 2001.Amelioration of Al toxicity and P deficiency inacid soils by additions of organic residues: acritical review of the phenomenon and themechanisms involved. Nutrient Cycling inAgroecosystems 59:47- 63.

Hinsinger, P. 2001. Bioavailability of soil inorganic Pin the rhizosphere as affected by root- inducedchemical changes: a review. Plant & Soil237:173- 195.

Horst, W.J., M. Kamh, J.M. Jibrin, and V.O. Chude.2001. Agronomic measures for increasing Pavailability to crops. Plant and Soil 237: 211-223.

Iyamuremye, F., and R.P. Dick. 1996. Organicamendments and phosphorus sorption by soils.Advances in Agronomy 56:139- 185.

Katyal, J.C., N.H. Rao, and M.N. Reddy. 2001.Critical aspects of organic matter managementin the Tropics: the example of India. NutrientCycling in Agroecosystems 61:77- 88.

Kling, G.W., G.W. Kipphut, and M.C. Miller. 1991.Arctic lakes and streams as gas conduits to theatmosphere: implications for tundra carbonbudgets. Science 251:298- 301.

Kobayashi, S., J.W. Turnbull, and C. Cossalter.1999. Rehabilitation of degraded tropical forestecosystems project, p. 1- 16, In S. Kobayashi,et al. (ed.) 1999. Rehabilitation of DegradedTropical Forest Ecosystems, Bogor, Indonesia.Centre for International Forestry Research(CIFOR), Bogor, Indonesia.

Kwabiah, A.B., C.A. Palm, N.C. Stoskopf , and R.P.Voroney. 2003. Response of soil microbialbiomass dynamics to quality of plant materialswith emphasis on P availability. Soil Biology &Biochemistry 35:207- 216.

Lal, R. 1999. Soil carbon and the acceleratedgreenhouse effect, In A. Sapek (ed.) 1999.Scientific basis to mitigate the nutrientdispersion into the environment,Falenty/Nadarzyn, Warsaw, Poland. InstytutMelioracji i Uzytkow Zielonych (Institute forLand Reclamation and Grassland Farming),Raszyn, Poland.

Lal, R. 2001. So il carbon sequestration and thegreenhouse effect. Proceedings of asymposium, 90th Annual Meeting, Baltimore,MD, USA, 18- 22 October 1998. Soil ScienceSociety of America Inc, Madison, USA 236.

Lessa, A.S.N., and D.W. Anderson. 1996.Laboratory estimation of nutrient losses byleaching on an Oxisol from Brazil. TropicalAgriculture 73:100- 107.

Leytem, A.B., R.L. Mikkelsen, and J.W. Gilliam .2002. Sorption of organic phosphoruscompounds in atlantic coastal plain soils. SoilScience 167:652- 658.

MacDonald, N.W., D.L. Randlett, and D.R. Zak.1999. Soil warming and carbon loss from aLake States Spodosol. Soil Science Society ofAmerica Journal 63:211- 218.

MacKay, A.D., J.K. Syers, R.W. Tillman, and P.E.H.Gregg. 1986. A simple model to describe thedissolutio n of phosphate rocks in soils. SoilScience Society of America Journal 50:291-296.

Magid, J., H. Tiessen, and L.M. Condron. 1996.Dynamics of organic phosphorus in soils undernatural and agricultural ecosystems, p. 429-466, In A. Piccolo, ed. Humic Substances inTerrestrial Ecosystems. Elsevier, Amsterdam,The Netherlands.

Magill, A.H., and J.D. Aber. 2000. Dissolved organiccarbon and nitrogen relationships in forest litteras affected by nitrogen deposition. Soil Biology& Biochemistry 32:603- 613.

Maguir e, R.O., and J.T. Sims. 2002. Measuringagronomic and environmental soil phosphorussaturation and predicting phosphorus leachingwith Mehlich 3. Soil Science Society of AmericaJournal 66:2033- 2039.

Marinari, S., G. Masciandaro, B. Ceccanti, and S.Grego. 2000. Influence of organic and mineralfertilisers on soil biological and physicalproperties. Bioresource Technology 72:9- 17.

Fadly H. Yusran


Ohno, T., and B.S. Crannel. 1996. Green and animalmanure- derived organic matter effects onphosphorus sorption. Journal of EnvironmentalQuality 25:1137- 1143.

Paustian, K., H.P. Collin, and E.A. Paul. 1997.Management control of soil carbon, p. 15- 49, InE. A. Paul, et al., eds. Soil Organic Matter inTemperate Agroecosystem. CRC Press, BocaRaton, USA.

Priya, K., and V.K. Garg. 2004. Dynamics ofbiological and chemical parameters duringvermicomposting of solid textile mill sludgemixed with cow dung and agricultural residues.Bioresource Technology 94:203- 209.

Pushparajah, E. 1998. Nutrient management andchallenges in managin g red and lateritic soils.Red & lateritic soils 1:293- 304.

Rhue, R.D., and W.G. Harris. 1999. Phosphorussorption/desorption reactions in soils andsediments, p. 187- 206, In K.R. Reddy, et al.,eds. Phosphorus Biogeochemistry inSubtropical Ecosystems. Le wis Publishers,Boca Raton, USA.

Rodolfi, G., and C. Zanchi. 2002. Climate changerelated to erosion and desertification: 1.Mediterranean Europe, p. 67- 86, In R.C. Sidle,ed. Environmental Changes and GeomorphicHazards in Forests. CABI Publishing,Wallingford, UK.

Soil Survey Staff. 1975. Soil Taxonomy. A BasicSystem of Soil Classification for Making andInterpreting Soil Surveys. US Department ofAgriculture- Soil Conservation Service, NewYork.

Schnitzer, M. 2000. A lifetime perspective on thechemistry of soil organic matter. Advances inAgronomy 68:1- 58.

Stewart, J.W.B., and A.N. Sharpley. 1987. Controlson dynamics of soil and fertilizer phosphorusand sulfur, p. 101- 121, In R. F. Follet, et al.,eds. Soil Fertility and Organic Matter as CriticalComponents of Production, Vol. 19. SSSAASA, Madison, USA.

Tan, Z.X., R. Lal, R.C. Izaurralde, and W.M. Post.2004. Biochemically protected soil organiccarbon at the North Appalachian experimentalwatershed. Soil Science 169:423- 433.

Traina, S.J., G. Sposito, D. Hesterberg, and U.Kafkafi. 1986. Effects of pH and organic acidson orthophosphate solubility in an acidic,montmorillonitic soil. Soil Science Society ofAmerica Journal 50:45- 52.

Violante, A., and L. Gianfreda. 1993. Competition inadsorption between phosphate and oxalate onan aluminum oxides. Soil Science Society ofAmerica Journal 57:1235- 1241.

West, L.T., F.H. Beinroth, M.E. Sumner, and B.T.Kang. 1998. Ultisols: Characteristics andImpacts on society, p. 179- 236, In D. L. Sparks,ed. Advances in Agronomy, Vol. 63. AcademicPress, San Diego, USA.

Yao, Q., F. Qing, X. Li, and P. Christie. 2002.Utilization of sparingly soluble phosphate byred clover in association with Glomus mosseaeand Bacillus megaterium. Pedosphere 12:131-138.

Yusran, F.H. 2005. Soil Organic MatterDecomposition: Effects of Organic MatterAddition on Phosphorus Dynamics in LateriticsSoils. Thesis. The University of WesternAustralia.

Yusran, F.H. 2010a. The relationship betweenphosphate adsorption and soil organic carbonfrom organic matter addition. Journal ofTropical Soils 15:1- 10.

Yusran, F.H. 2010b. The balance betweenrespiration and leaching, and phosphorusmobility in lateritic soils. Journal of TropicalSoils 15:245- 254.

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