USE OF THE BRAY SOIL TEST IN FORESTRY 1. PREDICTING PHOSPHATE RETENTION CAPACITY

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1 N USE OF E BRAY SOIL TEST IN FORESTRY 1. PREDICTING PHOSPHATE RETENTION CAPACITY R. BALLARD Frest Research Institute, New Zealand Frest Service, Rtrua* (Received fr publicatin 1 December 1977) ABSTRACT Relatinships between phsphate retentin and Bray (0.1M HC M NH 4 F) extractable aluminium, irn and calcium were examined in the tpsils f 128 frest sils cllected frm thrughut New Zealand. Aluminium extracted using 1- and 30-minute extractin perids was highly significantly crrelated with P retentin (r = and respectively). Irn and Ca in the same extracts were clsely related t P retentin nly within a few specific sil grups and nt ver all sils. Other sil prperties cmmnly used t characterise frest sils; carbn, catin exchange capacity, ph and ttal P, were als significantly crrelated with P retentin ver all sils. Hwever the crrelatin cefficients were smaller than thse frm Bray extractable Al and stepwise regressin prcedures indicated their effects were predminantly indirect thrugh assciatin with extractable Al. In the interest f efficient fertiliser use, critical levels f Bray 2 (1-minute extractin) extractable Al belw r abve which water-sluble fertilisers shuld nt be used n frest sils are tentatively prpsed. INTRODUCTION Phsphatic fertilisers are being used n a rutine basis in many f New Zealand's extic frests. Currently abut 6000 ha f radiata pine are being fertilised with P annually and it is prjected that this culd increase five r six fld ver the next decade (Ballard and Will, 1978). Almst all f the P fertiliser applied is in the frm f superphsphate. In mst frestry peratins it is nt practicable t make frequent applicatins f fertiliser and thus there is an interest in the duratin f the effectiveness f single applicatins. The tw sil cnditins mst likely t restrict the lng-term effectiveness f sluble phsphate fertilisers, such as superphsphate, are (1) very lw sil P-retentin capacities which allw leaching f applied P frm the rt zne and (2) excessively high P-retentin capacities which result in cnversin f P t unavailable frms. Under bth these cnditins in acid frest sils, water-insluble P fertilisers such as rck phsphate have been shwn t have superir lng-term effects cmpared t sluble P surces (Humphreys and Pritchett, 1971; Pritchett and Smith, 1974). In additin t acting as * Present address: Department f Frestry, NC State University, Raleigh, NC 27650, USA. N.Z. J. Fr. Sci. 8(2): (1978).

2 240 New Zealand Jurnal f Frestry Science Vl. 8 a guide t the selectin f suitable P fertilisers, a knwledge f a sils' P-retentin capacity is als f value where mnitring f the tree nutrient status by fliar analysis is practised. As the duratin f P fertiliser effectiveness tends t be related t sil P-retentin, it can be used as a guide t the frequency f fliage sampling required n any sil type t effectively mnitr the need fr refertilisatin. The methd rutinely used t characterise the P-retentin capacity f sils in New Zealand invlves a 24-hur equilibratin (r 16 hurs by sme labratries) f the sils with a buffered P slutin cntaining 500 mg P per 100 g air-dry sil (Saunders, 1965). Althugh this single equilibratin methd is a lt less labrius than thse which rely n cnstructin f adsrptin istherms, its use fr rutine advisry testing wuld nevethless invlve a cnsiderable labratry wrk-lad. This wuld be reduced if P retentin culd be predicted frm currently r mre readily determined sil prperties related t it. Ballard and Pritchett (1974) fund that fr sils in the SE U.S.A. the levels f aluminium (Al) and t a lesser extent irn (Fe) extracted by several sil test methds used fr estimating available P, including the Bray 2 methd, were clsely crrelated with P retentin. The Bray 2 sil test is currently used fr rutine estimatin f available P in New Zealand frest sils (Ballard, 1974) and determinatin f an extra element in the extract wuld invlve little extra wrk. The bjectives f this study were (1) t btain infrmatin n the P-retentin capacities f a wide range f sils used fr frestry in New Zealand and (2) t examine the relatinships between P retentin and ther sil prperties, in particular levels f Al, Fe and Ca extracted by the Bray 2 sil test, fr these sils. MATERIALS AND MEODS Sils The 128 sils used in this investigatin were the tpsil (0-7.5 cm) samples cllected by Dr D. S. Jacksn during a natin-wide survey f envirnmental variables influencing the prductivity f Pinus radiata D..Dn. Each sample was a cmpsite f 7 t 10 subsamples cllected frm randm pints within a 0.04-ha plt. Fr distributin f the plts thrughut New Zealand, see Jacksn and Giffrd (1974) Fig. 2. Fr purpses f statistical analysis and interpretatin the sils were gruped accrding t the New Zealand genetic classificatin system (N.Z. Sil Bureau, 1968). There were 11 recent sils (Recent), 14 yellw-brwn sands (YBS), 5 brwn-grey earths (BGE), 12 yellwgrey earths (YGE), 23 yellw-grey earth/yellw-brwn earth intergrades (YG/YBE), 14 suthern yellw-brwn earths (SYBE), 26 central and nrthern yellw-brwn earths (YBE), 6 pdzlised yellw-brwn earths and pdzls (PYBE), 7 yellw-brwn pumice sils (YBP) and 10 yellw-brwn lam, brwn lam and brwn granular lams (BL). Chemical Analysis Phsphrus retentin was determined by equilibrating 5 g air-dry sil samples fr 24 hurs with 25 ml f 0.032M KH 2 P0 4 (additin f 5 mg P per gram f sil), buffered at ph 4.6 with NaOAc/HOAc. Phsphrus in the equilibrium slutin was determined clrimetrically by an autmated prcedure f the vanad-mlybdate methd. The P retentin value was btained by expressing the amunt f P remved frm the slutin as a percentage f the riginal amunt. Saunders (1965) fund that the retentin value

N. 2 Ballard Predicting Phsphate Retentin 241 btained by this methd crrelated very clsely with the amunt retained frm adding the active ingredient f superphsphate (mn calcium phsphate) t sil.

3 N. 2 Ballard Predicting Phsphate Retentin 241 btained by this methd crrelated very clsely with the amunt retained frm adding the active ingredient f superphsphate (mn calcium phsphate) t sil. Duplicate 2.5 g air-dry sil samples were extracted with 25 ml f a 0.1M HC M NH 4 F slutin using extractin perids f 1 minute (Bray 2) and 30 minutes (Bray 3). Fllwing extractin and filtratin, Al, Fe, and Ca were determined in the slutin by atmic adsrptin spectrphtmetry using lanthanum chlride as a releasing agent. Ttal P, ph, carbn, and catin exchange capacity (CEC) f sils were determined by standard N.Z. Sil Bureau prcedures (Blakemre, Searle and Daly, 1972). Results f all sil chemical analyses were expressed n an ven-dry basis. RESULTS AND DISCUSSION Mean P retentin values fr each sil grup, tgether with ther sil prperties are given in Table 1. The sil grups are arranged in apprximate rder f increasing degree f weathering except fr the last tw grups (YBP and BL) which are intraznal sils frmed frm vlcanic parent material. Phsphrus retentin values fr znal sils shw the same relatinship t degree f weathering as fund by Saunders (1965); increasing frm the weakly weathered brwn-grey earths up t a maximum fr the mderately weathered suthern yellw-brwn earths and declining fr the mre strngly weathered sils. The P retentin values recrded fr the varius sil grups are clse t thse recrded fr the same grups by Saunders (1965) except the mean value fr the YBS grup is a lt lwer (9.8 v. 2.3). This is prbably a reflectin f mst castal frests being situated n the mre recently stabilised members f the YBS grup. Over all sil grups levels f Al extracted by bth the Bray 2 and Bray 3 methds are highly significantly crrelated with P retentin (Table 2). Althugh the crrelatin fr the Bray 3 methd is slightly better than that fr the Bray 2 methd the slightly imprved predictin f P retentin is unlikely t justify using a lnger extractin perid and altering an extractin technique which is already used fr ther purpses. The precisin f the predictin given by Bray 2 extractable Al is at least the equivalent f that fund fr the mre cnventinally used Tamm extractable Al by Saunders (1965) fr a similar range f New Zealand sils. Other elements in the Bray extract such as Fe and Ca, which in certain frms in the sil are knwn t be invlved in P retentin, are prly crrelated with P retentin (Table 2), althugh within certain sil grups they are significantly crrelated (Table 3). Hwever, nly in the case f the YGE grup are they mre clsely assciated with P retentin than Bray extractable Al. Other sil prperties such as ph, carbn, CEC and ttal P, cmmnly determined t characterise frest sils fr varius purpses, are als highly significantly crrelated with P retentin ver all sil grups (Table 2). Carbn and CEC in particular shw ptnetial as predictr variables. Hwever, tw cnsideratins, ne practical and the ther theretical, wuld tend t mitigate against their use as rutine predictrs f P retentin. Firstly, neither carbn nr CEC are rutinely determined n frest sil samples sent int the Frest Research Institute, particularly thse sent t btain fertiliser recmmendatins; thus their use fr predictin f P retentin wuld invlve additinal analyses the techniques fr determining bth these prperties are fairly labrius. Secndly, as there is n evidence that carbn and CEC are directly invlved in retaining P (see discussin belw) there is always the danger that the relatinship will nt hld

4 TABLE 1Mean values fr sil prperties by sil grups Sil Number f P* Bray 2 Bray 3 grup samples retentin Al Fe Ca Al Fe Ca ph Carbn CEC Ttal P % me/loog me/loog % me/loog Recent ± YBS ± BGE ± YGE YG/YBE SYBE YBE ± 26.2 ± 38.6 ± 33.7 ± D O PYBE ± YBP ± BL ± All * Mean value and its standard errr. <

5 N. 2 Ballard Predicting Phsphate Retentin TABLE 2Selected simple crrelatins between sil variables 243 Variable P retentin Al Bray 2 Fe Carbn ph Bray 3 Al 0.920** 0.945** Fe Ca 0.221* Al-f Fe 0.915** Bray 2 Al 0.882** Fe Ca * Al + Fe 0.901** Carbn 0.794** 0.688** ** CEC 0.883** 0.755** ** 0.448** ph 0.360** 0.242** 0.201* 0.349** Ttal P 0.447** 0.400** ** * Significant at the 5% level. ** Significant at the 1% level. fr sils utside the range used in the calibratin. Fr instance, Saunders (1965) fund that carbn was significantly crrelated with P retentin ver all the sils they examined except pdzls and gley sils, as in these latter sils higher than nrmal levels f carbn accumulate because f their very lw ph and pr aeratin respectively. An examinatin f crrelatins within sil grups (Table 3) shws that carbn, CEC, ph and ttal P, in additin t being significantly crrelated with P retentin, are als highly significantly crrelated with Bray extractable Al and inter-crrelated with each ther (Table 2). Stepwise regressin analysis (Table 4) suggests that while their strng crrelatin with P retentin is mainly due t their crrelatin with extractable Al (nte reductin in partial F values fllwing entry f extractable Al), bth CEC and carbn d make a significant independent cntributin t accunting fr variatin in P retentin. The significant crrelatin f ph and ttal P can be almst entirely accunted fr by their relatinship t extractable Al and CEC. The nature f the small independent cntributin f CEC and carbn is nt clear, but as neither are directly invlved in the retentin f phsphate ins in the sil (Saunders, 1965) it is prbably thrugh their being crrelated with sme unmeasured cmpnent directly invlved in P retentin. Despite cnsiderable variatin in slpes and intercepts f regressins within sil grups (Table 5) the verall relatinship between P retentin and Bray 2 extractable Al (Fig. 1) gives a reasnably gd differentiatin f sils int a lw, intermediate and high P retentin range. In a calibratin f Bray 2 extractable Al values against leaching lsses f superphsphate applied in the field t sils in the sutheastern U.S.A., Ballard

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7 N. 2 Ballard Predicting Phsphate Retentin 245 TABLE 5Regressins f P-retentin (%) n Bray 2 extractable aluminium () Sil grup Recent YBS BGE Number f samples Regressin cefficient Cnstant Crrelatin cefficient ** YGE YG/YBE SYBE YBE PYBE YBP BL ** 0.741** 0.744** 0.997** ** Overall ** ** Significant at the 1% level. and Pritchett (1974) fund excess leaching lsses ccurred in sils cntaining 400 r less Bray 2 extractable Al. Using the regressin in Fig. 1, this extractable Al value crrespnds t a P retentin value f 11%. Hwever a Bray 2 extractable Al value f 700 apparently gives a much better separatin f New Zealand sils with P retentins f apprximately 11% and belw frm thse with higher retentin values (Fig. 1). What cnstitutes excessive P retentin in a frestry cntext is nt really knwn. The sil (Bladen silty clay lam) n which Pritchett and Smith (1974) fund rck phsphate t give a better lng-term respnse than superphsphate, the authr (Ballard and Fiskell, 1974) fund t cntain abut 1500 Bray 2 extractable Al. At this value there is a fairly wide range f P retentins in New Zealand sils and a BRAY 2 At ( ) FIG. 1Relatinship between P retentin and Bray 2 extractable Al.

8 246 New Zealand Jurnal f Frestry Science Vl. 8 value f abut 2000 gives a clearer differentiatin between sils in this range and thse abve it (Fig. 1). It is hped that a series f trials currently being established, which cmpare superphsphate with varius rck phsphates n sils with a range f P retentins, will give mre precise definitin t these critical pints which at presentare largely based n cnjecture. Perhaps the mst cnvenient and rapid means f btaining an indicatin f a sil's prperties is thrugh its classificatin. Hwever since sils are seldm classified directly n the basis f the prperty f interest, particularly in a genetic classificatin such as New Zealand has (N.Z. Sil Bureau, 1968) there is usually cnsiderable variatin in a sil prperty within any particular classificatin unit even thugh there may be brad crrelatin ver classificatin units. This is certainly true fr P retentin fr the range f sils used in this study (Fig. 1). Mst r all f the Recent, YBS, and BGE sils fall int the lw range and als sme f the PYBE sils. Other members f the PYBE grup fall int the high range. The three sils f this grup in the lw range are all pdzls. There is a less clear-cut differentiatin between the intermediate and high range, but in general the YGE, YG/YBE and YBE sils fall in the intermediate range, the BL and YBP sils fall int the high range and the SYBE ccur abut equally ver the tw ranges. Brad classificatin units such as sil grups d nt appear t be entirely satisfactry fr separating sils int distinct P retentin grups suitable fr advisry purpses. Mst P fertilisers used in current frest fertilisatin peratins are applied t sils in the YG/YBE, PYBE, YBE and BL grups. Of immediate cncern insfar as efficient use f superphsphate is cncerned shuld be pdsl members f the PYBE grup and BL sils. These sils are readily identifiable by levels f Bray 2 extractable Al. Althugh it is advcated that insluble rck phsphate fertilisers be used in preference t superphsphate n sils exhibiting extremes f P retentin, it must be remembered that rck phsphates need t be slubilised befre they can be taken up by plants and a sil ph f belw 5.5 is usually required fr an adequate rate f slubilisatin. Mst frest sils in New Zealand with ph's higher than this, i.e., members f the Recent and YBS grups, are nt currently fertilised with P, but may be at sme future date fllwing nutrient remval in harvested prducts. Mst members f these grups als fall in the lw P-retentin range and thus sme strategy ther than the use f rck phsphates, such as use f frequent small applicatins f sluble fertiliser, will have t be emplyed t increase fertiliser efficiency. In cnclusin, it appears that the determinatin f Al levels in the 1-minute Bray 2 extract ffers a practical and reasnably precise means f estimating the P status fr frest sils in New Zealand. ACKNOWLEDGMENTS The authr wuld like t thank Dr D. S. Jacksn fr making the sil samples available and Mr Phillip Allen fr ding the chemical analyses. REFERENCES BALLARD, R. 1974: Use f sil testing fr predicting phsphate fertiliser requirements f radiata pine at time f planting. N.Z. J. Fr. Sci. 4: BALLARD, R. and FISKELL, J. G. A. 1974: Phsphrus retentin in Castal Plain frest sils: I. Relatinship t sil prperties. Sil Sci. Sc. Amer. Prc. 38:

9 N. 2 Ballard Predicting Phsphate Retentin 247 BALLARD, R. and PRITCHETT, W. L. 1974: Phsphrus retentin in Castal Plain frest sils: II. Significance t frest fertilisatin. Sil Sci. Sc. Amer. Prc. 38: BALLARD, R. and WILL, G. M. 1978: Past and prjected use f fertilisers in New Zealand frests. N.Z. J. Fr. Sci. 8(1): BLAKEMORE, L. C, SEARLE, P. L. and DALY, B. K. 1972: A. Methds fr chemical analyses f sils. N.Z. Sil Bureau, Scientific Reprt IOA. HUMPHREYS, F. R. and PRITCHETT, W. L. 1971: Phsphrus adsrptin and mvement in sme sandy frest sils. Sil Sci. Sc. Amer. Prc. 35: JACKSON, D. S. and GIFFORD, H. H. 1974: Envirnmental variables influencing the increment f radiata pine. (1) Peridic vlume increment. N.Z. J. Fr. Sci. 4: N.Z. SOIL BUREAU, 1968: Sils f New Zealand. Part 1. N.Z. Sil Bureau. Bull. 26(1). PRITCHETT, W. L. and SMI, W. H. 1974: Management f wet savanna frest sils fr pine prductin. Univ. Fla. Agric. Expt. Stn., Tech. Bull SAUNDERS, W. M. H. 1965: Phsphate retentin by New Zealand sils and its relatinship t free sesquixides, rganic matter, and ther sil prperties. N.Z. J. Agric. Res. 8:

Bootstrap Method > # Purpose: understand how bootstrap method works > obs=c(11.96, 5.03, 67.40, 16.07, 31.50, 7.73, 11.10, 22.38) > n=length(obs) >

Bootstrap Method > # Purpose: understand how bootstrap method works > obs=c(11.96, 5.03, 67.40, 16.07, 31.50, 7.73, 11.10, 22.38) > n=length(obs) > Btstrap Methd > # Purpse: understand hw btstrap methd wrks > bs=c(11.96, 5.03, 67.40, 16.07, 31.50, 7.73, 11.10, 22.38) > n=length(bs) > mean(bs) [1] 21.64625 > # estimate f lambda > lambda = 1/mean(bs);