LEONARD, FISKELL, DIAMOND: CLAY-LIME-POSPATE 27 EFFECT OF CLAY MATERIALS, LIME, AND POSPATE ON GROWT OF YOUNG ORANGE TREES C. D. Leonrd2 j. g.. plskell nd r. b. dimond3 Abstrct In field experiment, single pplictions of collodil phosphte nd clcined fuller's erth (both high-cly mterils), lime nd phosphorus fertilizers were mde t plnting time to 'mlin' ornge trees growing on double-dded Leon fine snd. The growth of both cnopy nd trunk of trees treted with colloidl phosphte or ful ler's erth in the plnting hole ws significntly greter thn tht of the untreted checks during the first 2 yers of the experiment. Significnt increses in trunk growth followed tretment with 20 pounds per tree of colloidl phosphte or 0.5 pounds of fuller's erth plus.5 pounds of ordinry superphosphte s compred with the checks fter 4 yers. Some significnt increses in lef content of potssium, clcium, mg nesium, nd phosphorus were obtined the first yer. Significntly more extrctle soil phos phorus, clcium, nd potssium resulted from some of the cly tretments thn from the checks in the fourth yer. Introduction Most of Florid's citrus groves re locted on cid, sndy soils. A mjority of the older plnt ings re on the well-drined sndy soils typicl of the Ridge re. During the pst few yers, thousnds of cres of new plntings hve en mde on poorly-drined sndy "fltwoods" soils of centrl nd south Florid. oth the welldrined nd the imperfectly-drined sndy soils hve low wter-holding cpcity nd low ction exchnge cpcity. Mny fltwoods res plnted to citrus consist of mixture of soil types, including some irregulr res of lightcolored sndy soils lmost devoid of orgnic mt ter. Citrus trees growing in such res my present specil problem, in tht they require more frequent ppliction of both wter nd ferlflorid Agriculturl Experiment Sttions Journl Series No. 2228. 2University of Florid Citrus Experiment Sttion, Lke Alfred. 3University of Florid Agriculturl Experiment Sttions, Ginesville. tilizer thn those on the drker-colored, more fertile res surrounding them. In the work reported here, cly mterils were incorported into the soil round newly plnted 'mlin' ornge trees in grove on Leon fine snd () to evlute the effects of cly mendments on soil properties nd (2) to deter mine the effects of such mendments on the growth nd lef composition of the trees. y in cresing moisture nd fertilizer retention nd improving the buffer cpcity of the soil, it ws hoped to produce more productive soil within the rooting re immeditely surrounding the tree. Colloidl phosphte (lso known s soft rock phosphte or wste pond phosphte) nd fuller's erth were the 2 cly mterils used. igh cl cium limestone, ordinry superphosphte, nd ground rock phosphte were lso used s com prtive tretments. Literture Review For more thn 20 yers, colloidl phosphte hs en used by few growers in Florid to limited extent by mixing it in the plnting hole round newly-plnted citrus trees. This mteril contins out 20 per cent totl phosphorus s rock phosphte but is lso high in cly content. Experiments with colloidl phosphte reported by vrious Florid reserch workers, however, hve emphsized its phosphte vilility rther thn the properties of the ssocited cly. Stemed bone nd "cid phosphte" resulted in 5-yer verge grpefruit yields slightly higher thn those from colloidl phosphte nd pebble phosphte (5). Colloidl phosphte used s the source of phosphorus in 6-4-8-2 fertilizer with minor elements outyielded no*phosphte tret ments pplied to "Pinepple" ornge trees, but superphosphte nd bsic slg outyielded col loidl phosphte (). On phosphorus-deficient Dvie mucky fine snd, colloidl phosphte tret ments produced ornges tht were mofe mture thn those from no-phosphte tretments, but superphosphte produced higher yields thn col loidl phosphte or rock phosphte (9). Ornge seedlings in pots of Lkelnd fine snd incresed in growth s rtes of ppliction of colloidl phosphte incresed from to 3 to 9
28 FLORIDA STATE ORTICULTURAL SOCIETY, 965 tons per cre, but mono-clcium phosphte p plied every 4 weeks t 20 pounds of phosphorus per cre produced more growth (8). Colloidl phosphte mixed with snd in cylinders incresed both root nd top growth of ornge seedlings over snd lone (7). Significnt increses in slsh pine growth over 5-yer period resulted from single ppliction of Vz ton to 2 tons of colloidl phosphte per cre t the time of plnt ing. Disking fter ppliction of colloidl phos phte incresed yields by out 3 cords per cre over the sme tretment without disking (3). No other sources of phosphorus were used in the slsh pine test, so it is not cler whether the growth effects were due primrily to the phos phorous or the cly experimentl methods. 'mlin' ornge trees on sweet ornge rootstock were plnted on double-row ds on Leon fine snd in the Vill Grove citrus development out 6 miles est of Wuchul, Florid on Feb rury 7, 962. Leon fine snd is somewht poorly drined nd formed from modertely thick de posits of snd. Drk gry fine snd 4 to 6 inches thick overlys light gry leched lyer 0 to 20 inches thick. An orgnic hrdpn out 6 inches thick occurs from 4 to 24 inches low the surfce. Some physicl nd chemicl properties of the surfce 6 inches of this soil re shown in Tle. It should noted, however, tht in building the ditches nd ds for wter control in the experimentl grove the soil ws ltered by plcing mteril from the ditches over the originl Leon profile on the ds. The experimentl re consisted of 4 ds with 2 rows of trees on ech d, spced 25 feet tween rows nd 20 feet tween trees within the row. The experimentl design ws rn domized block for mendments with plcement rndomized in split-plot within ech tretment. Ech min plot consisted of 8 trees with 4 con secutive trees in ech row on d. The plce ment tretments were pplied in the plnting hole for 4 trees (2 in ech row), nd brodcst round n equl numr of trees over n re of 0-foot dimeter. The 4 replictions were lo cted on djcent ds. The soil mendments were pplied only once when the trees were set. They included colloi dl phosphte t 0, 20, nd 50 pounds per tree, clcined fuller's erth (Diluex-A) t 0.5 pounds per tree with nd without phosphte dditives, high clcium limestone, ordinry superphosphte, nd ground rock phosphte. Colloidl phosphte is mixture of finely divided rock phosphte nd cly which ws wshed from rock phosphte in the mining process (6). It contins out 20 percent totl phosphorus, 70 percent cly, hs ction exchnge cpcity of out 23 milliequivlents per 00 grms, nd reltively high wterholding cpcity. Dileux-A is clcined fuller's erth mined nd processed in Florid. It hs ction exchnge cpcity slightly higher thn tht of colloidl phosphte nd much higher wter-holding cpcity. Some physicl nd chemicl properties of colloidl phosphte, ful ler's erth, nd Leon fine snd from the experi mentl grove re shown in Tle. Prior to plnting of the trees, holes were dug 5 inches in dimeter nd inches deep in the subplots where mendments were pplied in the plnting hole. About 00 pounds of soil were removed from the hole nd spred on 6- by 8-foot cnvs, nd the mendment or mend ments were spred over the soil. The mterils were mixed by rolling them 4 times from one end of the cnvs to the other. This mixture ws then returned to the plnting hole. The trees were plnted in the center of the mixtures in the holes nd in the stked positions in the plots receiving brodcst tretments. After the trees were plnted, mendments were brodcst in the pproprite res nd mixed into the top 2 or 3 inches of soil by hoeing. A wter bsin ws then built round ech tree. Further mixing of the soil with the brodcst mendments occurred when the trees were bnked nd unbnked. The trees were fertilized 4 times the first yer, using pound per tree of 6-4-6-3-%-% (N-P205-K20-Mg0-Mn0-Cu0) nlysis for Tretments to 0 inclusive, nd 6-0-6-3-%-% nlysis for Tretments nd 2. Lter in the yer, the mngnese ws in cresed to V2 unit MnO equivlent cuse of widespred mngnese deficiency symptoms on the trees. The trees received 2, 3, nd 4 pounds of similr fertilizer per tree t ech ppliction during the second, third, nd fourth yers re spectively. A pint mrk ws mde on the trunk of ech tree inch ove the bud union soon fter plnt ing. The trunk dimeter ws mesured for ech tree t tht time nd gin fter ech of the first 4 growing sesons s mesurement of growth. Tree height ove the pint mrk ws lso mes ured fter ech yer but gve errtic results cuse of vrying top dmge by the 962 freeze. eight mesurements, therefore, re not reported here.
-- -_ LEONARD, PISKELL, DIAMOND: CLAY-LIME-POSPATE 29 Tree growth out 4 months fter plnting ws estimted visully on June 9, 962. Trees were rted from 0 for the poorest ppernce of top growth to 0 for the st. In June, 963, 6 months fter plnting, photogrphs of indi vidul trees were tken. A projection screen ws set hind the tree, nd crds contining letters nd numrs to identify individul trees were plced in holder ttched to the screen. Photo grphs were tken t distnce of 9.5 feet from the cmer to the tree. Negtives of the photo grphs were plced in slide mounts, nd the imge ws projected onto screen grid with %-inch squres. The distnce from the projector lens to the screen ws 44 inches. The reltive cross-section re ws then re corded s the numr of squres covered by the imge of tree folige. Tle. Chemicl nd physicl properties of colloidl phosphte (CP), fuller's erth (FE), nd Leon fine snd from experimentl grove, Leon Property CP FE (0-6) f.s, Ction-exchnge cpcity by: N N40Ac, p 7.0, me/00 g 23.3 29.2 3.3- Ctions, extrcted by N N^OAc, p 7.0: K, 220 760 22 C, 4380 5880 97 Mg, 253 832 22 p in: Wter 7.6 8.2 4.6 N KC 6.9 7. 3.9 Phosphorus extrcted by: N^OAc, p 4.8, 0.03 N N4F in 0.025 N C, 53 800 0.5 5.0 7 6 Cly minerls present:' M, K At, M K Other minerls present:' Ap Q Specific surfce re of cly by: Glycerol dsorption, m /g 60 252 Moisture content t: 0.0 br tension, % weight (field cp.) 0.33 br tension, % weight 3.00 br tension, % weight 5.00 br tension, % weight (per. wilt) 62.48 44.20 36.77 28.48 7.0 4.24 99.09 85.83 -- -- -- Mechnicl nlysis: Snd, % Silt, % Cly, % 0.4 9.7 69.9.6 8.3 80. 97.23 2.47 0.30 ^Abbrevitions for minerls re s follows: Ap - ptite, At - ttpulgite, G - gibbsite, K - kolinite, M - montmorillonite, Q - qurtz, nd V - vermiculite.
30 FLORIDA STATE ORTICULTURAL SOCIETY, 965 Anlyses of leves, soils, nd clys were cr ried out with stndrd methods descrid in (2). Results nd Discussion Only those differences tht re sttisticlly significnt will reported nd discussed here, lthough the lck of significnt differences tween certin tretments will stted. The letter "" following tretment numr in the text nd in the tles refers to plnting-hole plcement, nd "" refers to brodcst plce ment of the mendments. Visul Rting of Trees. The visul rting of trees for cnopy growth mde on June 9, 962, 4 months fter plnting, showed tht plntinghole plcement of mendments contining lrge mounts of cly produced greter cnopy growth thn comprle brodcst tretments (Tle 2). For mendments not contining lrge mounts of cly, no differences existed for plce ment of the mendments. Plnting-hole pplic tion of ll mendments except lime (Tretment 6-) nd superphosphte lone (Tretment 0-) showed greter cnopy growth thn the check (Tretment ). Greter cnopy growth ws produced by ppliction of 0.5 pounds of fuller's erth with or without superphosphte (Tretments 7- nd 8-) thn by the sme mount of superphosphte lone (Tretment 0-). More cnopy growth resulted from mendment with 0.5 pounds of fuller's erth lone (Tretment 7-) thn from lime (Tret ment 6-). ence, incresed folir growth did not pper to phosphte response since greter folige ws produced with fuller's erth with or without superphosphte thn with super phosphte lone. Photogrphic Rting of Folige. The pro jected cross-sectionl re of the tree cnopies from photogrphs mde in June, 963, ws greter for ll mendments except superphos phte lone (Tretment 0) thn for the checks. From these observtions, it is pprent tht clys, liming, nd phosphte were fctors tht incresed growth of the young trees. Growth in Trunk Dimeter. Trunk growth of the trees ws greter from plnting-hole p pliction of colloidl phosphte t 0, 20, nd 50 pounds per tree (Tretments 2-, 3-, 4-, nd -) nd from fuller's erth t 0.5 pounds per tree with nd without phosphte dditives (Tretments 7-, 8-, nd 9-) thn from the checks during the first 2 yers of the experiment (Tle 3). Greter trunk growth ws obtined from brodcst ppliction of colloidl phosphte t 20 pounds per tree (Tretments 3- nd -) nd from 0.5 pounds of fuller's erth plus.5 pounds of superphosphte (Tretment 8-) thn from the checks fter 2 yers. More trunk growth resulted from brodcst ppliction of 7.5 pounds of lime per tree (Tret ment 6-) nd from plnting-hole ppliction of rock phosphte (Tretment 5-) thn from the checks fter 2 yers. Only colloidl phosphte t 20 pounds per tree (Tretments 3 nd ) nd 0.5 pounds of fuller's erth plus.5 pounds of ordinry superphosphte (Tretment 8) pro duced greter trunk growth thn the checks fter the third nd fourth yers. Evidence of the cly effect nd of the need for phosphte thus per sisted for 4 yers fter ppliction of these mendments. The growth dvntge of some of the plnting-hole tretments with the cly mendments over similr brodcst tretments during the first 2 yers decresed fter the third nd fourth yers. Lef Composition. Smples of young spring flush leves tken on My 2, 962, were n lyzed to determine the effects of the mend ments on lef composition. The potssium con tent of the leves ws not ffected by the mend ments or their plcement. Clcium concentrtion in the leves, however, ws greter from ll of the mendments pplied in the plnting hole thn from the checks (Tle 4). igher lef clcium ws obtined from plcement of the mendments in the plnting hole thn from brodcst plce ment except where superphosphte ws pplied lone (Tretment 0) or fuller's erth nd su perphosphte were combined (Tretment 8). igher lef mgnesium ws obtined from the fuller's erth mendments (Tretments 7, 8 nd 9) thn from the other tretments, nd plntinghole plcement enhnced this effect. The lef phosphorus ws not pprecily ffected by the mendments or their plcement. The reltively high levels of lef phosphorus re due to the nlysis of young leves. In Octor, 964, tht yer's spring flush leves were smpled for nutrient nlysis. No increses in lef phosphorus, clcium, potssium, or mgnesium over the check resulted from ppli ction of the soil mendments. Levels of lef phosphorus, potssium, nd mgnesium were dequte from ll tretments, including both checks (Tretments nd 2). Lef clcium levels were dequte from ll tretments except
LEONARD, PISKELL, DIAMOND: CLAY-LIME-POSPATE 3 Tle 2- Rtings of growth of young 'mlin' ornge trees t Vill Groves on mended Leon fine snd. Trt. Mterilst Tree rting No. Lbs per tree First yer" Second yer* 2 0 CP 24.0 7.5 59.3 53.5 3 20 CP 2.8 8.2 56.4 52.9 4 50 CP 25.0 8.5 63. 58.6 20 CP (-P) 22.5 58.2 7.2 56.0 7 0.5 FE 26.0 6.5 60. 57.2 8 0.5 FE + 0.2 OSP 0.5 FE + 25.2 20.0 65.3 49.6 9 0.5 FE + 26.2 5.2 64.5 49.4 6 lime 7.5 lime 5.8 6.0 58.8 77.5 5 2.2 5.5 65.6 54.6 0 0.2 OSP 7.2 7.5 44.5 47.9 (+P) 4.5 5.0 39.7 40.7 2 (-P) 6.5 7.0 42.6 5.7 S. E. of mens, tretments.54 8.3 S. E. of mens, plcement 0.47 2.49 + CP colloidl phosphte; FE fuller's erth; RP rock phosphte; lime high-clcium limestone; OSP ordi nry superphosphte; ( P) no-phosphte fertilizer. + + Visul rting is the sum for 4 trees. + + +Photogrphic rting which is the projected cross-sectionl re of the cnopy on the individul tree bsis.
32 FLORIDA STATE ORTICULTURAL SOCIETY, 965 Tle 3. Effect of cly, lime, nd phosphte mendments pplied brodcst nd in plnting holes on trunk growth of 'mlin' ornge trees growing on Leon fine snd. Trt. No. Mterils"** Lbs per tree yer Men growth in 2 yers trunk dimeter 3 ^rers (Cm) 4 yers 2 3 4 7 8 9 6 5 0 2 0 CP 20 CP 50 CP 20 CP (-P) 0.5 FE 0.5 FE+ 0.2 OSP 0.5 FE+ 0.5 FE+ lime 7.5 lime 0.2 OSP (+P) (-P) 0.98** A.77.99**.86*.64.89*.79.93*.73.78.80.58.68.86*.8.64.79.73.55.60 c ACD fg A c.07** A ACD e CD efg ACD e ACD fg AC ed ACD. 00** A efg ACD fg^ ACD fg D CD defg ACD e ACD edef CD efg ACD fg ACD efg fg i **ighly significnt over both checks (P = 0.0). D g CD.28*.2.66**.66**.5**.24.56**.55**.58**.7.82**.48**.59**.93.2.63**.44**.23.2.5.02.84 *Significnt over both checks (P = 0.05). Significnt over 2 (P = 0.05). CDEFG ef CDEFG A A ACDEF ed CDEFG defg ACDEF c ACDEF c ACDE c DEFG efsh A ACDEF de ACD c G hi CDEFG AC ACDEF def CDEFG defg CDEFG EFG fghi G ghi 3.20 3.6 3.4 3.36 3.6 3.72* 3.59 3.37 3.45 3.4 2.9 3.66 3.39 3.22 3.5 3.4 3.08 2.46 CDE ef CDE ef 4.02** A 4. 3** A 4.20** A ACD de ACD e AC ed AC c ACD ed ACD de 4.5** A ACD de CDE ef CDE efg AC ed ACD de CDE ef CDE ef CDE ef CDE def E g 5.66 5.82 6.68* 6.55* 5.32 5.73 7.34** A 6.5 6.27 6.3 6.29 6.02 5.72 4.64 6.25 5.77 5.33 5.59 5.4 5.4 4.49 CDEFG CDEF AC c ACD ed DEFG ghij CDEFG ACDE fg ACD def ACDE fg ACD de 6.7** A CDE fg CDEFG FG ij ACD fg CDEF efgh DEFG fghij CDEFG efgh CDEFG efghi CDEF efghi **CP - Colloidl phosphte; FE - fuller's erth; OSP - ordinry superphosphte; RP - rock phosphte; (+P) - OSP included in fertilizer; (-P) - no phosphorus included in fertilizer. '' Within ny column, mens followed by the sme cpitl letter do not differ t P = 0.0; mens followed by the sme lower cse letter do not differ t P = 0,05. G i
LEONARD, FISKELL, DIAMOND: CLAY-LIME-POSPATE 33 Tle 4. Chemicl composition of leves from young 'mlin' ornge trees t Vill Groves grown in mended Leon fine snd. Trt. Mterils' K Chemicl C composition Mg P No. Lbs per tree % % % % 2 0 CP.85.93 3.72 3.02 0.44 0.45 3 20 CP.92 2.5 4.03 3.27 0.39 0.44 0.29 0.33 4 50 CP.75.7 4.30 3.34 0.36 0.45 20 CP (-P) 2.06 4.0 0.36 2.4 3.02 0.40 0.28 7 0.5 FE.9 3.05 0.69.82 2.77 0.52 0.25 8 0.5 FE + 0.2 OSP.94 3.50 0.63 0.5 FE +.80 3.65 0.48 9 0.5 FE + 9.5 OSP.88 3.36 0.68.84 2.90 0.50 6 lime 7.5 lime.96 2.04 3.63 3.3 0.36 0.4 0.25 5.82 3.58 0.39 0.28.85 2.69 0.43 0 0.2 OSP.84 3.04 0.40.85 3.06 0.40 (+P).88 2.56 0.47 0.24.84 2.44 0.48 2 (-P).88 2.4 0.48.98 2.7 0.46 S,. E. of mens, tretments 0.46 0.243 0.040 0.06 S.. E. of mens, plcement 0.033 0.064 0.009 0.004 CP colloidl phosphte; Fe fuller's erth; RP rock phosphte; lime high-clcium limestone; OSP ordinry superphosphte ; ( P) no-phosphte fertilizer.
34 FLORIDA STATE ORTICULTURAL SOCIETY, 965 Tle 5. Effect of cly, lime, nd phosphte mendments pplied to Leon fine snd on extrctle soil clcium, phos phorus, nd potssium. Trt No. Mterils^ Lbs per tree Extrctle elements*'* Clcium Phosphorus Potssium 2 3 4 7 8 9 6 5 0 2 0 CP 20 CP 50 CP 20 CP (-P) 0.5 FE 0.5 FE + 0.5 FE + lime 7.5 lime (+P) (-P) 346 60* 439 495 59 377 39 344 500 390 405 228 95 24 308 A A A A 76** ' A ed A c A A A ed A A de e de e 7.0 CD 2.8** A e 9.6** AC 0.8** A 9.0** C 9.6** AC 9.4** AC 5.9 CDE def 7.8* CD 8.9** C 7.7* CD 7. CD 3.2 E e 4.2 DE fg 4.8 DE efs 5.0 DE **ighly significnt over both checks (P = 0.0), efg 38 76** 40 3 45 86** *Significnt over both checks (P = 0.05). ^CP - colloidl phosphte; FE - fuller!s erth; OSP - ordinry superphosphte; RP - rock phosphte; (+P) - OSP included in fertilizer; (-P) - no phosphorus in fertilizer. ' 'Within ny column, mens followed by the sme cpitl letter do not differ t P = 0.0; mens followed by the sme lower cse letter do not differ t P = 0.05. 35 58 40 37 4 38 43 37 43 37 A d A d A
LEONARD, FISKELL, DIAMOND: CLAY-LIME-POSPATE 35 plnting-hole plcement of rock phosphte (Tretment 5-) nd lime (Tretment 6-), nd from both checks, ll of which were in the low rnge but not in the deficient rnge for cl cium (4). This shows tht the plcement of lime or rock phosphte in the plnting hole ws not s effective s the cly mendments in supply ing clcium for the trees over 3-yer period. Soil Composition, In June, 965, soil ws smpled from ech of the brodcst plots nd from plots receiving 4 of the plnting-hole tret ments. The ltter included 20 pounds of colloidl phosphte (Tretment 3-), 0.5 pounds of ful ler's erth lone (Tretment 7-), pound of lime (Tretment 6-), nd the check receiving phosphte (Tretment -). No differences in soil p or extrctle mgnesium were found. More extrctle soil phosphorus ws obtined from plots receiving either 20 or 50 pounds of colloidl phosphte per tree (Tretments 3-, 3-, 4-, nd -), 0.5 pounds of fuller's erth lone or with rock phosphte (Tretments 7-, 7-, nd 9-, nd lime (Tretments 6- nd 6-) thn from the checks (Tle 5.) Only the 2 cly mterils pplied in the plnting holes (Tretments 3- nd 7-) showed more extrctle potssium thn the checks. Clcium ex trcted from the soil ws highest where 20 pounds of colloidl phosphte ws pplied (Tretments - nd 3-). From these soil nlyses, it ppers tht t lest prt of the effectiveness of colloidl phosphte nd fuller's erth s soil mendments my ttributed to tter soil retention of clcium, potssium, nd ville phosphorus. Conclusions Increses in growth of young 'mlin' ornge trees were obtined by mending Leon fine snd with clys. oth colloidl phosphte nd fuller's erth pper to stisfctory mendments. The results show tht both of these mterils when finely ground nd thoroughly mixed with sndy soil in the plnting hole offer considerle prom ise of incresing citrus tree growth for t lest the first 2 yers. The results reported here indi cte tht 20 to 40 pounds of colloidl phosphte per tree, mixed with 00 to 200 pounds of soil from the plnting hole, is desirle level. If brodcst, lrger mounts pper to necessry for good results, nd the mteril should cut 6 or 8 inches into the soil fore plnting if possible. Fuller's erth t somewht lower levels mixed with superphosphte should give compr le results. For plnting-hole tretment, thor ough mixing of the cly with the soil to void poorly erted sticky cly pockets in the root zone is emphsized. Acknowledgments We wish to thnk the Florence Citrus Grow ers' Assocition nd Mr. Wilbur Chrles, Pro duction Mnger, for their fine coopertion in providing use of the trees nd in ppliction of the fertilizers used in this experiment. We lso thnk the Soft Rock Phosphte Reserch Insti tute, Inc. for ssisting in the finncil support of this work nd for supplying the colloidl phosphte. Apprecition is lso expressed to the Floridin Compny for furnishing the fuller's erth use in this experiment. REFERENCES. ryn, O. C, nd J. NeSmith. 956. Fertilizer nd soil mendment studies with Pinepple ornges on Lkelnd snd. Soil Sci. Found. ull. 3. 2. Dimond, R.. 963. Amendment of sndy soil by soft rock phosphte or fuller's erth nd response of young citrus trees. Ph.D. Disserttion, Univ. of Fl., Ginesville, pp. 33-48. 3. Pritchett, W. L., nd K. R. Swinfo-d. 96. Fesponse of slsh pine to colloidl phosphte fertiliztion. Soil Sci. Soc. Am. Proc. 25: 397-400. 4. Reuther, Wlter, nd Pul F. Smith. 954. Lef nlysis of citrus, Chpter 7, p. 279. in Minerl Nutrition of Fruit Crops, published by orticulturl Publictions, Rutgers University, New runswick, New Jersey. 5. Ruprecht, R. W. 923. Treted phosphtes vs. rw phosphtes for citrus. Proc. Fl. Stte ort. Soc. 36: 2-24. 6. Suchelli, V. 95. Phosphtes in Agriculture. The Dvidson Chemicl Corportion, ltimore, Md. Rev. 7. Smith, P. F., nd G. K. Rsmussen. 957. Effects of nitrogen source, subsoil p nd substrte mendments on the growth of ornge seedlings. Soil nd Crop Sci.- Soc. Fl. Proc. 7: 262-273. 8. Wnder, I. W. 954. Avilility of phosphorus, potssium, nd mgnesium from insoluble sources s indi cted by the growth nd lef nlysis of sweet ornge seed lings. Proc. Fl. Stte ort. Soc. 67: 60-66. 9. Young, T. W., nd W. T. Forsee, Jr. 949. Fertilizer experiments with citrus on Dvie mucky fine snd. Fl. Agr. Exp. St. ull. 46.