Fractionation of Inorganic and Organic Phosphorus in ... - PubAg - USDA

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Amounts of phosphorus (P) in inorganic and organic pools were ... (calcareous soils only): organic P; labile (0.5M Na HCO3), moder- .... Co., MS. Coshocton Forest Corn-wheat-meadow. Co., OH meadow rotation ... OP in each pool, although overall OP chemistry was .... Hedley, M.J., J.W.B. Stewart, and B.S. Chauhan. 1982.
Fractionation of Inorganic and Organic Phosphorus in Virgin and Cultivated Soils' A. N. SHARPLEY AND S. J. SMITH2 amounts of P within inorganic and organic pools. Such information is needed to evaluate the effect of longterm cultivation (over 30 yr) on soil P fertility and to determine if transformations between inorganic and organic pools are related to soil properties. Recently, Hedley et al., (1982) reported that extractable (resin + NaHCO 3 + CHC1 3/NaHCO 3 ) IP and OP constituted 26 and 22%, respectively, of the decrease in P content of a Black Chernozemic soil in Canada cropped in a wheat - fallow rotation for 65 yr, compared to the same soil under pasture. The remainder of the change originated from more stable residual P. The following study investigates the change in amounts and distribution of IP and OP pools of differing chemical extractability, with the cultivation of eight soils. This study is a continuation of earlier work on the same soils which investigated the effect of cultivation and associated fertilizer application on the total IP and OP content (Sharpley and Smith, 1983) and the amount and distribution of N forms (Smith and Young, 1975).

ABSTRACT Amounts of phosphorus (P) in inorganic and organic pools were determined for three noncalcareous and five calcareous surface soils (0-150 mm) which had been cultivated for at least 15 yr, and their virgin analogues, to ascertain if relative pool sizes or soil P fertility are being changed by cultivation and associated fertilizer application. The soils were representative of major agricultural areas of the USA, with total P concentrations ranging from 200 to 1920 mg kg (approximately 50% inorganic P) and P applications from 0 to 90 kg ha' yr'. P forms in the pools and extractants used were as follows: inorganic P; loosely-bound (1.OM NH4C1), nonoccluded (0.5M NH4F + 0.1M NaOH), occluded (citrate-dithionite-bicarbonate + 0.5M NH4F + 0.1M NaOH), and Ca bound (1.OM HC1) (calcareous soils only): organic P; labile (0.5M Na HCO3 ), moderately labile (1.OM H2SO4 + 0.5M NaOH), moderately resistant (03M NaOH/HC1 soluble), and resistant (0.5M NaOH/HC1 insoluble). Distribution of inorganic P in virgin noncalcareous soils was, on average, 2% loosely-bound, 52% nonoccluded, and 46% occluded. Cultivation resulted in an increase in nonoccluded and decrease in occluded P. Average distribution in the virgin calcareous soils was 2% loosely-bound, 11% nonoccluded, 9% occluded, and 78% Ca-bound, with no significant change in pool size with cultivation observed. On average, organic P in the virgin soils was 7% labile, 48% moderately labile, 33% moderately resistant, and 12% resistant, with no significant change in relative amounts due to cultivation. Amounts of fertilizer P applied and organic P mineralized and immobilized in stable inorganic P pools during cultivation, were related to P sorption index of the soils. The conversion of organic to inorganic P may be reversed by management practices allowing a build up of soil organic matter. Since little change in amounts of loosely-bound inorganic and labile organic P was observed during cultivation, the more stable pools may represent a better estimate of long-term soil fertility.

MATERIALS AND METHODS The classification, location, and available management history are summarized in Table 1. More detailed information on the management history and chemical and physical properties of the eight paired virgin and cultivated soils has been given previously (Sharpley and Smith, 1983; Sharpley et al., 1983). The virgin and cultivated soils were divided into noncalcareous and calcareous groups based on the presence of free CaCO 3 (Sharpley et al., 1983). Several soil samples were taken at each location, composited, and packed in ice for transportation to the laboratory for analysis. Each location was level, minimizing erosional and/or depositional changes and the cultivated sites represent average to above average management for that area. As little change in the amount of total IP and OP in subsoil (150900 mm depth) was observed with cultivation of these soils (Sharpley and Smith, 1983), fractionation of IP and OP in surface samples (0-150 mm) only, was carried out. Inorganic P fractionation of the noncalcareous soils was carried out by the modified Chang and Jackson (1957) procedure of Peterson and Corey (1966). In this study looselybound IP represents that extracted by l.OM NH 4CI, nonoccluded IP by 0.5M NH 4 F and 0.1MNaOH, and occluded IP by citrate-dithionite-bicarbonate, 0.5M NH4F and a second 0. 1M NaOH extraction. For the calcareous soils, the modified Chang and Jackson (1957) procedure of Williams et al., (1971) was used. In these soils, loosely-bound IP represents that extracted by 1.OM NH 4C1, nonoccluded IP by 0.1 M NaOH, occluded IP by citrate-dithionite-bicarbonate (CDB) and a second 0. IM NaOH extraction, and Ca-bound IP by IM HC1. According to Chang and Jackson (1957), nonoccluded IP is that fraction associated with discrete Al and Fe phosphate particles such as variscite, strengite, and barrandite, and occluded IP represents Al and Fe phosphate occluded in Fe oxides. Soil OP in both noncalcareous and calcareous soils was fractionated by the sequential extraction procedure of Bowman and Cole (1978) into four pools: a labile pool, extracted by 0.5M NaHCO 3 ; a moderately labile pool, consisting of l.OM H 2SO4 soluble OP and 0.5M NaOH soluble OP; a moderately resistant pool, soluble in 0.5M NaOH and acid (pH 1.0-1.8,HC1) (fulvic acid fraction); and a resistant pool

Additional Index Words: labile P, P mineralization, P sorption.

Sharpley, A. N., and S. J. Smith. 1985. Fractionation of inorganic and organic phosphorus in virgin and cultivated soils. Soil Sci. Soc. Am. J. 49:127-130.

associated fertilizer application affect soil fertility and productivity (Williams, 1981). Previous studies have investigated changes in amounts of soil nitrogen (N) (Smith and Young, 1975) and P (Sharpley and Smith, 1983; Thompson et al., 1954; Tiessen et al., 1982) associated with cultivation. For example, Sharpley and Smith (1983) observed that c ultivation and fertilizer P application tended to increase total amounts of inorganic P (IP) and decrease organ i c P (OP) in surface horizons (0-300 mm) of agriculturally important soils. Little information exists, however, on the effects of cultivation and associated fertilizer P application on the distribution and C

ULTIVATION and

' Co ntribution of the Dep. of Agronomy, Oklahoma Agricultural Experiment Station, Oklahoma State Univ., Stillwater, OK, and W ater Quality & Watershed Research Laboratory, USDA-ARS, D urant, Okla. Agric. Exp. Stn. Journ. Set. no. 4443. Received 9 Apr. 1984. Approved 7 Aug. 1984. Soil Scientists. The first author is under a cooperative agreement With USDA-ARS, Durant, and Oklahoma State Univ., Agreement no. 5 8-7B30-822 Address: Water Quality & Watershed Research La boratory, USDA-ARS, P. o. Box 1430, Durant, OK 74702-1430.

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Table 1. Classification, location, and management history of the virgin and cultivated soils. Management Calcium carbonate Soil Designation Location Virgin Cultivation Fertilizer P Cultivated " eniod applied Virgin virgin Cult. yr kgha- —gkg Noncalcareous soils Caribou silt Alfic Aroostook Forest Potato-potato-fallowloam 50 2660 Haplorthods Co., ME red clover rotation Dundee silt Aeric Sunflower Forest Cotton loam 60 Ochraqualfs Co., MS Keene silt Aquultic Coshocton Forest Corn-wheat-meadow loam 30 1240 Hapludalfs Co., OH meadow rotation Calcareous soils Fargo silty Vertjc Polk Co., Native grass Small grains and alfalfa clay loam 60 238 Haplaquolls MN 29 62 Houston Black Udic Bell Co., Native grass Grain sorghum clay 60 Pellusterts 435 327 382 TX Leeper silty Vertic Oktibbeha Native brush Corn and soybeans clay loam 40 Haplaquepts 360 Co., MS 184 35 Reakor loam Typic Eddy Co., Native range Cotton, barley, sorghum, 16 Calciorthjds 140 NM 209 184 and sudangrass Webster clay Typic Story Co., Native grass Corn, soybeans, loam 72 Haplaquolls 96 IA 55 3 small grains meadow

sQluble in 0.5M NaOH but insoluble in HCI (humic acid fraction). For all samples P concentration was determined colori metrically on filtered samples by the molybdenum-blue method (Murphy and Riley, 1962). Acid or alkali filtrates were neutralized prior to P determination. In the following discussion, differences indicated statistically significant refer to the 5% level, as determined by analysis of variance (Snedecor and Cochran, 1971), unles s noted otherwise.

RESULTS AND DISCUSSION

was observed. For Webster, the decrease may result from a reduction in pH of the cultivated (6.3) compared to the virgin soil (7.4) (Sharpley et al., 1983), although no pH change was observed for the Leeper soil. The amount of OP in each pool decreased with cultivation with the exception of Keene silt loam (Table 3). This decrease was due mainly to a reduction in amounts of moderately labile and moderately resistant OP. In the Keene soil, which received additional OP in the form of manure, most of the soil OP increase occurred in the moderately labile (37%) and moderately resistant (59%) pools. In an earlier study, Sharpley et al. (1984) observed that application of manure (176 to 1614 tons ha -1 ) to irrigated continuous grain sorghum grown on Pullman clay loam over an 8 yr period, also resulted in increased amounts of OP in each pool, although overall OP chemistry was not changed. Distribution of total IP in the virgin noncalcareous soils was, on the average, 2% loosely-bound, 52% nonoccluded, and 46% occluded. Percentages for the virgin calcareous soils were 2% loosely-bound, 11% nonoccluded, 9% occluded, and 78% Ca-bound. Cultivation of the noncalcareous soils resulted in an increase

On average, total IP was 236 mg kg-' higher in the cultivated soils, and amounts of IP in each pool were increased compared to the virgin soil (Table 2). Relatively little of the P added as fertilizer, plant residue, or manure during cultivation, remained in the readily available, loosely-bound pool. For the noncalcareous soils, nonocciuded IP accounted for more than 50% of the IP increase (Table 2). In the case of the Dundee soil, no fertilizer P was added during cultivation. Consequently, increased amounts of IP in nonoccluded and occluded fractions in this soil result from residue incorporation and sorption of mineralized OP. For the calcareous soils, Ca-bound IP comprised over 69% of the increase in IP with cultivation (Table I). In the Webster and Leeper soils, a decrease in Ca-bound IP Table

a

Amounts of inorganic pse1ufldflIdd occluded,

Soil

Virgin Cult. Virgin Cult.

and c alcium-bound pools of the virgin and cultivated soils

Virgin

Occluded P Calcium-bound P Cult. Virgin Cult. Virgin Cult. P kg

Noncalcareous soils 646 1383 1 649(54) 392 170 201 3 4(1)t 253 1)-6) 110 139(93) 57 730(45) trt tr 47 230 1 2(1) 24 139(63) 22 61(13) tr tr 89(36) tr tr Calcareous soils Fargo sicl 331 Houston Black 234 567 4 29(11) 23 70(20) 19 19(0) 551 2 285 449(69) Leepersicl 158 56 1 5(1) 7 7(0) tr tr 225 539(99) 2(1) 8 10(2) tr Reakorl 178 562 3 tr 149 45(-102) Webster cl 156 259 7 10(1) 6 7)1) tr tr 169 545)98) 14(7) 57 137(78) 60 83(22) 32 25)-7) f Figures in parenthesis are percent contribution of each pool to the change in inorganic P content with cultivation. Trace amounts present. Caribou sil Dundee sil Keene sil

pp SHARPLEY & SMITH: FRACTIONATION OF PHOSPHORUS IN VIRGIN AND CULTIVATED SOILS

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Table 3. Amounts of organic Pin labile, moderately labile, moderately resistant, and resistant pools of the virgin and cultivated soils. Resistant P Moderately resistant P Total organic P Labile P Moderately labile P Virgin Cult. Virgin Cult. Virgin Cult. Virgin Cult. Virgin Cult. Soil mgPkg Noncalcareous soils 23 22(-1) 75 52(-17) 305 167 71 36(-25)t 136 57(-57) Caribou sil 15 5)-8) 43 17(-22) 75(-58) 7(-12) 144 22 224 104 Dundee sil 33 31(-2) 83 152(59) 93 133(34) 16(8) 7 216 332 Keene sil Calcareous soils 8 3(-2) 45(-43) 233 66)-53) 190 6 8)1) 437 122 Fargo sicl 4 1)-3) 120 53) —37) 150 42(-60) 1 1(0) Houston Black c 277 97 80 67(-9) 86(-17( 110 144 47(-67) 14 4(-7) 348 204 Leepersicl 43 40(-9) 32)-16) 222 190 4 2(-6) 127 105)-69) 48 Reakorl 129 98)-10) 139(-37) 253 51)-40( 10(-13) 175 49 606 298 Webster el Figures in parenthesis are percent contribution of each pool to the change in organic P content with cultivation. t

in non-occluded and decrease in occluded IF (Fig. 1). These changes were statistically significant. Webster soil was included in the statistical analysis, as the major proportion of IP in this soil was in the nonoccluded and occluded pools. For the remaining calcareous soils, the relative size of each IP pool was not significantly changed with cultivation (Fig. 1). In terms of overall IP distribution, then, only the noncalcareous soils exhibited a change. No difference between OP distribution in the noncalcareous and calcareous soils was observed. On average, OP in the virgin soils was 7% labile, 48% moderately labile, 33% moderately resistant, and 12% resistant, with no significant change in the relative amounts in each pool observed with cultivation of the eight soils (Fig. 1). Similarly, Smith and Young (1975) observed that cultivation had little effect on the distribution of organic N forms in the same eight soils as used in the present study. The pool of plant available, loosely-bound IP is maintained at a fairly constant level by fertilizer, residue, and manure addition and OP mineralization (Table 2). If this pool exceeds crop needs, it will be INORGANIC P [ ORGANIC P Noncolcoreous sods *

—j 0 I C.) W

0

Z $00

[1rm1rE

CJ Virgin souls

r

CM Cultivated souls - Calcorsous soils Z 0 50

0 0 rr ___ —S---Loosely Nonocc Occluded Calciun, Labile Mod Mod t.tSISTdflT labile resistant bound bound

Fig. 1—Proportion of inorganic P in loosely-bound, nonoccluded, occluded, and Ca-bound pools and organic P in labile, moderately labile, moderately resistant, and resistant pools averaged for the noncalcareous and calcareous soils. * Designates a significant diference (0.05% level) between virgin and cultivated soils, as determined by analysis of variance.

depleted by sorption, and movement from the soil surface by erosion and leaching. The net result of the cycling of P between loosely-bound and more stable IP and OP pools during cultivation can be quantified. Thus, the proportion of applied fertilizer P and mineralized OP immobilized in nonoccluded and occluded pools during cultivation was calculated for each soil from the amount of fertilizer P applied (Sharpley and Smith, 1983), OP mineralized (Table 3), and increase in nonocciuded and occluded IP pools (Table 2). Although the contribution of IP from residue incorporation could not be accounted for, this input will be partially reflected in the OP changes (Table 3). The proportion of IP, supplied by fertilizer P and OP mineralization, and immobilized in nonoccluded and occluded fractions was 93, 26, 43, 57, 16, 54, and 20% for Caribou, Dundee, Fargo, Houston Black, Keene, Reakor, and Webster soils, respectively. In the case of the Leeper soil, no net immobilization of IP in the nonoccluded and occluded pools occurred during cultivation. The immobilization of IP varied widely, with no apparent difference between calcareous and noncalcareous soils. Using P sorption data presented earlier (Sharpley and Smith, 1983), 92% of the variation in immobilization of IP between soils during cultivation, can be accounted for by P sorption index (Fig. 2). 100 Z

0 8o NJ —J

60

0 40

I— z LLJ 20 Li CL 0

R' 0.92 o NoncalcareOus • Calcoreous

y 15.57+0.58 x-0.0007 x2 0 200 400

P SORPTION INDEX

Fig. 2—The proportion of inorganic P, contributed by fertilizer P addition and organic P mineralization, immobilized in nonoccluded and occluded inorganic P pools during cultivation. Leeper was not included as no net immobilization of inorganic P occurred during cultivation.

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The conversion of loosely-bound IP and OP to nonoccluded and occluded IP and consequent reduction in soil fertility during cultivation, may be reversed by the introduction of management practices resulting in a build up of soil organic matter. The breakdown of plant residues and formation of an intimate mixture of decomposed residues and soil material generally requires an input of IP (Hedley et aL, 1982; McGill and Cole, 1981). This process may therefore, in the long term, result in an increase in the availability of nonocciuded and occluded IP forms, in terms of plantuptake. CONCLUSIONS Cultivation had no effect on the relative distribution of P within inorganic and organic pools for the five calcareous soils, but the three noncalcareous soils exhibited an increase in nonoccluded and decrease in occluded pools. As little change in the relative distribution of organic N forms was also observed with cultivation of these soils (Smith and Young, 1975), the chemical patterns for both organic P and N in soil organic matter tended to be preserved during cultivat ion. This appears to be the case whether P applications are in mineral or manure forms, and whether total organic P content of the soil increases or decreases during cultivation. Amounts of soil IP increased with cultivation and associated fertilizer P application, with nonoccluded and Ca-bound IP constituting the major proportion of the change. In the case of OP, moderately labile and moderately resistant pools exhibited the greatest amount of change. On the other hand, amounts of P in the most chemically unstable inorganic (looselybound) and organic pools (labile) changed little with cultivation. Inorganic P added to the loosely-bound pool during cultivation was immobilized in nonoccluded, occluded, and Ca-bound pools as a function of P sorption index. In the case of labile OP, it is suggested that this pool is maintained at a fairly constant level unless severely depleted during mineralization. Following this, a shift occurs from moderately labile and moderately resistant OP, to labile OP. The increase in amounts of nonoccluded, occluded, and Ca-bound IP and decrease in moderately labile and moderately resistant OP with cultivation, indicates a general decrease in soil P fertility. A similar reduction in the P supplying power of two Canadian chernozems, greater than may be expected from changes in total P contents, was also observed by Ties-

sen et al., (1983). This trend may be reversed by implementation of cultivation practices which increase soil organic matter and as a result, OP. It is apparent, therefore, that the stable IP (nonocciuded and occluded IF) and OP (moderately labile and moderately resistant OP) pools represent an estimate of long-term fertility of the soil, whereas the more labile pools (loosely-bound IF and labile OP) represent an immediate or short-term fertility. REFERENCES 1. Bowman, R.A., and C.V. Cole. 1978. An exploratory method for fractionation of organic phosphorus from grassland soils. Soil Sci. 125:95-101. 2. Chang, S.C., and M.L. Jackson. 1957. Fractionation of soil phosphorus. Soil Sci. 84:133-144. 3. Hedley, M.J., J.W.B. Stewart, and B.S. Chauhan. 1982. Changes in inorganic and organic soil phosphorus fractions induced by cultivation practices and by laboratory incubations. Soil Sci. Soc. Am. J. 46:970-976. 4. McGill, W.B., and C.V. Cole. 1981. Comparative aspects of cycling of organic C, N, S and P through soil organic matter. Geoderma 26:267-286. 5. Murphy, J., and J.P. Riley. 1962. A modified single solution method for the determination of phosphate in natural waters. Anal. Chjm. Acta. 27:31-36. 6. Peterson, G.W., and R.B. Corey. 1966. A modified Chang and Jackson procedure for' routine fractionation of inorganic soil p hosphates. Soil Sci. Soc. Am. Proc. 30:563-565. 7. Sharpley, AX, and S.J. Smith. 1983. The distribution of phosphorus forms in virgin and cultivated soils and potential erosion losses. Soil Sci. Soc. Am. J. 47:581-586. 8. Sharpley, AX, S.J. Smith, and L.W. Reed. 1983. Selected properties of paired virgin and cultivated soils from major land resource areas. Okla. State Univ., Agric. Expt. Stn. Tech. Bull. T- 159. 9. Sharpley, AN., S.J. Smith, B.A. Stewart, and A.C. Mathers. 1984. Phosphorus forms in soil receiving cattle feedlot waste. J. Environ. Qual. 13:211-215. 10. Smith, S.J., and Young, L.B. 1975. Distribution of nitrogen forms in virgin and cultivated soils. Soil Sci. 120:354-360. 11. Snedecor, G.W., and W.G. Cochran. 1971. Statistical methods. 6th ed. The Iowa State University Press, Ames. 12. Thompson, L.M., C.A. Black, and J.A. Zoellner. 1954. Occurrence and mineralization of organic phosphorus in soils, with particular reference to associations with carbon, nitrogen and pH. Soil Sci. 77:185-196. 13. Tiessen, H., J.W.B. Stewart, and J.R. Bettany. 1982. Cultivation effects on the amounts and concentrations of carbon, nitrogen, and phosphorus in grassland soils. Agron. J. 74:831-835. 14. Tiessen, H.,J.W.B. Stewart, and J.O. Moir. 1983. Changes in organic and inorganic phosphorus composition of two grassland soils and their particle size fractions during 60-90 years of cultivation. J. Soil Sci. 34:815-823. 15. Williams, J.D.H., J.K. Syers, R.F. Harris, and D.F. Armstrong. 1971. Fractionation of inorganic phosphate in calcareous lake sediments. Soil Sci. Soc. Am. Proc. 35:250-255. 16. Williams, J.R., Chairman, National Soil-Erosion Productivity Research Planning Committee, USDA-ARS. 1981. Soil erosion effects on soil productivity: a research perspective. J. Soil Water Conserv. 36:82-90.