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Environmental thresholds of phosphorus saturation in Manitoba soils

D. V. Ige1; O. O. Akinremi1, 3, D. N. Flaten1 and G.H. Crow2

1Department of Soil Science; 2Department of Animal Science University of Manitoba, Winnipeg,

Canada R3T 2N2; 3To whom correspondence should be addressed ([email protected])

Abbreviation list: Degree of P saturation (DPS); Langmuir adsorption maximum (Smax); P

sorption index at 150 mg L-1 of added P (P150).

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Ige D. V., Akinremi O. O., Flaten D. N. and Crow G.H. 2008 DegreeEnvironmental thresholds

of phosphorus saturation in Manitoba soils.Can. J. Soil Sci. ZZ: Y-X. The degree of phosphorussaturation (DPS) is the percent ratio of phosphorus (P) retained by soil to the total capacity of

soil to retain P. It is a risk indicator that requires a threshold for determining the P loss risk

potential. In a previous study, we developed methods for calculating DPS for neutral to

calcareous soils of Manitoba. The objectives of this study were to evaluate the DPS methods and

to determine the DPS threshold for Manitoba soils. Forty representative surface soil samples

were collected from across Manitoba. The soils were incubated with six rates of P for 4 weeks

after which Mehlich-3, Olsen and water extractable P were measured. The DPS was calculated as

the percent ratio of Mehlich-3 or Olsen extractable P to P sorption indices estimated as the

Langmuir adsorption maximum (Smax), single point sorption index (P150) or the sum of Mehlich-3

extractable Ca and Mg {(Ca+Mg)M3}. The DPS thresholds of the soils were estimated as the

change point of the split-line regression plot of DPS against water extractable P. The use of more

easily measure P sorption indices, P150 or (Ca+Mg)M3 with a saturation coefficient () of 0.2

produced DPS threshold that was greater than 100 % which was unrealistic. As such, we

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Key words: adsorption maximum; degree of phosphorus saturation; degree of phosphorus

saturation threshold; phosphorus sorption capacity; sorption indices.

The deteriorating water quality with its attendant environmental, social and economic

implications has been a major issue in recent times; and agricultural activities have been

identified as one of the most significant causes (Chambers et al., 2001, Gaballah, 2005,

Tyrchniewicz and Tyrchniewicz, 2006). Long-term application of P fertilizer and animal manure

results in build up of soil P (Schreiber, 1988; Pote et al., 1999) which increases the potential of P

loss to surface water through overland flow and subsurface drainage. Thus, there is a pressing

need for efficient management and monitoring of P in agricultural soils. However, to effectively

manage P in soils, we need a reliable risk indicator to assess the potential of P loss from soil to

surface and subsurface water.

Different methods have been proposed for estimating the potential of P loss from P

enriched soils. McDowell and Sharpley (2001) suggested the use of water and 0.01 M CaCl 2

extractable P for estimating the potential of P loss to runoff. Pote et al. (1999) reported that

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buffering capacities of soils resulting from varying levels of Fe and Al hydroxyoxides, clay,

carbonates and organic matter content of soils (Sharpley et al., 1996). Thus, two soils with the

same extractable P may not necessarily pose the same risk to the environment. Sibbesen and

Sharpley (1997) also reported that the relationship between P loss to water and soil test P varies

with crops grown and between runoff episodes.

The degree of P saturation has been suggested as a better index of the risk of P loss to

surface water (Sharpley 1995, Sharpley et al., 1996, Sims et al. 2002). It is based on the fact that

although soils have capacity to retain applied P, this P retention capacity is finite; and as more P

is added to the soil, the soils capacity to retain P decreases and the risk of P loss increases. Thus,

DPS is determined as the percent ratio of phosphorus (P) retained by the soil (intensity factor) to

the total capacity of the soil to retain P (capacity factor). The intensity factor represented soil P

that could be potentially released and the capacity factor represented the total P that could be

retained in the soil. Thus, the DPS takes both the P intensity and capacity factors of the soil into

consideration, hence accounting for the variability due to soil types in assessing the risk of P loss

from soil to surface water.

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of Olsen or Mehlich-3 extractable P to the sum of Mehlich-3 extractable Ca and Mg using an

value of 0.2. However, Ajiboye et al. (2007) adopted the DPS method of Ige at al. (2005a) and

noted that the DPS from Mehlich-3 Ca and Mg were small compared to that from S max; an

indication that the method needs some refinement.

The degree of P saturation has been shown to be closely correlated with dissolved runoff

P (Sharpley et al., 1996). Research conducted in Canada (Gurin et al., 2007) and elsewhere

(Breeuwsma et al., 1995) on acidic soils indicated that DPS was a very useful index to predict

the concentration of P in surface and drainage waters. New fertilizer application guidelines have

been developed for potatoes and corn in Quebec, using the DPS concept for acidic soils (Quebec

Ministry of Environment and Fauna, 1999).

In assessing the potential for P loss, however, there is a need to establish a critical limit,

beyond which the loss of P is greatly increased, which will serve as a reference point for

determining the risk of P loss. Breeuwsma and Silva (1992) established a threshold of 25 % for

the acid soils of Netherlands. Beyond this value, P loss to runoff becomes unacceptable. Casson

et al. (2006) obtained a DPS threshold of 27% for Alberta soils by using a critical desorbable P

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MATERIALS AND METHODS

For this study, 40 representative surface soil samples (0-15 cm) were collected from across

Manitoba. The samples comprised of 20 soils with history of manure application and 20 without

history of manure application. Of the 20 manured soil samples, 16 had a non-manured pair. The

soils were collected from the farmers fields or experimental plots generally used for grain crop

cultivation. The soil samples were air dried, gently crushed and made to pass through a 2 mm

sieve.

The chemical and physical properties of the soils were determined by routine laboratory

analysis. The soil pH was determined in 0.01 M CaCl 2 solution using a soil to solution ratio of

1:5. The soil particle size distribution was determined by the pipette method (Gee and Bauder,

1996). Mehlich-3 extractable P, Ca and Mg were determined as described by Mehlich (1984)

while the method of Self-Davis et al. (2000) was used to determine the water soluble P. Olsen

extractable P was determined as described by Olsen and Sommers (1982). Mehlich-3, water and

Olsen extractable P were analyzed colorimetrically for P using the ascorbic acid-molybdate blue

method (Murphy and Riley, 1962). Mehlich-3 extractable Ca and Mg were determined by

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where S' is the amount of P sorbed, K is the linear sorption coefficient, C is the equilibrium P

concentration at low concentration of added P (in our case, 0 to 5 mg P L-1

), and So is the native

sorbed P. The plot of S' against C gives So as the negative value of the intercept. The sum of S'

and So (S' + So) represents the amount of P sorbed (S) at the respective equilibrium P

concentration. The linear form of the Langmuir adsorption model was then fitted to the corrected

sorption data to determine the Langmuir adsorption maximum (Smax).

Phosphorus Incubation Study

For the P incubation study, all 40 soils were incubated with six rates of P (10, 50, 100, 200, 400,

and 800 mg P kg-1 of soil). A 25 g portion of soil sample was incubated with P (as KH 2PO4) at

field moisture capacity for four (4) weeks. At the end of the incubation period, the incubated

soils were air dried, gently crushed and made to pass through a 2 mm pore size sieve. Water,

Olsen and Mehlich-3 extractable P were determined for the incubated soils. The DPS of the soils

was determined using the formulas proposed by Ige et al. (2005a) as:

1001max

=

S

PDPS ZZ

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where, DPSZ is the DPS determined from either the Mehlich-3 or Olsen soil P extraction method

and PZ is Mehlich-3 or Olsen extractable P; P150 is the P sorption index from single point sorption

isotherm at 150 mg P L-1 added P; Smax is the Langmuir adsorption maximum; CaM3 and MgM3 are

Mehlich-3 extractable Ca and Mg (all expressed in mmol kg-1) and is the saturation coefficient

and has a value of 0.2. We adopted the use of Ca and Mg as sorption index instead of Al and Fe

that had been widely reported in literature because our previous studies showed that Al and Fe

were not good predictor of P sorption in Manitoba soils (Ige et al. 2005b). Mehlich-3 extractable

P was used because it is widely used for soil P test and DPS that are based on Mehlich-3 P are

well reported in literature making it possible to compare our results to those in the literature.

Another advantage of using Mehlich-3 extractable P is that it could be determined from the same

extract along with Ca and Mg. We also used Olsen extractable P to generate DPS because it is

the traditional method for soil P test and for regulating P in Manitoba.

Equation 2 is the preferred method for calculating DPS. However, the tedious nature of S max

determination might make its adoption difficult. Thus, equations 3 and 4, both referenced to

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and Sharpley, 2001). Statistical analysis showed that the data point for the highest rate of P

addition had a high leverage effect on the relationship between DPS and water extractable P for 5

of the 40 soils. Since no significant difference was observed in the change point obtained from

the 7-point and 6-point regression for the other soils with no leverage effect; the last point was

eliminated from the regression analysis of all the soils for consistency. The student t-test was

used to compare the DPS values for the manured and non-manured soils. Also, the student t-test

was used to compare the DPS determined from the various methods to test the null hypothesis

that the DPS means from these methods are the same.

RESULTS AND DISCUSSION

Evaluation of a DPS Threshold for Manitoba Soils

The general properties of the soils used in this study are presented in Table 1. Extractable P

(Mehlich-3, Olsen and water) and DPS values of the soils increased steadily with increasing

amounts of added P (Table 2). The increase in extractable P became significant (P


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of P is an indication of increasing saturation of P sorption sites as the P added increased. The

DPS for manured soils were significantly greater than those of the non-manured pair probably (P

< 0.05) due to the reduction in PSC of soil following manure application (Hue, 1991; He et al.,

1990, Ajiboye et al. 2007).

Figures 1 and 2 shows the plots of DPS against water extractable P for some of the soils

used in this study. The change point in the plot corresponds to the threshold, above which the

risk of P loss increases more rapidly with additional P application. Thirty of the 40 soils

exhibited change points. The change point was absent for 10 soils 9 of which had high

extractable P in the range of 70 to 389 mg kg -1 probably because the threshold has been exceeded

in the original soils before further P addition, considering the high level of extractable P in these

soils. It might also be that some soils lack change points. Figures 1 and 2 showed the split-line

plot of some soils that did not exhibit change point. This was observed mostly among the

manured soils probably because of the lower P sorption maximum observed in the manured soils

compared to the non-manured soils and the build-up of soil P from past history of manure

application. This illustrates the impact of continuous manure application on soil P saturation. The

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The degree of P saturation threshold varied widely depending on the method used to

calculate it (Tables 3 and 4). The thresholds for DPSM3 1 (that used Smax as the capacity factor)

ranged from 11 to 68 % with a mean of 25 % while the values for DPS Ols 1ranged from 3 to 97

% with a mean of 22 %. The DPSM3 2 and DPSM3 3 thresholds (which used P150 and (Ca+Mg)M3,

respectively) for the soils ranged between 17 and 122 % with a mean of 43 % and between 6 and

134 % with a mean of 19 %, respectively. On the other hand, the thresholds for DPS Ols 2 and

DPSOls 3 ranged between 6 and 160 % with a mean of 34 % and between 2 and 53 % with a mean

13 %, respectively. The mean thresholds obtained for Olsen P based DPS were not significantly

different from those obtained from Mehlich-3 (P > 0.05) despite the fact that Olsen reagent

extracted less P than the more acidic Mehlich-3 (Sims 2000, Ige et al. 2006). The similarity in

the DPS values obtained from these two soil test P methods showed that either of them could be

used to determine the DPS of soils. The choice will be guided by the method generally adopted

for routine soil test in the region.

Comparing the thresholds from the same extractable P (either Olsen- or Mehlich-3

extractable P), the DPS values estimated from P150 (DPSM3 2 and DPSOls 2) were significantly

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data were corrected for the native sorbed P to obtain the S max, neither of (Ca+Mg)M3 nor P150 was

corrected for native sorbed P. Graetz and Nair (2000) and D'Angelo et al.(2003) suggested the

correction of soil P sorption indices for native sorbed P because soils have different P

fertilization histories.

Refinement of the DPS Equations for Manitoba Soils

Based on the suggestion of Ajiboye et al (2007) that the DPS equations need some

refinement, we propose two new equations for estimating DPS in neutral to calcareous soils.

1007.1

4

150

+

=

Z

Z

Z

PP

PDPS

Eq. 5

100)(

53

++

=

ZM

Z

ZPMgCa

PDPS

Eq. 6

is the slope of the regression line of Smax against (Ca + Mg)M3 forced through the origin and has

l f 0 1 hi h i h lf f h l d b l (200 ) h f f 1

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0.61 for DPSZ 4 and DPSZ 5, respectively, which were similar to what was reported in our earlier

study for equation 2 (Ige et al. 2005a). Using these new methods for calculating the DPS gives

the threshold range of 9 to 58 % for DPSM3 4 and between 12 to 76 % for DPSM3 5 (Table 3).

With Olsen extractable P, the DPS threshold range of 3 to 46 % for DPSOls 4 and 5 to 56 % for

DPSOls 5 (Table 4).

The DPS Threshold for Manitoba Soils

Using DPSM3 1 and DPSOls 1, the mean DPS threshold values for Manitoba soils were 25 % and

22 %, respectively. These are similar to the thresholds obtained from the newly proposed method

in this study (DPSZ 4 and DPSZ 5). The mean DPS threshold for DPSZ4 is 21 % with Mehlich-3

P and 16 % with Olsen P while for DPSZ5 the values are 26 and 20 % for Mehlich-3 and Olsen

extractable P, respectively. Except for soil 9 where the value of DPSZ 4 (27 %) was much smaller

than that of DPSZ 5 (76 %) when the soil test P was PM3, the DPS values obtained from the two

methods are statistically the same (P>0.05). The lack of a significant difference between DPSZ 4

and DPSZ 5 indicated that the two parameters used as the denominator provided estimates of PSC

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evaluating soil DPS. In the alternative, the sum of Mehlich-3 Ca and Mg which is well adapted

for routine analysis can be used to calculate DPS in soil as shown in the equation for DPSZ 5.

The DPS threshold values of 25 % (with Mehlich-3 P) and 22 % (with Olsen P) are

similar to the DPS threshold reported by Breeuwsma and Silva (1992) for the acid soils of the

Netherlands. Casson et al. (2006) reported a DPS threshold of 27 % for Alberta soils and Pautler

and Sims (2000) reported that DPS values of 25 to 40 % are generally associated with high risk

of P loss to water.

CONCLUSION

We used the equation proposed by Ige et al. (2005a) to evaluate the DPS threshold of Manitoba

soils, and obtained several DPS thresholds that exceeded 100 %, which was unrealistic. This was

an indication that the P sorption indices used to calculate DPS did not provide adequate estimates

of PSC. While the Langmuir adsorption maximum is the best parameter for calculating the DPS

(providing a realistic measure of PSC), the tedious and time consuming nature of its

determination makes it unsuitable for practical application. When we used the relationship

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Overall, the DPS threshold for Manitoba soils is 25 % based on Mehlich-3 extractable P

and 22 % based on Olsen P. Above these values, the loss of P from soil may increase greatly.

ACKNOWLEDGEMENTS

The study was supported by Manitoba Livestock Manure Management Inc. (MLMMI),

Sustainable Development Innovation Fund (SDIF) and Manitoba Rural Adaptation Council

(MRAC).

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Ajiboye, B., Akinremi, O. O., Flaten, D. N. and Racz, G. J. 2007. Influence of biosolids on

phosphorus sorption characteristics of a Vertisol in comparison with manures and fertilizer. Can.

J. Soil Sci. 87:511-521.

Bache, B. W. and Williams, E. G. 1971. A phosphate sorption index for soil. J. Soil Sci.

22:289-301.

Beck, M. A., Zelazny, L. W., Daniels, W. L. and Mullins, G. L. 2004. Using the Mehlich-1

extract to estimate soil phosphorus saturation for environmental risk assessment. Soil Sci. Soc.

Am. J. 68:1762-1771.

Borling K., E. Otabbong, and E. Barberis. 2004. Soil variables for predicting potential

phosphorus release in Swidish noncalcareous soils. J. Environ. Qual. 33: 99-106.

Breeuwsma, A. and Silva, S. 1992. Phosphate fertilization and environmental effects in the

Netherlands and the Po Region (Italy). Report 57, Agric. Res. Dep. The Winand Staring Centre

for integrated Land, Soil and Water Research, Wageningen.

Breeuwsma, A., Reijerink, J. G. A. and Schoumans O. F. 1995. Impact of manure on

accumulation and leaching of phosphate in areas of intensive livestock farming. pages 239-251.

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7

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9

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D'Angelo, E. M., Vandiviere, M. V., Thom, W. O. and Sikora F. 2003. Estimating soil

phosphorus requirements and limits from oxalate extract data. J. Environ. Qual. 32:1082-1088.

Gee, G. W., and Bauder, J.W. 1996. Particle-size analysis. pages 399403. in A. Klute (ed.)

Methods of soil analysis. Part 1. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI.

Graetz, D. A., and Nair, V. D. 2000. Phosphorus sorption isotherm determination. pages 3538.

in G.M. Pierzynski, ed. Methods of phosphorus analysis for soils, sediments, residuals, and

waters. Bull. 396. Southern Ext./Res. Activity-Info. Exchange Group (SERA-IEG-17), Kansas

State Univ., Manhattan.

Gurin, J., Parent L. and Abdelhafid R. 2007. Agri-environmental Thresholds using Mehlich

III Soil Phosphorus Saturation Index for Vegetables in Histosols. J. Environ. Qual. 36:975-982.

He, Z. L., Zhu, Z. X. and Yuan, K.N. 1990. Competitive adsorption of some organic ligands

with phosphate in soils. Acta Pedologica Sinica 27:377-384.

Hue, N.V. 1991. Effect of organic acids/anions on P sorption and phytoavailability in soils with

different mineralogies. Soil Sci. 152:463-471.

Ige, D. V, Akinremi, O. O., and Flaten, D. N. 2005a. Environmental index for estimating the

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7

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Khiari, L., Parent, L. E., Pellerin, A., Alimi, A. R. A., Tremblay, C., Simard, R. R. and

Fortin, J. 2000. An agri-environmental phosphorus saturation index for acid coarse-textured

soils. J. Environ. Qual. 29:15611567.

McDowell, R. W., and Sharpley, A. N. 2001. Approximating phosphorus release from soils to

surface runoff and subsurface drainage. J. Environ. Qual. 30:508520.

McDowell, R. W., Sharpley, A. N., Condron, L. M., Haygarth, P. M., and Brookes, P. C.

2001. Processes controlling soil phosphorus release to runoff and implications for agricultural

management. Nutr. Cycl. Agroecosyst. 59:269-284.

Mehlich, A. 1984. Mehlich 3 soil test extractant: A modification of Mehlich 2 extractant.

Commun. Soil Sci. Plant Anal. 15:1409-1416.

Murphy, J. and Riley, J. P. 1962. A modified single solution method for the determination of

phosphate in natural waters. Anal. Chim. Acta. 27:31-36.

Nair, V. D., Portier, K. M., Graetz, D. A. and Walker, M. L. 2004. An environmental

threshold for degree of phosphorus saturation in sandy soils. J. Environ. Qual. 33:107-113.

Olsen S R and Sommers L E 1982 Phosphorus p 403-429 In: A L Page et al (ed )

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Parent, L. E. and Marchand, S. 2006. Response to phosphorus of cranberry on high phosphorus

testing acid sandy soils. Soil Sci. Soc. Am. J. 70:1914-1921.

Pautler, M. C. and Sims, J. T. 2000. Relationships between soil test phosphorus, soluble

phosphorus, and phosphorus saturation in Delaware soils. Soil Sci. Soc. Am. J. 64:765-

773.

Pote, D.H., Daniel, T.C., Sharpley, A.N., Moore, P.A., Jr., Edwards, D.R. and Nichols, D.J.

1996. Relating extractable soil phosphorus to phosphorus losses in runoff. Soil Sci. Soc. Am. J.

60:855859.

Pote, D. H., Daniel, T. C., Nichols, D. J., Sharpley, A. N., Moore, P. A., Jr., Miller, D. M.

and Edwards, D. R. 1999. Relationship between phosphorus levels in three Ultisols and

phosphorus concentrations in runoff. J. Environ. Qual. 28:170175.

Quebec Ministry of the Environment and Fauna. 1999. Guide egro-environmental de

fertilisation.

Reddy, K. R., OConnor, G.A. and Gale, P.M. 1998. Phosphorus desorption capacities of

l d il d di i d b d i ffl i Q l 2 1 10

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Sharpley, A., Daniel, T. C., Sims, J. T. and Pote, D. H. 1996. Determining environmentally

sound soil phosphorus levels. J. Soil Water Conserv. 51:160-166.

Sharpley, A. N., Smith, S. J. and Menzel, R.G. 1986. Phosphorus criteria and water quality

management for agricultural watersheds. pages 177182. in Proc. 5th Ann. Conf. Int. Symp.

Appl. Lake Watershed. Manage., Lake Geneva, WI. 1316 Nov. 1985. North Am. Lake Manage.

Soc., Lake Geneva, WI.

Sibbesen, E. and Sharpley, A. N. 1997. Setting and justifying upper critical limits for

phosphorus in soils. pages 151176. in H. Tunney, O.T. Carton, P.C. Brookes, and A.E. Johnson,

eds. Phosphorus loss from soil to water. CABI Publ., New York.

Sims, J. T. 2000. Soil test phosphorus: Olsen P. pages 20-21. in G.M. Pierzynski, ed. Methods

of phosphorus analysis for soils, sediments, residuals and waters. Southern Cooperative Series

Bull. No. 396 Kansas St. University, Manhttan, KS.

Sims, J. T., Maguire, R. O., Leytem, A. B., Gartley, K. L., and Pautler, M. C. 2005.

Evaluation of Mehlich 3 as an agri-environmental soil phosphorus test for the mid-Atlantic

United States of America. Soil Sci. Soc. Am. J. 66:2016-2032.

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Table 1. General properties of the soils used in the studyz (n=40)

Soil properties Minimum Maximum Mean Median

pHCaCl2 5.8 7.6 6.8 7.0

Sand (g kg-1) 25 873 457 409

Silt (g kg-1) 50 619 267 277

Clay (g kg-1) 77 777 276 222

CaM3 (mg kg-1) 584 10841 4931 4263

MgM3 (mg kg-1) 67 3266 973 764

PM3 (mg kg-1) 5.7 389 68 37

PH2O (mg kg-1) 0.3 39 7.8 4.2

POls (mg kg-1) 3.4 273 43 27

zCaM3, MgM3 and PM3 are Mehlich-3 extractable Ca, Mg, and P, respectively and PH2O is water extractable P.

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Table 2. Ranges of extractable P in the soil at 6 levels of added P after 4

weeks of incubation (n=40)

Added P

(mg P kg-1)

Minimum Maximum Meanz Median

PH2O (mg kg-1) y

10 0.5 68.3 9.5 d 4.9

50 1.1 77.0 14.0 d 10.2

100 3.6 90.8 24.7 d 21.8

200 11.6 143.5 53.3 c 47.1400 42.9 230.0 111.4 b 107.6

800 126.5 425.3 258.4 a 257.6PM3 (mg kg-1) y

10 17.8 455.0 88.6 e 59.8

50 40.1 483.0 117.5 de 85.9100 68.6 477.0 147.1 d 113.1

200 143.0 595.0 240.3 c 208.0

400 255.8 795.0 399.3 b 372.3

800 570.6 1227.5 755.5 a 722.5

POls (mg kg-1

)y

10 11.6 268.0 52.0 e 34.650 25.0 304.0 71.0 de 51.9

100 48.2 312.0 97.0 d 75.9

200 72.9 346.5 147.3 c 147.3400 163.5 450.0 258.8 b 258.8

800 348.5 668.8 509.5 a 516.0zMeans followed by the same letter are not significantly different atP= 0.05

yPOls, PM3, and PH2O represent Olsen, Mehlich-3, and water extractable P, respectively

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Table 3. The degree of P saturation (DPS, %) threshold determined from the split-line regression plot of the Mehlich-3 P based DPS

against water extractable Pz

Soil ID DPSM3 1yt DPSM3 2

xt DPSM3 3wt DPSM3 4

vt DPSM3 5ut Soil ID DPSM3 1

yt DPSM3 2xt DPSM3 3

wt DPSM3 4vt DPSM3 5

ut

Soil 1 NCP NCP NCP 18 (2.1) 19 (2.3) Soil 21 67 (11.3) 116 (19.5) 30 (5.1) 36 (2.0) 37 (2.0)

Soil 2 14 (-) 21 (-) 6 (-) 10 (1.8) 12 (2.1) Soil 22 29 (1.2) 53 (2.3) 17 (0.7) 21 (0.7) 25 (0.7)

Soil 3 11 (-) 17 (-) NCP 17 (1.2) 31 (1.5) Soil 23 NCP NCP NCP NCP NCP

Soil 4 30 (1.5) 41 (2.1) 13 (0.7) 21 (0.5) 26 (0.5) Soil 24 NCP NCP NCP NCP NCP

Soil 5 16 (9.8) 27 (16.5) 7 (4.4) 15 (3.2) 16 (3.3) Soil 25 NCP 92 (-) 25 (-) 37 (3.9) 38 (3.8)


Soil 7 29 (3.6) 41 (5.2) 18 (2.2) 20 (1.1) 30 (1.2) Soil 27 16 (1.4) 24 (2.1) 15 (1.3) 11 (0.5) 24 (0.7)


Soil 9 51 (1.6) 68 (2.2) 134 (4.3) 27 (0.5) 76 (0.4) Soil 29 49 (7.4) 72 (10.9) 18 (2.7) 29 (2.5) 29 (2.4)

Soil 10 11 (-) NCP NCP 34 (1.9) 43 (1.8) Soil 30 NCP NCP NCP 58 (3.7) NCP

Soil 11 33 (1.0) 47 (1.4) 17 (0.5) 20 (0.3) 26 (0.4) Soil 31 68 (1.9) 122 (3.3) 30 (0.8) 39 (0.5) 38 (0.5)

Soil 12 NCP NCP NCP NCP NCP Soil 32 NCP NCP NCP 54 (0.6) NCP

Soil 13 26 (1.4) 36 (2.0) 14 (0.7) 17 (0.5) 24 (0.6) Soil 33 15 (0.5) 23 (0.7) 12 (0.4) 10 (0.2) 19 (0.4)

Soil 14 14 (1.1) 23 (1.8) 12 (1.0) 11 (0.6) 21 (0.9) Soil 34 27 (11.7) 50 (21.8) 13 (5.9) 21 (4.8) 22 (4.9)

Soil 15 30 (3.3) 41 (4.6) 21 (2.30 19 (1.1) 33 (1.3) Soil 35 16 (1.7) 28 (2.9) 11 (1.1) 13 (0.9) 19 (1.1)


Soil 17 18 (2.9) 26 (4.1) 8 (1.2) 14 (1.1) 17 (1.2) Soil 37 NCP NCP NCP 35 (2.8) 42 (2.3)

Soil 18 18 (2.4) 26 (3.5) 10 (1.3) 12 (1.0) 16 (1.2) Soil 38 12 (1.8) 17 (2.7) 8 (1.2) 14 (1.3) 23 (1.5)

Soil 19 NCP NCP NCP 9 (10.7) 18 (5.3) Soil 39 17 (1.2) 29 (2.1) 9 (0.7) 13 (0.6) 16 (0.7)


Minimum 11 17 6 9 12

Maximum 68 122 134 58 76

Mean s 25 43 19 21 26

zNCP indicatedthere was no change point;

y

1001max

3

3 =

S

PDPS

M

M

; x1002

150

3

3 =

P

PDPS

M

M

; w

100)(

333

3

3

+

=

MM

M

MMgCa

PDPS

; =0.2;

v 1007.1

43150

3

3

+

=

M

M

MPP

PDPS ; u 100

)(5

33

3

3

++

=

MM

M

MPMgCa

PDPS

; =0.1;

tfigures in parenthesis represented the standard error and (-) indicated that the standard error was not estimated;

23

1

2

3

4

5

1


24/28

s the mean was obtained from soils that exhibited change points.

24

1

1


25/28

Table 4. The degree of P saturation (DPS, %) threshold determined from the split-line regression plot of the Olsen P based DPS

against water extractable PzSoil ID DPSOls 1

yt DPSOls 2xt DPSOls 3

wt DPSOls 4vt DPSOls 5

ut Soil ID DPSOls 1yt DPSOls 2

xt DPSOls 3wt DPSOls 4

vt DPSOls 5ut

Soil 1 19 (2.6) 28 (3.9) 8 (1.1) 15 (0.1) 16 (0.2) Soil 21 21 (3.4) 36 (6.5) 10 (1.7) 26 (2.6) 26 (2.7)

Soil 2 NCP 13 (-) NCP 7 (0.7) 8 (0.8) Soil 22 15 (1.7) 28 (2.7) 9 (0.9) 13 (0.6) 15 (0.6)

Soil 3 16 (1.6) 26 (2.7) 14 (1.5) 11 (0.9) 22 (1.4) Soil 23 29 (15.0) 79 (40.2) 22 (11.1) 28 (5.2) 31 (5.2)

Soil 4 24 (1.0) 32 (1.3) 11 (0.4) 16 (0.3) 20 (0.4) Soil 24 27 (3.5) 51 (6.9) 11 (1.5) 22 (2.4) 20 (1.6)

Soil 5 13 (4.8) 21 (8.1) 6 (2.1) 11 (2.8) 12 (2.9) Soil 25 28 (3.1) 55 (6.1) 15 (1.6) 28 (2.0) 29 (2.0)

Soil 6 10 (0.6) 16 (1.1) 7 (0.5) 8 (0.1) 14 (0.2) Soil 26 97 (3.4) 160 (5.9) 38 (1.4) 45 (0.7) 44 (0.7)

Soil 7 10 (9.9) 15 (14) 6 (6.0) 8 (0.2) 16 (1.2) Soil 27 NCP NCP NCP NCP NCP

Soil 8 3 (2.1) 6 (3.7) 2 (1.4) 3 (1.2) 5 (1.6) Soil 28 6 (0.2) 11 (0.3) 3 (0.1) 5 (0.1) 6 (0.1)


Soil 10 37 (4.6) 50 (6.3) 19 (2.4) 21 (1.2) 28 (1.4) Soil 30 50 (-) NCP 28 (-) 46 (4.8) 42 (5.1)

Soil 11 14 (0.6) 20 (0.8) 7 (0.3) 11 (0.3) 15 (0.3) Soil 31 39 (1.0) 71 (1.8) 18 (0.4) 28 (0.4) NCP


Soil 13 24 (1.0) 34 (1.4) 13 (0.5) 15 (0.4) 22 (0.5) Soil 33 10 (0.4) 16 (0.6) 8 (0.3) 7 (0.2) 14 (0.4)Soil 14 8 (1.2) 13 (2.0) 7 (1.1) 6 (0.5) 13 (0.7) Soil 34 16 (4.1) 30 (7.7) 8 (2.1) NCP NCP

Soil 15 15 (0.7) 21 (1.0) 11 (0.5) 11 (0.7) 21 (1.0) Soil 35 5 (1.6) 9 (2.8) 4 (1.1) 5 (0.7) 8 (0.6)


Soil 17 10 (3.5) 15 (5.0) 4 (1.5) 7 (0.5) NCP Soil 37 39 (8.8) 62 (14.0) 22 (4.9) 24 (2.0) 30 (2.0)

Soil 18 6 (0.3) 8 (0.5) 3 (0.2) 5 (0.3) 8 (0.4) Soil 38 7 (5.1) 10 (7.5) 4 (3.3) 7 (0.2) 12 (0.6)

Soil 19 6 (-) NCP NCP 5 (9.9) 10 (15.1) Soil 39 7 (1.0) 13 (1.8) 4 (0.6) 6 (0.8) 8 (1.0)

Soil 20 12 (0.8) 19 (1.1) 8 (0.5) 9 (0.4) 15 (0.5) Soil 40 7 (0.3) 12 (0.5) 4 (0.2) 6 (0.2) 7 (0.3)

Minimum 3 6 2 3 5

Maximum 97 160 53 46 56

Means 22 34 13 16 20

zNCP indicatedthere was no change point;

y

1001max

=

S

PDPS

Ols

Ols

; x1002

150

=

P

PDPS

Ols

Ols

; w

100)(

333

+

=

MM

Ols

OlsMgCa

PDPS

; =0.2;

v 1007.1

4150

+

=

Ols

Ols

OlsPP

PDPS ; u 100

)(5

3

++

=

OlsM

Ols

OlsPMgCa

PDPS

; =0.1;

tfigures in parenthesis represented the standard error and (-) indicated that the standard error was not estimated;

25

1

2

3

4

5

1


26/28

s the mean was obtained from soils that exhibited change points.

26

12

1


27/28

Figure 1: Split-line plot of Mehlich-3 extractable P based degree of P saturation against water extractable P to determine the degree of P

saturation threshold.

Soil 4

20

20

40

60

60

100

80

100

08040

Soil 9

0 40

0

80

20

120

40

60

80

6020 100

DPSM3

1 (%)

Wate

r

extra

cta

ble

P

(mg

kg-

1)

Soil 15

70 8010

80

0

20

40

60

20

30

60

70

10

50

504030

DPSM3

1 (%)

W

ate

rex

tra

ctabl

e

P

(m

gkg-1)

Soil 22

20

60

25

80

35

100

40

401510 30

20

Soil 31

40 80

50

120

100

150

200

60 100DPS

M31 (%)

W

ater

ex

tracta

bl

eP(m

g

kg-

1)

Soil 39

10

5

20

15

30

25

40

50

60

02010 30

WaterextractableP(mgkg-1)

DPSM3

1 (%)

Soil 19

0 10 20 40

0

60

20

80

40

60

80

100

120

30 7050

DPSM3

1 (%)

Wate

r

extra

cta

bl

eP

(m

g

kg-

1)

Soil 30

050

20

150

40

250

60

80

100

100 300200

W

ate

r

extra

cta

bl

eP

(mg

kg-

1)

DPSM3

1 (%)

Soil 36

40

50

50

150

60

70

0

20

100

30

200

10

DPSM3

1 (%)

Water

extra

ctabl

e P(mg

kg-1)

Wa

ter

ext

ractabl

e P(m

gkg-

1)

DPSM3 1 (%)

DPSM3 1 (%)

Water

extractableP(mgkg-1)

27

1

2

3

4

5

1


28/28

Figure 2: Split-line plot of Olsen extractable P based degree of P saturation against water extractable P to determine the degree of P

saturation threshold.

Soil 4

0 10 20 40

0

60

20

40

60

80

100

30 7050

DPSOls

1 (%)

WaterextractableP(mg

kg-

1)

Soil 9

0 10 20 40

0

60

20

40

60

80

30 50

WaterextractableP(mg

kg

-1

)

Soil 15

30

80

40

10

30

50

70

20

20

60

10

40

500

DPSOls

1 (%)

Soil 22

15

80

20

100

30

40

25105

60

20

DPSOls

1 (%)

Soil 31

20 40 50 60 80

50

100

150

200

7030

DPSOls

1 (%)

WaterextractableP

(mgkg-1)

Soil 39

2.5 7.50

12.5

10

17.5

20

30

40

50

60

5.0 15.010.0 20.0

DPSOls

1 (%)

Waterextractable P

(mgkg-1)

Soil 2

0

0

20

20

40

40

60

60

80

100

120

10 5030

Waterextracta

bleP(mgkg-1)

DPSOls

1 (%)

Soil 27

40

5

50

15

60

25

70

80

0

20

10

10

20

30

Waterextra

cta

bleP(mgkg-1)

DPSOls

1 (%)

Soil 37

0

10

20

30

40

50

60

70

80

0 50 100 150

DPSOls

1 (%)

Waterextra

ctable

P(mgkg-1

)

WaterextractableP(m

gkg-1)

Wat

erextractableP(mg

kg-1)

DPSOls 1 (%)

28

1

2

3

4

5

1

degree of p saturation cjss revised 4 1

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