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Transformation of phosphorus in highly calcareous soils under field capacity and waterlogged conditions.

Introduction

Phosphorus (P) reactions with calcareous soils significantly influence the efficiency of P fertilisers and environmental quality (Sample et al. 1980). Di-calcium phosphate dehydrate is probably the initial product of orthophosphate reaction with CaC[O.sub.3] (Cole et al. 1953; Freeman and Rowell 1981) which may be transformed to octa-calcium phosphate (OCP) or overlain by newly formed OCP after prolonged reaction (Freeman and Rowell 1981). Most of the compounds identified as probably soil-fertiliser reaction products have been surmised by simulating the chemical environment near the site of fertiliser application (Lindsay 1979). Inorganic P fractionation sequences are used to study P status and transformation in soils and sediments (Solis and Torrent 1989b; Barbanti et al. 1994; Samadi and Gilkes 1998, 1999), although they have their own restrictions (Barbanti et al. 1994; Adhami et al. 2007). Solis and Torrent (1989b) reported that for soils incubated with P, much of the added P was recovered in citrate-bicarbonate-extractable P (CB-P), attributed to pedogenic Ca-P, whereas no significant changes were observed for NaOH-P, attributed to Fe- and Al-P. This contrasts somewhat with the findings of P adsorption studies of calcareous soils that show the ability of active and crystalline Fe oxides to remove P from soil solution (Ryan et al. 1985a; Solis and Torrent 1989a). Ryan et al. (1985b) reported that no detectable amount of added P was in CB-dithionite (CBD) extract and that the distribution of P in various forms varied widely within the soils. Samadi and Gilkes (1999) observed that, after 160-day incubation, the average recoveries of added P to [Ca.sub.2]-P, [Ca.sub.8]-P, Al-P, Fe-P, occluded-P, and [Ca.sub.10]-P were, respectively, 40, 16, 23, 13, 3, and 1% of added P.

When soils are waterlogged, anoxic conditions are initiated and the chemical properties of the soils will be affected. Changes are mainly dependent on both pH and Eh (redox potential) variation, and differences have been observed in P chemistry of acidic and calcareous soils under waterlogging (Williams and Patrick 1973; Sah and Mikkelsen 1986; Heiberg et al. 2010). Although inorganic P is not directly involved in the reaction of redox changes, it is greatly affected by waterlogging. The reduction of ferric phosphate to ferrous phosphate by waterlogging may increase P solubility (Williams and Patrick 1973). Soil reduction, however, may increase amorphous soil Fe and, consecutively, P sorption (Patrick and Khalid 1974; Khalid et al. 1977). Sah and Mikkelsen (1986) observed that the Fe-P fraction decreased when soils were flooded. They also reported that flooding increased Ca-P in two soils with high levels of Ca-P but had almost no effect in two other soils with lower Ca-P. Mahapatra and Patrick (1969) observed that, on average, Al-P and Fe-P increased ~35 and 64%, respectively, due to waterlogging. They concluded that part of the increase in Fe-P was apparently due to the release of reductant-soluble Fe-P. Singhania and Goswami (1978) reported that 33-55% of added P was recovered in Fe-P and 17.7-29.5% in Al-P under waterlogged conditions.

Agricultural soils in Iran receive large amounts of P fertiliser annually, and little information exists about prolonged reaction of applied P, especially under waterlogged conditions. The area of Fars Province includes arid to semi-arid regions of Iran. Average annual rainfall varies from 100 mm in the southern parts to >400 mm in the northern parts of the province. The climate of Fars is complex, ranging from cold in the mountainous regions to warm in southern and eastern areas. Flooded rice culture is the fourth crop in Fars province, but the extent of flooded rice culture depends on annual conditions and was reported to be >380 000ha in 2011. In the present study, we evaluated P transformation under field capacity and waterlogged conditions, and the effect of soil properties on P transformation in some highly calcareous soils.

Materials and methods

Soil samples, physical and chemical properties

Twenty surface soil samples (0-30 cm depth) with a wide range of physical and chemical characteristics, from Fars Province in Iran, were selected for this experiment. The soil samples were air-dried and passed through a 2 mm-sieve before analysis.

Sand, coarse silt, fine silt, and clay contents were separated by the pipette method. Chemical characterisations included: cation exchange capacity (CEC) by replacing exchangeable cations with N[H.sub.4.sup.+]; calcium carbonate equivalent (CCE) by neutralising with HCl and active CCE (ACCE); organic matter content (OM) by wet oxidation; pH from a saturated paste; and Olsen-P. The CBD- and oxalate-extractable Fe ([Fe.sub.d] and [Fe.sub.o]), citrate- and citrate-ascorbate-extractable Fe ([Fe.sub.c] and [Fe.sub.CAs]), CBD- and oxalate-extractable Al ([Al.sub.d] and [Al.sub.o]), neutral ammonium acetate-hydroquinone and hydroxylamine hydrochloride extractable Mn ([Mn.sub.q] and [Mn.sub.h]) were determined (Adhami et al. 2007) (Table 1).

Incubation

The experimental design was a factorial combination of two P rates (0 and 300 mgP[kg.sup.-1] as K[H.sub.2]P[O.sub.4]) and two moisture regimes (field capacity, FC; waterlogged, WL) in a completely randomised design in duplicate. Phosphorus was added to 150 g of soil as K[H.sub.2]P[O.sub.4] solution, mixed thoroughly, and incubated at room temperature for 160 days. As it was not possible to adjust each sample to FC, 20% w/w was chosen as the average index of FC (Samadi and Gilkes 1999); moisture content was adjusted to 20% w/w by weighting each 3 days. For WL, 0.5-1 cm water was kept on the surface of soil samples during incubation. Fractionation of P was conducted on the incubated samples at 80 and 160 days.

Inorganic P fractionation

A measured weight (~1 g) of wet-incubated (for WL from saturated paste) soil was placed in a suitable centrifuge tube; at the same time, a sample was taken for determining soil moisture content, and the sample dry weight was calculated for P fractionation. The inorganic P sequential fractionation scheme followed a slight modification of the sequence of Jiang and Gu (1989), which was adopted by Adhami et al. (2006) for the highly calcareous soils of Iran. Details of this sequence are presented in Table 2. Briefly, the procedure includes successive cxtraction with NaHC[O.sub.3] to remove readily soluble P; N[H.sub.4] acetate buffer (N[H.sub.4]OAc) for pedogenic Ca-P; Mg[Cl.sub.2] for P readsorbed in the previous step; N[H.sub.4]F for Al-bound P; NaOH-[Na.sub.2]C[O.sub.3] (HC) for P associated with free iron oxides; Na citrate-bicarbonate-dithionite (CBD) for P occluded in crystalline Fe oxides; and [H.sub.2]S[O.sub.4] to remove mostly lithogenic apatite. All extractions were carried out with a ratio of 1:50 soil:extractant. Following each step, the samples were centrifuged at 6000G for 15 min and the supernatant was filtered through Whatman #42 filter paper. Reactive P in the supernatant was determined using the ascorbic acid method at 882 nm (Murphy and Riley 1962). The interferences of CBD and N[H.sub.4]F on P determination were eliminated by digesting in HCl[O.sub.4] : [H.sub.2]S[O.sub.4] : HN[O.sub.3] (1 : 2 : 7) mixture, and adding boric acid, respectively. To remove OM from HC-P extract, 1 mL of concentrated [H.sub.2]S[O.sub.4] was added to precipitate OM, followed by filtration through Whatman #42 filter paper.

Statistical analysis

Recovery of applied P in each fraction was calculated as the difference between samples that were treated and untreated with P. Analysis of variance and comparison of means by MSTATC software (Michigan State University, MI) were used to evaluate the influence of moisture and soil on P recovery in each fraction. Relationships between recovery of P in each fraction and soil properties were assessed using SPSS software v. 11.5.

Results and discussion

Readily soluble P

Moisture regimes significantly affected the recovery of applied P as NaHC[O.sub.3]-P for both incubation periods (80 and 160 days) (Table 3). Recovery of applied P as NaHC[O.sub.3]-P decreased with time under both moisture conditions, which shows the fixation of readily soluble P and its transformation to less soluble forms (Tables 4, 5). For both incubation periods, recovery of NaHC[O.sub.3]-P was higher under FC than WL (Tables 4, 5). Average recovery of the NaHC[O.sub.3]-P fraction at 80 and 160 days, respectively, was 49 and 40% of applied P under FC, whereas it was 42 and 31% of applied P under WL. The NaHC[O.sub.3]-P in the sequence used was attributed to [Ca.sub.2]-P (Jiang and Gu 1989), and generally could be regarded as readily soluble P (Samadi and Gilkes 1999; Adhami et al. 2006). There is little agreement on the effect of waterlogging on readily soluble P. Some evidence indicates that the increment of readily soluble P results from reduction of Fe(III)-P compounds (Mandal and Khan 1977; Sharma and Mishra 1985). Williams and Patrick (1973) observed that at pH 5-7, an Eh value of less than -200 mV was required to initiate substantial FeP[O.sub.4] dissolution. Williams and Patrick (1971) observed that crystalline strengite can be rendered soluble under pH 5 by lowering solution redox potential to values less than -200 mV, which are not normally found in submerged conditions. Obviously, the conditions required for Fe(III)-P dissolution could not be attained in calcareous soils under submerged conditions. Although pH and Eh of calcareous soils will be decreased under waterlogging, the reduction is very low. Kalbasi and Hosseinpour (1997) observed that after submergence of three calcareous soils for 3 months, the least pH and Eh values were 7 and 0, respectively. Clearly, this condition is far from those required for Fe(III)-P dissolution.

There was a high negative correlation between the recovery of applied P in the NaHC[O.sub.3]-P fraction and [Fe.sub.c], [Fe.sub.o], and [Fe.sub.CAs] under both moisture conditions at 80 days; under WL, [Mn.sub.h], [Mn.sub.q], and [Al.sub.d] also showed a significant negative correlation with NaHC[O.sub.3]-P (Table 6). Recovery of P in NaHC[O.sub.3]-P at 160 days showed a negative significant correlation with [Fe.sub.c], [Fe.sub.o], [Fe.sub.CAs], [Al.sub.d], [Mn.sub.h], and [Mn.sub.q] under FC, whereas under WL, only [Al.sub.d] and [Mn.sub.q] significantly correlated with NaHC[O.sub.3]-P. Reduction in available P with time has been reported previously (Ryan et al. 1985b; Solis and Torrent 1989b; Afif et al. 1993); however, little information exists about the effects of soil properties on reduction in available P in highly calcareous soils, especially under waterlogged conditions. Generally, soil properties such as CEC, [Al.sub.d], clay, and [Fe.sub.o] (Samadi and Gilkes 1999), [Fe.sub.d] (Ryan et al. 1985b; Afif et al. 1993), and CCE (Afif et al. 1993) have been reported as factors controlling available P. Results presented here are in agreement with findings of Patrick and Khalid (1974) and Khalid et al. (1977), suggesting that oxalate-extractable Fe is the most influential property affecting P adsorption in flooded soils.

Pedogenic Ca-P

Moisture condition in the 160-day treatment significantly affected N[H.sub.4]OAc-P, whereas Mg[Cl.sub.2]-P was not significantly affected by moisture condition. Average recovery of N[H.sub.4]OAc-P under FC was 77 mg [kg.sup.-1] at 80 days, which increased to 87 mg [kg.sup.-1] at 160 days; meanwhile, average N[H.sub.4]OAc-P under WL decreased from 76 to 55 mg [kg.sup.-1] (Tables 4, 5). At 160 days, 29% of applied P was recovered in the N[H.sub.4]OAc-P fraction under FC, and 18% under WL. This trend was consistent in most of the studied soils.

Phosphorus extractable with acetate buffer is attributed to [Ca.sub.8]P (Jiang and Gu 1989) and more broadly to pedogenic Ca-P (Ruttenberg 1992; Ruiz et al. 1997). The Mg[Cl.sub.2] step was introduced into the fractionation sequence of Jiang and Gu (1989) to remove P remaining after N[H.sub.4]OAc extraction (Adhami et al. 2006). The recovery of applied P in the N[H.sub.4]OAc-P fraction in the present study was higher than that reported by Samadi and Gilkes (1999) in 14 calcareous soils of Australia. Solis and Torrent (1989b) reported that 64-92 mg [kg.sup.-1] of 100 mg [kg.sup.-1] of applied P was recovered in CB-P, which is attributed to pedogenic Ca-P.

In the present study, recovery of applied P in the N[H.sub.4]OAc-P fraction showed significant negative correlation with free iron oxides ([Fe.sub.o], [Fe.sub.c], and [Fe.sub.CAs]) under both moisture regimes (Table 6). No significant relationship was observed between recovery of applied P in the Mg[Cl.sub.2]-P fraction and soil properties.

Samadi and Gilkes (1999) observed that recovery of applied P in the N[H.sub.4]OAc-P fraction was negatively correlated with [Al.sub.d] and ACCE. Probably, precipitation of pedogenic Ca phosphate is the dominant reaction in calcareous soils at P concentration >[10.sup.-4.5]M (Castro and Torrent 1998; Tunesi et al. 1999). It is believed that pedogenic Ca compounds such as octa-calcium phosphate or tri-calcium phosphate will be formed during prolonged reaction of phosphate with CaC[O.sub.3] (Griffin and Jurinak 1974; Freeman and Rowell 1981). Evans and Jurinak (1976) showed the precipitation of Ca phosphate on calcium carbonate with electron-microscopic studies.

Al-P and Fe-P

Recovery of applied P in N[H.sub.4]F-P and HC-P was significantly affected by moisture content for both incubation periods (Table 3), although the effect of moisture content was more pronounced at 160 days. Average recovery in the N[H.sub.4]F-P fraction at 80 and 160 days was 8 and 9%, respectively, of applied P under FC, which increased to 10 and 15% under WL. Recovery of applied P in the N[H.sub.4]F-P fraction at 160 days was considerably higher under WL than FC for all studied soils (Table 5). Recovery of applied P in HOP fraction showed a similar trend to N[H.sub.4]F-P. An average of 4% of applied P was recovered in the HC-P fraction at 80 and 160 days under FC, increased to 5 and 8% under WL. Solis and Torrent (1989b) observed that after 5 months of incubation of 25 highly calcareous soils with 100 mg P [kg.sup.-1], a negligible amount of applied P was recovered in the NaOH-P fraction (known as Al- and Fe-P). Similar results were reported by Ryan et al. (1985b). In contrast to this, Samadi and Gilkes (1999) observed that after 160 days of incubation under 20% w/w moisture, 23 and 13% of applied P was recovered in N[H.sub.4]F-P and HC-P fractions, respectively. Transformation of P under waterlogging of highly calcareous soils is rarely studied; however, studies on acidic soils have showed that applied P under waterlogging is considerably transformed to Al- and Fe-P forms (Singhania and Goswami 1978; Sah and Mikkelsen 1986). Heiberg et al. (2010) observed that, although substantial proportions of FeIII oxide sorbents were dissolved in anoxic soils, the majority of anoxic soils had higher maximum sorption than their oxic counterparts, most likely due to precipitation of iron(II) phosphates such as vivianite. Heiberg et al. (2010) observed that most of the FeII released during anoxic incubation did not stay in solution but was sorbed.

This is attributed to the conversion of ferric oxy-hydroxide to more soluble and highly dispersed ferrous form, and/or hydration of free iron oxide compounds, which increases the activity and the surface area of the iron oxide compounds (Patrick and Khalid 1974). As previously described, the conversion of Fe(III)-P to Fe(II)-P is not likely to occur under submerged conditions in highly calcareous soils; therefore, probably the later mechanism is responsible for more transformation of applied P to Al- and Fe-P under waterlogged conditions.

Recovery of applied P in the N[H.sub.4]F-P fraction showed a positive significant correlation with [Fe.sub.o], [Fe.sub.c], and [Fe.sub.CAs] in most cases (Table 6), which supports the idea that N[H.sub.4]F is not a selective extractant for Al-P and is capable of dissolving P bonds to free Fe oxides (Adhami et al. 2006; Williams et al. 1971; Chang and Jackson 1957). Recovery of applied P in HC-P showed a high positive and significant correlation with free iron oxide (i.e. [Fe.sub.o], [Fe.sub.c], [Fe.sub.CAs]).

Recovery of applied P in the CBD-P fraction was not significantly affected by soil moisture content. Average recovery of applied P in the CBD-P fraction at 80 and 160 days was 6 and 13 mg [kg.sup.-1], respectively, under FC and 15 and 20 mg [kg.sup.-1] under WL (Tables 4, 5). Recovery of applied P in the CBD-P fraction did not show significant correlation with soil properties under FC, whereas it showed significant correlation with [Fe.sub.c], [Al.sub.d], and [Mn.sub.q] under WL (Table 6). Samadi and Gilkes (1999) observed that an average of 1% of applied P was recovered in CBD-P. Solis and Torrent (1989b) found that 2.5-29.5% of applied P was recovered in the CBD-P fraction, and reported a significant positive correlation between recovery in CBD-P and [Fe.sub.d].

[H.sub.2]S[O.sub.4]-P

Moisture regimes did not significantly affect recovery of applied P in the [H.sub.2]S[O.sub.4]-P form. Average recovery in the [H.sub.2]S[O.sub.4]-P form at 80 and 160 days was 12 and 17 mg [kg.sup.-1], respectively, under FC and 14 and 28 mg [kg.sup.-1] under WL. Samadi and Gilkes (1999) reported that almost 1% of applied P was recovered in [H.sub.2]S[O.sub.4]-P, while Solis and Torrent (1989b) reported that an average of 10.5 of 100 mg [kg.sup.-1] of applied P was recovered in HCl-P after 5 months of incubation. There was no significant correlation between P recovery in [H.sub.2]S[O.sub.4]-P and soil properties.

Conclusion

Moisture regimes played a significant role in the inorganic P transformation and recovery in various fractions. In comparison with FC, the WL regime caused a greater decrease in the recovery of applied P in NaHC[O.sub.3]-P at 80 and 160 days, and decreased applied P recovery in the N[H.sub.4]OAc-P fraction (known as pedogenic Ca-P compounds) at 160 days only. Transformation of applied P into Al- and Fe-P constituted a small portion of applied P under FC, but under WL, recovery of applied P in Al- and Fe-P was higher. This indicates that, even in highly calcareous soils, Al- and Fe-compounds are so transformed in waterlogged conditions that possess a higher capacity and affinity for P retention. Results of the present study reveal that transformation of applied P into Al- and Fe-P fractions is not as low as previously reported in highly calcareous soils and that Al- and Fe-P oxides could be important in P transformation of these soils, especially in waterlogged conditions.

References

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E. Adhami (A,C), A. Ronaghi (B), N. Karimian (B), and R. Molavi (A)

(A) College of Agriculture, Yasouj University, Yasouj, Iran.

(B) Department of Soil Science, College of Agriculture, Shiraz University, Shiraz, Iran.

(C) Corresponding author. Email: eadhami@gmail.com

http://dx.doi.org/ 10.1071/SR11250
Table 1. Statistics of the determined soil properties
CCE, Calcium carbonate equivalent; ACCE, active CCE; OM, organic
matter content; CEC, cation exchange capacity; [Fe.sub.o], [Al.sub.o]:
oxalate extractable Fe, AI; [Fe.sub.d], [Al.sub.d]: citrate
bicarbonate-dithionite-extractable Fe, Al; [Fe.sub.c],
citrate-extractable Fe; [Fe.sub.CAs]., citrate-ascorbate-extractable
Fe; [Mn.sub.q], neutral ammonium acetate--hydroquinone-extractable
Mn; [Mn.sub.h], hydroxylamine hydrochloride-extractable Mn

Soil properties                Minimum   Average   Maximum    Standard
                                                              deviation

Sand (g [kg.sup.-1])                26       196       593         148
Course silt (g [kg.sup.-1])         22       143       357          74
Fine silt (g [kg.sup.-1])          126       354       487          96
Clay (g [kg.sup.-1])               131       308       492         105
CCE (g [kg.sup.-1])                218       406       650          98
ACCE (g [kg.sup.-1])                54       148       239          55
OM (g [kg.sup.-1])                3.00     18.95     34.00        8.10
pH                                7.30      7.64      7.90        0.16
CEC (cmol(+)[kg.sup.-1])          5.90     20.70     34.20        8.30
[Fe.sub.o] (mg [kg.sup.-1])       0.35      1.10      2.20        0.52
[Fe.sub.CAs] (mg [kg.sup.-1])     0.07      0.57      2.16        0.61
[Fe.sub.c] (mg [kg.sup.-1])       0.08      0.18      0.39        0.09
[Fe.sub.d] (mg [kg.sup.-1])       3.18      6.14     13.47        2.78
[Al.sub.o] (mg [kg.sup.-1])       0.16      0.41      0.84        0.18
[Al.sub.d] (mg [kg.sup.-1])       0.17      0.37      0.62        0.13
[Mn.sub.h] (mg [kg.sup.-1])       0.05      0.19      0.43        0.08
[Mn.sub.q] (mg [kg.sup.-1])       0.03      0.12      0.22        0.05

Table 2. Details of the fractionation sequence used

Step    Extractant                     pH    Description

1       0.25 M NaHC[0.sub.3]           7.5   1 h shaking

2       0. 5 M N[H.sub.4]0Ac           4.2   4 h standing;1 h
                                               shaking
3       1 M Mg[Cl.sub.2]                       2 times, 2 h
                                               shaking
4       0. 5 M N[H.sub.4]F             8.2   1 h shaking
5       0.1 m NaOH-0.1 N [Na.sub.2]    --    2 h shaking;
        C[O.sub.3]
                                             16 h standing;
                                             2 h shaking
6       0.3 M [Na.sub.3][C.sub.6]      --    16 h shaking
        [H.sub.5][0.sub.7]-[Na.sub.2]
        [S.sub.2][0.sub.4]-NaOH
7       0.25 M [H.sub.2]S[O.sub.4]     --    1 h shaking

Step    Extractant                             P form

1       0.25 M NaHC[0.sub.3]             Di-calcium phosphate and
                                           more-soluble compounds
2       0. 5 M N[H.sub.4]0Ac             Octa-calcium phosphate and
                                           more-soluble compounds
3       1 M Mg[Cl.sub.2]                 P remaining from
                                           previous step
4       0. 5 M N[H.sub.4]F               Mostly Al- and Fe-P
5       0.1 m NaOH-0.1 N [Na.sub.2]      Mostly Fe-P
        C[O.sub.3]

6       0.3 M [Na.sub.3][C.sub.6]        Reductant-soluble P
        [H.sub.5][0.sub.7]-[Na.sub.2]
        [S.sub.2][0.sub.4]-NaOH
7       0.25 M [H.sub.2]S[O.sub.4]       Mostly lithogenic apatite

Step    Extractant                       Abbreviation

1       0.25 M NaHC[0.sub.3]             NaHC[0.sub.3]-P

2       0. 5 M N[H.sub.4]0Ac             N[H.sub.4]0Ac-P

3       1 M Mg[Cl.sub.2]                 Mg[C.sub.12]-P

4       0. 5 M N[H.sub.4]F               N[H.sub.4]F-P
5       0.1 m NaOH-0.1 N [Na.sub.2]      HC-P
        C[O.sub.3]

6       0.3 M [Na.sub.3][C.sub.6]        CBD-P
        [H.sub.5][0.sub.7]-[Na.sub.2]
        [S.sub.2][0.sub.4]-NaOH
7       0.25 M [H.sub.2]S[O.sub.4]       [H.sub.2]S[O.sub.4]

Table 3. Analysis of variance for the amount of
added P recovered in various fractions as affected by moisture level

* P<0.05; ** P<0.01; n.s., non-significant

Source of variation      d. f.   NaHC[O.sub.3]-P   N[H.sub.4]OAc-P

                                        80 days

Soil                        19           4191 **           32438 **
Moisture regime              1           2714 *             1n.s.
Soil x moisture regime      19           1080 *           531n.s.
Error                       40            246             598

                                       160 days

Soil                        19           3053 **            5745 **
Moisture regime              1          31205 **           14365 **
Soil x moisture regime      19            696 **             903 **
Error                       40            246                183

                                      Mean square

Source of variation          Mg[Cl.sub.2]-P     N[H.sub.4]F-P

                                      80 days

Soil                                274n.s.              461 **
Moisture regime                     177n.s.              594 *
Soil x moisture regime              116n.s.           123n.s.
Error                                  312               102

                                      160 days

Soil                                 1418 **             636 **
Moisture regime                     120n.s.             4821 **
Soil x moisture regime                621 **             395 **
Error                                 123                116

Source of variation                  NaOH-P             CBD-P

                                            80 days

Soil                                   570 **           136n.s.
Moisture regime                        370 *            219n.s.
Soil x moisture regime                 117 *            227n.s.
Error                                   61               404

                                           160 days

Soil                                   796 **          1106n.s.
Moisture regime                       2714 **            5216 *
Soil x moisture regime                 232 **          626n-s.
Error                                     46              888

Table 4. Recovery (mg [kg.sup.-1]) of phosphorus added
at 300 mg [kg.sup.-1] in various fractions after
incubation for 80 days under field capacity (FC) or
waterlogging (WL)

                   NaHC[O.sub.3]-P  N[H.sub.4]OAc-P

Soil #             FC    WL          FC    WL

1                  102   73          66    68
2                  98    76          72    35
3                  160   175         69    46
4                  170   116         105   82
5                  149   112         77    84
6                  130   109         65    59
7                  190   134         49    55
8                  164   153         48    66
9                  98    93          102   102
10                 146   150         89    80
11                 116   74          60    57
12                 148   96          67    74
13                 109   100         138   133
14                 170   178         69    70
15                 202   149         70    88
16                 153   140         82    67
17                 167   185         87    87
18                 144   141         56    88
19                 159   137         77    82
20                 134   139         95    91
Av.                147   127         77    76
Ls.d. (P=0.05)       17.92            17.29

                   Mg[Cl.sub.2]-P   N[H.sub.4]F-P

Soil #             FC    WL           FC    WL

1                  13    16           19    30
2                  7     11           24    50
3                  10    15           23    27
4                  15    14           16    29
5                  13    10           20    27
6                  8     7            18    28
7                  7     0            15    25
8                  9     32           36    20
9                  9     21           13    30
10                 8     2            30    26
11                 9     5            56    57
12                 18    18           22    19
13                 0     15           17    12
14                 5     11           21    19
15                 9     7            23    21
16                 8     2            32    33
17                 15    2            15    10
18                 6     5            23    31
19                 8     10           8     15
20                 27    20           32    62
Av.                10    11           23    29
Ls.d. (P=0.05)       12.49              7.14

                      NaOH-P           CBD-P

Soil #              FC    WL          FC    WL

1                   32    33          0     33
2                   23    61          4     29
3                   0     18          0     7
4                   14    9           9     3
5                   9     21          18    9
6                   8     13          4     43
7                   15    9           0     23
8                   21    8           15    9
9                   3     13          0     19
10                  12    16          2     12
11                  41    46          16    11
12                  13    23          0     13
13                  1     4           3     12
14                  16    6           3     32
15                  10    8           2     28
16                  11    15          20    23
17                  3     0           0     0
18                  5     9           6     0
19                  1     1           0     0
20                  0     1           15    0
Av.                 12    16          6     15
Ls.d. (P=0.05)        5.54              5.15

                     [H.sub.2]S[O.sub.4]-P

Soil #                   FC    WL

1                        21    17
2                        40    43
3                        1     0
4                        2     0
5                        0     15
6                        20    5
7                        0     48
8                        1     18
9                        50    0
10                       8     0
11                       0     2
12                       0     30
13                       25    10
14                       15    0
15                       0     20
16                       0     0
17                       0     24
18                       28    19
19                       31    16
20                       0     l0
Av.                      12    14
Ls.d. (P=0.05)             12.62

Table 5. Recovery (mg [kg.sup-1]) of phosphorus added at 300 mg
[kg.sup-1] in various fractions after incubation for 160 days under
field capacity (FC) or waterlogging (WL)

                NaHC[O.sub.3]-P      N[H.sub.4]OAc-P

Soil #           FC      WL          FC     WL

1                94      54          79     41
2                72      57          49      0
3               120      76          76     50
4               132      92         103     68
5                98      47          99     31
6               122      92          55     25
7               130      78         106     30
8               125     129          69     66
9                84      58         110     88
10              134      78         117     80
Il              116      77          71     41
12              133     144          87     63
13              122     122         110     90
14              133      83         104     62
15              120     132          66     62
16              135     115          82     15
17              151     126          86     54
18              124      88          92     55
19              131      97         110     48
20              130      96          60     80
Av.             120      92          87     55
Ls.d. (P=0.05)     11.09               9.57

                  Mg[Cl.sub.2]-P     N[H.sub.4]F-P

Soil #          FC      WL           FC     WL

1                19       0           47     47
2                 8      24           35     65
3                 8      10           20     15
4                 0     II            21     36
5                12       7           34     44
6                13       8           39     76
7                10      22           23     63
8                14       6           16     38
9                10      26           25     28
10               25      27           33     37
Il                6       8           60     68
12                7       7           26     38
13                8      13           18     22
14                9      20           23     27
15                7      21           15     41
16               20      25           30     62
17               16      14           16     47
18               18      14           42     63
19               10      35            2     48
20               20       0           23     28
Av.              12      15           27     45
Ls.d. (P=0.05)      7.83                7.62

                      NaOH-P              CBD-P

Soil #          FC      WL          FC     WL

1                26      63           8     54
2                23      55          19     28
3                 1      15          17     26
4                 6      18           0     16
5                10      31          29     37
6                29      58           9     46
7                14      25           0     14
8                11      14          27      5
9                12       6           3     13
10                8      17           9     24
Il               39      60         il      47
12               14      20         il       0
13                0       1          14     14
14                8      16           0     17
15                5      14          22     36
16               18      16          11     17
17                8      27          19      4
18                0      20           0      1
19                6       9          28      0
20                1       3          25      3
Av.              12      24          13     20
Ls.d. (P=0.05)      4.82               6.63

                [H.sub.2]S[O.sub.4]-P

Soil #           FC      WL

1                 0      34
2                32      39
3                37      69
4                21      20
5                17      57
6                 5       0
7                16      19
8                26      42
9                11      20
10                1      19
Il                2      19
12                0      20
13                6       0
14               22      33
15               35       0
16               21      50
17                0      25
18               30      34
19                0      19
20               55      35
Av.              17      28
Ls.d. (P=0.05)        12.16

Table 6. Correlation coefficients for the recovery of
applied P in various fractions with soils properties under
field capacity (FC) or waterlogging
(WL)

* P<0.05; ** P<0.01; other values, not statistically significant

                        NaHC[O.sub.3]-P         N[H.sub.4]0Ac-P

Soil property      FC           WL              FC         WL

                                          80 days

Sand               0.02       0.39 *          0.20          0.10
Course silt       -0.14      -0.21            0.17          0.23
Fine silt          0.29       0.09           -0.15          0.00
Clay               0.20      -0.49 *         -0.26         -0.30
OM                -0.16      -0.23            0.17          0.02
CCE               -0.07       0.23            0.06          0.07
ACCE               0.19      -0.07            0.43 *        0.19
[Fe.sub.o]        -0.50 *    -0.64 **        -0.40 *       -0.50 *
[Fe.sub.CAs]      -0.59 **   -0.73 **         0.33          0.49 *
[Fe.sub.c]         0.62 **   -0.71 **        -0.23         -0.45 *
[Fe.sub.d]        -0.13      -0.07           -0.11         -0.20
[Al.sub.o]        -0.09      -0.18            0.17          0.07
[Al.sub.d]        -0.25      -0.40 *         -0.33         -0.48 *
[Mn.sub.h]        -0.34      -0.56 **        -0.05          0.22
[Mn.sub.q]        -0.43 *    -0.61 **         0.04         -0.05

                                160 days

Sand               0.10       0.06           -0.02          0.19
Course silt        0.28       0.37           -0.04          0.23
Fine silt          0.09       0.15            0.00         -0.13
Clay              -0.42 *    -0.49 *          0.06         -0.31
OM                 0.11       0.32           -0.02         -0.13
CCE                0.12       0.14            0.09          0.12
ACCE               0.06      -0.01            0.05         -0.10
[Fe.sub.o]        -0.52 **   -0.23            0.48 *       -0.57 **
[Fe.sub.CAs]      -0.48 *    -0.28            0.45 *        0.45 *
[Fe.sub.c]        -0.55 **   -0.19           -0.70 **      -0.55 **
[Fe.sub.d]        -0.28      -0.36           -0.12         -0.12
[Al.sub.o]        -0.14      -0.04            0.08          0.14
[Al.sub.d]        -0.60 **   -0.65 **         0.21         -0.55 **
[Mn.sub.h]        -0.49 *    -0.35           -0.31         -0.28
[Mn.sub.q]        -0.77 **    0.51 *         -0.21         -0.18

                          N[H.sub.4]F-P            NaOH-P
Soil property

                       FC          WL          FC             WL

                                        80 days

Sand                   -0.05     -0.04       -0.27           -0.11
Course silt             0.57 **   0.26        0.17            0.01
Fine silt              -0.41 *   -0.32       -0.28           -0.33
Clay                    0.04      0.17        0.52 **         0.46 *
OM                      0.12     -0.07       -0.02            0.04
CCE                     0.10      0.01       -0.10            0.02
ACCE                    0.39 *    0.01        0.48 *          0.21
[Fe.sub.o]              0.51 *    0.42 *      0.78 **         0.85 **
[Fe.sub.CAs]            0.51 *    0.50 *      0.80 **         0.87 **
[Fe.sub.c]              0.39 *    0.63 **     0.67 **         0.81 **
[Fe.sub.d]             -0.12      0.12        0.13            0.09
[Al.sub.o]             -0.31     -0.27       -0.10            0.15
[Al.sub.d]              0.00      0.23        0.38 *          0.48 *
[Mn.sub.h]             -0.14      0.25        0.18            0.28
[Mn.sub.q]              0.00      0.38        0.18            0.39 *
                      160 days
Sand                   -0.20     -0.52 **        -0.35        -0.28
Course silt             0.22      0.02            0.20        -0.09
Fine silt              -0.34      0.21            0.18         0.09
Clay                    0.44 *    0.52 **         0.52 **      0.54 **
OM                     -0.06      0.25            0.16        -0.03
CCE                    -0.19      0.52 **        -0.29        -0.22
ACCE                    0.27      0.27            0.10         0.18
[Fe.sub.o]              0.66 **   0.60 **         0.80 **      0.76 **
[Fe.sub.CAs]            0.73 **   0.53 **         0.87 **      0.82 **
[Fe.sub.c]              0.64 **   0.55 **         0.79 **      0.80 **
[Fe.sub.d]              0.21      0.15            0.27         0.27
[Al.sub.o]             -0.07      0.45 *          0.29         0.15
[Al.sub.d]              0.44 *    0.48 *          0.51 *       0.61 **
[Mn.sub.h]              0.27      0.414 *         0.50 *       0.49 *
[Mn.sub.q]              0.19      0.14            0.32         0.27

                       CBD-P

Soil property       FC              WL

                        80 days

Sand              -0.14      -0.09
Course silt        0.44 *    -0.38 *
Fine silt         -0.07       0.04
Clay              -0.05       0.35
OM                 0.28      -0.12
CCE                0.07      -0.32
ACCE               0.25      -0.24
[Fe.sub.o]         0.24       0.28
[Fe.sub.CAs]       0.10       0.35
[Fe.sub.c]         0.22       0.50 *
[Fe.sub.d]        -0.10       0.62 **
[Al.sub.o]        -0.22       0.29
[Al.sub.d]         0.19       0.47 *
[Mn.sub.h]        -0.03       0.51 *
[Mn.sub.q]         0.26       0.20

                        160 days

Sand               0.03      -0.22
Course silt        0.01      -0.08
Fine silt          0.20      -0.09
Clay              -0.22       0.45 *
OM                 0.04      -0.25
CCE                0.19      -0.27
ACCE               0.07       0.09
[Fe.sub.o]         0.10       0.47 *
[Fe.sub.CAs]      -0.02       0.56 **
[Fe.sub.c]         0.06       0.53 *
[Fe.sub.d]        -0.42 *     0.279
[Al.sub.o]         0.02       0.083
[Al.sub.d]        -0.08       0.57 **
[Mn.sub.h]        -0.09       0.51
[Mn.sub.q]         0.34       0.40 *
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Author:Adhami, E.; Ronaghi, A.; Karimian, N.; Molavi, R.
Publication:Soil Research
Article Type:Report
Geographic Code:7IRAN
Date:May 1, 2012
Words:6992
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