Inorganic Phosphorous, Lime and Vermicompost Induced Changes on Phosphorus Fractions and Other Properties of Acidic Soil of Cheha District,

Background: In acid soils, soluble inorganic phosphorus is xed by aluminum and iron, so that phosphorous availability to plant would be inhibited. Thus, an incubation study was conducted to evaluate the effects of lime, vermicompost, and mineral P fertilizer on the distribution of P fractions and oxalate and dithionite extractable aluminum and iron. The treatments consisted of three rates of phosphorous (0, 74.51 and 149.01 kg P ha -1 ), three rates of vermicompost (0, 5 and 10 ton VC ha -1 ) and four rates of lime (0, 5.70, 9.20, and 11.50 ton CaCO 3 ha -1 ). The experiment was laid out as a complete randomized design in a factorial arrangement. Results: Combined application of lime, vermicompost and mineral P signicantly increased (p<0.05) labile phosphorus fractions and decreased potential sorption capacities of the soil. As the increased soil pH, reduced exchangeable acidity and oxalate extractable Fe and Al the integrated applications of these amendments xed aluminum and iron instead of phosphorus, thus rendering phosphorus available by keeping the inorganic phosphorus in a bioavailable labile phosphorus pool compared to sole application of the amendments. Conclusions: Combined applications of lime, vermicompost and inorganic P to acidic soils of Goha-1 in Cheha district could convey enhanced amount of available P and ensures the maintenance of higher levels of labile P. It might also contribute towards meeting crop P requirements. incubation. the integrated of homogenized and incubation study was conducted for eight as underneath. A factorial combination of vermicompost and tons ha -1 soil), lime soil) and P and 149.01 executed to The eld and incubated. Few small holes were made each permit aerobic conditions during incubation. Soil samples were then removed for analysis at 60 days.

Consequently phosphorus is de cient in most acid soils because soluble inorganic P is xed by Al and Fe (Adnan et al. 2003). This reaction contributes to less availability of P for crops (Chandrasekaran et al. 2010).
In highly weathered acidic soils, Fe and Al oxyhydroxides are the dominant species with which P readily interacts (Tan 2000 Erich et al. 2002). Therefore, crop production on these soils can be improved greatly by adjusting the pH to near neutrality (Whalen et al. 2000). The availability of P is in uenced by soil organic matter, pH, and exchangeable and soluble Al, Fe, and Ca (Smithson, 1999).
Conventionally, large amounts of lime and inorganic P fertilizers are used to saturate Al and Fe ions. This approach alone has not been successful because it is not economical and not environmentally friendly (Ch'ng et al. 2014).
Soils contain inorganic P (Pi) and organic P (Po) compounds that are important P sources for plants, but Po rarely represents a major portion of soil P. The inorganic P (Pi) compounds mainly couple with amorphous and crystalline forms of Al, Fe, and Ca (Negassa and Leinweber 2009). Information of P fraction dynamics in acidic soils is signi cant to evaluate P mobility in order to reduce the P retention by soils. In soils, P is found in several forms or pools, and different forms are often designated as either inorganic or organic P (Hedley et al. 1982; Reddy et al. 1998). These descriptions imply differences among P forms with respect to reactivity in the environment. Moreover, P fertilization can result in changes in soil P fractions which provide valuable facts on the impacts of P additions on soil P transformations Lan et al. 2012).
In natural or agricultural ecosystems having low P soils, mineralization of organic P is the main source of P supply to plants, especially in highly weathered tropical soils (Vincent et al. 2010). The contribution of soil organic P to increase available P (labile P) can be more relevant when organic fertilization or other practices which can increase the soil organic matter content (OM) are part of the soil management. Organic fertilization affects the P availability, Pi release (Hue et al., 1994) or microbial immobilization of soil Pi (Chen et al. 2000), competition between organic acid anions and phosphate anions for adsorption sites (Andrade et al. 2003; Guppy et al. 2005). Moreover, Pi compound dissolution by organic acids and metal complexation, particularly of Al 3+ and Fe 2+ (Andrade et al. 2003), with lower phosphate anion precipitation reactions can occur because of organic fertilization.
The maintenance of adequate amounts of P in the soil and keeping the wellbeing of the soil through organic and inorganic fertilizer applications are critical for the long term sustainability of agricultural systems. Moreover, a clearer understanding of the change in distribution and solubility of P forms in soil may provide important information for the evaluation process of P availability for plants and to enhance the fertilizer management strategy (Sharply et al. 2004). For example, there is an increasing interest in the potential use of vermicompost (VC) as soil amendment (Lordan et al. 2013). Reshid (2016) noted that application of VC showed remarkable improvements in the soil physical and biochemical properties, which in turn enhance the availability of P to plants in acidic soils.
Low soil acidity, higher oxyhydroxides of Al and Fe content, low P concentrations in the soil solution and higher P adsorption capacity are the characteristic features of the studied soil (Ayenew et al. 2018b). The impact of integrated application of lime, vericompost and mineral P on the distribution of oxyhydroxides of Fe and Al, organic P, and inorganic P fractions have not yet been evaluated in the study area. Thus, for proper P fertilizer management and surmount the low plant availability of soil P, the effects of applications of amendments on adsorption characteristics, P fractions dynamics and related properties are required to be tested. Moreover, in spite of the existing P xation problem in highland soils of Ethiopia, little work has been done on dynamics of P (inorganic and organic fractions) and related properties up on sole or combined applications of organic and inorganic amendments. Studies focusing merely on inorganic P forms have been conducted by Dawit et al. (2002); Wakene and Heluf (2003); Berhane and Sahlemedhin (2003); Shiferaw (2004); Achalu et al. (2014) and Asmare et al. (2015). However, since available P in soil is not a single entity, complete accounts of the P forms (organic and inorganic) present in the soils have to be appreciated in order to determine the fate of the applied P fertilizers (Dawit et al. 2002). Therefore the purpose of this study was to evaluate the effects of sole and combined applications of lime, VC and inorganic P on dynamics and distribution of different P fractions as well as related soil properties.

Materials And Methods
Description of the study area The study was conducted in Cheha district of Gurage zone in south western Ethiopia. The district is situated between 8 0 32' 0" and 8 0 20' 0" N, and 37 0 41' 20" and 38 0 2' 40" E, at an elevation that ranges from 900 to 2812 masl. EIAR (2011) classi ed the area into three agro-ecological zones i.e. highlands (2300 -3200 masl), midlands (1500 -2300 masl), and lowlands (500 -1500 masl) based on the bimodal rainfall system. The ten years mean annual rainfall of the district is about 1268 mm. The mean annual maximum and minimum temperatures are 24.97 and 10.69 0 C, respectively. The dominant soil types in the study area are: Nitisols, Leptisols, and Pellic Vertisols [FAO (Food and Agriculture Organization) 1988].
Site selection, soil sampling and analysis A preliminary soil survey and eld observation was made using topographic map (1:50,000) of the study area. Soil pH (potentiometer), altitude (GPS), and slope (clinometer) were used as criteria for selection of soil sampling sites. Fifteen (15) sub-samples were collected from Goha 1 (SC1) study site to make one composite sample. Accordingly, one composite soil sample (0 -15 cm) having pH value of less than 5.5 was obtained within an altitudinal range of 2000 -3000 masl and slope less than 8%. Soil pH was measured at eld condition using portable pH meter to select soils having a pH of less than 5.5. The soil samples were put in plastic bag, tagged, and transported to laboratory for analysis. Consequently, about 1 kg of composited soil sample was air dried and ground to pass through a 2 mm sieve for analysis of selected soil properties except organic carbon (0.5 mm sieve) according to the standard methods.
Soil P fractions and other related properties Different forms of P were determined following the P fractions scheme suggested by Hedley et al. (1982) as modi ed by Chen et al. (2000). The oxalate extractable P, Al and Fe (P ox , Al ox and Fe ox ) were determined with 0.05 M ammonium oxalate ((NH 4 ) 2 C 2 O 4 .2H 2 O, pH 3.3) in the dark (Mckeague and Day 1966).
Citrate bicarbonate dithionite-extractable Fe and Al (Fe d and Al d ) were determined by the method of Mehra and Jackson (1960). The degree of P saturation (DPS) was determined as the percentage of the ratio of the different forms of P to the oxalate extractable Al and Fe (Al ox and Fe ox ) (Van der Zee et al., 1988).
The P adsorption capacity (PSC, mmol kg -1 ) of the soil was calculated and estimated according to Börling et al. (2001).

Analysis of the composition of vermicompost and lime
Parthenium hysterophorus, wheat straw, cow dung and poultry manure, were used as substrates in preparing the vermicompost. Consequently the pH, OC, C:N, and total concentrations of nitrogen (N), phosphorous (P), potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na) in the vermicompost were determined. The total nutrient contents of vermicompost were measured in suspensions obtained after dry ashing at 500 o C, followed by cooling to room temperature in mu e furnace, slowly removal of ashed samples and dissolving with 1N HCl and diluted to 50 ml volume. Each element was analyzed based on standard laboratory procedure suggested by Gavlak et al. (2005). Phosphorous was determined by the Vanado-molybdate colorometric procedure using spectrophotometer at 460 m wavelength. Calcium and Mg were determined by FAAS, as Na, and K were determined with ame photometer. The total N contents of the vermicompost samples were determined by the micro-Kjeldhal method as described by Gavlak et al. (2005). Organic matter was determined by the dichromate oxidation method of Walkley and Black (1934). Vermicompost pH values was measured in water (sample: water ratio of 1:5) using a pH meter. The calcium carbonate equivalents (CCE) of the lime was determined by dissolving the lime using excess of standard 0.5 M HCl and followed by gentle boiling. After ltration, the excess HCl was back titrated with standard 0.1 M NaOH solution using phenolphthalein as an indicator. From the amount of NaOH used to neutralize the excess acid of the blank and the ltrate, the CCE values of the lime were calculated.

Incubation experiment
The composited soil sample (0-15cm) was air dried, ground and passed through 2 mm sieve and then 300 g soil was placed in plastic pot in the green house for the next step. Three rates of lime were decided of which two of them 9.20, and 11.50 tons CaCO 3 ha -1 were separately applied to obtain target pH values of 6.0, 6.5 and the third one was 5.70 tons CaCO 3 ha -1 which is half of the lime required to bring a pH value of 6.5 for soil from Goha 1 (SC1) sampling site. The lime used for this particular study had a CCE of 96.15 %. Hence, the actual eld application rates of lime were 0, 5.93, 9.57, and 11.96 tons lime ha -1 for the soil. Vermicompost (<0.25mm sieve) with 0, 5, and 10 tons ha -1 rates and inorganic P at the rates of 0, 74.51 and 149.01 kg P ha -1 were prepared for incubation. Accordingly the respective integrated or separate amendments were thoroughly mixed with a given amount of soil and homogenized and the incubation study was conducted for eight weeks as described underneath. A factorial combination of vermicompost (0, 5 and 10 tons ha -1 soil), lime (0, 5.93, 9.57 and 11.96 tons ha -1 soil) and inorganic P (0, 74.51 and 149.01 kg P ha -1 soil) was executed to nd out the interaction effects of the treatments in charge. The experiment was laid down in a completely randomized design (CRD) with three replications. Consequently, to the three hundred grams of surface (0-15 cm) air-dried soil (< 2 mm), the speci ed amount of lime, vermicompost (< 0.25 mm) and solid triple super phosphate (TSP) (sieved <1 mm) were applied jointly or separately. The amended soils were then mixed thoroughly and moistened to eld capacity and incubated. Few small holes were made in each container to permit aerobic conditions during incubation. Soil samples were then removed for analysis at 60 days.

Statistical analysis
The study was a factorial experiment in completely randomized design (CRD) with three factors, namely, organic amendments (vermicompost), lime and mineral P. Statistical analysis of the data including Pearson's simple correlation coe cient, analysis of variance (ANOVA) and comparison of means was executed using Statistical Analysis System (SAS) version 9.1 (SAS Institute, 2004).

Results And Discussion
Physicochemical properties of experimental soil

Vermicompost compositions
The vermicompost that has been harvested after sixty days of decomposition was dark brown in color. As depicted in Table 2 the vermicompost prepared by using parthinium, wheat straw, cow dung and poultry manure as a substrate had a pH value of 8.63. Therefore, the pH value obtained for the vermicompost veri es that it could be used for liming the soil. The vermicompost was analyzed for nutrients concentrations and the corresponding values were found N (2.  After eight weeks incubation period the soil was found to have pH ranging from 4.68 to 6.73 (Table 3). It is generally believed that applications of organic materials reduce pH of a soil (Abdala et al. 2015). However, contrary to the general contemplation, the results of the present study con rmed that application of vermicompost resulted in higher and signi cant effect on the pH of studied soils as compared to the control treatment ( Table 3). The alkaline reaction in vermicompost, and the presence of strongly soluble cations in higher concentrations might have contributed to lessening acidic reactions of the soil. In addition, decomposition of vermicompost in soil during incubation might have produced soluble organic acids, which could interact with soil through the oxyhydroxide functional group of clay surfaces and release OHto soil solution. Similar results have been reported that vermicompost application alone could Analysis of variance also revealed that the application of inorganic P alone had no signi cant effect on pH of the soil; however the interaction of two factors (lime x inorganic P, lime x vermicompost, inorganic P x vermicompost) and three factors (vermicompost x inorganic P x lime) in uenced signi cantly the pH of the soil (Tables 3). Furthermore, the highest pH (6.73) value of the soil was recorded at combined application of lime, vermicompost and inorganic P (lime x vermicompost x inorganic P) in a proportion amounted 11.50 ton CaCO 3 ha -1 , 10 ton VC ha -1 and 149.01 kg P ha -1 whilst, the lowest pH value (4.68) was achieved from the control. The ndings of the present study was in concurrent with that of Ashoka et al. (2014) which reported addition of inorganic P alone did not have any appreciable effect on soil pH values.
The acidity reduced by lime, vermicompost and inorganic P was synergistic having a mechanism that calcium from lime replaces the exchangeable forms of Al and Fe, which reacts with hydroxide ion released from water in the soil solution forming insoluble Al and Fe hydroxides (Buni, 2015); while compost forms insoluble Al and Fe organic acid complex bounding to the exchangeable Al and Fe (Haynes and Mokolobate 2001). In the meantime, the adsorption of the added phosphate at the exchange site might have contributed to the raise in pH of the studied soil through ligand exchange. In agreement with this, a study revealed that there was a steady increase in the pH of the supernatant solution as sorption progressed, because sorption occurs by the replacement of hydroxyl groups, exposed on surface sites, by phosphate in solution (Goldberg et al. 2008).
The results obtained after eight weeks incubation period showed that the amount of available P extracted by Mehlich-III, method ranged from 8.77 to 21.89 mg kg −1 at SC1 study site ( Table 3). Analysis of variance also revealed that the main factors (vermicompost and inorganic P) applied to soil signi cantly increased Mehlich-III P content of the soil compared to the control treatment. Similar results have been reported by Ilker and Tavali (2014) showing that vermicompost applied to soil signi cantly increased available phosphorous. Moreover, statistically signi cant (P < 0.05) in uences were observed whenever the three factors are interacted (vermicompost x lime x inorganic P). Consequently, the highest (21.89 mg kg -1 ) value of Mehlich-III P was recorded when vermicompost was applied in combination with lime and inorganic P at the rates of 10 ton VC ha -1 , 9.20 ton CaCO 3 ha -1 and 149.01 kg P ha -1 , while the lowest (8.77 mg kg -1 ) was recorded from the control. The compelling reason for the enhanced increase in available P of soils after incubation could be due to with ability of the lower molecular organic acids (decomposition product of vermicompost) and their anionic carboxylate functional groups to interact with soil, by occupying P adsorption sites and competing with phosphate (Guppy et al. 2005). The increased amount of phosphate adsorbed on free metal oxyhydroxides and the presence of soluble cations in lime and vermicompost, which displace acidic caions, might have triggered the availability of P. In harmony with this, Kamprath (1984) reported that the Ca 2+ in lime, and Ca 2+ , K + , Na + in vermicompost (organic matter) could displace Al 3+ , Fe 2+ and H + ions from the soil sorption sites, so that P xation would be reduced.
The increase in soil pH was re ected by corresponding decrease in exchangeable acidity from 2.57 cmol c kg −1 in control to 0.31 cmol c kg −1 (P < 0.05). The main factors (lime, vermicompost and inorganic P), the interaction between two factors (lime x inorganic P, vermicompost x lime, inorganic P x vermicompost) and three factors (lime x vermicompost x inorganic P) signi cantly altered the levels of exchangeable acidity in the studied soil (Tables 3). Moreover, the greatest (87.94%) change was obtained from the integrated applications of lime, vermicompost and inorganic P at the rates of (11.50 ton ha -1 , 10 ton VC ha -1 , 149.01 kg P ha -1 ), while the lowest (1.53%) was recorded from the control the soil. The reduction in exchangeable acidity can partially be attributed to an initial increase in soil pH that was observed with lime and vermicompost.
Similar analysis showed that except for the sole applications of inorganic P, the other factors including two factors (lime x inorganic P, vermicompost x lime, inorganic P x vermicompost) and three factors interactions (lime x vermicompost x inorganic P) had signi cant decreasing effects on exchangeable aluminum. It could also be noted that the three factors interaction appeared to have a signi cant effect and decreased the exchangeable Al of the soil by 88.09 to 95.23% compared to the control, indicating the synergistic effects of the three factors on the exchangeable aluminum in the studied soil. An increase in soil pH might have resulted in precipitation of exchangeable and soluble Al, as insoluble Al hydroxides (Ritchie 1994), thus reducing concentration of Al in soil solution. However, there are other mechanisms involved in the reactions of Al with OM, which are intricate and probably involve complex formation with low-molecular weight organic acids, such as citric, oxalic, and malic acids, and humic material produced during the decomposition of the OM and adsorption of Al onto the decomposing organic residues (Ritchie, 1994). In agreement with this result, Teshome et al. (2017) reported that integrated application of lime, mineral P and compost had reduced the exchangeable aluminum, due to the formation of organo-Al (chelation) complexes, insoluble aluminum hydroxide precipitate, and aluminum phosphate precipitate from compost, lime and inorganic P respectively.
As far as CEC of the soil is concerned, the interactions of three factors had signi cant (P< 0.01) in uence on the CEC of the soil (Tables 3). After eight weeks incubation period, CEC values of the soil was found in the range of 22.05 cmol c kg -1 (control) and 29.53 cmol c kg -1 in combined applications of vermiccompost, lime and inorganic P at the rates of 10 ton VC ha -1 , 11.50 ton CaCO 3 ha -1 , and 149.01 kg P ha -1 . Sole applications of inorganic P had no signi cant effect on CEC of incubated soil ( Table 3). The possible reason for the enhancement of CEC during combined (lime x vermicompost x inorganic P) application of those amendments could be the increase in pH of the soils. Because with increasing pH (i.e. increasing activity of OHions) H + is dissociated from oxide surfaces or from organic functional groups, thus resulting in a negative charge, which could be allied with the CEC of the soils. Means followed by the same letter within a column are not signi cantly different; ** = signi cant at P ≤ 0.01 using the Duncan's multiple range test; CV = coe cient of variation of treatments; exAc = exchangeable acidity; exAl = exchangeable Al; PAcs = percentage of acid saturation; PAls = percentage of Al  (Table 4). As a case in point, Torrent et al. (1990) reported that the nature, amount and distribution of iron and aluminum oxides in soil affect the ionic charge, chemical characteristics, and ion adsorption especially phosphorous sorption.
Data showing main and interaction effects of treatments on oxalate extractable aluminium (Al ox ) are exhibited in The effects of treatments on oxalte extractable iron (Fe ox ) are also shown in Table 4. The values of Fe ox obtained after incubation was ranged from 88.59 -96.39 mmol kg -1 in which the maximum (96.39 mmol kg -1 ) was recorded from the application of vermicompost at the rate of 10 ton ha -1 alone and the least (88.59 mmol kg -1 ) recorded from the integrated applications of lime vermicompost and inorganic P at the highest rates. The highest value obtained from sole application of vermicompost may be ascribed to organo-metal complex formed during the incubation period. It has been reported that in Fe-and Al-rich soil, organic matter could inhibit the crystallization of Al and Fe by forming stable complexes with them, which in turn can increase P sorption as noncrystalline Al and Fe increases (Kang et al. 2009). A signi cant (p<0.01) decreases in oxalate (Fe ox ) and dithionite extractable iron (Fe d ) were observed as a result of integrated applications of lime, vermicompost and inorganic P as two factors (lime x inorganic P, lime x vermicompost, inorganic P x vermicompost) and three factors (vermicompost x lime x vermicompost x inorganic P) compared to the control. Accordingly, the maximum (9.32%) reduction in Fe ox at the exchange sites was recorded from integrated applications of lime, vermicompost and inorganic P at the rates of 11.50 ton CaCO 3 ha -1 , 10 ton VC ha -1 and 149.01 kg P ha -1 respectively, whereas the least (1.34%) was obtained from the sole application of vermicompost at the rates of 10 tone ha -1 .
Similarly, amalgamated applications of these amendments at the rates of 11.50 ton CaCO 3 ha -1 , 10 ton VC ha -1 and 149.01 kg P ha -1 had brought the maximum (1.73%) reduction in Fe d , and the least (0.16%) variation from the control compared to the native soil. Similar results were reported by Asmare et al. Ammonium oxalate extractable phosphorous is associated with oxalate extractable iron and aluminum, because Fe and Al oxyhydroxides are good indicators for P sorption as they act as a sink for soluble phosphates (Vaananen et al. 2008). It is a potentially useful measure of the P associated with the amorphous iron and aluminum oxides in the soil (Wolf and Baker 2008). In the current study, upon the exclusive (main factor), integrated [two factors (lime x vermicompost, inorganic P x lime, vermicompost x inorganic P) and three factors (lime x vermicompost x inorganic P)] applications to soils for eight weeks incubation period appreciable (p<0.001) differences in oxalate extractable P (P ox ) were observed in the soil. In the case where integrated application of amendments (lime x vermicompost x inorganic P) at the rates of 11.50 ton CaCO 3 ha -1 , 10 ton VC ha -1 and 149.01 kg P ha -1 was executed, the highest (8.70 extractable form of those metal oxides reduced from the exchange sites, phosphorous extracted by ammonium oxalate (P ox ) obviously enhanced. Similar to the present study, it has been noted that sole or integrated applications of P sources (organic and inorganic) had a signi cant effect on the oxalate extractable Al and Fe (Gikonyo et al. 2011) which in turn in uence P ox , since P adsorbed by soil mainly attributed to P adsorbed on amorphous metal oxides (Fe ox and Al ox ) (Cui et al. 2017).
Phosphorous sorption capacities was signi cantly (P<0.05) in uenced by the main and joined applications of treatments (Table 4). After the incubation period, the highest sorption capacity was recorded from the soil incubated solely with vermicompost at the rate of 10 ton ha -1 (132.98 mmol kg -1 ) and the lowest (123.31 mmol kg -1 ) value was obtained due to combined applications of the treatments (lime x vermicompost x inorganic P) at the rates of 9.20 ton CaCO 3 ha -1 , 10 ton VC ha -1 , and 149.01 kg P ha -1 . It can also be seen that the adsorption capacity of the soil decreased signi cantly with increasing applications rates of integrated amendments while applications of vermicompost solely increased the sorption capacity of the two soils under study. The increased adsorption capacity of the soil because of the exclusive application of vermicompost may be due to hindrance of crystallization of Fe and Al oxides.
In Fe and Al rich soil, organic matter could inhibit the crystallization of Al and Fe by forming stable complexes with them, which in turn can increase P sorption as non-crystalline Al and Fe increases (Borggaard et al. 1990; Kang et al. 2009). The reduction in magnitude of phosphorous sorption capacities due to integrated application could be attributed to the coating of metal oxyhydroxides species by organic molecules from vermicompost applications, which reduce the availability of binding sites for phosphate ions, formations of insoluble aluminum hydroxides from the applications of lime, which reduces adsorptions of phosphate on the exchange site and addition of inorganic P, which occupy the exchange sites where P is expected to be adsorbed. Thus, the result of the present study is in concurrent with the study made by Gikonyo et al. (2011), which showed that sole or integrated applications of P sources (organic and inorganic) had a signi cant effect on the PSC of a soil.
The change in DPS of the soil was presented in Table 4. The phosphate ion is negatively charged and hence, continued P xation leads to a "semi-permanent" increase in surface negative charge, resulting in a decrease in the electric potential of the reacting soil particle (Barrow et al. 1998;Celi et al. 2000). Consequently, increasing P saturation leads to weaker and weaker retention of P, implying that the degree of phosphorus saturation (DPS) appears to govern solution P concentration (Magdoff et al., 1999). Furthermore, recent studies have shown that the degree of P saturation (DPS) is a good indicator of the soil's potential to release P (Hooda et al., 2000).
The incubated soil was found to have DPS (%) values ranging from 4.49-7.06%. The DPS (%) value was signi cantly (P<0.01) affected by individual (lime, vermicompost, inorganic P) and combined applications of these treatments ( Table 4). The maximum DPS (7.06%) value was recorded from the integrated applications of (lime x vermicompost x inorganic P) amendments at the rates of 11.50 ton CaCO 3 ha -1 , 10 ton VC ha -1 , and 298.03 kg P ha -1 . Whereas the minimum DPS (4.49%) value was observed from the control, Thus, the result of present study is in concurrent with the study made by Gikonyo et al. (2011) which showed that sole or integrated applications of P sources (organic and inorganic) had a signi cant effect on the DPS of soils. It can be inferred that the observed increase in the DPS of the soils as a result of application of these amendments might have brought the better mobility of P in the soils. In this regard Yan et al. (2017) reported that due to decrease of the sorption sites for further P sorption, the concentrations of exchangeable P increased with increasing DPS and soil P mobility increases. Amendments effect on forms and distributions of P The combined and sole applications of the amendments altered signi cantly the chemical properties expected to impact the distributions of phosphorous in the soil ( Table 5). The forms and distribution of the various P fractions [NH 4 Cl-P, NaHCO 3 -Pi, NaHCO 3 -Po NaOH-Pi, NaOH-Po (NaOH-Pi) sn , (NaOH-Po) sn HCl-Pi, residual P and total P] following incubation of the soil are shown in Table 5 too. After eight weeks incubation period, the distributions and forms of Pi were in the order of magnitude: NH 4 Cl-P < NaHCO 3 -Pi < (NaOH-Pi) sn < HCl-Pi < NaOH-Pi. The highest percentage change in each fraction was recorded from the The NaOH-Pi was the largest extractable inorganic P fraction and the most abundant active P form contributing to about 22.66 -45.49% and 17.76 -42.07% of the total P, in the studied soil. Thus, NaOH-P was the major sink for the applied P. Previous studies also reported that organic amendments with high P contents could signi cantly increase NaOH-Pi contents (and to a lesser extent NaOH-Po) Li et al. 2015). The increase of this fraction observed in these soils amended by phosphorus fertilizer and vermicompost was possibly as a result of phosphate released from phosphorus fertilizer and vermicompost. Similar result has been reported by Pavan and Andmcioli (1995) where application of compost was able to promote NaOH-Pi. It can be deduced that since NaOH-Pi fraction is a site for P sorption; increase in this fraction provide evidence that P-rich amendments in the studied soil may decrease After eight weeks of incubation period the least (2.04 mg kg -1 ) concentration of the readily available NH 4 Cl extractable P (Gunatilaka, 1988), was recorded from the control and the highest (33.37 mg kg -1 ) was obtained from the combined applications of lime, vermicompost and inorganic P at the rates of 11.50 ton CaCO 3 ha -1 , 10 ton VC ha -1 , 149.01 kg P ha -1 respectively.
According to the result of the present study (Table 5) lime alone had no signi cant effect on readily available fractions (NH 4 Cl-P) at both study sites.
Contrasting result was mentioned by Hartono et al. (2000) that lime had signi cant effect on readily available Pi but it agrees with that of  where lime didn't affect readily available Pi. Even though sole applications of lime didn't appreciably affect the readily available fractions of P (NH 4 Cl-P) the magnitude of enhancement varied along with the rates of lime. This change in magnitude may be attributed to the decrease of exchangeable Al that is precipitated by OH -. In the case where lime was applied in combination with other materials like inorganic P and vermicompost, signi cant differences were observed over the control (Table 5). On the other hand, the readily available fraction (NH 4 Cl-P) was signi cantly affected by single or combined applications of inorganic P and vermicompost as compared to the control.
The HCl-Pi fraction is associated with the primary minerals such as apatite (Tiessen et al. 1984) and with calcium-bound P, which is little or missing in highly weathered soils (Walker and Syers 1976). In the present exploration, it appeared that integrated applications of the amendments of two factors (lime x vermicompost, inorganic P x lime, vermicompost x inorganic P) and three factors (lime x vermicompost x inorganic P) tended to enhance HCl-Pi signi cantly (Table 5). Consequently, the highest value of HCl-Pi was recorded from the interaction of lime, vermicompost and inorganic P, at the respective maximum rates, whereas the lowest was recorded from the control. However, in the current study, HCl-P did not varied signi cantly with the sole applications of those treatments. The absence of substantial changes in HCl-Pi is explicable because the soil is acidic which would favor formation of Al and Fe P inorganic compounds over Ca products (Hartono et al. 2000). Similar result was reported by Pavan and Androcioli (1995) that application of compost didn't signi cantly in uence HCl-Pi. Hartono et al. (2000) found that applications of inorganic phosphorous or lime to acidic soils had no signi cant effects on the concentrations of HCl-Pi.
Generally, the dynamics of the two labile P fractions (NH 4 Cl-P, NaHCO 3 -P i ) varied considerably (p<0.05) when combined applications of lime, vermicompost and inorganic P were executed at both sampling sites. Whilst, the lower plant available chemisorbed Pi associated with amorphous and crystalline Fe and Al hydroxides and clay minerals (NaOH-pi) and moderately labile, easily mineralisable (NaHCO 3 )-Po and less labile (NaOH)-Po were signi cantly altered during the incubation period.

Correlation among soil properties
The correlation between soil properties after incubation with amendments is exhibited in Table 6. The readily available NH 4 Cl extractable P was strongly positively correlated with Mehlich 3-P, NaHCO 3 -Pi, NaHCO 3 -Po, HCl-P, NaOH-Pi, NaOH-Po and P ox . This could be an indication for the presence of higher concentration of NH 4 Cl extractable P in soils where there are prominently higher concentrations of Mehlich 3-P, NaHCO 3 -Pi, NaHCO 3 -Po, HCl-P, NaOH-Pi, NaOH-Po and P ox in the soil. In addition, the correlation result veri ed the scienti c speculation that P ox thought to be P adsorbed initially (native P) and the higher the concentrations of native P the smaller the size of the adsorption sites left over for P added in the form of amendments. Therefore, up on additions of P bearing amendments to soils having higher P ox only smaller amounts of P tend to be adsorbed and the remaining P would be forced to soil solution and become available. According to the correlation result from incubated soils, enhanced amount of available P was manifested where there was higher HCl extractable P (Ca bound P) as liming materials are applied. The strong rationale for strong positive association between HCl-P and readily available P might be the occurrence of dissolution rather than precipitation in acidic soils.
Meanwhile, those readily available fractions of P (NH 4 Cl-P, NaHCO 3 -Pi and NaHCO 3 -Po) in the studied soils had strong and negative association with oxalate extractable Fe (Fe ox ), oxalate extractable Al (Al ox ) and PSC. The results pointed out that the availability of P was very low in soils dominated by higher concentrations of free oxyhydroxides of Fe and Al. In addition, NaOH-Pi and NaOH-Po were strongly and negatively correlated with Fe ox , Al ox and PSC. This could be an indication for reduction in free metallic oxyhydroxides (Al ox , Fe ox ) and PSC with increasing amount of P added through inorganic P and vermicompost application as well as lime.

Conclusions
It can be seen that unlike separate applications of inorganic P, both lime and vermicompost had signi cant effect in enhancing the pH of the studied soil.
Combined application of lime, vermicompost and inorganic P is more effective in reducing exchangeable acidity, exchangeable aluminum compared to the single treatment. Even though, sole applications of lime, vermicompost and inorganic P had signi cant effects on Mehlich-III extractable available P; combined applications of these amendments had brought higher and better available P. Oxalate and dithionite citrate bicarbonate extractable Fe and Al, which indicate the potential adsorption capacity of soils, could be reduced signi cantly by combined use of the treatments over single applications. Despite having no signi cant effects on the distributions of P forms, sole application of lime with increasing rates reduced the magnitude of NaOH extractable P and enhanced the readily available P fractions (NH 4 Cl-P, NaHCO 3 -Pi and NaHCO 3 -Po).
Therefore, combined applications of lime, vermicompost and inorganic P to acidic soils of Goha-1 in Cheha district could convey enhanced amount of available P. It can also ensure the maintenance of higher levels of labile P in the soil and highly signi cantly in uenced those soil properties as well. Sole can be concluded that integrated applications of these amendments could contribute towards meeting crop P requirements. Therefore, the smallholder farmers and stakeholders in the study area should implement technologies like low input P management strategy and application of lime, to alleviate phosphorous and acidity related problems. Authors' contributions Bereket Ayenew collected, analyzed, interpreted the data and made the nal write up. Asmare Melese as a co-authors edited and approved the nal manuscript