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

doi:10.21203/rs.3.rs-250222/v1

Background: In acid soils, soluble inorganic phosphorus is fixed 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 CaCO₃ 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 significantly 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 fixed 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.

Environmental Engineering

Environmental Policy

oxyhydroxides

soil acidity

inorganic amendment

phosphorous fraction

Soil acidity is the most central factor affecting plant growth and limiting crop production (Van Straaten 2007; Fageria 2009; Achieng et al.2010). It is common in regions where rainfall is high enough to leach appreciable amounts of exchangeable bases from soil surface (Achalu et al.2012b). Soil acidification affected large areas of Ethiopian highlands estimated at 40% of the total arable land of the country (Mesfin 2007; Hirpa et al. 2013). Particularly, it becomes a serious threat to western and southern highlands of Ethiopia (Wassie and Boke 2009). Soil acidification arises from leaching of bases down the profile through the action of rainfall, continuous cropping, and crop removal of basic cations (Oluwatoyinboet et al. 2009). Consequently phosphorus is deficient in most acid soils because soluble inorganic P is fixed 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; Sims and Pierzynski 2005; Ahmed et al. 2008; Rayment and Lyons 2011). These oxyhydroxides create new functional groups for P adsorption (Roderigo et al. 2016) and may be found as distinct surface layers on soil particles or in complexes with the organic fraction of the soil (Sims and Pierzynski 2005). These short range crystalline oxyhydroxides (amorphous) are well known to affect P sorption in soils (Janardhanan and Daroub 2010).

In acid soils, high levels of exchangeable Al and Fe play a significant role in controlling orthophosphate concentration in the soil solution (Iyamuremye and Dick 1996; Haynes and Mokolobate 2001; 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 influenced 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 significant 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 (Zhang et al. 2006; 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 Al³⁺ and Fe²⁺ (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 fixation 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.

Description of the study area

The study was conducted in Cheha district of Gurage zone in south western Ethiopia. The district is situated between 8⁰ 32’ 0” and 8⁰ 20’ 0” N, and 37⁰ 41’ 20” and 38⁰ 2’ 40” E, at an elevation that ranges from 900 to 2812 masl. EIAR (2011) classified 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 ⁰C, 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 field 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 field 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 modified 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 ((NH₄)₂C₂O₄.2H₂O, 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^oC, followed by cooling to room temperature in muffle 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 ɳm wavelength. Calcium and Mg were determined by FAAS, as Na, and K were determined with flame 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 filtration, 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 filtrate, 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 CaCO₃ ha^-1 were separately applied to obtain target pH values of 6.0, 6.5 and the third one was 5.70 tons CaCO₃ 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 field application rates of lime were 0, 5.93, 9.57, and 11.96 tons lime ha^-1for 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 find 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 specified 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 field 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 coefficient, analysis of variance (ANOVA) and comparison of means was executed using Statistical Analysis System (SAS) version 9.1 (SAS Institute, 2004).

Physicochemical properties of experimental soil

Table 1 Selected characteristics of the experimental soil

Parameters	Soil (SC1)
Soil group	Nitisol
Sand (%)	23.2
Silt (%)	28.6
Clay (%)	48.2
Bulk density (gcm^-1)	1.32
Field capacity (%)	29.5
Permanent wilting point (%)	19.6
pH (H2O)	4.65
Cation exchange capacity (cmol_ckg^-1)	21.15
Exchangeable acidty (cmol_ckg^-1)	3.76
Exchangeable Al (cmol_ckg^-1)	2.54
Organic carbon (%)	1.58
Mehlich-III P (mg kg^-1)	8.09
Alox (mmolkg^-1)	147.37
Feox (mmolkg^-1)	174.69
Phosphorous sorption Capacity (PSC) (mg P Kg^-1)	133.54

Source: Ayenew et al. (2018b)

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 verifies that it could be used for liming the soil. The vermicompost was analyzed for nutrients concentrations and the corresponding values were found N (2.41%), OC (24.40%), and C:N (10.12), P (109.23 ppm), K (577.54 ppm ), Ca (1198.28 ppm ), Na (127.12 ppm ), Mg (137.20 ppm ).

Table 2 Characterization of vermicompost

Treatments	pH	OC	N	P	K	Na	Ca	Mg	C:N
		….. (%) ......		……………………. (mg kg^-1) ………….………………
VC	8.68	24.40	2.41	109.23	577.54	133.92	1198.28	137.20	10.12

OC = organic carbon, VC = Vermicompost

pH, exchangeable acidity, CEC and available P after Incubation

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 confirmed that application of vermicompost resulted in higher and significant 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 OH^-to soil solution. Similar results have been reported that vermicompost application alone could have increased the pH of the soil (Gopinath and Mina 2011; Gopinath, et al. 2011, Ilker and Tavali 2014).

Analysis of variance also revealed that the application of inorganic P alone had no significant 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) influenced significantly 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 CaCO₃ 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 findings 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 significantly 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 significantly increased available phosphorous. Moreover, statistically significant (P < 0.05) influences 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 CaCO₃ 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 Ca²⁺ in lime, and Ca²⁺, K⁺, Na⁺ in vermicompost (organic matter) could displace Al³⁺, Fe²⁺ and H⁺ ions from the soil sorption sites, so that P fixation would be reduced.

The increase in soil pH was reflected by corresponding decrease in exchangeable acidity from 2.57 cmol_c kg⁻¹ in control to 0.31 cmol_ckg⁻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) significantly 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 significant decreasing effects on exchangeable aluminum. It could also be noted that the three factors interaction appeared to have a significant 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 significant (P< 0.01) influence 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^-1in combined applications of vermiccompost, lime and inorganic P at the rates of 10 ton VC ha^-1, 11.50 ton CaCO₃ ha^-1, and 149.01 kg P ha^-1. Sole applications of inorganic P had no significant 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 OH^- ions) 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.

Table 3 Effects of amendments on selected chemical properties of soil (SC1)
				exAc	exAl	CEC	Mehlich 3 P	PAcs	PAls
Treatments			pH ………………( cmol_ckg^-1) ……………… .…. (mg/kg)…					………. ( % ) .........
P0	V0	L0	4.68v	2.57a	1.37a	22.05op	8.77r	11.76a	6.27a
		L1	5.67o	0.59i	0.11i	22.15op	9.06rq	2.70i	0.49i
		L2	5.93k	0.42k	0.11i	22.33on	9.43q	1.89k	0.48i
		L3	6.33f	0.37m	0.11i	22.48n	10.09p	1.70m	0.48i
	V1	L0	4.79u	2.15b	0.33b	23.42m	9.39q	9.85b	1.49b
		L1	5.85m	0.68h	0.03j	25.39g	12.18n	3.11h	0.12j
		L2	6.03i	0.59i	0.11i	25.83def	12.10n	2.70i	0.48i
		L3	6.67bc	0.33o	0.11i	28.71b	12.73m	1.51o	0.48i
	V2	L0	4.99t	1.99c	0.31cd	24.02jkl	10.36po	9.14c	1.41cd
		L1	5.94k	0.59i	0.03j	25.60gf	10.75o	2.70i	0.12j
		L2	6.11h	0.42k	0.11i	25.93cde	12.59m	1.89k	0.48i
		L3	6.71ba	0.35n	0.03j	29.45a	13.17l	1.59n	0.12j
P1	V0	L0	4.68v	2.56a	0.32bc	23.08p	16.73k	11.71a	1.44bc
		L1	5.68o	0.68h	0.11i	23.79l	16.86k	3.11h	0.48i
		L2	5.76n	0.50j	0.11i	24.16j	17.95i	2.31j	0.48i
		L3	6.32f	0.39l	0.11i	24.46hi	18.28ih	1.79l	0.48i
	V1	L0	5.18s	1.82d	0.29e	23.44m	16.99kj	8.34d	1.35e
		L1	5.95jk	0.50j	0.03j	25.40g	17.36j	2.31j	0.12j
		L2	6.02i	0.35n	0.11i	25.84c-f	18.09ih	1.59n	0.48i
		L3	6.66c	0.33o	0.11i	28.73b	18.41h	1.49o	0.48i
	V2	L0	4.99t	1.56f	0.27f	24.07jk	18.26ih	7.13f	1.21f
		L1	5.99ji	0.42k	0.11i	25.64fg	19.37feg	1.89k	0.48i
		L2	6.29f	0.59i	0.11i	25.99cd	19.30fg	2.70i	0.48i
		L3	6.68abc	0.34no	0.11i	29.48a	19.41fe	1.56no	0.48i
P2	V0	L0	4.68v	2.54a	0.31cde	22.12op	18.99g	11.76a	1.40cde
		L1	5.36q	0.42k	0.11i	23.84kl	19.13fg	1.89k	0.48i
		L2	5.86lm	0.42k	0.19h	24.19ij	20.54dc	1.89k	0.85h
		L3	6.39e	0.33o	0.03j	24.52h	20.73c	1.49o	0.12j
	V1	L0	5.19s	1.74e	0.29de	23.45m	19.35fg	7.93e	1.37de
		L1	5.55p	0.50j	0.11i	25.42g	19.06fg	2.30j	0.48i
		L2	5.94k	0.59i	0.11i	25.87c-f	19.77e	2.70i	0.48i
		L3	6.55d	0.35n	0.11i	28.76b	20.17d	1.60n	0.48i
	V2	L0	5.24r	1.47g	0.25g	24.11jk	21.37b	6.73g	1.15g
		L1	5.91kl	0.59i	0.19h	25.66efg	21.62ba	2.70i	0.85h
		L2	6.24g	0.42k	0.11i	26.12c	21.89a	1.89k	0.48i
		L3	6.73a	0.31p	0.03j	29.53a	21.82a	1.43p	0.12j
Mean			5.82	0.86	0.17	25.11	16.45	3.91	0.79
F-test			**	**	**	**	**	**	**
CV(%)			4.49	1.05	4.49	0.68	1.47	1.05	4.49

Means followed by the same letter within a column are not significantly different; ** = significant at P ≤ 0.01 using the Duncan’s multiple range test; CV = coefficient of variation of treatments; exAc = exchangeable acidity; exAl = exchangeable Al; PAcs = percentage of acid saturation; PAls = percentage of Al saturation; L0 = No lime; L1 = 5.93 tons lime ha^-1; L2 = 9.57 tons lime ha^-1; L3 = 11.96 tons lime ha^-1; V0 = No vermicompost; V1 = 5 tons vermicompost ha^-1; V2= 10 tons vermicompost ha^-1; P0 = No mineral P; P1 = 74.51 kg P ha^-1; P2= 149.01 kg P ha^-1.

Amendments effect on oxalate and dithionite extractable P, Al and Fe

Data revealing the distribution of extractable P, Fe and Al after eight weeks incubation of the soil is presented in Tables 4. In view of a study results reported by Asmare et al. (2015) on eight Ethiopian acidic soils the soil considered in the current study had high oxalate extractable Al and Fe and dithionite citrate bicarbonate extractable Al and Fe (Ayenew et al. 2018a). Since oxalate and dithionite extractable iron and aluminum contents of the soil were high; Fe and Al oxyhydroxides could be the dominant species with which P interacts. The changes in some of the properties of soil upon applications of amendments might be ascribed to the change in concentration of the extractable form of Fe and Al present in the soil (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 Table 4. The highest (152.64 mmol kg^-1) value of Al_ox from sole application of vermicompost at the rate of 10 ton ha^-1 and the least (141.93 mmol kg^-1) from the integrated applications of lime, vermicompost and inorganic P were recorded for the soil. Thus, the highest (6.85%) reduction in oxalate extractable Al was obtained from combined applications of lime, vermicompost and inorganic P at the rates of 9.20 ton CaCO₃ ha^-1, 10 ton VC ha^-1 and 149.01 kg P ha^-1. After a given incubation period the results of analysis of variance revealed that sole (inorganic P, lime and vermicompost), combined applications of the ammendments had significant (p<0.01) effect on the oxalate extractable aluminum over the control (Table 4).

The effects of treatments on dithionite citrate bicarbonate extractable aluminium (Al_d) are also presented in Table 4. In the interim sole and integrated applications of amendments had substantial (p<0.01) influence on dithionite citrate bicarbonate extractable aluminum (Al_d). Consequently, the highest (173.77 mmol kg^-1 dithionite citrate bicarbonate extractable (Al_d) value was obtained from the control while the lowest (169.23 mmol kg^-1) attained from pooled applications of lime, vermicompost and inorganic P at the rates of 9.20 ton CaCO₃ ha^-1, 10 ton VC ha^-1 and 149.01 kg P ha^-1.

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 significant (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 CaCO₃ 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 CaCO₃ ha^-1, 10 ton VC ha^-1 and 149.01 kg P ha^-1had 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. (2015) who found that individual and combined applications of organic and inorganic minerals had significant effect on oxalate (Al_ox, Fe_ox) and dithionite (Al_d, Fe_d) extractable aluminum and iron free oxides.

It could be noted that synergistic effects of the three factors on the oxalate and dithionite extractable Fe and Al were remarkable. This might have occurred through different reaction mechanisms like the liming effect which develops negative charge through abstraction of H⁺ by OH^- ions and Ca⁺² ions displacement of Al at the exchange sites forming insoluble precipitates Al(OH)₃ as a result of applications of liming materials. Additionally, formations of organo-metal complexes from soluble organic molecules that arouse from organic amendments could in turn occupy the exchange sites and inhibit the interaction between the metallic oxyhdroxides and oxalate extractants. Furthermore, adsorption reaction through which soil interacts with foreign materials; i.e along with the application of inorganic P the amount of phosphate adsorbed on metal oxyhydroxides increased and this could reduce free metallic oxides at exchange sites. In this regard, the results of the present study were in concomitant with that of Asmare et al. (2015), in which the reductions in Al_ox, Fe_ox, Al_d and Fe_d contents as the result of application of P bearing materials to a soil was reported and justified by the fixation of Al and Fe in the form of Al-P and Fe-P as a cause for reduction in amount extracted by oxalic acid.

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 CaCO₃ ha^-1, 10 ton VC ha^-1 and 149.01 kg P ha^-1 was executed, the highest (8.70 mmol kg^-1) was achieved whereas the lowest (5.88 mmol kg^-1) recorded from the control. It can be observed that as the amount of oxalate and dithionite 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 significant effect on the oxalate extractable Al and Fe (Gikonyo et al. 2011) which in turn influence 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 significantly (P<0.05) influenced 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 CaCO₃ 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 significantly 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 significant 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 fixation 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 significantly (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 CaCO₃ 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 significant 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.

Table 4 Effects of amendments on Oxalate and dithionite extractable iron, Aluminum and phosphorous of SC1 Soil
			Al_ox	Al_d	Fe_ox	Fe_d	P_ox	PSC	DPS
			……………………………………………….. mmolkg^-1……………………………………………………………………………………………..						%
P0	V0	L0	150.35a	173.77a	94.29a	634.82a	5.88r	130.64a	4.499n
		L1	147.16b	171.60b	92.53b	630.72b	6.62q	127.99b	5.17m
		L2	145.94b-g	171.51b	92.37bc	630.33b	6.74qp	127.26b-e	5.29lm
		L3	144.44h-k	170.65b-f	92.29bcd	629.02c	6.88op	126.41c-h	5.44kl
	V1	L0	151.59ab	171.43b	95.89ab	628.38cd	6.74qp	132.15a	5.09r
		L1	146.84bc	171.37bc	91.79b-f	627.99cde	6.75qp	127.43bcd	5.29lm
		L2	146.35b-e	171.23bcd	91.69b-f	627.63def	7.15lm	127.11b-e	5.63ij
		L3	144.91f-j	171.13bcd	91.61b-f	627.51def	7.17lkm	126.30d-i	5.68hi
	V2	L0	152.64a	171.35bcd	96.39a	626.79efg	6.79op	132.98a	5.11qr
		L1	145.33d-h	171.29bcd	91.27b-h	626.65e-h	6.83op	126.35d-i	5.41kl
		L2	144.63h-k	171.20bcd	91.08b-i	626.61e-i	7.54hi	125.87f-k	5.99ef
		L3	144.48h-k	171.03bcd	90.75c-i	626.49f-j	7.62hg	125.62g-k	6.07ef
P1	V0	L0	147.12b	171.57b	90.99b-i	630.76b	6.91on	127.15b-e	5.44kl
		L1	142.84l-o	171.45b	90.87c-i	628.58cd	6.85op	124.80jkl	5.49jk
		L2	143.14l-o	171.03bcd	90.69d-j	627.71c-f	7.68g	124.87jkl	6.150e
		L3	142.87l-o	170.98b-e	90.59e-j	627.67c-f	7.06nm	124.67kl	5.66hi
	V1	L0	146.47bcd	171.14bcd	91.19b-i	625.92g-k	7.18lkm	126.91b-f	5.66hi
		L1	146.04b-f	170.79b-f	90.96b-i	625.89g-k	7.31jk	126.56c-g	5.78ghi
		L2	143.92i-l	170.69b-f	90.66d-j	625.83g-k	8.11e	125.26h-l	6.47cd
		L3	145.67c-h	170.52b-g	90.52e-k	625.63g-k	8.27d	126.13e-i	6.56c
	V2	L0	145.12e-h	170.47b-g	90.19f-l	625.25h-l	7.43ji	125.65g-k	5.91fg
		L1	143.57k-n	170.44b-g	90.14f-l	625.13jkl	7.58hg	124.80jkl	6.07ef
		L2	145.39d-h	170.21b-g	90.03g-l	625.03jkl	8.53bc	125.72g-k	6.79b
		L3	142.99l-o	169.95c-g	89.79h-l	624.61klm	8.61bac	124.31lm	6.93ab
P2	V0	L0	145.18e-i	171.25bcd	90.29e-k	625.25h-l	7.65hg	125.74g-k	6.08e
		L1	143.64j-m	170.86b-f	90.26e-k	625.21h-l	7.27lk	124.89jkl	5.82gh
		L2	142.28no	170.83b-f	90.25e-l	625.16i-l	7.87f	124.17lm	6.34d
		L3	142.18o	170.75b-f	90.23e-l	625.08jkl	8.48c	124.11lm	6.83b
	V1	L0	145.97b-g	170.73b-f	91.11b-i	625.91g-k	8.28d	126.60c-g	6.54c
	Continues…
		L1	144.45h-k	170.50b-g	90.83c-i	625.85g-k	7.68hg	125.64g-k	6.11e
		L2	144.81f-k	170.47b-g	90.62e-k	625.79g-k	8.25ed	125.72g-k	6.56c
		L3	143.11l-o	170.42b-g	90.52e-k	625.62g-k	8.65ba	124.76jkl	6.93ab
	V2	L0	144.88f-j	169.94d-g	89.57i-l	623.99mn	8.64ba	125.19i-l	6.90ab
		L1	144.74g-k	169.53fg	89.08jkl	623.55mno	8.21ed	124.86jkl	6.57c
		L2	141.93o	169.23g	88.99kl	622.82no	8.67ba	123.31m	7.03a
		L3	142.37mno	169.59efg	88.59l	622.65o	8.70a	123.33m	7.06a
Mean			144.95	170.86	91.08	626.61	7.57	126.04	6.01
F-test			**	**	**	**	**	**	**
CV			0.74	0.41	1.12	0.12	1.17	0.72	1.83

Means followed by the same letter within a column are not significantly different; ** = significant at P ≤ 0.01 using the Duncan’s multiple range test; CV = coefficient of variation of treatments; exAc = exchangeable acidity; exAl = exchangeable Al; PAcs = percentage of acid saturation; PAls = percentage of Al saturation; L0 = No lime; L1 = 5.93 tons lime ha^-1; L2 = 9.57 tons lime ha^-1; L3 = 11.96 tons lime ha^-1; V0 = No vermicompost; V1 = 5 tons vermicompost ha^-1; V2= 10 tons vermicompost ha^-1; P0 = No mineral P; P1 = 74.51 kg P ha^-1; P2= 149.01 kg P ha^-1.

Amendments effect on forms and distributions of P

The combined and sole applications of the amendments altered significantly the chemical properties expected to impact the distributions of phosphorous in the soil (Table 5). The forms and distribution of the various P fractions [NH₄Cl-P, NaHCO₃-Pi, NaHCO₃-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: NH₄Cl-P < NaHCO₃- Pi < (NaOH-Pi)_sn < HCl-Pi < NaOH-Pi. The highest percentage change in each fraction was recorded from the interactions of three factors (lim x vermicompost x inorganic P) whereas; the lowest was obtained from the control. Results of the analysis of variance also indicated that integrated applications of both two factors (lime x vermicompost x inorganic P) and three factors (lim x vermicompost x inorganic P) amendments had statistically significant (P<0.01) effect on the amount and distributions of NH₄Cl-P, NaHCO₃-Pi, NaOH-Pi)sn, HCl-Pi, and NaOH-Pi fractions in the soil.

The distributions of easily mineralisable (NaHCO₃)-Po and less labile (NaOH)-Po were in the order of magnitude: NaOH-Po < (NaOH-Po)_sn < NaHCO₃-Po. The highest percentage change in each fraction was recorded from the interactions of three factors (lime x vermicompost x inorganic P) and the lowest was obtained from the control. According to analysis of variance all the treatments influenced significantly (p<0.01) the amount and distributions of the extracted organic form of P (Tables 5).

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 significantly increase NaOH-Pi contents (and to a lesser extent NaOH-Po) (Iyamuremye et al. 1996; 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 future P sorption in soil by reacting with these sorption sites (Daly et al. 2001; Yan et al. 2013). This result is also in concomitant with what has been reported by Elias et al. (2010) that goat manure and inorganic phosphate addition influenced NaOH-P_i to greater extent.

After eight weeks of incubation period the least (2.04 mg kg^-1) concentration of the readily available NH₄Cl 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 CaCO₃ 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 significant effect on readily available fractions (NH₄Cl-P) at both study sites. Contrasting result was mentioned by Hartono et al. (2000) that lime had significant effect on readily available Pi but it agrees with that of Iyamuremye et al. (1996) where lime didn’t affect readily available Pi. Even though sole applications of lime didn’t appreciably affect the readily available fractions of P (NH₄Cl-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, significant differences were observed over the control (Table 5). On the other hand, the readily available fraction (NH₄Cl-P) was significantly 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 significantly (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 significantly 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 significantly influence HCl-Pi. Hartono et al. (2000) found that applications of inorganic phosphorous or lime to acidic soils had no significant effects on the concentrations of HCl-Pi.

Generally, the dynamics of the two labile P fractions (NH₄Cl-P, NaHCO₃-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 (NaHCO₃)-Po and less labile (NaOH)-Po were significantly altered during the incubation period.

Table 5 Effects of amendments on Inorganic and organic P fractions of SC1, Soil

Treatment

(Kg ha^-1)

NH4Cl-pi

NaHCO₃-pi

NaHCO₃-po

NaOH-pi

NaOH-po

NaOH-pi) sn

NaOH-po) sn

HCl-pi

Residual

P

Total P

…………………………………………………………………………..………..mg kg-1………………………………………………………………………………………………..

P0

V0

L0

2.04r

2.46z

2.79z

142.35j

153.85i

34.09ef

36.27klm

65.53hi

167.34i

606.34v

L1

2.15r

2.49

2.79z

142.24j

153.81i

33.68f

35.96lm

65.76hi

167.31i

606.31v

L2

2.21r

2.59y

2.79z

142.10j

153.72i

33.68f

35.86m

65.96ghi

167.54i

606.43v

L3

2.16r

2.75x

2.79z

141.83j

153.47i

34.06ef

36.01lm

66.17ghi

167.74i

607.25v

V1

L0

2.64q

2.59y

3.21t

146.06i

166.33h

35.31def

39.45j

65.96ghi

168.56i

630.12u

L1

4.76o

6.72w

3.25s

146.57i

165.87h

35.14def

39.18jk

69.35ghi

175.84h

646.70tu

L2

4.77o

6.90v

3.29q

156.46h

165.74h

35.56def

38.76j-m

74.04d

175.88h

661.42st

L3

4.82o

7.07u

3.45ij

156.40h

165.41h

35.62def

38.84jkl

82.91c

176.71h

671.25rs

V2

L0

3.23p

2.73x

3.27r

171.19g

170.61g

36.66de

43.78i

68.08ghi

169.37i

668.96s

L1

5.36n

6.91v

3.40l

171.54g

170.24g

36.25def

43.29i

73.65de

176.85h

687.52qr

L2

5.37n

7.08u

3.44j

171.26g

170.01g

36.17def

43.66i

86.48bc

177.15h

700.64pq

L3

5.41n

7.28t

3.47g

171.65g

169.97g

36.77d

43.54i

97.04a

177.45h

712.61p

P1

V0

L0

14.71m

7.87s

3.10y

395.58f

182.73f

53.22c

81.24e

64.8i

185.08g

988.36o

L1

16.80l

10.62p

3.12wx

395.15f

182.50f

53.61c

78.19f

65.93ghi

190.26ef

996.21o

L2

16.84l

10.79o

3.14v

395.28f

182.29f

53.48c

78.55ef

65.10i

190.70ef

996.19o

L3

16.89l

10.99n

3.18u

395.36f

182.17f

52.99c

78.47ef

66.30ghi

191.07e

997.44o

V1

L0

17.32k

8.19q

3.31p

400.66e

233.43c

55.52bc

53.61h

65.67hi

187.82fg

1025.54n

L1

19.45i

14.97h

3.32o

400.17e

233.37c

55.29bc

53.43h

72.64def

198.39d

1051.06m

L2

19.46i

15.09g

3.33n

400.46e

233.23c

55.55bc

53.57h

84.58bc

198.79d

1064.07lm

L3

19.50i

15.25f

3.37m

400.08e

233.01c

55.39bc

52.73h

95.64a

199.10d

1074.09l

V2

L0

17.92j

8.11r

4.34f

527.87c

228.14d

57.29b

58.57g

68.16ghi

189.88ef

1160.29k

L1

20.04h

15.10g

4.39e

527.24c

228.00d

57.73b

58.25g

73.87de

201.06cd

1185.70hi

L2

20.05h

15.26f

4.39e

527.39c

227.78d

57.41b

58.37g

86.79bc

201.29cd

1198.75gh

L3

20.09h

15.46e

4.39e

527.70c

227.70d

57.59b

58.58g

97.35a

201.42cd

1210.33g

P2

V1

L0

27.84g

11.85m

3.12xy

471.75d

215.86e

69.28a

101.99b

65.79hi

201.02cd

1168.53jk

L1

29.24f

14.57j

3.13vwx

471.36d

215.79e

69.13a

102.11b

69.96efg

205.71b

1181.03ij

L2

29.98e

14.74i

3.13vw

471.16d

215.42e

69.62a

102.30b

75.03d

206.53b

1187.94hi

Continues…

L3

30.03e

14.92h

3.13v

471.13d

215.39e

69.50a

102.44b

86.91bc

206.66b

1200.13gh

V1

L0

30.46d

12.25k

3.42k

601.62b

278.81b

69.41a

118.36a

65.88h

203.98bc

1384.21f

L1

32.58b

18.95d

3.45ij

601.20b

278.65b

69.47a

118.83a

72.85def

214.63a

1410.62e

L2

32.59b

18.96d

3.46hi

601.11b

278.59b

69.46a

118.44a

84.79bc

214.51a

1421.93de

L3

32.64b

19.29b

3.46gh

601.29b

278.24b

69.57a

118.55a

95.85a

215.10a

1434.02d

V2

L0

31.05c

12.05l

4.44d

628.42a

373.69a

70.26a

81.35e

68.39ghi

205.80b

1475.47c

L1

33.17a

18.98d

4.50c

628.02a

373.55a

70.47a

91.17d

74.09d

216.72a

1510.71b

L2

33.19a

19.11c

4.54b

628.06a

373.34a

70.48a

93.52cd

87.03b

217.12a

1526.40ab

L3

33.37a

19.44a

4.58a

627.13a

373.29a

70.23a

96.19c

97.58a

217.65a

1539.49a

Mean

17.78

11.12

3.49

387.63

222.34

53.47

68.98

75.89

192.44

1033.17

F-test

**

CV%

1.46

0.39

0.21

0.42

0.74

3.07

2.65

3.26

0.92

1.01

Means followed by the same letter within a column are not significantly different; ** = significant at P ≤ 0.01 using the Duncan’s multiple range test; CV = coefficient of variation of treatments; exAc = exchangeable acidity; exAl = exchangeable Al; PAcs = percentage of acid saturation; PAls = percentage of Al saturation; L0 = No lime; L1 = 5.93 tons lime ha^-1; L2 = 9.57 tons lime ha^-1; L3 = 11.96 tons lime ha^-1; V0 = No vermicompost; V1 = 5 tons vermicompost ha^-1; V2= 10 tons vermicompost ha^-1; P0 = No mineral P; P1 = 74.51 kg P ha^-1; P2= 149.01 kg P ha^-1.

Correlation among soil properties

The correlation between soil properties after incubation with amendments is exhibited in Table 6. The readily available NH₄Cl extractable P was strongly positively correlated with Mehlich 3-P, NaHCO₃-Pi, NaHCO₃-Po, HCl-P, NaOH-Pi, NaOH-Po and P_ox. This could be an indication for the presence of higher concentration of NH₄Cl extractable P in soils where there are prominently higher concentrations of Mehlich 3-P, NaHCO₃-Pi, NaHCO₃-Po, HCl-P, NaOH-Pi, NaOH-Po and P_oxin the soil. In addition, the correlation result verified the scientific speculation that P_oxthought 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 (NH₄Cl-P, NaHCO₃-Pi and NaHCO₃-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_oxand 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.

Table 6 Correlation matrix obtained from soil properties in SC1 sampling site

	M-3	NH₄Cl-P	NaHCO₃-Pi	NaHCO₃-Po	NaOH-pi	NaOH-po	HCl-p	Al_ox	Fe_ox	P_ox	PSC
pH	0.19*	0.09ns	0.38**	0.26**	0.07ns	0.13ns	0.75**	-0.54**	-0.27**	0.46**	-0.48**
M-3		0.94**	0.91**	0.59**	0.95**	0.78**	0.35**	-0.61**	-0.69**	0.82**	-0.73**
NH₄Cl-P			0.91**	0.49**	0.96**	0.83**	0.29**	-0.54**	-0.61**	0.79**	-0.64**
NaHCO₃-Pi				0.56**	0.88**	0.77**	0.53**	-0.59**	-0.63**	0.82**	-0.69**
NaHCO₃-Po					0.64**	0.73**	0.44**	-0.35**	-0.59**	0.66**	-0.51**
NaOH-pi						0.85**	0.27**	-0.49**	-0.63**	0.79**	-0.62**
NaOH-po							0.33**	-0.37**	-0.60**	0.77**	-0.53**
HCl-p								-0.39**	-0.39**	0.66**	-0.44**
Al_ox									0.56**	-0.60**	0.92**
Fe_ox										-0.69**	0.84**
P_ox											-0.72**

It can be seen that unlike separate applications of inorganic P, both lime and vermicompost had significant 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 significant 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 significantly by combined use of the treatments over single applications. Despite having no significant 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 (NH₄Cl-P, NaHCO₃-Pi and NaHCO₃-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 significantly influenced those soil properties as well. Sole application of inorganic P and vermicompost increased the labile inorganic P fractions in the soil and decreased the potential sorption capacities of the soil. It 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.

ANOVA

Analysis of variance

CCE

Calcium carbonate equivalents

CEC

Cation exchange capacity

CRD

Completely randomized design

DPS

Degree of P saturation

EIAR

Ethiopian institute of agricultural research

FAAS

Flame atomic absorption spectroscopy

FAO

Food and Agriculture Organization

PSC

Phosphorous adsorption capacity

OM

Organic matter

SAS

Statistical Analysis System

TSP

Triple super phosphate

VC

Vermicompost

Ethics approval and consent to participate

Not applicable

Consent for publication

Not applicable

Availability of Data and materials

Not applicable

Competing interest

No conflict of interest

Funding

Swedish International Cooperation Development Agency (SIDA) and Madda Walabu University, only for sample collection and laboratory analysis.

Authors’ contributions

Bereket Ayenew collected, analyzed, interpreted the data and made the final write up. Asmare Melese as a co-authors edited and approved the final manuscript

Acknowledgments

The project was funded by SIDA (Swedish International Development Cooperation Agency and Madda Walabu University. Thus we would like to thank these institutions. We would also thank the anonymous reviewers who contributed significantly to the improvement of the article.

Authors’ information

¹Madda Walabu University, College of Natural and Computational Sciences, Department of Chemistry, Bale-Robe, Ethiopia; ²Debre Berhan University, College of Agriculture and Natural Resource Sciences, Department of Plant Science, Debre Berhan, Ethiopia

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

Status:

Version 1

Abstract

Background

Materials And Methods

Results And Discussion

Physicochemical properties of experimental soil

Vermicompost compositions

pH, exchangeable acidity, CEC and available P after Incubation

Amendments effect on oxalate and dithionite extractable P, Al and Fe

Amendments effect on forms and distributions of P

Correlation among soil properties

Conclusions

Abbreviations

Declarations

References

Status:

Version 1