Impacts of chicken manure and peat-derived biochars and inorganic P alone or in combination on phosphorus fractionation and maize growth in an acidic ultisol
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The forms of phosphorus (P) in animal manure and peat are different from synthetic P fertilizers and will affect soil P fractions when they are used as P amendments. Effects of chicken manure (CMB) and peat (PB) derived biochars (CMB and PB) alone or in combination with P fertilizer (KH2PO4) and rock phosphate (RP) on plant/soil health and soil P fractions in an acidic ultisol were examined with greenhouse pot experiments. The total P rate was constant at 120 mg kg−1 in all treatments. Soil P fractions, P uptake, and maize growth were determined after 56 days. Application of CMB combined with P fertilizer or alone significantly increased soil pH, water extractable and relatively labile P, dry matter yield of maize, chlorophyll contents in maize leaves, while decreasing the Fe and Al binding P. Moreover, sole application of CMB and PB showed greater effects than application of P fertilizer alone regarding plant growth and P fractionation. Integration of synthetic inorganic P sources with CMB or sole application of CMB is more beneficial than application of inorganic P sources to improve plant growth and P availability.
KeywordsAcidic soil Manure-derived biochar Peat-derived biochar Inorganic P fertilizer P fractions Plant P uptake
Phosphorus is an essential element for plant growth and development (Kamran et al. 2018b). However, its deficiency in plants is a serious problem in acidic soils. P availability in many acidic soils around the world is very low. In China about 22% of total arable land is suffering from soil acidification which leads to the deficient nutrient availability, especially low-available P values (Hong et al. 2018; Li et al. 2018). Therefore, continued higher application of P fertilizers in these acidic soils is required to maintain plant productivity. Unfortunately, it is estimated that less than 20% of fertilizer P can be used by crops during the growing season in China (Zhang et al. 2008). P is fixed in acidic soils through various mechanisms. Acidic soils usually contain great amounts of Fe and Al oxides. They react with phosphate and convert P into less soluble/available forms (Zhang et al. 2009). On the other hand, excessive application of P fertilizers in China to maintain plant growth in acidic soils led to severe eutrophication and other environmental constraints due to runoff (Zhang et al. 2012). Therefore, P management in acidic soils is necessary to improve P availability to plants and reduce P losses from the soils.
Organic amendments such as manures can be used as alternative to chemical fertilizer and other P sources (Kashem et al. 2004; Nziguheba et al. 1998). These manures can provide great amounts of essential nutrients in acidic soils and also improve other physiochemical properties of the highly weathered soils (Molnár et al. 2016). Application of manure amendments can initially build up P concentration in P-deficient soils as manures contain higher amount of P, but their repeated application can lead to environmental concerns regarding P losses by runoff and leaching. C/N/P ratios are not same in various manures, which makes them not suitable as organic amendments applied mostly on the basis of C/N ratio. Application of these amendments on the basis of C/N ratio resulted in excessive application of P in the soils which caused other potential issues (Liang et al. 2014).
To avoid these environmental concerns, converting manure into biochar is a good option. Thermal combustion of animal manure at low temperature in oxygen-limited conditions is recommended for soil amendment production to improve soil quality and physiochemical characteristics (Hass et al. 2012). Higher CEC, exchangeable cations, and functional groups of these manure-derived biochars can improve soil structure, nutrient sorption and enable more P retention in soils (Cao and Harris 2010). Manure biochar inhibits the P losses by reducing leaching and runoff. Addition of these organic amendments can greatly influence soil chemical properties, which ultimately affects the P magnitude and fractionations in acidic soils. Micro and macro nutrients present in manure-derived biochars significantly affected soil characteristics and productivity (DeLuca et al. 2009; Jin et al. 2016). Different forms of P in the biochars can also play a key role in soil P availability to plants in highly weathered soils.
Various organic amendments increased P concentrations and changed P forms in soils (Ajiboye et al. 2004; Sharpley and Moyer 2000). P species showed diverse behavior when these amendments were applied to different soil types, some species showed more conversion into plant-available P than others. Essential nutrients in organic amendments also affected the P forms and their stability in different types of soils. In acidic soils, various forms of P added by organic amendments have shown similarity in P availability to plants (Chan et al. 2008). Along with this, P availability has also been affected by changes that occurred in rhizosphere with increase in soil pH and plant–microbe interaction. Some other factors such as organic anion exudations, ligand exchange reactions, and enzymatic hydrolysis also influence P availability to plants. However, few studies have involved in the effect of manure biochar on P fractions and their availability to plants.
The effectiveness of mineral P and P from manure-derived biochars may differ from each other in terms of their availability to crops and their fractions in different soils (Xu et al. 2014). Comparison of these amendments can provide a detailed framework or strategy for proper management of these amendments in P-deficient acidic soils. Some previous studies suggested that P availability to plants was less affected by organic amendments; other studies reported that P from organic amendments is equally or more available than inorganic P from P fertilizers (Xu et al. 2014; Jin et al. 2016; Kamran et al. 2018a, b). Determining the forms of P by applying these inorganic and organic amendments can give clear information about the plant-available P.
Some attempts have been made to observe the changes in P fractions and P availability to crops by addition of manure into soils (Hansen et al. 2004; Hass et al. 2012), but very few studies investigated the effects of manure and peat-derived biochars on P fractions in acidic soils and P availability to crops. Moreover, very little attention has been given to combined application of these manure-derived biochars along with inorganic P fertilizer in acidic soils and its effect on P fractionation and P availability to plants. In the present study, the interactive effects of alone and co-application of P fertilizer with manure and peat-derived biochars on soil P fractionation and maize growth have been investigated. The hypothesis of the study was that there would be an interactive effect between fertilizer application and biochar treatment on soil P fractionation in acidic ultisol and plant P uptake. The objective of this study was to determine the effect of organic (manure and peat-derived biochars) and inorganic sources of P alone or combined on P fractions and P uptake by maize plant in an acidic ultisol with P deficiency.
2 Materials and methods
2.1 Soil and biochar preparation
Basic properties of the ultisol used in the experiment
Quaternary red earth
Properties of biochars produced from chicken manure (CMB) and peat (PB) at 400 ℃ for 4 h
2.2 Experimental treatments
Prior to transplanting, soil sample was thoroughly mixed with the organic and inorganic amendments. There were nine treatments including the following: (1) control, (2) chicken manure biochar (CMB), P at the rate of 120 mg kg−1, (3) peat biochar (PB), P at the rate of 120 mg kg−1, (4) KH2PO4, P at the rate of 120 mg kg−1 (5) rock phosphate (RP), P at the rate of 120 mg kg−1, (6) CMB + KH2PO4, P at the rate of (60 + 60) mg kg−1, (7) CMB + RP, P at the rate of (60 + 60) mg kg−1, (8) PB + KH2PO4, P at the rate of (60 + 60) mg kg−1, (9) PB + RP, P at the rate of (60 + 60) mg kg−1. There were three replicates for each treatment.
2.3 Green house experiment
Maize was used for pot experiment, because it is a common crop in the region from where the soil sample was taken. The experiment was conducted for 8 weeks in greenhouse of the Institute of Soil Science, Chinese Academy of Sciences, Nanjing, China, in natural light conditions during 2017. Temperature ranged from 25 to 27 °C during day time and around 18–20 °C in the night time. 2.5 kg of acidic Ultisol sample was placed in plastic pots. Basel dose of N and K was applied to reach the same rate of 200 mg N kg−1 as Urea and 80 mg K kg−1 as KOH in all treatments to meet the fertilizer requirements. 100 mg kg−1 N as urea was also added to maize crop for top dressing. Seeds of Zhengdan-958 maize variety were scarified with 10% H2O2 for 15 min and then washed several times with deionized water. After washing, seeds were placed on moist towels in trays and kept in dark in a growth chamber at 25 °C. After germination, seven seeds/pot were transferred to green house pots and thinned to five seeds per pot after one week. Deionized water was added through the experiment period to maintain 70% soil water holding capacity.
2.4 Plant and soil analyses
Soil P fractions scheme used in the experiment
Fairly labile, Pi (mobile P)
Relatively labile Pi, microbial P, Po adsorbed on soil surface
0.5 M NaHCO3
Crystalline Fe and Al phosphates, as well as P strongly bound by chemisorption to Fe and Al compounds
0.1 M NaOH
Al–P and Fe–P
1 M HCl
Concentrated H2SO4 and 30% H2O2
2.5 Statistical analysis
SPSS 20.0 (SPSS Inc., Chicago, IL, USA) and origin Pro 9.0 were used for the statistical analysis of the data. Analysis of variance (ANOVA) was used to test the significant differences (p < 0.05) among the different treatments.
3.1 Biochar characteristics and effects of various amendments on soil pH
The chemical properties of biochars are given in Table 1. Total N, H, C, and P contents were higher in CMB than PB. The pH, CEC, and EC were also higher in CMB. Fixed C and ash content were greater in CMB than in PB. Higher nutrient contents in CMB are due to the quality of char material. It indicates that biochar is in more stable conjugated aromatic structures than in the feedstocks (Enders et al. 2012; Krull et al. 2009). The contents of heavy metals differed between the two biochars: CMB contained 1.03, 0.13, 109.1 and 361.3 mg kg−1 of Pb, Cd, Cu, and Zn, respectively; and PB had 19.4, 0.23, 104.5, and 88.4 mg kg−1 of the corresponding metals (Kamran et al. 2018a, b).
3.2 Effects of various amendments on soil P fractions
Effects of biochars and inorganic P sources added into the acidic ultisol on soil P fractions (mg kg−1)
2.6 ± 0.5d
8.8 ± 0.6g
61.4 ± 2.2e
71.5 ± 2.2g
158.6 ± 3.6d
135.1 ± 2.1f
11.4 ± 0.7f
6.1 ± 0.2bc
19.4 ± 0.4a
87.7 ± 3.0b
99.8 ± 2.7c
160.2 ± 5.5cd
155.4 ± 4.7d
22.0 ± 2.6cd
4.4 ± 0.6cd
15.8 ± 1.1cd
79.7 ± 2.3c
107.7 ± 2.1b
161.8 ± 8.5cd
160.7 ± 4.7bc
26.4 ± 0.9bc
7.9 ± 0.5b
18.5 ± 1.5b
69.8 ± 4.4d
120.1 ± 4.4a
165.6 ± 11.2b
164.3 ± 6.2b
13.2 ± 0.8rf
3.5 ± 0.1cd
10.5 ± 0.8fg
66.3 ± 5.8d
120.1 ± 2.4a
173.7 ± 4.4a
171.3 ± 8.5a
12.3 ± 0.5f
CMB + Pi
10.5 ± 0.4a
22.9 ± 1.0a
92.6 ± 3.5a
77.7 ± 5.1f
159.9 ± 13.2cd
159.8 ± 7.8c
17.6 ± 1.1de
CMB + RP
5.2 ± 0.7cd
15.0 ± 0.8de
77.0 ± 2.2c
87.4 ± 2.6e
162.7 ± 4.3bc
157.2 ± 2.3cd
35.3 ± 3.1a
PB + Pi
7.9 ± 0.6b
17.6 ± 1.7bc
85.7 ± 3.8b
90.9 ± 4.6d
171.3 ± 6.2a
148.4 ± 4.2e
26.4 ± 1.0c
PB + RP
5.2 ± 0.6cd
13.2 ± 2.1ef
78.1 ± 4.5c
97.1 ± 3.0c
165.9 ± 10.9b
161.6 ± 7.8c
30.0 ± 3.2b
The NaOH–P fraction was generally associated with less available P due to binding with Fe and Al oxides and presented on adsorption sites. NaOH–P was greater in application of KH2PO4 or RP alone and the concentration of NaOH–Pi decreased in CMB alone or combined application with KH2PO4 (Table 4). Moreover, NaOH–Po was higher in RP treatment alone, while CMB + KH2PO4 had lower NaOH–Po than all other treatments (Table 4). The HCl–P fraction generally reflects the insoluble mineral P, especially Fe and Al bound. In present study, the treatments with application of RP or KH2PO4 alone contained the highest HCl–P, while the combined application of biochars with KH2PO4 (CMB + KH2PO4 followed by PB + KH2PO4) and the sole application of CMB and PB contained intermediate HCl–P compared with other treatments (Table 4). Residual-P which is more chemically stable Po form and relatively insoluble Pi form has less proportion of total P percentage in this study (Table 4).
3.3 Effects of various amendments on phosphorus uptake and plant growth
4.1 Effects of various amendments on soil P fractions
The distribution of different P fractions reflects the quality of applied P sources. CMB and CMB + KH2PO4 treatments showed significant increase in available P fractions by sequential extraction method. The increase in labile P by the addition of CMB reflects the large amount of P present in the manure-derived biochar. Higher amount of H2O–P availability with application of CMB + KH2PO4 and alone application of CMB rather than sole or combined application of RP and PB reflected the influence of CMB on increased P availability and decreased P adsorption by the soil. Higher available P content was observed in the treatment of CMB + KH2PO4 compared with CMB + RP. This was due to the changes in soil properties as well as higher availability of P in CMB and KH2PO4. However, the less available P content in RP reduced P availability in the soil. NaOH–P generally described as less available or sorbed P due to Fe and Al oxides. CMB sole or CMB + KH2PO4 treatments decreased NaOH–P more than all other treatments, which showed the role of biochar in P adsorption and desorption. Generally there was significant difference among the organic P pool as well as inorganic P pool. Incorporation of CMB with KH2PO4 showed significant increase in plant-available P over the other treatments and control, and decrease in NaOH–P. Phosphorus availability to plants was affected by several processes like adsorption of P to Fe and Al oxides, mineralization, dissolution and precipitation to mineral pools (Li et al. 2011). The acidic soils have higher P sorption capacity than calcareous soils which was due to the presence of high amounts of free Fe and Al oxides. In the present study, the phosphorus availability in the acidic ultisol was also mainly affected by the adsorption of Fe and Al oxides. Organic amendments positively affected P distribution and P fractionation in the soil (Kashem et al. 2004; Xu et al. 2014). Application of such materials which have high contents of organic matter can decrease P adsorption by soil surface due to competition of organic compounds with phosphate for adsorption sites on soils. Our results is supported by the previous study of Cui et al. (2011) who observed that application of biochar decreased P adsorption on ferrihydrite and that P desorption was increased by combined application of P with biochar. The results presented in this study were also consistent with previous reports by others (Iyamuremye et al. 1996; Kashem et al. 2004).
Incorporation of biochar alone or in combination with synthetic P fertilizer increased the negative surface charge on the soil which increased the repulsion of soil surface to phosphate and thus decreased phosphate adsorption by the soil (Jiang et al. 2015b). Manure biochar is also a rich source of phosphorus and using manure biochar as organic amendment can be a valuable solution to cater P scarcity in acidic soils. Biochar has ability to influence soil P availability in acidic soils by changing soil pH and soil sorption capacity. Biochar reduced adsorption of phosphate to Fe and Al oxides by increasing soil pH (Atkinson et al. 2010; Maranguit et al. 2017). Soil P availability had been increased by biochar application while P sorption to Fe and Al oxides had been decreased. The use of manure-derived biochar in an increasingly P-constrained agricultural industry appears attractive.
In this study CMB was more effective than PB. Biochar properties mainly depend on char material. It is due to higher nutrient content in manure than peat. CMB has higher pH and CEC. Application of CMB increased the soil pH and CEC and thus improved soil quality. Some studies also suggested that soil P availability was increased due to increasing soil pH (Barrow 2017; Kamran et al. 2018a, b). In this study, increased soil pH was one of the factors which increased soil P availability along with desorption of P from the soil. Results of previous studies suggested that application of biochar alone or in combination with fertilizer enhanced P availability by improving the soil’s physical and chemical properties, such as soil surface area, soil microbial community, soil water holding capacity, and soil CEC, which improved soil health and plant growth. In the present study, combined application of CMB with KH2PO4 or alone application of CMB significantly increased the soil P availability. However, the PB application alone or combined with KH2PO4 was intermediate between CMB and P fertilizer alone application.
4.2 Effects of various amendments on phosphorus uptake and plant growth
Statistical analyses suggested that effects of amendments were significant on soil pH, plant growth, and P uptake by maize plant. Higher nutrient values and pH of biochar resulted in increased soil pH which ultimately increased nutrient uptake due to better plant growth (Silber et al. 2010). CMB was rich in other essential nutrients which increased soil fertility and plant dry matter yield as compared to other treatments. The higher pH of CMB led to more increase in post-harvest soil pH than PB (Fig. 1). The increase in soil pH by addition of biochar resulted in higher plant dry weight by increasing essential nutrient availability to plants (Anugoolprasert et al. 2012). The higher base cations in applied biochar increased soil Ca2+, Mg2+, and K+ contents significantly, which also contributed to the increase in plant dry biomass. Previous studies showed that plant mass was higher in the treatment with organic amendments applied compared to synthetic fertilizer application (Carry and Gunn 2003). Organic amendments improved soil fertility which ultimately improved plant growth. Addition of macro- and micronutrients affected the soil P dynamics by improving soil characteristics which behaves differently in sole application of P fertilizer and other treatments (Jindo et al. 2012).
The correlation between P fractions and soil and plant characteristics multivariate ANOVA
Lone application of RP and KH2PO4 has lower labile P fractions in acidic soils which led to lower P uptake by maize plant as well. However, when biochars were applied alone the P uptake by maize plants was higher in CMB than that in PB. Combined application of inorganic P fertilizer with biochar had more effect on P availability than sole application of inorganic P fertilizer. This is due to the changes in soil properties by application of the biochar. The combined application of inorganic and high-quality organic amendments was found to be more effective to enhance P uptake by plants in acidic soils. Results of present study suggested that application of high-quality organic P source could be a better option to improve plant growth and development in acidic soils.
The CMB as high-quality organic amendment showed great positive effects on soil chemical properties and P fractions, thus improved maize growth and increased P uptake by the plant. The CMB application was effective in increasing soil pH, chlorophyll contents, and dry weight of plants. Combined application of CMB with KH2PO4 resulted in the greatest increase in soil labile P followed by CMB alone. This increase was due to the release of P from applied sources and the decrease in P adsorption to Fe and Al oxides by biochar addition. The P uptake by plants was also greater in the combination of CMB with KH2PO4. This treatment also has other benefits associated with integrated soil fertility management. The sole application of CMB and PB increased the P availability to plant to greater extent than application of KH2PO4 alone due to improving soil characteristics by application of these biochars. The combination of CMB with KH2PO4 is more suitable for the plant growth and soil fertility improvement of acidic soils. Future research is needed to examine the effects of these treatments on transformations of P and the effect of application rate of P in acidic soils where P availability is a major problem.
This study was supported by the National Key Research and Development of China (No. 2016YFD0200302). The first author is highly grateful to CAS-TWAS President’s Fellowship for his PhD studies in China.
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