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Treatment by acidification followed by solid–liquid separation affects slurry and slurry fractions composition and their potential of N mineralization
Bioresource Technology 100 (2009) 4914–4917
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Short Communication
Treatment by acidification followed by solid–liquid separation affects slurry and slurry fractions composition and their potential of N mineralization David Fangueiro a,*, Henrique Ribeiro a, Ernesto Vasconcelos a, João Coutinho b, Fernanda Cabral a a b
UIQA Instituto Superior de Agronomia, TU Lisbon, Tapada da Ajuda, 1349-017 Lisboa, Portugal C. Química, Dep. Edafologia, UTAD, Ap. 1013, 5001-911 Vila Real, Portugal
a r t i c l e
i n f o
Article history: Received 5 March 2009 Received in revised form 14 April 2009 Accepted 16 April 2009 Available online 22 May 2009 Keywords: Pig slurry Acidification Solid–liquid separation N mineralization Organic fertilizer
a b s t r a c t The aim of the present work was to assess the effect of treatments by acidification, solid–liquid separation or acidification followed by solid–liquid separation on the physical and chemical composition of pig slurry (S) and pig slurry fractions (non acidified and acidified solid (SF and ASF) and liquid (LF and ALF) fractions), as well as on the potential of N mineralization of these pig slurry derived materials. Acidification strongly decrease the inorganic carbon content of S, SF and LF and it also affects the distribution of P, Ca and Mg between the solid and liquid fraction leading to an ALF more equilibrated than LF in terms of nutrients. Acidification increases the potential of organic N mineralization in SF and decreases the potential of N immobilization in S and LF. It can be concluded that the proposed treatment generates valuable slurry fractions with distinct characteristics and potential of N mineralization that may be incorporated to soil at different periods after sowing to comply with plant nutrient requirements. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction Pig slurry is widely used as fertilizer to provide nutrients to plants and increase the soil organic matter content. However, pig slurry management leads to N losses due to ammonia (NH3) volatilization during storage and soil application (Sommer and Hutchings, 2001; Eriksen et al., 2008). Ammonia volatilization may be reduced by lowering slurry pH, whereby the NH3/NHþ 4 equilibrium shifts towards a NHþ 4 concentration. Slurry acidification is currently used by farmers in The Netherlands and Denmark (Schils et al., 1999; Eriksen et al., 2008) as a tool to reduce NH3 emissions from slurry during storage and soil application. Still, to avoid hazards this technology needs to be improved. It is expected that an improved technology will be developed and used in more countries since the European Directive (2001/81/CE) promotes a decrease of atmospheric pollutants such as NH3 and countries like Spain have already defined targets to reduce such emissions (Castrillón et al., 2009). On the other hand, slurry separation may be a solution to enhance slurry management. Indeed, it may help to increase slurry storage capacity, improve slurry handling and has also been pointed out as a solution to reduce N losses during storage and after incorporation to soil (Fangueiro et al., 2008a). Slurry separation produces two fractions: a solid fraction with high dry matter, N and P content and a liquid fraction poor in organic N with low dry matter content (Fangueiro et al., 2008a).
* Corresponding author. Tel.: +351 213653199; fax: +351 213653180. E-mail address: [email protected] (D. Fangueiro). 0960-8524/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2009.04.032
However, there is little information on how acidification affects the composition, namely the potential of N mineralization, of pig slurry and pig slurry fractions obtained after solid–liquid separation. Indeed, a significant part of the N contained in pig slurry is in an organic form and becomes available to plants only after mineralization (Rees and Castle, 2002). Long term laboratory incubations are generally used to assess such information (Griffin, 2007; Fangueiro et al., 2008b) but they are time consuming and can not be used in routine. Alternatively, a short term anaerobic incubation method has been successfully used by Fangueiro et al. (2008c) to assess the potential of N mineralization of cattle slurry. The main objectives of the present study were to assess the effect of treatments by acidification, and acidification followed by solid–liquid separation on the physical and chemical composition of pig slurry and pig slurry fractions (non acidified and acidified solid and liquid fractions), as well as on the potential of N mineralization of these pig slurry derived materials. 2. Methods 2.1. Slurry acidification and solid–liquid separation The slurry used in this study was sampled in the slurry storage lagoon of a pig livestock farm located in the centre-West of Portugal. Half of the untreated slurry (S) was preserved at its original pH and the second half was acidified to pH 6 by addition of concentrated sulphuric acid (H2SO4) in order to obtain the acidified slurry (AS). S and AS were subsequently divided in two more sub-sam-
D. Fangueiro et al. / Bioresource Technology 100 (2009) 4914–4917
4915
ples: one to be conserved and one to be centrifuged at 3000 rpm during 15 min to provide a liquid and a solid fraction leading to four slurry fractions: liquid fraction (LF), solid fraction (SF), acidified liquid fraction (ALF) and acidified solid fraction (ASF).
of the mean differences was determined using the least significant difference (LSD) tests based on a t-test at a 0.05 probability level. The statistical software package used was Statistix 7.0.
2.2. Analytical methods
3. Results
All these organic materials were fully characterized using the following methods: to determine dry matter, 100 g of fresh material were placed in a capsule and then dried in a heater at 105 °C to constant weight for at least 24 h. Ash content was determined using dry material (2 g), which was incinerated in a muffle furnace at 450 °C, for 12 h. Total and inorganic carbons were determined using a Primacs TOC Analyser (Skalar). pH was determined directly in S, AS, LF and ALF and after 1 h of contact with occasional agitation in a sample-water (1:5 w/v) suspension in SF and ASF. The Kjeldhal method was used to assess the total N content of the samples. Mineral N content was determined by extraction with 2 M KCl (1:5 w/v) (Mulvaney, 1994) followed by ammonium (NHþ 4 ) and nitrate (NO 3 ) quantification by molecular absorption spectrophotometry in a Skalar segmented flow analyser using the Berthelot and sulphanilamide methods, respectively (Houba et al., 1989). Soluble organic N was calculated by subtracting mineral N from soluble N. Ca, Mg, K and P contents were quantified after hydrochloric acid (HCl) treatment of the ash through graphite furnace atomic absorption spectrophotometry (Unicam M Series), except for phosphorous, which was determined using the ammonium vanadomolybdate method by molecular absorption spectrophotometry (Hitachi 2000).
3.1. Slurry and slurry fractions composition
2.3. Short-term incubation method To estimate the potential of N mineralization of the acidified and non acidified slurry and slurry fractions an anaerobic incubation method described by Fangueiro et al. (2008c) was used as follows: an amount of organic material equivalent to 0.05 g of total N was added to 10 g of field moist soil in a 60 ml syringe and the amount of water was adjusted to have a total amount of 25 ml. The soil was collected from the arable layer of a Cambic Arenosol (WRB, 2006), which is a sandy textured soil with a total N content of 0.27 g kg1, an organic C content of 4.57 g kg1, an ammonium-N content of 15.75 mg kg1 and a nitrate N content of 11.14 mg kg1. Ten replicates were prepared for each organic material and one half were incubated for 7 days at 40 °C, while the other half were immediately extracted by the injection of 25 ml of 4 M KCl into each syringe to give a 1:5 soil/slurry 2 M KCl extraction ratio. After shaking for 1 h, the suspensions were transferred to centrifuge tubes and centrifuged at 3000 rpm during 5 min. The supernatant was then analysed for NHþ 4 –N content as described above. Soil only treatments were used as controls. The same extraction method was used after the 7 days incubation period. The potential of net N mineralization (PM) was calculated as the difference between post- and pre-incubation NHþ 4 –N concentrations and the potential of apparent net N mineralization (PAM), expressed as a percentage of the organic N of the treated and non treated slurry was calculated using the following equation:
n o PAM ¼ ð½NHþ4 t¼7 ½NHþ4 t¼0 Þsample ð½NHþ4 t¼7 ½NHþ4 t¼0 Þcontrol =Norg applied 100 2.4. Statistical analysis Results were analyzed by analysis of variance (one way-ANOVA) to test the effects of each treatment. The statistical significance
Table 1 shows the main characteristics of the pig slurry used in the present work. The slurry used here had an initial pH value of 8.5 and the H2SO4 addition decreased pH to a value of 6.0 in slurry and slurry fractions. Values of most parameters are in the range of those reported by Vasconcelos and Cabral (1996), Vasconcelos et al. (1997) as well as Sánchez and Gonzalez (2005) in a study where more than 150 pig slurries from Spain were fully characterized. Slurry acidification led to a significant increase of ash (19%) and DM (26%) content in AS relative to S. Such increase of DM was previously reported by Veltof and Oenema (1993) but no clear explanation for this have been proposed. It is to believe that such increase was likely due to the sulphate ion added via the H2SO4. Acidification also significantly (P < 0.05) increased the DM (300%) and ash (227%) contents of the ALF relative to LF. However, the DM content of the SF and ASF were similar but considering the percentage distribution relative to the initial slurry, the ASF contains only 65% of the slurry DM against 86% in the SF. This may be due to the solubilization of some slurry compounds, occurring at a lower pH, which were transferred to the acidified liquid fraction. Acidification led to a significant (P < 0.05) decrease of the total carbon content of S which should be due to the removal of most 2 of the inorganic C. Indeed, important losses of HCO 3 /CO3 should occur during acidification. Slurry acidification converts the HCO 3/ CO2 3 to H2CO3 and CO2 and the proportion of bicarbonate/carbonate converted to CO2 at pH 5–6 is 72–96% (Stevens et al., 1989). The carbon content of the solid and liquid fraction obtained after centrifugation of the acidified slurry was also significantly lower (P < 0.05) than in the respective non acidified fractions, SF and LF. Acidification had no effect on the potassium content neither on the organic N and nitrate content of slurries and slurry fractions whereas the ammonium content was significantly higher in AS, ALF and ASF relative to S, LF and SF, respectively. Such differences should be due to the lower NH3 losses occurring during the treatment and handling of acidified slurry and acidified slurry fractions. Total P, Ca and Mg contents were not significantly different (P > 0.05) in S and AS. However, a significant increase on the content of these elements was detected in ALF relative to LF. Indeed the LF shows only 3% of the total P against 53% in the ALF. The increase in the total amount of P in the ALF can be justified by the increased solubility of phosphate salts at decreasing pH. On the other hand, the increase observed for the Ca and Mg content may be explained by the effect of sulphuric acid addition on the solubilization of insoluble Ca and Mg carbonates, phosphates and hydroxides and further solubilization of these elements in the LF. Acidification enables a ALF richer in total P, Ca and Mg and more equilibrated in terms of nutrients (see N:P:K ratio) than LF what may be viewed as a positive aspect if LF or ALF are used for fertigation. Acidification and centrifugation affect the N:P:K ratio and the proposed treatment may be helpful for farmers to better adapt the organic amendments to soil requirement since it provides materials with distinct nutrients contents and N:P:K ratio. Even if the solid–liquid separation process used here was more efficient to remove the DM to the solid fraction than the traditional on-farm processes, the nutrient partitioning obtained was similar to values obtained with on-farm processes. The SF has a higher total P, Ca, and Mg content than S as previously reported by Cabral et al. (1998). Acidification led to a reduction of these elements retained
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D. Fangueiro et al. / Bioresource Technology 100 (2009) 4914–4917
Table 1 Composition of treated and untreated pig slurry and pig slurry fractions and proportion of treated and untreated pig slurry fractions relative to non separated slurry. Liquid fraction
Acidified liquid fraction
Slurry
Acidified slurry
22 ± 1 194.8 ± 8.2 86 10.45 ± 0.27 52 4.72 ± 0.67 93 2.03 ± 0.16 17 8.34 ± 0.29 <1 2.11 ± 0.03 72.41 ± 1.61 2.41 ± 0.31 8.5 ± 0.1 70.8 ± 5.9 10.60 ± 0.53 4.69 ± 0.38 8.7 ± 0.4 1:0.45:0.19
21 ± 1 195.5 ± 5.3 65 9.91 ± 0.14 51 2.09 ± 0.19 45 2.49 ± 0.33 24 7.72 ± 0.15 <1 2.18 ± 0.02 67.63 ± 2.09 0.99 ± 0.46 6.0 ± 0.0 59.6 ± 3.8 6.72 ± 0.91 2.80 ± 0.08 8.8 ± 0.3 1:0.21:0.25
78 ± 1 10.2 ± 0.2 16 2.76 ± 0.04 52 0.04 ± 0.00 3 2.19 ± 0.15 70 0.83 ± 0.05 <1 1.92 ± 0.01 2.75 ± 0.18 0.40 ± 0.02 8.6 ± 0.1 5.9 ± 0.0 0.13 ± 0.02 0.05 ± 0.00 3.3 ± 0.4 1:0.02:0.79
79 ± 1 30.9 ± 0.6 38 2.86 ± 0.11 52 0.69 ± 0.06 53 2.23 ± 0.37 75 0.68 ± 0.09 <1 2.18 ± 0.02 1.90 ± 0.09 0 6.0 ± 0.0 13.4 ± 0.3 0.93 ± 0.12 0.49 ± 0.04 2.8 ± 0.3 1:0.24:0.58
100 49.6 ± 1.8
100 62.6 ± 1.6
4.19 ± 0.06
4.29 ± 0.06
1.06 ± 0.04
1.01 ± 0.02
2.48 ± 0.31
2.32 ± 0.20
2.21 ± 0.08 <1 1.98 ± 0.04 14.86 ± 0.37 0.77 ± 0.20 8.5 ± 0.5 19.3 ± 0.8 2.37 ± 0.05 1.05 ± 0.06 6.7 ± 0.4 1:0.25:0.59
2.13 ± 0.04 <1 2.16 ± 0.10 13.31 ± 0.33 0.04 ± 0.01 6.0 ± 0.0 22.9 + 0.6 2.38 ± 0.09 1.01 ± 0.04 6.3 ± 0.1 1:0.24:0.40
in the SF which were transferred to the ALF as referred above. SF is either composted and sold or is stored and applied in the field during the crop growth period. 3.2. Potential of N mineralization of slurry and slurry fractions Nitrogen is a plant nutrient that has a high impact on crop yield and quality. The amount of N applied has to be adequate to ensure drop N-needs but should not be in excess to avoid environmental pollution (nitrate leaching and N gaseous emissions). Since part of the organic N applied can be mineralized after soil incorporation, knowledge of the potential N mineralization of slurry and slurry fractions is a useful tool to accurately define the amount of these materials to be applied. Fig. 1 shows the PM determined in the acidified and non acidified slurry and slurry fractions. Nitrogen mineralization occurred in SF, ASF, AS treatments and in the control whereas evidence of N immobilization was observed in all other treatments. Nevertheless, the N mineralization observed in AS treatment was lower than in the control (soil only). Indeed, considering the PAM (Fig. 2), it appears that organic N has potential to be mineralized only in the SF and ASF whereas in all other slurries and slurry fractions, N immobilization occurred. The PAM was significantly higher (P < 0.05) in ASF than in SF. On the contrary, the potential of net N immobilization was significantly higher (P < 0.05) in S than in AS and the same situation was observed in the LF and ALF even if in the liquid fractions differences were not statistically different
Potentialof apparentN mineralization (% of organic N applied)
Acidified solid fraction
20.00
ASF 10.19
15.00 10.00
SF 2.50
5.00
LF -27.86
0.00
S -13.45
ALF -25.34
AS -4.18
-5.00 -10.00 -15.00 -20.00 -25.00 -30.00 -35.00
Fig. 2. Potential of apparent N mineralization of the acidified and on acidified slurry and slurry fractions (% of organic N applied) (mean value and standard error of 5 replicates).
15.00
Potential of N mineralization (% of organic N applied)
Relative proportion (%) Dry matter content (g kg1) (%) Total N (g kg1) (%) Total P (g kg1) (%) Total K (g kg1) (%) Organic N (g kg1) 1 NO 3 –N (mg kg ) 1 –N (g kg ) NHþ 4 Total C (g kg1) Inorganic C (g kg1) pH Ash content (g kg1) Ca (g kg1) Mg (g kg1) C:Norg Ratio N:P:K ratio
Solid fraction
ASF
10.00 5.00 0.00 -5.00
SF 0
2
4
6
8
AS
10
-10.00 -15.00 -20.00
S ALF
y = 5.6156x - 43.852 2 R = 0.8989
-25.00 -30.00
LF
-35.00
1.000
ASF 0.737
C:Norganic ratio
-1
mg NH4-N g dry soil
0.800 0.600
SF 0.376
Soil only 0.255
0.400 AS 0.128
0.200 0.000 -0.200 -0.400
LF -0.252
ALF -0.114
S -0.170
-0.600
Fig. 1. Potential N mineralization of the acidified and non acidified slurry and slurry fractions (mean value and standard error of 5 replicates).
Fig. 3. Correlation between the C:Norganic ratio and the potential of apparent N mineralization of the acidified and on acidified slurry and slurry fractions (mean value and standard error of 5 replicates).
(P > 0.05). The amounts of N potentially mineralized or immobilized observed here were in the range of those reported by other authors who performed long term N mineralization in soils amended with different pig and cattle slurry (Chadwick et al., 2000; Kyvsgaard et al., 2000; Kirchmann and Lundvall, 1993; Fangueiro et al., 2008b). As can be seen on Fig. 3, a good relationship was observed between the C:Norganic ratio and the potential of N mineralization/immobilization (R2 = 0.899) and it is to highlight that N mineralization occurred in treatments (SF and ASF) with
D. Fangueiro et al. / Bioresource Technology 100 (2009) 4914–4917
the higher amounts of C and organic N. Such relationship between N mineralization and the C:N ratio were previously reported in other studies (Chadwick et al., 2000; Fangueiro et al., 2008c). Even if the C:Norg ratio was not significantly affected by acidification, a significant (P < 0.05) effect of acidification on PAM was observed in SF and S probably due to the effect of acidification on microbial processes, namely ammonification and nitrification. Hence, the utilization of the C:N ratio as an indicator to predict the N mineralization may not be valid when slurry treatment by acidification is performed. 4. Conclusions A combined treatment of pig slurry, acidification followed by solid–liquid separation, affects the slurry and slurry fractions composition namely their potential of N mineralization. Indeed, it provides an ALF and ASF more equilibrated in terms of nutrients than the LF and SF. Furthermore, the results obtained here indicated that acidification increases potential organic N mineralization in SF and decreases potential N immobilization in S and LF. The proposed treatment generates valuable slurry fractions with distinct characteristics and potential of N mineralization that may be applied at different periods after sowing to comply with plant nutrient requirements. References Cabral, F., Vasconcelos, E., Cordovil, C.M.D.S., 1998. Effects of solid phase from pig slurry on iron, copper, zinc, and manganese content of soil and wheat plants. J. Plant Nutr. 21 (9), 1955–1966. Castrillón, L., Fernández-Nava, Y., Marañón, E., García, L., Berrueta, J., 2009. Anoxic– aerobic treatment of the liquid fraction of cattle manure. Waste Manage. 29, 761–766. Chadwick, D.R., John, F., Pain, B.F., Chambers, B., Williams, J., 2000. Plant uptake of nitrogen from the organic nitrogen fraction of animal manures: a laboratory experiment. J. Agric. Sci. 134, 159–168. Eriksen, J., Sorensen, P., Elsgaard, L., 2008. The fate of sulfate in acidified pig slurry during storage and following application to cropped soil. J. Environ. Qual. 37, 280–286.
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Fangueiro, D., Coutinho, J., Chadwick, D., Moreira, N., Trindade, H., 2008a. Cattle slurry treatment by screw-press separation and chemically enhanced settling: effect on greenhouse gases and ammonia emissions during storage. J. Environ. Qual. 37 (6), 2322–2331. Fangueiro, D., Pereira, J.L., Chadwick, D., Coutinho, J., Moreira, N., Trindade, H., 2008b. Laboratories estimates of the effect of cattle slurry pre-treatment on organic N degradation after soil application and N2O and N2 emissions. Nutr. Cycl. Agroecosyst. 80, 107–120. Fangueiro, D., Bol, R., Chadwick, D., 2008c. Assessment of the potential N mineralization of six particle size fractions of two different cattle slurries. J. Plant Nutr. Soil Sci. 171, 313–315. Griffin, T.S., 2007. Estimates of gross transformation rates of dairy manure N using 15N pool dilution. Commun. Soil Sci. Plant Anal. 38 (11), 1451–1465. Houba, V.J., Lee, J.J., Novozamsky, I., Walling, I., 1989. Soil and Plant Analysis, Part 5. Soil Analysis Procedures. Wageningen. Kirchmann, H., Lundvall, A., 1993. Relationship between N immobilization and volatile fatty acids in soil after application of pig and cattle slurry. Biol. Fertil. Soils 15, 161–164. Kyvsgaard, P., Sorensen, P., Moller, E., Magid, J., 2000. Nitrogen mineralization from sheep faeces can be predicted from the apparent digestibility of the feed. Nutr. Cycl. Agroecosyst. 57, 207–214. Mulvaney, R.L., 1994. Nitrification of Different Nitrogen Fertilizers. Illinois Fertilizer Conference, January 24–26. Rees, R., Castle, K., 2002. Nitrogen recovery in soils amended with organic manures combined with inorganic fertilisers. Agronomie 22, 739–746. Sánchez, M., Gonzalez, J.L., 2005. The fertilizer value of pig slurry. I. Values depending on the type of operation. Bioresour. Technol. 96, 1117–1123. Schils, R.L.M., van der Meer, H.G., Wouters, A.P., Geurink, J.H., Sikkema, K., 1999. Nitrogen utilization from diluted and undiluted nitric acid treated cattle slurry following surface application to grassland. Nutr. Cycl. Agroecosyst. 53, 269–280. Sommer, S.G., Hutchings, N.J., 2001. Ammonia emission from field applied manure and its reduction—invited paper. Eur. J. Agron. 15, 1–15. Stevens, R.J., Laughlin, R.J., Frost, J.P., 1989. Effect of acidification with sulphuric acid on the volatilization of ammonia from cow and pig slurries. J. Agric. Sci. 113, 389–395. Vasconcelos, E., Cabral, F., 1996. Influence of the concentrated pig slurry on soil and corn fodder yield and chemical composition in presence of N top dressing. Fertil. Res. 45, 25–29. Vasconcelos, E., Cabral, F., Cordovil, C.M.D.S., 1997. Effects of solid phase from pig slurry on soil chemical characteristics, nitrate leaching, composition and yield of wheat. J. Plant Nutr. 20 (7&8), 939–952. Veltof, G.L., Oenema, O., 1993. Nitrous oxide flux from nitric-acid-treated cattle slurry applied to grassland under semi controlled conditions. Neth. J. Agric. Sci. 41, 81–93. WRB, 2006. World Reference Base for Soil Resources 2006 World soil Resources Reports no. 103. Food and Agriculture Organization (FAO), Rome, Italy.
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Short Communication
Treatment by acidification followed by solid–liquid separation affects slurry and slurry fractions composition and their potential of N mineralization David Fangueiro a,*, Henrique Ribeiro a, Ernesto Vasconcelos a, João Coutinho b, Fernanda Cabral a a b
UIQA Instituto Superior de Agronomia, TU Lisbon, Tapada da Ajuda, 1349-017 Lisboa, Portugal C. Química, Dep. Edafologia, UTAD, Ap. 1013, 5001-911 Vila Real, Portugal
a r t i c l e
i n f o
Article history: Received 5 March 2009 Received in revised form 14 April 2009 Accepted 16 April 2009 Available online 22 May 2009 Keywords: Pig slurry Acidification Solid–liquid separation N mineralization Organic fertilizer
a b s t r a c t The aim of the present work was to assess the effect of treatments by acidification, solid–liquid separation or acidification followed by solid–liquid separation on the physical and chemical composition of pig slurry (S) and pig slurry fractions (non acidified and acidified solid (SF and ASF) and liquid (LF and ALF) fractions), as well as on the potential of N mineralization of these pig slurry derived materials. Acidification strongly decrease the inorganic carbon content of S, SF and LF and it also affects the distribution of P, Ca and Mg between the solid and liquid fraction leading to an ALF more equilibrated than LF in terms of nutrients. Acidification increases the potential of organic N mineralization in SF and decreases the potential of N immobilization in S and LF. It can be concluded that the proposed treatment generates valuable slurry fractions with distinct characteristics and potential of N mineralization that may be incorporated to soil at different periods after sowing to comply with plant nutrient requirements. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction Pig slurry is widely used as fertilizer to provide nutrients to plants and increase the soil organic matter content. However, pig slurry management leads to N losses due to ammonia (NH3) volatilization during storage and soil application (Sommer and Hutchings, 2001; Eriksen et al., 2008). Ammonia volatilization may be reduced by lowering slurry pH, whereby the NH3/NHþ 4 equilibrium shifts towards a NHþ 4 concentration. Slurry acidification is currently used by farmers in The Netherlands and Denmark (Schils et al., 1999; Eriksen et al., 2008) as a tool to reduce NH3 emissions from slurry during storage and soil application. Still, to avoid hazards this technology needs to be improved. It is expected that an improved technology will be developed and used in more countries since the European Directive (2001/81/CE) promotes a decrease of atmospheric pollutants such as NH3 and countries like Spain have already defined targets to reduce such emissions (Castrillón et al., 2009). On the other hand, slurry separation may be a solution to enhance slurry management. Indeed, it may help to increase slurry storage capacity, improve slurry handling and has also been pointed out as a solution to reduce N losses during storage and after incorporation to soil (Fangueiro et al., 2008a). Slurry separation produces two fractions: a solid fraction with high dry matter, N and P content and a liquid fraction poor in organic N with low dry matter content (Fangueiro et al., 2008a).
* Corresponding author. Tel.: +351 213653199; fax: +351 213653180. E-mail address: [email protected] (D. Fangueiro). 0960-8524/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2009.04.032
However, there is little information on how acidification affects the composition, namely the potential of N mineralization, of pig slurry and pig slurry fractions obtained after solid–liquid separation. Indeed, a significant part of the N contained in pig slurry is in an organic form and becomes available to plants only after mineralization (Rees and Castle, 2002). Long term laboratory incubations are generally used to assess such information (Griffin, 2007; Fangueiro et al., 2008b) but they are time consuming and can not be used in routine. Alternatively, a short term anaerobic incubation method has been successfully used by Fangueiro et al. (2008c) to assess the potential of N mineralization of cattle slurry. The main objectives of the present study were to assess the effect of treatments by acidification, and acidification followed by solid–liquid separation on the physical and chemical composition of pig slurry and pig slurry fractions (non acidified and acidified solid and liquid fractions), as well as on the potential of N mineralization of these pig slurry derived materials. 2. Methods 2.1. Slurry acidification and solid–liquid separation The slurry used in this study was sampled in the slurry storage lagoon of a pig livestock farm located in the centre-West of Portugal. Half of the untreated slurry (S) was preserved at its original pH and the second half was acidified to pH 6 by addition of concentrated sulphuric acid (H2SO4) in order to obtain the acidified slurry (AS). S and AS were subsequently divided in two more sub-sam-
D. Fangueiro et al. / Bioresource Technology 100 (2009) 4914–4917
4915
ples: one to be conserved and one to be centrifuged at 3000 rpm during 15 min to provide a liquid and a solid fraction leading to four slurry fractions: liquid fraction (LF), solid fraction (SF), acidified liquid fraction (ALF) and acidified solid fraction (ASF).
of the mean differences was determined using the least significant difference (LSD) tests based on a t-test at a 0.05 probability level. The statistical software package used was Statistix 7.0.
2.2. Analytical methods
3. Results
All these organic materials were fully characterized using the following methods: to determine dry matter, 100 g of fresh material were placed in a capsule and then dried in a heater at 105 °C to constant weight for at least 24 h. Ash content was determined using dry material (2 g), which was incinerated in a muffle furnace at 450 °C, for 12 h. Total and inorganic carbons were determined using a Primacs TOC Analyser (Skalar). pH was determined directly in S, AS, LF and ALF and after 1 h of contact with occasional agitation in a sample-water (1:5 w/v) suspension in SF and ASF. The Kjeldhal method was used to assess the total N content of the samples. Mineral N content was determined by extraction with 2 M KCl (1:5 w/v) (Mulvaney, 1994) followed by ammonium (NHþ 4 ) and nitrate (NO 3 ) quantification by molecular absorption spectrophotometry in a Skalar segmented flow analyser using the Berthelot and sulphanilamide methods, respectively (Houba et al., 1989). Soluble organic N was calculated by subtracting mineral N from soluble N. Ca, Mg, K and P contents were quantified after hydrochloric acid (HCl) treatment of the ash through graphite furnace atomic absorption spectrophotometry (Unicam M Series), except for phosphorous, which was determined using the ammonium vanadomolybdate method by molecular absorption spectrophotometry (Hitachi 2000).
3.1. Slurry and slurry fractions composition
2.3. Short-term incubation method To estimate the potential of N mineralization of the acidified and non acidified slurry and slurry fractions an anaerobic incubation method described by Fangueiro et al. (2008c) was used as follows: an amount of organic material equivalent to 0.05 g of total N was added to 10 g of field moist soil in a 60 ml syringe and the amount of water was adjusted to have a total amount of 25 ml. The soil was collected from the arable layer of a Cambic Arenosol (WRB, 2006), which is a sandy textured soil with a total N content of 0.27 g kg1, an organic C content of 4.57 g kg1, an ammonium-N content of 15.75 mg kg1 and a nitrate N content of 11.14 mg kg1. Ten replicates were prepared for each organic material and one half were incubated for 7 days at 40 °C, while the other half were immediately extracted by the injection of 25 ml of 4 M KCl into each syringe to give a 1:5 soil/slurry 2 M KCl extraction ratio. After shaking for 1 h, the suspensions were transferred to centrifuge tubes and centrifuged at 3000 rpm during 5 min. The supernatant was then analysed for NHþ 4 –N content as described above. Soil only treatments were used as controls. The same extraction method was used after the 7 days incubation period. The potential of net N mineralization (PM) was calculated as the difference between post- and pre-incubation NHþ 4 –N concentrations and the potential of apparent net N mineralization (PAM), expressed as a percentage of the organic N of the treated and non treated slurry was calculated using the following equation:
n o PAM ¼ ð½NHþ4 t¼7 ½NHþ4 t¼0 Þsample ð½NHþ4 t¼7 ½NHþ4 t¼0 Þcontrol =Norg applied 100 2.4. Statistical analysis Results were analyzed by analysis of variance (one way-ANOVA) to test the effects of each treatment. The statistical significance
Table 1 shows the main characteristics of the pig slurry used in the present work. The slurry used here had an initial pH value of 8.5 and the H2SO4 addition decreased pH to a value of 6.0 in slurry and slurry fractions. Values of most parameters are in the range of those reported by Vasconcelos and Cabral (1996), Vasconcelos et al. (1997) as well as Sánchez and Gonzalez (2005) in a study where more than 150 pig slurries from Spain were fully characterized. Slurry acidification led to a significant increase of ash (19%) and DM (26%) content in AS relative to S. Such increase of DM was previously reported by Veltof and Oenema (1993) but no clear explanation for this have been proposed. It is to believe that such increase was likely due to the sulphate ion added via the H2SO4. Acidification also significantly (P < 0.05) increased the DM (300%) and ash (227%) contents of the ALF relative to LF. However, the DM content of the SF and ASF were similar but considering the percentage distribution relative to the initial slurry, the ASF contains only 65% of the slurry DM against 86% in the SF. This may be due to the solubilization of some slurry compounds, occurring at a lower pH, which were transferred to the acidified liquid fraction. Acidification led to a significant (P < 0.05) decrease of the total carbon content of S which should be due to the removal of most 2 of the inorganic C. Indeed, important losses of HCO 3 /CO3 should occur during acidification. Slurry acidification converts the HCO 3/ CO2 3 to H2CO3 and CO2 and the proportion of bicarbonate/carbonate converted to CO2 at pH 5–6 is 72–96% (Stevens et al., 1989). The carbon content of the solid and liquid fraction obtained after centrifugation of the acidified slurry was also significantly lower (P < 0.05) than in the respective non acidified fractions, SF and LF. Acidification had no effect on the potassium content neither on the organic N and nitrate content of slurries and slurry fractions whereas the ammonium content was significantly higher in AS, ALF and ASF relative to S, LF and SF, respectively. Such differences should be due to the lower NH3 losses occurring during the treatment and handling of acidified slurry and acidified slurry fractions. Total P, Ca and Mg contents were not significantly different (P > 0.05) in S and AS. However, a significant increase on the content of these elements was detected in ALF relative to LF. Indeed the LF shows only 3% of the total P against 53% in the ALF. The increase in the total amount of P in the ALF can be justified by the increased solubility of phosphate salts at decreasing pH. On the other hand, the increase observed for the Ca and Mg content may be explained by the effect of sulphuric acid addition on the solubilization of insoluble Ca and Mg carbonates, phosphates and hydroxides and further solubilization of these elements in the LF. Acidification enables a ALF richer in total P, Ca and Mg and more equilibrated in terms of nutrients (see N:P:K ratio) than LF what may be viewed as a positive aspect if LF or ALF are used for fertigation. Acidification and centrifugation affect the N:P:K ratio and the proposed treatment may be helpful for farmers to better adapt the organic amendments to soil requirement since it provides materials with distinct nutrients contents and N:P:K ratio. Even if the solid–liquid separation process used here was more efficient to remove the DM to the solid fraction than the traditional on-farm processes, the nutrient partitioning obtained was similar to values obtained with on-farm processes. The SF has a higher total P, Ca, and Mg content than S as previously reported by Cabral et al. (1998). Acidification led to a reduction of these elements retained
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Table 1 Composition of treated and untreated pig slurry and pig slurry fractions and proportion of treated and untreated pig slurry fractions relative to non separated slurry. Liquid fraction
Acidified liquid fraction
Slurry
Acidified slurry
22 ± 1 194.8 ± 8.2 86 10.45 ± 0.27 52 4.72 ± 0.67 93 2.03 ± 0.16 17 8.34 ± 0.29 <1 2.11 ± 0.03 72.41 ± 1.61 2.41 ± 0.31 8.5 ± 0.1 70.8 ± 5.9 10.60 ± 0.53 4.69 ± 0.38 8.7 ± 0.4 1:0.45:0.19
21 ± 1 195.5 ± 5.3 65 9.91 ± 0.14 51 2.09 ± 0.19 45 2.49 ± 0.33 24 7.72 ± 0.15 <1 2.18 ± 0.02 67.63 ± 2.09 0.99 ± 0.46 6.0 ± 0.0 59.6 ± 3.8 6.72 ± 0.91 2.80 ± 0.08 8.8 ± 0.3 1:0.21:0.25
78 ± 1 10.2 ± 0.2 16 2.76 ± 0.04 52 0.04 ± 0.00 3 2.19 ± 0.15 70 0.83 ± 0.05 <1 1.92 ± 0.01 2.75 ± 0.18 0.40 ± 0.02 8.6 ± 0.1 5.9 ± 0.0 0.13 ± 0.02 0.05 ± 0.00 3.3 ± 0.4 1:0.02:0.79
79 ± 1 30.9 ± 0.6 38 2.86 ± 0.11 52 0.69 ± 0.06 53 2.23 ± 0.37 75 0.68 ± 0.09 <1 2.18 ± 0.02 1.90 ± 0.09 0 6.0 ± 0.0 13.4 ± 0.3 0.93 ± 0.12 0.49 ± 0.04 2.8 ± 0.3 1:0.24:0.58
100 49.6 ± 1.8
100 62.6 ± 1.6
4.19 ± 0.06
4.29 ± 0.06
1.06 ± 0.04
1.01 ± 0.02
2.48 ± 0.31
2.32 ± 0.20
2.21 ± 0.08 <1 1.98 ± 0.04 14.86 ± 0.37 0.77 ± 0.20 8.5 ± 0.5 19.3 ± 0.8 2.37 ± 0.05 1.05 ± 0.06 6.7 ± 0.4 1:0.25:0.59
2.13 ± 0.04 <1 2.16 ± 0.10 13.31 ± 0.33 0.04 ± 0.01 6.0 ± 0.0 22.9 + 0.6 2.38 ± 0.09 1.01 ± 0.04 6.3 ± 0.1 1:0.24:0.40
in the SF which were transferred to the ALF as referred above. SF is either composted and sold or is stored and applied in the field during the crop growth period. 3.2. Potential of N mineralization of slurry and slurry fractions Nitrogen is a plant nutrient that has a high impact on crop yield and quality. The amount of N applied has to be adequate to ensure drop N-needs but should not be in excess to avoid environmental pollution (nitrate leaching and N gaseous emissions). Since part of the organic N applied can be mineralized after soil incorporation, knowledge of the potential N mineralization of slurry and slurry fractions is a useful tool to accurately define the amount of these materials to be applied. Fig. 1 shows the PM determined in the acidified and non acidified slurry and slurry fractions. Nitrogen mineralization occurred in SF, ASF, AS treatments and in the control whereas evidence of N immobilization was observed in all other treatments. Nevertheless, the N mineralization observed in AS treatment was lower than in the control (soil only). Indeed, considering the PAM (Fig. 2), it appears that organic N has potential to be mineralized only in the SF and ASF whereas in all other slurries and slurry fractions, N immobilization occurred. The PAM was significantly higher (P < 0.05) in ASF than in SF. On the contrary, the potential of net N immobilization was significantly higher (P < 0.05) in S than in AS and the same situation was observed in the LF and ALF even if in the liquid fractions differences were not statistically different
Potentialof apparentN mineralization (% of organic N applied)
Acidified solid fraction
20.00
ASF 10.19
15.00 10.00
SF 2.50
5.00
LF -27.86
0.00
S -13.45
ALF -25.34
AS -4.18
-5.00 -10.00 -15.00 -20.00 -25.00 -30.00 -35.00
Fig. 2. Potential of apparent N mineralization of the acidified and on acidified slurry and slurry fractions (% of organic N applied) (mean value and standard error of 5 replicates).
15.00
Potential of N mineralization (% of organic N applied)
Relative proportion (%) Dry matter content (g kg1) (%) Total N (g kg1) (%) Total P (g kg1) (%) Total K (g kg1) (%) Organic N (g kg1) 1 NO 3 –N (mg kg ) 1 –N (g kg ) NHþ 4 Total C (g kg1) Inorganic C (g kg1) pH Ash content (g kg1) Ca (g kg1) Mg (g kg1) C:Norg Ratio N:P:K ratio
Solid fraction
ASF
10.00 5.00 0.00 -5.00
SF 0
2
4
6
8
AS
10
-10.00 -15.00 -20.00
S ALF
y = 5.6156x - 43.852 2 R = 0.8989
-25.00 -30.00
LF
-35.00
1.000
ASF 0.737
C:Norganic ratio
-1
mg NH4-N g dry soil
0.800 0.600
SF 0.376
Soil only 0.255
0.400 AS 0.128
0.200 0.000 -0.200 -0.400
LF -0.252
ALF -0.114
S -0.170
-0.600
Fig. 1. Potential N mineralization of the acidified and non acidified slurry and slurry fractions (mean value and standard error of 5 replicates).
Fig. 3. Correlation between the C:Norganic ratio and the potential of apparent N mineralization of the acidified and on acidified slurry and slurry fractions (mean value and standard error of 5 replicates).
(P > 0.05). The amounts of N potentially mineralized or immobilized observed here were in the range of those reported by other authors who performed long term N mineralization in soils amended with different pig and cattle slurry (Chadwick et al., 2000; Kyvsgaard et al., 2000; Kirchmann and Lundvall, 1993; Fangueiro et al., 2008b). As can be seen on Fig. 3, a good relationship was observed between the C:Norganic ratio and the potential of N mineralization/immobilization (R2 = 0.899) and it is to highlight that N mineralization occurred in treatments (SF and ASF) with
D. Fangueiro et al. / Bioresource Technology 100 (2009) 4914–4917
the higher amounts of C and organic N. Such relationship between N mineralization and the C:N ratio were previously reported in other studies (Chadwick et al., 2000; Fangueiro et al., 2008c). Even if the C:Norg ratio was not significantly affected by acidification, a significant (P < 0.05) effect of acidification on PAM was observed in SF and S probably due to the effect of acidification on microbial processes, namely ammonification and nitrification. Hence, the utilization of the C:N ratio as an indicator to predict the N mineralization may not be valid when slurry treatment by acidification is performed. 4. Conclusions A combined treatment of pig slurry, acidification followed by solid–liquid separation, affects the slurry and slurry fractions composition namely their potential of N mineralization. Indeed, it provides an ALF and ASF more equilibrated in terms of nutrients than the LF and SF. Furthermore, the results obtained here indicated that acidification increases potential organic N mineralization in SF and decreases potential N immobilization in S and LF. The proposed treatment generates valuable slurry fractions with distinct characteristics and potential of N mineralization that may be applied at different periods after sowing to comply with plant nutrient requirements. References Cabral, F., Vasconcelos, E., Cordovil, C.M.D.S., 1998. Effects of solid phase from pig slurry on iron, copper, zinc, and manganese content of soil and wheat plants. J. Plant Nutr. 21 (9), 1955–1966. Castrillón, L., Fernández-Nava, Y., Marañón, E., García, L., Berrueta, J., 2009. Anoxic– aerobic treatment of the liquid fraction of cattle manure. Waste Manage. 29, 761–766. Chadwick, D.R., John, F., Pain, B.F., Chambers, B., Williams, J., 2000. Plant uptake of nitrogen from the organic nitrogen fraction of animal manures: a laboratory experiment. J. Agric. Sci. 134, 159–168. Eriksen, J., Sorensen, P., Elsgaard, L., 2008. The fate of sulfate in acidified pig slurry during storage and following application to cropped soil. J. Environ. Qual. 37, 280–286.
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