Artigo com resultados da ESA/IPVC

Brito, L. M., Saldanha, J., Mourão, I., Nestler, H., 2011. Composting of Acacia longifolia and Acacia melanoxylon
invasive species. Artigo submetido para publicação na Acta Horticulturae (ISHS): International Symposium on
Growing Media, Composting and Substrate Analysis, 17-21 October, 2011, Universitat Politècnica de Catalunya,
Barcelona, Spain.
Composting of Acacia
Invasive Species
longifolia and Acacia melanoxylon
L.M. Brito, J. Saldanha and I. Mourão
Mountain Research Center (CIMO),
Instituto Politécnico de Viana do Castelo,
Escola Superior Agrária, Refóios, 4990-706
Ponte de Lima, Portugal, E-mail:
[email protected]
H. Nestler Grupo Leal &
Soares, Zona Industrial,
Apartado 9 EC Mira, 3071-909
Mira, Portugal E-mail:
[email protected]
Abstract
Acacias are invasive Fabaceae species that are highly competitive and a serious threat to local biodiversity and
natural habitats. Taking into account their high availability and low cost, a valorization approach for acacia shrubs
may be composting to produce horticultural organic amendments and substrate components. With this aim, two big
piles (100 m3) were set up with ground and screened Acacia longifolia and Acacia melanoxylon shrubs, and managed
with different turning frequency, to analyze the physicochemical characteristics during composting and to model the
breakdown of acacia organic matter (OM). Time-temperature conditions in both piles exceeded the more stringent
criteria for complete pathogen inactivation as temperatures were between 65 ºC and 75 ºC for several months,
indicating high amount of 20 biodegradable OM in this material, as found here by the high amount of mineralizable
OM (640-690 g kg-1 of initial OM). High temperature and high pH conditions promoted significant N losses (455465 g kg-1 of initial N). Nevertheless, these were smaller compared to C losses and so the C/N ratio decreased from
50 to 29-32 after 231 days of composting. This study indicates that composting acacia can produce organic
amendments with high OM content, and low electrical conductivity (< 1.3 dS m-1). However, a long period of
composting (> 231 days) is required to achieve full compost maturation. Key words: C/N ratio, compost,
mineralization, organic matter, temperature
INTRODUCTION
Acacia longifolia (Andrews) Willd. and Acacia melanoxylon R. Br. were introduced in Portugal to fix biological
nitrogen (N) for soil restoration. However, these invasive Fabaceae species are highly competitive and a serious
threat to local biodiversity and natural habitats. They also represent a significant fire risk. Taking into account their
high availability and low cost a new valorization approach for these shrubs may be composting to produce soil
organic amendments and horticultural substrate components. Acacias have large recalcitrant lignin, polyphenol and
cellulose contents (Fioretto et al., 2005) that do not contribute to raise composting temperatures. However, acacia is
also rich in N, and when N is easily available the slowgrowing fungi that are able to decompose lignin, such as the
basidiomycetes, are eliminated from the decomposer community because they are not capable to compete with fastgrowing microbes (Fioretto et al., 2005). In addition to the C/N ratio and material composition, the speed at which the
microorganisms grow and operate and, therefore, the production of heat inside a composting pile, depends on the
moisture content and aeration, whereas other conditions, including pile dimensions and turning frequency(Brito et al.,
2008), affect heat loss and so, final pile temperature. The objective of this work was to investigate the
physicochemical characteristics, and to model the breakdown of OM, during composting of ground and screened
Acacia longifolia and Acacia melanoxylonshrubs with different pile turning frequency, and to find out if composting
acacia may reach high enough temperatures for compost sanitation and weed seed destruction.
MATERIALS AND METHODS
Two big conical composting piles were set up outdoors on January 2011, with
approximately 100 m3 (8 m of base diameter and 3 m height), consisting of Acacia
longifolia (60%) and Acacia melanoxylon (40%) shrubs collected in the winter in Mira,
Portugal (40º25' N 8º44' W), to study the physicochemical characteristics during the
composting process (231 days), with higher (pile A) and lower (pile B) turning
frequency. The shrubs were harvested by basal cutting, shredded with a high speed
grinder (Doppstadt; AK 403 Profi) and screened using a Neuenhauser Super Screener
Portable Star Screen. The piles were built with particles < 4 cm on a layer (≈ 30 cm
high) of pine bark to prevent contamination with soil during the turnings performed
with a forest crane and a tractor front-end loader. Pile A was turned 28, 56, 84, and 147
days after the start of the composting process while the pile B was turned only at day 28
and 147. Compost temperature was monitored automatically with thermistors 21
(Delta–T Devices) positioned at approximately 0.5, 1.5 and 2.5 m high and recorded by
a data logger. Four replicate samples were periodically collected from the center of each
pile for analysis. Dry matter (DM) content, pH, electrical conductivity (EC), organic
matter (OM), and total Kjeldahl N were determined by standard procedures (CEN,
1999). The sodium salicylate method was used for analysis of nitrate N in compost
samples. The C/N ratio was estimated by dividing the OM by a factor of 1.8 to obtain
the C content in compost. Mass reduction and OM losses were calculated from the
initial (X1) and final (X2) ash contents according, respectively, to the formula (1) of
Tang et al. (2007) and the formula (2) of Paredes et al. (2000), as follows: Mass
reduction (g kg-1) = (1-X1/X2) × 1000
[1]
OM loss (g kg-1) = 1000 - 1000[X1(1000 - X2)]/[X2(1000 - X1)] [2] Losses of N were
calculated from the initial (X1) and final (X2) ash contents, and the initial (N1) and final
(N2) N contents by the following formula (Paredes et al., 2000): N loss (g kg -1) = 1000 1000 [(X1N2)/(X2N1)] [3] Mineralization of OM during composting, determined by the
OM lost, was described by the following two component kinetic model (adapted from
the N mineralization model of Molina et al., 1980):OM m = OM1 [1 - exp(-k1t)] + OM2 [1
- exp(-k2t)] [4] Were OM0, OM1 and OM2 are pools of mineralizable OM, k1 and k2 the
respective rates of mineralization (day-1), and t the time(days). The same procedure
followed for OM was carried out to describe N losses. Data referring to OM and N
losses during composting was fitted to the kinetic equation by the non-linear leastsquare curve-fitting technique (Marquardt–Levenberg algorithm). Mean comparisons
between compost treatments were performed by the least significant difference (LSD)
test. All statistical calculations were performed using SPSS v.17.0 software for
Windows (SPSS Inc.) and statistical significance was indicated at a probability level of
P <0.05.
RESULTS AND DISCUSSION
Initially, the temperature of composting piles rose indicating the rapid breakdown of
readily available compounds, up to a maximum temperature of 76 ºC, found in the top
of pile A (Fig. 1). Twenty eight days after composting commencement, piles were
turned and moisten. Following the initial drop, the temperature rose again steadily to
thermophilic values (> 55 ºC) within 2-5 days in both piles, till it peaked (77 ºC) in the
top of pile A two weeks after turning. After the second turn in pile A, the time taken to
reach peak temperatures increased compared to the first turn showing less rapidly
biodegradable OM. After turning both piles on day 147, temperatures increased faster in
pile B compared to pile A, showing that easily biodegradable OM still remained in the
edges of pile B. Measurements at different pile depths showed lower temperatures in the
bottom of the piles, which can be explained by the evaporative cooling effect of the
incoming air (Gao, 2010). However, bottom pile temperatures were kept higher with
lower turning frequency (pile B) compared with increased turning frequency (pile A).
The temperature conditions in these big acacia piles satisfied the compost sanitation
requirements specified by the U.S. Environmental 22 Protection Agency (USEPA,
1989). These indicate that a significant reduction in pathogens during composting is
achieved when the compost temperature is maintained above 55 ºC for ≥5 days.
Furthermore, time-temperature conditions in acacia piles also exceeded the more
stringent criteria for complete pathogen inactivation proposed by Wu and Smith (1999)
equivalent to 55 ºC for ≥15 days, as temperatures were kept between 65 ºC and 75 ºC
for several months, indicating high total amount of biodegradable OM in the
composting material, and also the effects of pile size, as the heat generation is
proportional to volume and the heat loss is proportional to surface area (Füleky, 2010).
Initial pile moisture content (MC) was 62% and composting proceeded at optimum MC
for microorganism activity (Table 1) as most favorable MC level for biodegradation of
different compost mixture varies from 50% to 70% (Kader et al., 2007). Therefore,
water evaporation was balanced by: (i) winter and spring precipitation; (ii) water
produced during OM degradation; and (iii) mass reduction. High MC also contributed
for long retention time of the high temperatures inside the composting piles (Petric et
al., 2009). As a consequence of the degradation of organic acids and ammonia
production, pH values increased early during the composting process (Table 1).
Thereafter, the pH of acacia material was generally alkaline and in the range 7.0-7.6.
These pH values do not limit the use of this compost as soil amendment to agricultural
land but the same is not true for the use as substrate component because pH of
horticultural growing media should be between 5 and 6.5 (Cáceres, et al. 2006). EC of
acacia material as 1.5 dS m-1 at the beginning of composting and decreased after two
weeks to values of 0.5-1.3 dS m-1 (Table 1). This decrease can be explained by the
volatilization of ammonia and the precipitation of mineral salts as suggested by Gao
(2010). High salt concentrations may cause phytotoxicity problems and the EC value of
compost is therefore important in evaluating the suitability and safety of compost for
agricultural purposes. In this investigation, final EC values of composts (1-1.3 dS m-1)
were well below the maximum value of 3 dS m-1 recommended for application to soil
(Soumaré et al., 2002).
Dry matter losses (data not shown) were 553 and 591 g kg -1 DM respectively for pile A
and B after 231 days of composting. These losses were higher than mass loss found by
Pereira et al. (1998) for Acacia longifolia litter decomposition in soil (44% after 16.5 months).
OM content, on a DM basis, decreased from 852 g kg-1 at the beginning of composting,
to a minimum of 637 g kg-1 found in the pile B. (Table 1). OM mineralization (640-690
g kg-1 after 231 days of composting), determined by OM losses (Fig. 2), showed two
different phases of OM degradation. The first phase was indicative of the rapid
decomposition of the readily biodegradable substrates and a high rate of microbial
activity. The second phase showed a slower rate of OM degradation when only the more
resistant compounds remained. The rates of mineralization were increased for the more
aerated pile A, compared to pile B (Fig.2), because turning provided oxygen for the
decomposition process.
Total N content increased from initial values of 9.5 g kg -1 DM to final values of
11.5−12.3 g kg-1 DM (Table 1). An increase in total N content during composting has
been widely reported (de Bertoldi and Civilini, 2006; Brito et al.,2008), and is due to a
lower rate of N loss than OM loss. Pile leaching was not observed during composting.
Most likely, leaching was prevented in these big 23 piles because of their small specific
surface area. Also, as would be expected, NO3--N content in composting piles (data not
shown) was negligible because the bacteria responsible for nitrification are strongly
inhibited by temperatures greater than 40 °C (Jimenez and Garcia, 1989). This implies
that the risk of N leaching was insignificant during this composting period. Therefore,
in addition to maintain high temperatures, big piles may be run without pile covers as
rain is needed to maintain pile moisture and is not percolated in the pile enough to leach
pile nutrients. However, high temperature and high pH conditions during the
thermophilic stage probably promoted intense ammonia emission, which would explain
high N losses (≈ 460 g kg-1 after 231 days of composting) found during acacia
composting (Fig. 2), mostly at the initial phase of the process when OM degradation
and ammonia production was at its most rapid. Differences in N losses between piles
were not significant, probably because the difference between turning frequency of both
piles was small.
The C/N ratio declined from 50 at the beginning of composting to final values of 29 and
32 respectively for piles with higher and lower turning frequency (Table 1). The C/N
ratio variation during composting occurs both as a result of OM mineralization (loss of
CO2) and N-loss by ammonia volatilization (de Bertoldi and Civilini, 2006). Therefore,
the C/N reduction was the result of a higher OM mineralization compared to N
volatilization. This study shows that a long period of composting (> 231 days) is
required to achieve full compost maturation and that acacia composting can produce
agronomical effective organic soil amendments containing significant amounts of OM
and N with a low EC. Further investigation will be carried out to evaluate compost
maturation and final compost quality for horticultural substrates.
CONCLUSIONS
Ground and screened acacia shrubs have sufficient biodegradability and structure to
allow effective composting with good air supply as thermophilic temperatures were
attained soon after pile construction, and were above 65 ºC for a period long enough to
satisfy the more stringent criteria for complete pathogen inactivation in big piles.
Organic matter losses were increased compared to N losses and the C/N ratio decreased
from an initial value of 50 to final values of 29-32.
Although most OM destruction occurred during the initial two months after composting
was initiated, a long period of composting (> 231 days) is required to achieve full
compost maturation with few pile turnings, as indicated here by compost temperature.
The low EC together with high OM and N contents in acacia composts suggests that
they are suitable as organic soil amendments for agricultural land.
ACKNOWLEDGEMENTS
This study was supported by project QREN/COMPETE/CEI_13584, funded by the
European Union.
Literature cited
Brito, L.M., Coutinho, J. and Smith, S.R. 2008. Methods to improve the composting
process of the solid fraction of dairy cattle slurry. Bioresour. Technol. 99: 8955-8960.
Cáceres, R., Flotats, X. and Marfà, O. 2006. Changes in the chemical and
physicochemical properties of the solid fraction of cattle slurry during composting using
different aeration strategies. Waste Manage. 26: 1081-1091.
CEN 1999 - European Standards - soil improvers and growing media. European
Committee for Standardization. de Bertoldi, M. and Civilini, M. 2006. High rate
composting with innovative process control. Compos. Sci. Util. 14: 290-295.
Fioretto A., Di Nardo C., Papa S. and Fuggi A. 2005. Lignin and cellulose degradation
and nitrogen dynamics during decomposition of three leaf litter species in a
Mediterranean ecosystem. Soil Biol. Biochem. 37: 1083-1091.
Füleky, G. 2010. Composting to recycle biowaste. p. 319–346. In: E. Lichtfouse (ed.),
Sociology, organic farming, climate change and soil science. Springer, Dijon, France.
Gao, M., Liang, F., Yu, A., Li, B. and Yang, L. 2010. Evaluation of stability and
maturity during forced-aeration composting of chicken manure and sawdust at different
C/N ratios. Chemosph. 78: 614-619.
Jimenez, E.I. and Garcia, V.P. 1989. Evaluation of city refuse compost maturity: a
review. Biol. Wastes 27: 115-142.
Kader, N.A., Robin, P., Paillat, J.M. and Leterme, P. 2007. Turning, compacting and the
addition of water as factors affecting gaseous emissions in farm manure composting.
Bioresour. Technol. 98: 2619-2628.
Molina, J.A.E., Clapp, C.E. and Larson, W.E. 1980. Potentially mineralizable nitrogen
in soil: The simple exponential model does not apply for the first 12 weeks of
incubation. Soil Sci. Soc. Am. J. 44: 442-443.
Paredes, C., Roig, A., Bernal, M.P., Sánchez-Monedero, M.A. and Cegarra, J.2000.
Evolution of organic matter and nitrogen during co-composting of olive mill wastewater
with solid organic wastes. Biol. Fertil. Soils 20: 222-227.
Pereira A.P., Graca M.A.S. and Molles M. 1998. Leaf litter decomposition in relation to
litter physico-chemical properties, fungal biomass, arthropod colonization, and
geographical origin of plant species. Pedobiologia 42: 316-327.
Petric, I., Sestan, A. and Sestan, I. 2009. Influence of initial moisture content on the
composting of poultry manure with wheat straw. Biosyst. Eng. 104:125-134.
Soumaré, M., Demeyer, A., Tack, F.M.G. and Verloo, M.G. 2002. Chemical
characteristics of Malian and Belgian solid waste composts. Bioresour. Technol. 81: 97101.
Tang, J.C., Shibata, A. Zhou, Q. and Katayama, A. 2007. Effect of temperature on
reaction rate and microbial community in composting of cattle manure with rice straw.
J. Biosci. Bioeng. 104: 321-328.
USEPA, 1989. Control of pathogens in municipal wastewater sludge for land
application. Center for Environmental Research Information. Cincinnati, OH, USA.
Wu, N. and Smith, J.E. 1999. Reducing pathogen and vector attraction for biosolids.
Biocycle, 40(11): 59-61.