Elsevier

Waste Management

Volume 114, 1 August 2020, Pages 25-32
Waste Management

Evolution of phytotoxicity during the active phase of co-composting of chicken manure, tobacco powder and mushroom substrate

https://doi.org/10.1016/j.wasman.2020.06.034Get rights and content

Highlights

  • Mushroom substrate addition to chicken manure improved compost maturity.

  • Mushroom substrate added to chicken manure compost led to reduced phytotoxicity.

  • Chicken manure composting entered the humification process after day 28.

  • GI was + vely correlated with catalase/peroxidase, −vely correlated with MDA.

  • The ions Fe3+> Mg2+ >Zn2+ correlated most significantly with germination of seed.

Abstract

This study systematically investigated the phytotoxicity of chicken manure co-composted with tobacco powder and mushroom substrate on seed germination during active phase of composting. All compost products met the sanitation requirements specified in the Chinese national standard; however, only the mushroom substrate compost satisfied the maturity standard. From day 28, the composting entered the end of active phase and the concentrations of K+, Zn2+, Na+, Cu2+ and Fe3+ decreased gradually. Redundancy analysis indicated that the germination index, catalase and peroxidase activities was positively correlated with K+, Zn2+, Na+, Cu2+, Fe3+ and NO3-N, and negatively correlated with NH4+-N, Mg2+ and Ca2+, among which the most significant ions were Fe3+, Mg2+ and Zn2+ for all treatments. The malondialdehyde concentration of germinated seeds had adverse correlation with the above ions parameters.

Introduction

Poultry production is an important agro-industry worldwide. To take an instance from the global demand for chicken meat and chicken eggs, it was predicted to grow by 61% and 39% up to 2030, and approximate 457 million tons of chicken manure (CM) were globally produced each year (Hwang et al., 2020, Mao et al., 2020). Composting is an effective and sustainable method of poultry manure waste treatment (Wan et al., 2020). Traditionally, composting is a bio-oxidative process involving the mineralization and partial maturation of the organic matter, leading to a stabilized final product, free of phytotoxicity and pathogens and with certain mature properties (Bernal et al., 2009). However, CM generally has high moisture content (75%–85%) and bulk density (700–800 kg·m−3), which can restrain the growth and respiration of aerobic bacteria and influence the compost quality. Besides, the high N content in CM could result in a low C to N ratio (C/N) (of about 10), which is too low for aerobic composting requirements (C/N = 25–35). And several studies showed that composting can be carried out with C/N ratio of 15–18, adding some high C material was needed (Kumar et al., 2010). Furthermore, co-composting with CM is an economic method, which could favor microorganisms to degrade different organic solid wastes into qualified compost and dispose two or more kinds of organic wastes at once.

Tobacco powder (TP) is a by-product of cigarette production. TP had higher C content and lower moisture content than CM and was added to adjust the C/N and moiture content of CM to improve the compost process (Silva et al., 2014). Co-composting of CM and TP is a routine disposal method in southwest China, because these two materials provide complementary properties for optimal composting. However, TP is characterized by high electrical conductivity (>8 mS·cm−1), and its small particle size resulted in low specific surface area, which may hinder ventilation of the compost pile. Therefore, mushroom substrate (MS) is usually added to regulate the manure porosity and optimize the mixture characteristics for composting. Previous studies have reported that MS addition as a bulking agent could help to adjust the water content, change the degradation kinetics, inoculate microorganisms, shorten the composting procedure and improve the final compost quality and safety (Shao et al., 2014).

Immature or unstable compost can compete with plants for oxygen and plant roots might rot under the anoxic conditions generated. Application of immature or unstable compost can lead to the addition of available heavy metals, pathogenic bacteria, parasites, salts and ions, and threaten the soil health and environmental safety (Nikaeen et al., 2015). Because of these potential negative consequences, the quality of composted CM fertilizer should be evaluated prior to farmland application. Compost phytotoxicity was an important criterion for the utilization of organic fertilize, because it has direct influence on seed germination and seedling growth.

Compost maturation is evaluated on the basis of physical (e.g., smell, color, structure), chemical (pH, EC, C/N, E4/E6, et al.) and biological parameters. Germination index (GI) is a biological criterion that indicates residual phytotoxicity. Composting is a complicated process, in which large fragments of organic matter is first aerobically degraded into fine pieces, and then later polymerized to macromolecular humus. At the end of the compost process, there are many water-soluble substances in compost, including ammonium N (NH4+-N), nitrate N (NO3-N), copper (Cu2+), zinc (Zn2+), iron (Fe3+), sodium (Na+), potassium (K+), calcium (Ca2+), magnesium (Mg2+) and others, which directly influence pH and EC, and then influence seed germination. Previous studies have indicated that mature compost has pH above 7 and EC below 4 mS·cm−1 will not cause any phytotoxicity to apply (Garcia et al., 1991), which is the result of low-molecular weight acids being produced during the initial composting phase and then being degraded as the composting proceeds; salt ions are also transformed into more stable forms during the maturation phase of composting (Zhang and Sun, 2015).

The water-soluble element was transformed to seeds from compost extract when seeds absorb nutrients from compost extract, it is important to analyze the effect of extract composition (such as ions) on seed germination. It has been reported that ions could affect germination through regulating osmotic, specificity and redox potential (Ibrahim, 2016). High concentration of salt ions could inhibit seed germination, leading to poor seed germination rate (Zhu et al., 2016). However, there are few studies showing the relationship between GI and ions, especilly metal ions. Sole-Bundo et al. (2017) investigated the toxicity of NH4+-N of the digestate from microalgae anaerobic digestion and co-digested with sewage sluge. Meng et al. (2019) reported that NO3-N was a better N source for plant growth than NH4+-N, as it was related to the mineralization of organic matter and the N concentrations of the mineral fraction. Gavilanes-Teran et al. (2016) showed that GI was positively correlated with humification parameters, which were related to organic matter, humus and salinity.

To counteract salinity stress, plants have evolved various antioxidant defense systems (enzyme reaction) to minimize the negative impacts of reactive oxygen species, which was generated as byproducts of unnormal aerobic metabolism under salinity stress, and led to the acumulation of malondialdehyde (MDA) (Wu et al., 2019). Thus, the activities of protective enzmes, such as catalase (CAT) and peroxidase (POD), and the content of MDA are important indicators of plant responses to abiotic stress. Nawaz et al. (2012) stated the activities of CAT and POD was enhanced and the content of MDA was reduced during the germination of tomato seed under salt stress. Shah et al. (2012) proved Cd2+ stress significantly increased the H2O2 and MDA levels together with increased activities of POD and CAT in rice seed. Zhang et al. (2017) found seed germination rate, germination potential, POD and CAT activity were significantly correlated with salt concentration.

However, the relationships between other mineral ions (such as K+, Na+, Fe3+, Mg2+ and Ca2+), heavy metals (Cu2+, Zn2+ et al.) and GI are not clear, and their effect sequence on GI has not been previously studied. Furthermore, how these elements influence seed germination is still unknown. Therefore, this study evaluated CM co-composted with TP and MS to investigate the effects of salt and metal ions of compost extract on GI; the ions were placed in order according to the extent of their effect on GI. The enzyme activities of CAT and POD and the concentration of MDA in seeds were also analyzed, to reveal the phytotoxicity mechanism of salt and metal ions of compost extract on seed germination.

Section snippets

Composting materials and design

The raw material was CM, which was collected from a local chicken farm (Beijing, China). The auxiliary materials, TP and MS, were obtained from Guizhou Tobacco Research Institute and a local mushroom garden, respectively, in Guizhou, China. The properties of the raw materials are shown in Table 1.

Composting was conducted in a 60 L cylindrical stainless-steel reactor (0.6 m high, 0.36 m inner diameter) at the Shangzhuang Experimental Station of China Agricultural University, Beijing, China. The

Maturity index

GI is the most important parameter to evaluate the phytotoxicity of mature compost as it directly examines the effect of compost on seed germination and seedling growth. Most studies found that compost with GI > 80% was considered free of phytotoxicity and adequately matured for use on plants (Nakhshiniev et al., 2014). The changes in GI during the composting process are shown in Fig. 1a. The GI of all treatments was very low in the initial stage because of the rapid degradation of organic

Conclusions

The GI had positively correlated with CAT and POD activities and negatively correlated with MDA content. GI was positively correlated with Cu2+, Zn2+, K+, Na+, Fe3+ and NO3-N, and negatively correlated with NH4+-N, Mg2+ and Ca2+ in the aqueous extract of compost. And Fe3+, Mg2+ and Zn2+ had the most significant impacts on seed germination (Fe3+ > Mg2+ > Zn2+). Mushroom substrate addition to chicken manure improved the maturity and reduced compost phytotoxicity.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This research was supported by the National Key R&D Program (2017YFD0800202) and a Research Project of the Cashmere Goat Industry (CARS-39-19) of China.

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