Elsevier

Bioresource Technology

Volume 297, February 2020, 122412
Bioresource Technology

Interaction effect of silo density and additives on the fermentation quality, microbial counts, chemical composition and in vitro degradability of rice straw silage

https://doi.org/10.1016/j.biortech.2019.122412Get rights and content

Highlights

  • As the silo density increased, the quality of rice straw silages improved.

  • Lactic acid bacteria (LAB) improved fermentation quality of rice straw silages.

  • Combination of enzymes and LAB and high silo density (>400 kg/m3) reached the best.

Abstract

This research evaluated the effect of molasses (M), cellulosic enzymes (E) and lactic acid bacteria (LAB) alone or in combination (M + LAB and E + LAB) on the fermentation quality, microbial counts, chemical composition and in vitro degradability of rice straw silages in different silo densities (200, 300, 400 and 500 kg/m3). The M or E groups alone increased the dry matter (DM) losses at low silo densities. Acetic acid produced by LAB-related groups significantly inhibited yeast and mould at the silo density of 300 kg/m3. Under high silo densities (>400 kg/m3), LAB-related additives significantly improved the fermentation quality and reduced the DM losses. The use of E + LAB further improved the in vitro degradability of rice straw silages at high silo densities. In conclusion, higher silo density and appropriate complex additives were of great significance to improve the quality of rice straw silage.

Introduction

Rice cultivation is the main form of agricultural production in the plain area of South China (Chen et al., 2011). Much of the rice straw is used for biofuel or roughage. In view of the humid and rainy climate in Southern China, ensiling is a feasible processing method for the storage of rice straw. The low water-soluble carbohydrate (WSC) content and lactic acid bacteria (LAB) counts in rice straw prevent the pH from decreasing rapidly, and the pH will not be low enough to inhibit harmful microorganisms (Oladosu et al., 2016). As a result, it is difficult to obtain high-quality silage from rice straw alone (Li et al., 2010).

In a previous study, the use of exogenous LAB was indicated to have good effects on rice straw silage (Gao et al., 2008). At present, most LAB additives used have been mixtures of homofermentative LAB and heterofermentative LAB (Oliveira et al., 2017). Complex LAB additives used in this study were shown to be effective for gramineous crops or grass silages (Liu et al., 2019). There are two ways to improve the WSC content in rice straw. One method is to add cheap sources of exogenous WSC, such as molasses and distiller grains (Yuan et al., 2016). The other method is to degrade cellulose into monosaccharides or oligosaccharides, which can be used by LAB with the addition of cellulose degradation enzymes (Tian et al., 2014). Sufficient WSC not only provides sufficient substrates for lactic acid bacteria fermentation but also increases the nutritional quality of rice straw silage.

The hollow stalk of rice straw is difficult to compact, resulting in a large amount of oxygen remaining in silage during early ensiling which made rice straw silages more susceptible to the negative effects of low silo densities in the actual production process than corn silages (Oladosu et al., 2016). Insufficient compacting density during silage production may lead to air permeability and aerobic deterioration of silage and then lead to the proliferation of yeasts, moulds, and other undesirable microorganisms, thereby increasing the loss of dry matter (DM) and nutrition (Anesio et al., 2017, Sucu et al., 2016). Yeasts, moulds and mycotoxins produced by moulds in rice also have potentially negative effects on animal and human health (Sun et al., 2017).

The studies mentioned above about the effect of additives on rice straw silages were mostly conducted under the condition of high silo density, while few studies have been conducted on whether different additives have effects under the condition of low silo density. On the basis of high silo density, higher density may not have any significant effect on the silage (Yildiz, 2017). It is of great practical significance to select the right additive combination for rice straw silage under several different silo density conditions, and more research is needed on the interaction between silo density and different additives. In this study, the effects of single and combinations of LAB, molasses and enzymes on the fermentation quality, nutritional value, microbial counts and in vitro degradability of rice straw silage with different silo densities were analysed.

Section snippets

Preparation of rice straw silages

The rice (Nanjing 46, hybrid rice supplied by the Institute of Food Crops, Jiangsu Academy of Agricultural Science, Jiangsu, China) was harvested at the full ripening stage at the experimental station of the Jiangsu Academy of Agricultural Science in November. The rice straw was obtained after threshing and cut to 1 cm using a guillotine cutter. The additive was evenly sprayed onto the rice straw, and the DM content was adjusted to 33.75% fresh matter (FM) (original DM content of rice straw was

Raw materials of rice straw

The WSC (6.86% DM) content of rice straw materials in our study was suitable for silage fermentation (Woolford and Pahlow, 1998) and was much higher than that reported (1.59% DM) in the study of Li et al. (2017), but similar to that reported (6.38% DM) in the study of Zhao et al. (2019). Study of Dong et al. (2012) have shown that there were significant differences of non-structural carbohydrates including soluble sugars and starches in rice straw among different varieties. The combination of

Conclusions

The quality of rice straw silage was determined by the characteristics of raw materials, silo density and additives. The use of the M or E group alone is risky for rice straw silages. L. buchneri is active at 300 kg/m3, while L. plantarum and L. paracasei gradually take the lead with increasing silo density. The use of complex additives, E + LAB, further improved the IVDMD, IVNDFD and IVADFD of rice straw silages. It is important to select compound additives according to the raw material and

CRediT authorship contribution statement

Jipeng Tian: Methodology, Investigation, Formal analysis, Writing - original draft. Nengxiang Xu: Methodology, Data curation, Resources, Investigation. Beiyi Liu: Resources, Investigation. Hailin Huan: Resources, Investigation, Validation. Hongru Gu: Methodology, Writing - review & editing. Chenfei Dong: Methodology, Writing - review & editing. Chenglong Ding: Conceptualization, Methodology, Project administration, Funding acquisition.

Acknowledgment

This work was financially supported by the Agricultural Innovation Fund of Jiangsu Province (grant no. CX[17]3037).

Declaration of Competing Interest

Authors declare that they have no competing interests.

Ethical approval

This article does not contain any study with human participants or animals reported by other authors.

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