Abstract
Rock phosphate (RP) addition in cow-dung waste-paper mixtures at rates above 2% P has been reported to increase the rate of bio-transformation and humification of organic waste mixtures during vermicomposting to produce organic fertilizer for organic farming. However, the optimization of RP for vermicomposting was not established. The objective of this study was to determine the optimal amount of RP integration rates for effective bio-transformation of cow-dung waste-paper mixtures. Arrays of RP integration degrees (0, 0.5, 1, 1.5, 2, and 4% P as RP) were thoroughly mixed with cow- dung waste-paper mixtures to achieve an optimized C:N ratio of 30 and allowed to vermidegrade following the introduction of earthworms at a stocking mass of 12.5 g-worms kg−1. The bio-transformation of the waste mixtures was examined by measuring C:N ratios and humification index (HI) and per cent ash and volatile solids. Application of 1% P as RP resulted in fast bio-transformation and maturation of cow-dung waste-paper mixtures. A scanning electron microscopy (SEM) was used to evaluate the morphological properties of the different vermicomposts affected by rates of RP showing the degree of degradation of initial compacted aggregates of cellulose and protein fibres in the mixtures at maturity. A germination test was used to further determine phytotoxicity of the final composts and microbial biomass assessment. The final vermicompost (organic fertilizer) had a C:N ratio of 7, MBC of 900 mg kg−1 and HI of 27.1%. The RP incorporation rate of 1% P of RP investigated is therefore, recommended for efficient vermidegradation and humification of cow-dung waste-paper mixtures. However, higher rates of RP incorporation should be considered where greater P enrichment of the final vermicompost (organic fertilizer) is desired.
Highlights
Vermicomposting has proved to be a suitable technique of processing biodegradable organic wastes and converting them to organic fertilizers, because of its low cost and the large quantity of wastes that can be processed (Lim et al 2016; Wu et al 2014)
The over 80% germination index (GI) observed for all test crops in this study indicated that addition of P as Rock phosphate (RP) to cow-dung-waste paper mixtures in the presence of E. fetida resulted in vermicompost that was free of phytotoxins, according to (Zucconi et al 1981; Tam et al 1998)
The results of this study have confirmed that incorporation of rock phosphate improves the biodegradation of cow-dung-paper-waste mixtures
Summary
Vermicomposting has proved to be a suitable technique of processing biodegradable organic wastes and converting them to organic fertilizers, because of its low cost and the large quantity of wastes that can be processed (Lim et al 2016; Wu et al 2014). Unuofin et al SpringerPlus (2016) 5:1986 by the types of the substrates used and the degree of composting (Matiullah and Muhammad 2012; Mupondi 2010; Yan et al 2012). In order to increase the acceptability of vermicompost products as sources of nutrients or as growing media, it is essential to increase their P contents. Biswas and Narayanasamy (2006) found that it is possible to increase the total P content of straw compost from 0.37% in control to 2.20% by adding 4% P as RP, while (Yan et al 2012) increased the total P of rice straw vermicompost from 0.392 to 0.82% by adding 2% P as RP. Biswas and Narayanasamy (2006) found that it is possible to increase the total P content of straw compost from 0.37% in control to 2.20% by adding 4% P as RP, while (Yan et al 2012) increased the total P of rice straw vermicompost from 0.392 to 0.82% by adding 2% P as RP. Matiullah and Muhammad (2012) increased the total P content in poultry litter from 0.3 to 1.02% by adding 4% P as RP
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