Effect of storage on the properties of vermicompost generated from paper waste: with focus on pre-drying and extent of sealing

M. Karthikeyan 0 S. Gajalakshmi 0 S. A. Abbasi 0 Corg Cdis Ntot NH 0 ?-N NO 0 --N 0 0 M. Karthikeyan S. Gajalakshmi S. A. Abbasi (&) Centre for Pollution Control and Environmental Engineering, Pondicherry University , Chinnakalapet, Puducherry 605014, India The beneficial effects of vermicast on soil fertility in general, and agriculture in particular, are widely recognized, but there are no reports on the effect of storage on vermicast quality. The present study is an attempt to cover this knowledge gap as it may assist in the formulation of guidelines for packaging and storing of vermicast in a manner that preserves the cast's fertilizer value. Vermicast generated from paper waste was packed in airtight and partially sealed bags with and without pre-drying for 24 h. Changes in several physical, chemical, and biological properties of the castings were monitored for 3 months with weekly assessments. The results reveal that the beneficial properties of vermicast were the highest when it was fresh. There was deterioration on storage, which can be minimized if the castings are contained in airtight bags after pre-drying the casts. - The vermicast that is deposited by the earthworms on the soil is known to fertilize the soil as well as influence its physical and chemical properties in a way that is beneficial to plant growth in particular and soil environment in general. Due to this realization, several studies have been conducted on the fate of vermicast, especially how the biological, chemical, and physical attributes of the vermicast change with time [111]. These studies have been on either vermicast generated from non-specific substrates in nature or from blends of soil and phytomass. The focus of the studies has been primarily on the stability of vermicast generated by anecic and endogeic (geophagous and geophytophagous) earthworm species as such casts are rich in soil and influence the stability of biogenic structures. Very few studies have been done on epigeic or phytophagous (humus feeder) species. Moreover, when vermicast is deposited in nature, its fate is strongly influenced by (a) soil dwelling invertebrateswhich colonize the vermicast and feed upon the organic matter it contains [5, 12]; (b) vegetationwhich takes up the nutrients from the castings [13]; (c) soil microbes including autotrophic algae, nitrification bacteria or fungiwhich are involved in fixation of atmospheric CO2 [13]; (d) immobilization or mineralization of nutrients in the vermicast by soil microorganisms [14], and (e) environmental factors such as rain, flooding, or drought. A few controlled studies have been reported on the change in the properties of vermicast upon aging [1, 6, 15 19]. These studies have primarily aimed to simulate the conditions which the biogenic structures experience in nature. For this, the casts were generated from either soil or blends of soil and phytomass and stored in soil/sand columns. It was seen that the soil particles present in the casts get chemically bound with organic matter, perhaps through chelation, which increases the stability of the casts. It also protects the organic matter content of the casts from decomposition [15, 20], as the organic matter that is attached to the minerals with strong chemical bounds is less accessible to microorganisms [21]. In addition, extracellular enzymes are protected from degradation or proteolysis by the clay minerals contributed by the soil [22]. In contrast to the focus of the prior art summarized as above, the conditions associated with the storage of vermicast when it is produced by anthropogenically controlled vermicomposting and for the specific purpose of use as a fertilizer are very different. The concern here is to ensure that the vermicast retains as many and as much of the plant-friendly attributes as does fresh vermicast and the physical integrity of the cast is not of much significance. The only pre-existing studies on the effect of storage on vermicompost [3, 4], have been based on the use of 2-month-old press-mud as feed for earthworms, and assessment of the changes in major nutrients (N, P and K), microbial activity and enzyme activity of the vermicast that was generated. In these studies, the environmental conditions under which the casts have been exposed during the agingeither in vermireactors or in a controlled systemhave not been defined. Also, the studies were done only at two stages15th and 30th day of vermicast generation. Hence, no useful pointers can be drawn from these studies on the impact of storage. The present study, which is perhaps the first of its kind, explores the changes in the physical, chemical and biological properties of vermicast that occur during storage with the objective of finding conditions that minimize the deterioration in the fertilizer value of the vermicast. The studies provide useful pointers on how best to store and package vermicast. Materials and methods Types of storage The vermicompost used in the present work was generated from paper waste and the epigeic species, Eudrilus eugeniae. As paper waste is almost entirely cellulosic, with only traces of elements other than C, H, and O, the feed was spiked with 9 % w/w of cow dung to provide NPK and other nutrients in adequate amounts. The vermicomposting was accomplished with a high-rate process recently developed by the authors group [23]. The vermireactors were fabricated with aluminum sheets and each had a volume of 135 l (15 cm height with surface area 150 9 60 cm). The vermicast was harvested after 30 days. One part of it was stored in two types of packs: (a) airtight sealed transparent polyethylene bags of 20 lm thickness (AUD) and (b) partially sealed nylon mesh (0.3 mm) bags (PUD). Both types of bags were 25 cm long and 18 cm wide, each capable of holding half kg of vermicompost. Another part of the casts was pre-dried for 24 h at room temperature (29 4 C) and stored in both airtight sealed transparent polyethylene bags (APD) and partially sealed nylon mesh bags (PPD). In each set, 36 packs were utilized; overall 144 packs were studied. All storage was at room temperature (29 4 C) as this is the temperature at which vermicast is handled in the region where the authors work. Three packs of vermicast were taken once in a week for physical and biochemical analysis from each storage. Physical properties. To estimate bulk density, sample volume was measured with a graduated cylinder and its dry weight determined by oven drying [24]. The particle density was determined by volumetric flask method [24]. The quotient value of weight of the sample and its volume which was measured through volume of water displaced by known amount of soil sample in the volumetric flask is reported as particle density. To measure the water holding capacity, the samples were filled in cylinders with a perforated base and immersed in water and drained. The quantity of water taken up by samples is determined by drying to constant (...truncated)