Soil erosion in hilly terrain contributes to declines in soil organic matter and fertility, which can be mitigated through regular application of organic inputs. Heterogeneous solid organic materials can be converted into compost through biological degradation under controlled, moist, self-heating and aerobic conditions, producing an organic fertilizer (Mandloi et al., 2026). Compost can increase soil organic matter, improve nutrient uptake and promote crop production (Luo et al., 2017; Seleiman et al., 2022). It can also function as a biofertilizer and soil amendment by increasing soil pH, improving soil properties and reducing greenhouse gas emissions (Razza et al., 2018). Composting is an effective approach for agricultural waste management and may help conserve energy (Cheptoek et al., 2021; Ho et al., 2022). However, traditional composting may result in losses of organic matter (approximately 55%) and nitrogen (30-50%) (Kumaraswamy, 2001). Enriched composts are receiving attention as alternatives to conventional compost because they are less bulky, require less production time and contain higher nutrient concentrations. Inclusion of nutrient-enriched compost in integrated nutrient management has been reported to increase field-crop productivity and improve soil quality parameters in Nagaland and Meghalaya (Bordoloi et al., 2019). Vermicompost, produced through decomposition of organic wastes by earthworms such as Eisenia fetida, Eudrilus eugniae and Perionyx excavates, is a rich source of plant nutrients and micronutrients and generally has a low C:N ratio with enhanced microbial and enzymatic activity that may facilitate nutrient uptake (Hussain et al., 2017). Integrated application of vermicompost with FYM, azotobacter and inorganic fertilizers has been reported to enhance maize yield and quality (Arumugam et al., 2025) and improve available nutrient contents and organic matter in soils under maize cultivation (Singh et al., 2024).
       
Azolla may contain 3-6% nitrogen, 0.5-0.9% phosphorus and 2-4.5% potassium (Sonowal et al., 2021). Enrichment of azolla has been reported to result in a lower C:N ratio and higher nitrogen content than fresh azolla (Ebrahim et al., 2024). Processing technology has enabled conversion of azolla biomass into powders, extracts and fortified ingredients (Chandrababu et al., 2025). Azolla can supply approximately 35-50% of fixed N to paddy fields, highlighting its potential as an organic fertilizer for other crops, including leafy vegetables (Rashid et al., 2024). Application of azolla compost can improve soil properties and nutrient uptake by crops (Sanjay-Swami and Singh, 2019). In India, organic farming is expanding in hilly areas (Shahane and Shivay, 2022), where composts can serve as important inputs for soil health management. Agriculture in Nagaland is organic by default. Increasing crop productivity through chemical fertilizers is not considered effective because fertilizer use efficiency is low under high-rainfall conditions. Some local communities also show reluctance towards synthetic fertilizers. Crop residues are abundantly available (Bujarbaruah, 2004), along with diverse weed species, providing scope for producing quality compost from crop residues and weed biomass in the North-Eastern hill region (Chatterjee et al., 2016). The present investigation was undertaken to produce PSN-enriched compost, vermicompost and azolla compost using locally available substrates and compare their chemical and biochemical properties under the local hill agro-ecological conditions of Nagaland.

The experiment was conducted over two consecutive years, 2023 and 2024, at the School of Agricultural Sciences, Nagaland University. Three compost types were produced using locally available substrates, viz. banana pseudo stem, green weed biomass (mixed weed spp.), finely chopped paddy straw and FYM. Phospho-sulpho-nitro enriched compost (PSN-enriched compost) was produced in earthen pits under a galvanized-sheet shed. Vermicompost was produced in portable vermibags placed under the shed, while azolla compost was produced in concrete pots under the shed. Five replicated units were used for each compost type.
 
Production of PSN-enriched compost
 
The substrate materials were chopped, mixed. Approximately 200 kg of dry + fresh substrate materials were placed in each replicated unit of size 1.8 m × 1.2 m × 0.5 m (l × b × h), layer-wise, following procedure described by Bordoloi et al. (2019). Cow dung slurry (1 part raw cow dung: 1 part water) was sprinkled over each layer. Mineral additives, viz. 0.5% urea, 1.5% rock phosphate and 0.5% elemental sulphur, were added for enrichment over each substrate layer. After filling the pit with substrate layers, each approximately 20 cm thick, up to 30 cm above ground level, the top was sealed with cow dung slurry. Units were monitored regularly. Watering and turning were carried out at 15-day intervals. Compost was harvested at 3.5 months ± 10 days.
 
Production of vermicompost
 
Vermicompost was produced in portable vermibags (2.4 m × 1.2 m × 0.5 m, l × b × h) using the same substrates as PSN-enriched compost. Chopped substrates were placed layer-wise, with well-decomposed cow dung between successive layers. Water was sprinkled to maintain adequate moisture and the top layer was covered with cow dung slurry. About 2000 earthworms of Eisenia fetida were released onto the top cow dung layer. Approximately 200 kg of substrate was used per unit. Turning and watering were carried out at 15-day intervals. Vermicompost was harvested after 3.5 months ± 10 days.
 
Production of azolla compost
 
Azolla caroliniana was mass-cultured in an earthen multiplication unit (1.5 m × 1.0 m × 0.5 m, l × b × h). Fresh azolla inoculum was collected from the ICAR Research Complex for the NEH region, Nagaland centre, Jharnapani (Nagaland). The interior of the earthen multiplication unit was lined with low-density polythene sheet and azolla was multiplied while maintaining a water level of 20 cm. Fresh azolla biomass was harvested weekly (average fresh weight 2.5 kg week^-1) and accumulated in concrete pots for composting under a shed. Batch-wise harvesting and accumulation continued for 2.5 months. Approximately 25 kg of fresh azolla was harvested in 10 weeks. For compost production, 20 kg of harvested azolla was mixed with 10 kg of well-decomposed cow dung (2:1 azolla:cow dung). The mixture was then divided equally among five replicated pots and cured for one month.
       
Although the three composting systems differed in substrates and biological processes, the maturation period was considered the same (3.5 months ± 10 days) based on apparent stabilization, indicated by conversion of original substrates into dark black, granular substances. This common period provided a standardized condition for comparison among compost types.
       
The stabilized compost in each unit was thoroughly mixed. Five samples were collected from each replicated unit, mixed and homogenized to get one composite sample. Altogether, 15 composite samples were collected from 15 replicated units for laboratory analysis. Oven-dried samples were used for chemical analysis, whereas fresh samples were used for biochemical analysis. Organic carbon (OC) was determined by wet oxidation method (Walkley and Black, 1934). Total carbon (TC) was determined using a TOC analyzer at the ICAR Research Complex for North Eastern Hill Region, Barapani. Compost samples were digested with concentrated sulphuric acid in the presence of digestion mixture and nitrogen content was determined by the Kjeldahl method (Jackson, 1973). Phosphorus and potassium contents were determined by wet digestion method. Samples were digested in a di-acid mixture (HNO₃ :HClO₄,3:1). In the filtered extract, phosphorus was determined by the vanadomolybdate yellow colour method using a spectrophotometer, while potassium was determined using a flame photometer (Jackson, 1973). The pH was determined in a 1:2.5 compost: water suspension using a glass-electrode pH meter (Jackson, 1973). Microbial biomass carbon (MBC) was determined by the fumigation-extraction method described by Vance et al., (1987). Ethanol-free chloroform was used for fumigation in a vacuum desiccator. After 24 h, fumigated and non-fumigated samples were extracted with 0.5 M K₂SO₄. Potassium dichromate, concentrated H₂SO₄ and concentrated H₃PO₄ were added to the filtered extract, which was titrated against 0.005 N ferrous ammonium sulphate adding diphenylamine indicator. Total extractable carbon in fumigated and non-fumigated samples was calculated. MBC was calculated as:

 

 

Where,
EC_F = Total weight of extractable C in the fumigated compost sample.
EC_NF = Total weight of extractable C in the non-fumigated compost sample.
K_EC = calibration factor ~ 0.38.
       
Dehydrogenase enzyme activity (DHA) was determined using the 2,3,5-triphenyl tetrazolium chloride reduction technique (Casida, 1977). A 10 g compost sample was mixed with 0.1 g CaCO₃, divided into three portions (3 g each) and transferred to three screw-cap, flat-bottom test tubes (15 ml capacity). Each tube received 0.5 ml of 1% 2,3,5-triphenyl tetrazolium chloride (TTC) and 1.25 ml of distilled water. The contents were mixed and incubated at 37°C for 24 h. The suspension was filtered through a glass funnel fitted with absorbent cotton. Methanol was added to extract the suspension until the cotton plug became colourless. The final volume was made up to 50 ml. Reddish colour intensity was measured using a spectrophotometer at 485 nm. Triphenyl formazan (TPF) concentration was determined against a standard graph prepared from known TPF concentrations. DHA was expressed as μg TPF g^-1 on a dry-weight basis. Acid phosphatase activity (PHA) was determined by the p-nitrophenyl phosphate method (Tabatabai and Bremner, 1969). One gram of compost sample was placed in a conical flask and 4 ml of Modified Universal Buffer (pH 6.5), 0.25 ml of toluene and 1 ml of p-nitrophenyl phosphate were added and incubated at 37°C for 1 h. After incubation, 1 ml of 0.5 M CaCl₂ and 4 ml of 0.5 M NaOH were added and the suspension was filtered. Yellow colour intensity in the filtrate was measured at 400 nm using a spectrophotometer. p-nitrophenol concentration was determined against a standard curve prepared from p-nitrophenol standard solution. PHA was expressed as μg PNP g^-1 on a dry-weight basis. Serial dilution plate-count method (Johnson and Curl, 1972) was used to enumerate bacteria. One gram of sample was transferred to a serial dilution tube containing 9 ml of sterile water. A 1 ml aliquot of the homogeneous suspension was transferred and serially diluted up to 10^-4 , from which, 0.1 ml of suspension was transferred to nutrient agar plates, spread uniformly and incubated at 30 ± 1°C for 24 h. Bacterial colonies were counted in colony counter and expressed as × 10⁴  CFU g^-1 compost on a dry-weight basis.
       
The data were statistically analyzed using IBM SPSS 28.0 (2022). Data from each year were analyzed separately, followed by pooled analysis using a Completely Randomized Design (CRD) with one-way analysis of variance (ANOVA) (Gomez and Gomez, 1984). Treatment differences were tested at P = 0.05. Following the F-test, treatment means were compared using Duncan’s Multiple Range Test (DMRT), as described by Duncan (1955).

Quality parameters of composts
 
Chemical parameters
 
Azolla compost exhibited significantly higher organic carbon (16.93%), followed by PSN-enriched compost (12.99%) and vermicompost (12.80%). Significantly higher total carbon was also recorded in azolla compost (30.92%), followed by vermicompost (20.02%) and PSN-enriched compost (18.54%) (Table 1). These findings are in conformity with Rashid et al., (2024), who reported higher total carbon in composted azolla. The higher total and organic carbon content in azolla compost may be associated with the slower decomposition of azolla biomass resulting from phase-wise collection and subsequent composting, which may have temporarily reduced microbial activity and thereby retained more carbon than in the other composts. In addition, the organic manure added as well-decomposed cow dung during production may have contributed to the higher carbon content of azolla compost.


       
A significantly lower C:N ratio was recorded in PSN-enriched compost (9.29), followed by azolla compost (10.30) and vermicompost (12.73) (Table 1). These findings agree with Qureshi et al., (2014), who reported higher nutrient extractability and a narrower C:N ratio in rock phosphate-enriched compost. The addition of urea and rock phosphate during production may have increased the availability of minerals i.e. labile forms of nitrogen and phosphorus which perhaps facilitated conversion of substrate to compost with low C:N ratio.
       
Near-neutral pH value were recorded for PSN-enriched compost (7.08) and vermicompost (7.25), whereas comparatively lower pH was recorded for azolla compost (6.48) (Table 1). Qureshi et al., (2014) also reported a reduction in pH in rock phosphate-enriched compost.

The relatively low pH of azolla compost may be associated with the accumulation of organic acids and other acidic products during decomposition.
       
Higher electrical conductivity (EC) was recorded in vermicompost (3.67 dS m^-1), followed by azolla compost (3.51 dS m^-1) and PSN-enriched compost (3.08 dS m^-1) (Table 1). Similar findings were reported by Rashid et al., (2024). The higher EC of composts may be associated with increased salt concentrations (Iacomino et al., 2022). Greater nutrient release during decomposition of organic matter may also have increased the concentration of soluble salts and ions, thereby influencing the EC of the composts under study.
       
Significantly higher total N (3.00%) was recorded in azolla compost, followed by PSN-enriched compost (2.00%) and vermicompost (1.58%) (Table 2). Higher nitrogen content in composted azolla was also reported by Rashid et al., (2024). Anabaena azollae, which occurs in association with azolla and facilitates atmospheric nitrogen (N₂) fixation, enriches the fern with nitrogen (Candra et al., 2025). Comparatively lower nitrogen content in vermicompost under Nagaland conditions was reported by Jatoliya et al., (2019). The higher nitrogen content of azolla compost may primarily be attributed to the inherently high nitrogen content of azolla biomass associated with its symbiotic relationship with nitrogen-fixing cyanobacteria. In contrast, the organic materials used for PSN-enriched compost and vermicompost may have had lower initial nitrogen contents, which could explain their comparatively lower nitrogen levels. Greater nitrogen losses during decomposition may also have contributed to the lower nitrogen content of PSN-enriched compost and vermicompost.


       
Significantly higher phosphorus and potassium contents (0.607% and 1.91%, respectively) were recorded in PSN-enriched compost (Table 2). However, phosphorus and potassium contents in vermicompost and azolla compost were statistically at par (Table 2). The findings are in conformity with Bordoloi et al., (2019), who reported an increased phosphorus concentration in PSN compost. Qureshi et al., (2014) also reported greater nutrient extractability in rock phosphate-enriched compost. Hussain et al., (2017) reported similar findings, with higher mineral matter contents in enriched composts, including phosphocompost, nitrogen-enriched phosphocompost, phosphorus-enriched vermicompost and vermicompost, compared with conventional compost. The higher total phosphorus content in PSN-enriched compost may be attributed to fortification of the substrate materials with rock phosphate, which increased the phosphorus content of the final product.
 
Biochemical parameters
 
The biochemical parameters differed among the compost types, reflecting differences in the degree of decomposition and stabilization. Dehydrogenase activity, which is closely associated with the metabolic activity of viable microorganisms, was comparatively lower in PSN-enriched compost (13.66 μg TPF g^-1) and vermicompost (23.07 μg TPF g^-1) than in azolla compost (42.62 μg TPF g^-1) (Table 3). Acid phosphatase activity showed a different trend, with higher values in PSN-enriched compost (241.62 μg PNP g^-1) and vermicompost (104.57 μg PNP g^-1) and the lowest value in azolla compost (94.93 μg PNP g^-1). Significantly higher microbial biomass carbon and bacterial population were recorded in azolla compost (695.37 μg g^-1 and 96.55 × 10⁴ CFU g^-1), followed by vermicompost and PSN-enriched compost (Table 3). These findings are in conformity with Singh and Ganguly (2005), who reported lower dehydrogenase activity in fully matured compost because decomposition slows during maturation. Higher phosphatase activity in compost was also reported by Tognetti et al., (2005), while Hussain et al., (2015) reported higher microbial biomass carbon associated with greater microbial populations. The lower dehydrogenase activity in PSN-enriched compost and vermicompost may indicate greater stabilization of the organic substrates and reduced microbial oxidation of readily decomposable organic matter. In contrast, the relatively high dehydrogenase activity in azolla compost suggests continued microbial metabolism and decomposition of comparatively labile organic substrates. Elevated phosphatase activity may indicate a greater potential for biological transformation of organic phosphorus into forms that may become available for plant uptake. In PSN-enriched compost, the presence of rock phosphate may have influenced microbial P-transforming processes, contributing to the enhanced phosphatase activity and indicating P-cycling potential. Similarly, the higher microbial biomass carbon in azolla compost (695.37 μg g-1), together with the greater bacterial population (96.55 × 10⁴  CFU g^-1), supports the presence of an actively decomposing microbial community. Conversely, the comparatively lower microbial activity in PSN-enriched compost and vermicompost may be consistent with greater stabilization of organic matter, in which the readily available carbon fraction has already been utilized. Overall, the biochemical indicators suggest that azolla compost was biologically more active and underwent comparatively greater microbial decomposition, whereas PSN-enriched compost and vermicompost appeared more stabilized while retaining substantial nutrient-cycling activity.

The present study indicates considerable potential for producing quality composts under Nagaland conditions. These composts can serve as valuable sources of organic matter and plant nutrients, thereby reducing dependence on chemical fertilizers and supporting sustainable soil fertility management. Compost quality should be assessed using a combination of biochemical, chemical and maturity indicators rather than relying on a single parameter. A compost with higher nutrient content and lower dehydrogenase activity may represent a more stable product, whereas elevated phosphatase activity may indicate greater potential for phosphorus mineralization.

The present study was supported by Nagaland University, HQ: Lumami.
 
Disclaimers
 
The views and conclusions expressed in this article are solely those of the authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.

The authors declare that there are no conflicts of interest regarding the publication of this article. No funding or sponsorship influenced the design of the study, data collection, analysis, decision to publish, or preparation of the manuscript.