Purpose The disposal of solid waste is a serious environmental problem for humanity. Vermicomposting is used as one of the methods for recycling of organic waste, resulting in a humified material of great agronomic potential which promotes carbon sequestration when applied to the soil. The aim of this study was to evaluate the chemical characteristics of vermicomposts from cattle manure (CM), orange peel (OP) and filter cake (FC). Methods Three compost piles were set up, 2:1 OP + CM, 3:1 FC + CM and CM. The piles were initially composted for 60 days. Thereafter, earthworms were added to the piles to initiate the vermicomposting process. Results The pH and the organic carbon contents were above the minimum recommended values for organic fertilizers. The N content was below the minimum value but the C/N ratio was in the required range. The C/N values where lower in OP + CM and FC + CM than in CM. Further, the N contents of treatments were different with OP + CM having the highest value. The C/N ratios of the piles were 9.52, 9.62 and 11.03 for OP + CM, FC + CM and CM, respectively, and were lower than the maximum recommended value by the Ministry of Agriculture, Livestock and Food (Ministry of Agriculture 2009). Conclusion Thus, co-vermicomposting of filter cake and orange peel with cattle manure has the potential for application sustainable agriculture.

Application of crop residues and biochar have been demonstrated to improve soil biological and chemical properties in agroecosystems. However, the integrated effect of organic amendments and hydrological cycles on soil health indicators are not well understood. In this study, we quantified the impact of hemp residue (HR), hemp biochar (HB), and hardwood biochar (HA) on five hydrolytic enzymes, soil microbial phospholipid (PLFA) community structure, pH, permanganate oxidizable carbon (POXC) soil organic carbon (SOC), and total nitrogen (TN). We compared two soil types, Piedmont and Coastal Plain soils of North Carolina, under (i) a 30-d moisture cycle maintained at 60% water-filled pore space (WFPS) (D-W1), followed by (ii) a 7-day alternate dry-wet cycle for 42 days (D-W2), or (iii) maintained at 60% WFPS for 42 days (D-W3) during an aerobic laboratory incubation. Results showed that HR and HB significantly increased the geometric mean enzyme activity by 1-2-fold in the Piedmont soil under the three moisture cycles and about 1.5-fold under D-W in the Coastal soil. In the presence of HA, the measured soil enzyme activities were significantly lower than control under the moisture cycles in both soil types. The shift in microbial community structure was distinct in the Coastal soil but not in the Piedmont soil. Under D-W2, HR and HB significantly increased POXC (600–700 mg POXC kg^-1 soil) in the Coastal soil but not in the Piedmont soil while HA increased nitrate (8 mg kg^-1) retention in the Coastal soil. The differences in amendment effect on pH SOC, TN, POXC, and nitrate were less distinct in the fine-textured Piedmont soil than the coarse-textured Coastal soil. Overall, the results indicate that, unlike HA, HR and HB will have beneficial effects on soil health and productivity, therefore potentially improving soil’s resilience to changing climate.

The combination of inorganic fertilizers and compost is a technique aimed at improving crop growth and maintaining soil health. Understanding the rate of nutrient release from enriched compost is important for effective nutrient management. A laboratory incubation study was conducted for 112 days to study the nutrient mineralization pattern of poultry manure compost enriched with inorganic nitrogen (N) and phosphorus (P) fertilizer nutrients in an Ultisol. Compost applied at the rate of either 5 or 10 g kg⁻¹ was blended with N (50 kg N ha⁻¹) and P (30 kg P ha⁻¹). Carbon dioxide evolution and N and P mineralization were measured fortnightly. The bacterial and fungal populations were determined at the mid and end of the experiment. The combination of compost and inorganic N and P increased carbon (C) and P mineralization by 4−8% and 56−289%, respectively, over the application of either compost or inorganic N and P. However, P addition influenced the amount of C mineralized. Inorganic N and P, on the other hand, were better at increasing N mineralization than compost blended with inorganic N and P over a short time. The addition of compost stimulated bacterial and actinomycete populations, while fungal populations were unaffected. Actinomycetes and bacteria had similar and higher relationship trend with C (R² = 0.24) and P (R² = 0.47) mineralization and were key determinants in nutrient mineralization from compost in this Ultisol. Integrating compost with inorganic fertilizers improves nutrient availability through the growth and activities of beneficial microorganisms.

Enhancing soil health is critical to improve crop productivity, fertilizer use efficiency, and resilience to climate change impacts for smallholder farmers in Africa. Increasing the use of mineral fertilizers is critical for achieving higher crop yield and residue return. However, it is crucial to consider the simultaneous use of carbon (C)-rich organic materials alongside mineral fertilizers to support soil health and enhance fertilizer use efficiency. It is proposed that increasing mineral fertilizer use without a concurrent increase in C-rich organic materials may not enhance soil organic carbon (SOC) and soil health in the long term. When the labile pool of nutrients is increased through mineral fertilizer, it can reduce microbial C use efficiency, thereby hindering the formation and stabilization of SOC. This reduction in efficiency can cause a more significant proportion of the returned plant residues to be lost as CO₂ through microbial respiration rather than being incorporated into the SOC pool. However, this effect can be mitigated by the concurrent application of large amounts of organic amendments, such as compost, manure or biochar, which provide a balanced supply of nutrients and C substrates to support microbial activity and enhance SOC formation.