Tropical agricultural soils have been claimed as a source of carbon. As agricultural systems in the tropics are highly diverse, it is useful to study soil organic C (SOC) of different agricultural systems. We quantified the SOC fractions, available nutrients, and aggregate stability in eight different tropical agricultural systems, including annual crops under different management scenarios, such as organic, inorganic, and combined fertilizer applications. Annual crops treated with organic fertilizer only (A–OF), inorganic fertilizer only (A–IF), both organic and inorganic fertilizers (A–O/IF), perennial crops (PC), home gardens (HG), and abandoned home gardens (AHG) in Eutrustox soils and annual crops with organic fertilizer only (A–OFS) and uncultivated land on Quartzipsamments soil (USR) were studied. The links between SOC fractions, available nutrients, and aggregate stability in these soils were analyzed. Regression models were fitted for SOC fractions and available nutrients. Our results indicated that the different land use types exhibited significant variations in organic carbon fractions, aggregate stability, and available nutrients in soils. The available macro and micronutrients, except for nitrogen, showed a significant positive correlation with either total organic C (TOC) or carbon fractions indicating the synergy between them. The differences in soil C stocks clearly reflected the differences in litter fall and soil disturbance, as indicated by the highest C stocks in AHG. The dry weight of collected litter showed that AHG accumulated the highest litter content (97.38 g/m²) compared to the lowest (37.63 g/m²) in A–I/F. Organic matter addition to soil also increased the C stocks, even in annual crops. Aggregate stability showed a positive correlation with C fractions. The regression models developed in this study can be used to predict available nutrients by measuring TOC or C fractions in similar land use types in the tropics. This study confirmed that tropical agricultural systems that include annual crops have potential for storing and maintaining C in soils, if appropriately managed. The beneficial influence of SOC on available nutrients and aggregate stability could be a driving force to increase carbon stock in tropical agricultural systems.

Ever growing population and environmental degradation lead to a rapid deterioration of global health, causing malnutrition and Ultra Violet radiation-induced skin damages to be more prevalent. It is critical to address these health issues quickly and sustainably. Compared to natural botanicals, cyanobacteria could be more promising due to their superior photosynthetic capabilities, rapid growth, low space and simple nutrients requirements, low capital investment, and zero environmental pollution. Therefore, this study explores the value added potential of freshwater cyanobacteria in addressing the above health issues sustainably. Eight cyanobacteria strains, isolated from freshwater reservoirs in the dry zone of Sri Lanka were analyzed for total carbohydrate, protein, macro and micro minerals using Dubois’ method, Lowry method, and Inductively Coupled Plasma Optical Emission Spectrometry. Mansur equation was applied to determine the Sun Protection Factor (SPF). Total carbohydrate and protein contents were in the range of 7.08 ± 0.32% - 53.08 ± 0.32% and 15.27 ± 0.90% - 49.77 ± 9.62%, respectively. Oscillatoriales had the highest total carbohydrate content (53.08 ± 0.32%), higher than the carbohydrate content of other previously reported Oscillatoria species. Calcium and iron were the most abundant macro and micro minerals, respectively. Oscillatoriales recorded the highest SPF (1.57 ± 0.002), whereas all the other strains had considerably greater or similar SPFs compared to other previously reported herbal extracts. Cyanobacteria with rich nutrition profiles and high SPF values may thus represent interesting alternatives for offering sustainable and ecofriendly solutions to significant health challenges associated with population growth.

The present study investigated the potential of two cyanobacterial species, namely Nostoc ellipsosporum (NE) and Spirulina subsalsa (SS), to remediate textile wastewater (TWW) while obtaining wastewater-grown biomass for biodiesel production. This study reports their multi-faceted benefits using unsterilized and undiluted (100%) TWW for the first time. Both cyanobacterial species were cultivated in TWW under greenhouse conditions, focusing on their growth, TWW decolorization, pollutant removal, phytotoxicity, lipid content, and fatty acid profile. Results demonstrated significant growth and decolorization of TWW by both species, highlighting their potential for sustainable treatment of TWW. NE-treated TWW (NE-TWW) achieved a chemical oxygen demand (COD) removal efficiency of 96.48%, while SS-treated TWW (SS-TWW) reached 93.11%. Ammonia removal efficiencies were recorded as 76.28% for NE-TWW and 96.86% for SS-TWW. NE-TWW and SS-TWW achieved nitrate removal of 69% and 73%, respectively. Phosphate removal was 81.14% for NE-TWW and 33.33% for SS-TWW. Both species exhibited more than 75% removal of heavy metals, particularly Cr, Fe, Zn, Cu, and Ni. Seed germination studies showed enhanced germination and seedling growth of green gram (Vigna radiata) when irrigated with NE-TWW and SS-TWW, indicating phytotoxicity reduction in treated TWW. Lipid yields (w/w) of 21.5% and 25% were recorded from TWW-grown biomass of NE and SS, respectively. Both species exhibited favorable fatty acid methyl ester (biodiesel) profiles, dominated by palmitic acid (C16:0), oleic acid (C18:1), stearic acid (C18:0), lauric acid (C12:0), and myristic acid (C14:0), indicating their suitability as biodiesel feedstocks. Overall, this integrated approach not only provides an eco-friendly and cost-effective strategy for TWW treatment but also offers a sustainable feedstock for biodiesel production.