Dual-action Organic Fertilizers: Growth-stimulatory and Nematicidal Potential of Azadirachta indica and Tagetes erecta Extracts

Abstract

Botanical resources such as Azadirachta indica (neem) and Tagetes erecta (marigold) are increasingly recognised for their potential to support sustainable agriculture through their combined growth-promoting and nematicidal properties. Neem comprises an extensive range of limonoids (e.g, azadirachtin, salannin), phenolics (e.g., tannins), and flavonoids (e.g., quercetin) that have been linked to reducing nematode infection in plants by inhibiting egg hatching, increasing juvenile mortality, and improving soil nutrient dynamics. Marigold, on the other hand, is a source of thiophenes, monoterpenes, and essential-oil constituents such as α-terthienyl that restrict nematode proliferation, induce oxidative stress, and inhibit reproductive development in Meloidogyne species. Along with their pest-suppressive ability, the organic amendments prepared from neem seed cake, marigold residues, composts, and integrated nutrient supplements have shown encouraging effects on chlorophyll content, nutrient assimilation, and overall vegetative and reproductive performance across several crops. Such amendments also enhance the activity of beneficial soil microbes, improving the soil quality. Although the degree of efficacy varies with environmental conditions and application methods, the findings suggest that both plants may serve as practical, environmentally safe alternatives to chemical fertilisers and synthetic nematicides. This review aims to integrate the current scientific knowledge about the two plant species, focusing on their phytochemical diversity, nematicidal functions, and their utility in enhancing soil and plant health. The available evidences suggest that neem and marigold can effectively contribute to holistic soil management and sustainable pest control, supporting efforts to reduce chemical inputs while maintaining crop productivity.