Influence of type and dose of organic wastes on the growth, quality and incidence of pests and diseases of carrots

Introduction Alternatives to chemical inputs are crucial for improving agricultural production and plant health management for sustainable agriculture, particularly in tropical environments, where pest dynamics and treatment effectiveness determine crop success. Because organic waste products differ in dry matter content, nutrient release, nutrient balance, and potential biological load, they may differentially affect plant nutrition, soil functioning, crop performance, and susceptibility to pests and diseases. These practices thus offer positive prospects for food quality and, consequently, human health while concomitantly reducing the risks associated with chemical inputs widely utilised in tropical agriculture. Material and methods We compared growth, quality and pest incidence of carrot crops repeated over three years and fertilised with a mineral fertilisers (MF) or different organic waste products (OWPs) at two levels (recommended dose-1 and double dose-1): sewage sludge (SS-1 and SS-2), poultry litter (PL-1 and PL-2), and methanisation digestate (AD-1 and AD-2). To ensure a nutritional balance consistent with the crop’s NPK requirements and between treatments, mineral nitrogen and potassium supplements were added to the OWPs when necessary. Results and discussion The results demonstrate that PL-2 significantly (p < 0.03) enhances leaf height, root size, dry matter content, and the number of marketable carrots. In contrast, AD-1 and AD-2 were associated with a higher incidence of Alternaria and dodder (p < 0.002), as well as with carrot root deformations related to dodder infestation (r = 0.88). Carrots cultivated with MF exhibited a higher incidence of nematode infestation compared to those under organic fertilisation, though these differences did not attain statistical significance (p > 0.1). These results indicate that OWP type and dose influence carrot growth, marketable quality, and susceptibility to pests and diseases through amendment-specific properties related to nutrient supply, moisture conditions, and probable biological interactions. Repeated applications of PL-2 resulted in the maintenance of a high proportion of first category roots over several cycles, while concurrently limiting pests and diseases pressure. Conclusion This finding underscores the significance of judicious selection and optimisation of the type of organic matter applied.