Nutrient composition and release patterns of selected organic materials: a guide for direct application and use in fertilizer formulations

Abstract

Limited availability of high-quality organic resources, inconsistent nutrient content, and unestablished nutrient-release patterns hinder the effective utilization of organic materials for soil fertility management. To address this, the present study characterizes the total nutrient content of fourteen organic materials and analysed their NPK fertilizer value following standards established by the Tanzanian Bureau of Standards (TBS) and African Standards for Organic Fertilizers (ARS). Four high-potential materials: comfrey, azolla, fish meal, wild sunflower and their mixtures were further tested in a fermentation experiment to examine nutrient release dynamics and their potential for direct-soil incorporation. The experiment was conducted at Sokoine University of Agriculture (SUA), in Morogoro region, Tanzania. In a screenhouse experiment, 150 g of the powdered material was fermented in 1.8 litres of water in pots for 84 days, in a Completely Randomized Design. Fermented samples were collected at 14-day intervals and analysed for available nitrogen, phosphorus, potassium and calcium. Results showed that fish meal had the highest NPK fertilizer value (21.23%), while rabbit urine had the lowest (0.3%). Peak nitrogen release reached 849.2 mg/L at 28 days in fish meal, and potassium 143.32 mg/L at 28 days in comfrey. Phosphorus release peaked (7.1 mg/L) at 42 days in fish meal, and calcium (29.8 mg/L) at 84 days in wild sunflower. Fish meal demonstrated its potential as a high-quality organic material for direct application or inclusion in liquid fertilizer formulations. Its combined formulation with azolla and comfrey could result in a balanced liquid NPK organic fertilizer suitable for a wide range of crops. These findings provide empirical evidence to guide the direct use of local organic resources for sustainable soil fertility management and the formulation of liquid organic fertilizers.