Organic fertilizer decomposition and nutrient loads in water reservoir with changing temperature, Wakiso – Ug

Abstract

Decomposition in aquatic ecosystems is controlled by various factors. The study investigated the trend of decomposition and the potential nutrients loaded in reservoir water. Analysis of water samples and organic fertilizer composition was according to APHA (1995) and Klute (1986) respectively. Reservoir water temperature ranged from 20.4 - 29.0 oC and was not significantly different (P = 0.778). Leaching experiments exhibited increase in both nutrient and ion mobility. Peak EC and ammonia concentration were after 48 hours respectively, and 96 hours for SRP. Nutrient concentration was similar for ammonia (P = 0.078) and significant for SRP (p = 0.030) over time. Rates of leaching for ammonia and SRP were 0.004 hr-1and 0.003 hr-1, and time setting had 49.4% and 64.5% on the rates respectively. Pearson correlation of temperature and organic weight loss in the reservoir was positive and significant (r2 = 0.657, P = 0.02). Phases of organic fertilizer decomposition were significantly different (P < 0.05), and the overall rate was estimated at 0.001 degree day-1. TP, TN and AFDW in the fertilizer during leaching ranged from 0.33 – 0.53 mg/l, 0.08 – 0.10 mg/l and 39.2 – 53.1 mg/l respectively within the 96 hours of incubation. Potential nutrient available for recycling in the reservoir water was estimated at 0.006 and 0.008 mg g-1 for TN and TP respectively. Actual loaded nutrient was 0.0009 and 0.0010 mgl-1day-1 for TN and TP respectively. Integration of functional dynamics in assessing water status is therefore important.

Key words: Decomposition, fertilizer, leaching, nutrients, loading, organic