Nitrogen Mineralization in Selected Solid Waste Dumpsites in Port Harcourt, Nigeria

Organic wastes in selected waste dumpsites in Port Harcourt were successively incubated with sandy-loam soils for days at 27oC, under aerobic conditions. The results showed marked decrease in total nitrogen in the organic wastes which was observed as loss of nitrogen. The process of nitrification and incorporation of (NH4)2SO4 affected the pH which ranged from 5.9 to 7.9. The cumulative mineral nitrogen released increased with incubation periods and the rate of organic application up to 28 day, with a maximum release of 456.40ppm at a rate of 61MT/ha organic application. The release of mineral N decreased on the 56 day with a minimum of 177.80ppm at a rate of 60MT/ha of organic fertilizer only. An enriched organic. Waste soil and organic waste treated soil had a boosting effect on the release of mineral nitrogen. The amount of mineral nitrogen released was higher for (NH4)2SO4 fertilizer treated soil than for organic waste treated soil. The mineralization rate was found to decrease with increasing age of the waste dumps. It was therefore recommended that organic wastes should be sorted and composted for use as organic fertilizers to augment inorganic fertilizer. @ JASEM Nitrogen is one of the primary inorganic or mineral nutrients necessary for biodegradation and other metabolic activities (Blacke, 1994). One of the best methods in assessing Nmineralization is to study the changes that occur when organic waste and soils are incubated under conditions which promote extensive incubation with soil N (Broadbent, 1979; Isirimah and Keeney, 1972). The mineralization of organic nitrogen compounds takes place in essentially three step reactions: Aminization, amonification, and nitrification Nitrogen mineralization has been defined as a complete conversion of organic nitrogen to the more mobile energetic state or a mineral formNH4, NO3, NO2, (Baker and Herson, 1994). Study (Broadbent, 1979) on nitrogen mineralization reported that chemical extraction and short-term incubation procedures are used to predict Nmineralization; the incubation procedures consider more of the biological and environmental variables. Microbial degradation of complex compounds does not always result in mineralization. Incomplete degradation, also called transformation of the compound may occur as a result of microbial activity. Nitrogen in soils exhibits high resistance to mineralization, usually only 1 to 3% of it being mineralized during the growing season. (Baker and Herson, 1994). Sims (1986) found that studies on N mineralization of organic waste have produced inconsistent, sometimes contradictory results due to microbial immobilization of nitrogen. Incubation experiments intended to stimulate nitrogen mineralization frequently show ammonia production to be initially rapid, and level off to a low rate (Broadbent, 1979; Isirimah and Keeney, 1972). The cumulative incubation period increases linearly with incubation time and with the amount of incorporated organic waste (Isirimah and Keeney 1972). Isirimah and Keeney (1972) reported that the organic nitrogen and carbon contents of incubated samples decline with time due to the loss of (NO3+ NO2)-N in most cases. For organic samples, the rate of mineralization (KR) has been estimated by using a modified first order kinetic equation. (Smith et al 1980; Molina et al, 1980).