Effects of nitrogen enrichment on heavy metals content of cattle dung/poultry manure compost and maize yield.
The research was carried out at John Ker Nigeria Organo-Mineral Company site at Ikot Ekpene, Akwa Ibom State, Nigeria, to investigate the effect of nitrogen enrichment on contents of heavy metals in cattle dung/poultry manure compost and the growth of maize. Cattle dung was mixed with poultry manure in the ratio of 3:1 volume/volume basis, respectively. The compost treatments were; (i) cattle dung/poultry manure (CDPM), (ii) cattle dung/poultry manure supplemented with 25 kg of urea (CDPMU) and (iii) cattle dung (CD) as control composted alone. The compost treatments; CDPM, CDPMU and CD were sampled periodically after 2, 6 and 10 weeks of composting for laboratory analysis. After 10 weeks, each of the compost treatments was mixed with 7 kg of dry soil sample at the rate of 10, 20 and 40 t/ha to test its effects on the growth of maize plant for 6 weeks. The enrichment of the CDPM compost resulted in an increase in the levels of all the heavy metals contained in the compost (CDPMU) at two weeks after composting. At 10 weeks of composting, the concentrations of Fe, Zn, Cu, V, Mn and Ni in CDPMU compost increased by 32.8, 25.6, 14.6, 40.0, 6.8 and 19.0 %, respectively compared with their contents in the CDPM. The C/N ratios ranged from 23.9 to 25.1 in the CD compost, 23.1 to 23.4 in the CDPM compost and 13.6 to 16.9 in the CDPMU compost within the 10 weeks of composting. The influence of the compost treatments on the growth of maize plant indicated that the plant fertilized with CDPMU compost at 40 t/ha were significantly (P<0.05) higher than those fertilized with the same compost treatment at 0, 10 and 20 t/ha. Those fertilized with CD and CDPM at the rate of 0, 10, 20 and 40 t/ha, had the same trends respectively.
Key words: Nitrogen Enrichment, Heavy Metals, Cattle Dung, Poultry Manure, Compost.