EVALUATION OF NITROGEN AVAILABILITY IN A SOIL TREATED WITH ORGANIC AMENDMENTS

In the search for an approach which could be used to predict available nitrogen (N) in organic amendments, biological and chemical methods were investigated in laboratory and growth chamber studies. Two biological methods [maize plants (Zea mays L.) grown in pots, and soil-amendment mixtures incubated aerobically at 2, 4, 6, 8, 12, and 16 weeks], and four chemical methods [autoclave, 0.5M potassium permanganate (KMnO4), pepsin, and 6M hydrochloric acid (HCl)] were compared to determine N availability in 36 organic amendments applied to soil. Total N mineralized in a soil amended with different organic amendments ranged from - 12 to 428 mg N/kg soil. The highest value was obtained from sludge number 11 and the lowest from cow manure 2, urban refuse, and grape-marc. In general, the aerobically-treated sewage sludges gave higher N-mineralization rates than other amendments. The 6M HCI and autoclave methods were more suitable for predicting N availability in these organic amendments than either the pepsin or KMnO4 methods. Prediction of N availability in the growth chamber experiments improved if several chemical and biological methods were combined in a multiple regression analysis.