Abstract:Effect of forms of N fertilizers on Cu bioavailablity in a contaminated red soil was investigated. Results show that contents of watersoluble and available Cu varied with the forms of N fertilizer. At the first days of cultivation, the application of CO(NH2)2 significantly decreased the two fractions of soil Cu, while the addition of (NH4)2SO4 and Ca(NO3)2 increased water-soluble Cu, and the effect of the latter was much higher than the former. But the two forms of N did not have as much effect on available Cu. After 60 days’ cultivation, the negative effect of CO(NH2)2 on the two fractions of Cu turned to be positive, and the positive effect of (NH4) 2SO4 was further more enhanced. The positive effect of Ca(NO3) 2 on the two fractions of Cu was, however, less than that of CO(NH2)2. The two fractions of Cu also varied sharply with the application rates of nitrogen fertilizer. When N levels were kept the same, the effect of N fertilizer on both watersoluble and available Cu differed significantly, showing an order of (NH4)2SO4 > CO(NH2)2> Ca(NO3) 2. The change in soil pH led to different effect of different N on Cu bioavailability. Significant negative correlation was observed between pH and two fractions of Cu.