Losses of Urea-Nitrogen Applied to Maize Grown on a Calcareous Fluvo-Aquic Soil in North China Plain

<正> Field experiments were conducted in a maize (Zea mays L.) field of a calcareous fluvo-aquic soil in North China Plain for studying the fate and ammonia loss of urea-N applied at seedling stage, as well as the effectiveness of coated calcium carbide (CCC) in reducing N loss and in improving the yield efficiency of urea. Results show that: (1) For the surface-broadcast treatment ammonia volatilization (measured with micro-meteorological technique) took place quickly, reached the peak 20-26 hr after application, and then declined gradually; the cumulative ammonia loss approached the maximum 188 hr after application (30% of the N applied), and increased only to 32% 284 hr after application; the latter accounted for 71 % of the total loss (45% of applied N). (2) In the case of point placement at a depth of 5-10 cm, ammonia loss 188 hr after application was only 12% of the N applied, accounting for 40% of the total loss. (3) There was no difference in total loss between the application depths of 6 cm and 10cm