LONG-TERM EXPERIMENTS ON THE FATE OF N-15 UREA IN SOIL PLANT-SYSTEMS UNDER OUTDOOR CONDITIONS/

The major loss of N applied to soil as urea N-15 was a result of volat ilization and denitrification rather than of leaching. This loss was h igher in sandy loam than in loamy sand; incorporation of straw slightl y increased it, whereas addition of the herbicide monolinuron decrease d the loss. The urea N-15 was utilized better by plants in the loamy s and than in the sandy loam and was utilized less after soil treatment with straw. The rotation crops in the second year appeared to utilize the N-15 residues, resulting from the application in the preceding yea r, only to a limited extent.