Recuperación del 15N-Urea aplicado a la siembra o al macollaje en trigo en un suelo somero

-1 for 0N, 80S and 80T treatments, respec- tively. There were significant differences between fertilized and 0N treatments (p<0.001). The pro- portion of plant-N derived from fertilizer had a decreasing trend toward the end of the growing cycle while total N did not decline, suggesting that plants lost labeled N from aerial parts and they simulta- neously took non labeled N from the soil. High NO - 3 -N accumulation in soil was not found after fertilizations probably due to a fast uptake by plants sustained by high water contents at these samplings time. There was an important N immobilization from fertilizer N in the organic pool for 80S (30 kg Ndff ha -1 ) and 80T (43 kg Ndff ha -1 ) treatments and a subsequent drop, in synchrony with the take-off in the plant-N accumulation rate.