| Summary: | The stable isotope <sup>15</sup>N was used to assess the recovery of mineral N fertilizer applied to fertigated and drip-irrigated spring muskmelon and autumn-winter sweet pepper crops grown in greenhouse soil plots. They received 92–96% of mineral N fertilizer as NO<sub>3</sub><sup>−</sup>. <sup>15</sup>N-labeled Ca (NO<sub>3</sub>)<sub>2</sub> fertilizer was applied to crops during vegetative growth and fruit production phases. Crops were grown with either conventional management or combined improved N and irrigation management. Improved management for both irrigation and N was based on the combined use of models, to estimate crop requirements, and of monitoring of soil parameters. In sweet pepper, from conventional management, <sup>15</sup>N recoveries from the <sup>15</sup>N applications made during vegetative growth and fruit production were 66% and 58%, respectively. With improved management in sweet pepper, the corresponding <sup>15</sup>N recoveries were 82% and 77%. In muskmelon, <sup>15</sup>N recoveries from conventional management from the <sup>15</sup>N applications made during vegetative growth and fruit production were 71% and 42%, respectively. With improved management, the corresponding <sup>15</sup>N recoveries were 68% and 44%, respectively. The results demonstrated that combined drip irrigation and fertigation systems with frequent irrigation and N fertilizer application can have very high recovery of applied N fertilizer, of 77–82%.
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