Irrigation method and application timing effect on potato nitrogen fertilizer uptake efficiency

Establishment of proper guidelines for irrigation and nitrogen (N) fertilizer management may lead to higher crop fertilizer N use efficiency (FNUE), increasing water conservation and reducing nutrient losses from agricultural systems. The objective of this study was to determine FNUE of potato for three application timings: at planting, emergence and tuber initiation cultivated under three irrigation methods: seepage, subirrigation and sprinkler. A total of 168 kg ha⁻¹ of N was equally split into three applications of 56 kg ha⁻¹ as ammonium nitrate (NH₄NO₃). FNUE from each application timing in all irrigation methods was evaluated substituting the conventional N fertilizer by an isotope labeled-ammonium nitrate (¹⁵NH₄ ¹⁵NO₃) with 1.18% enrichment in excess. Irrigation method had no significant effects on tuber yield and FNUE. The average tuber yield was 32.1 Mg ha⁻¹ and overall FNUE was 41%. Across the N application timing treatments, the lowest FNUE was measured for the at-planting application (18%), followed by the emergence N application (44%) and tuber initiation N application (62%). Unaccounted N fertilizer during the potato season amounted to 98 kg ha⁻¹ from the total 168 kg ha⁻¹ of N applied. N applied at emergence and tuber initiation were important to increase FNUE and tuber yield, however, some N was required at planting, even with the high potential of N losses for that application.