Nitrogen fertilizer rate and timing of application for potato under different irrigation methods

Splitting nitrogen (N) fertilizer application is key to increasing potato tuber yield and nitrogen fertilizer uptake efficiency (NUpE), particularly in coarse-textured soils. The study objective was to determine optimum N fertilizer rates and application timing to maximize yield and plant growth under four irrigation methods: seepage, subirrigation with drain tile, subsurface drip irrigation (SDI) for water table level management, and sprinkler. A factorial design of three N rates applied at planting (N_pl) (0, 56, and 112 kg ha⁻¹), followed by two N rates (56 and 112 kg ha⁻¹) applied at plant emergence (N_eme), and tuber initiation (N_ti) were randomized in a complete block design with four replicates in each irrigation method in the spring of 2015 and 2016. Rainfall events directly influenced the water table management and irrigation volume required to maintain the soil moisture range of 0.11–0.16 m³ m⁻³ in the 0–15 cm soil depth by irrigating or draining the field. The volume of water applied to maintain the soil moisture target in each irrigation method was 295, 144, 125, and 96 mm in 2015, and 287, 194, 165, and 89 mm in 2016 for seepage, subirrigation, SDI, and sprinkler, respectively. Consequently, the different drainage capabilities of each method impacted the soil moisture in the root zone, directly impacting soil N, plant growth, and yield. The NUpE was significantly lower for seepage (48 %) compared to other irrigation methods that averaged 60 %. Total yield was 32.2, 37.2, 34.7, and 33.3 Mg ha⁻¹ for seepage, subirrigation, SDI, and sprinkler, respectively. Irrigation water productivity was 8.9, 16.9, 18.8, and 27.7 kg m⁻³ for seepage, subirrigation with drain tile, SDI, and sprinkler, respectively. There was no interaction between irrigation method and N treatment on tuber yield; thus, an N fertilizer strategy of timing and rate of application for potato cultivated under these irrigation methods was determined. The N fertilizer strategy combining N rates of 56, 112, and 56 kg ha⁻¹ applied at planting, emergence, and tuber initiation, respectively, matches the potato N uptake curve while minimizing the risk of N loss. Seepage had the highest incidence of tuber disorders and the lowest tuber specific gravity, indicating that alternative irrigation methods, when managed to maintain ideal soil moisture in the rootzone, can potentially outperform the seepage method regarding water conservation, tuber yield and quality.