Pre-Planting and Supplementary In-Season Liquid Phosphorus Fertilization for Potato

The objective of this study was to evaluate potato growth, phosphorus (P) uptake, total and marketable yield response to multiple rates of P fertilizer applied at planting, emergence, and tuber initiation stages in 2019 and 2020. Varying pre-plant (P_pp) rates (0, 25, 49, 74 kg ha⁻¹ P) and two supplementary liquid P applications (0 and 12 kg ha⁻¹ P) at emergence (P_eme) and tuber initiation (P_ini) were tested. Initial Mehlich-3 soil P content varied from 128 to 160 mg kg⁻¹. There were no significant interactions among P_pp, P_eme, and P_ini for yield or P uptake across seasons. Tuber total yield ranged from 33.3 to 45.3 Mg ha⁻¹ across seasons. However, higher P_pp rates increased dry biomass, P uptake, and tuber yield, with no significant differences between 49 and 74 kg ha⁻¹ P rates. Liquid P applied at a rate of 12 kg ha⁻¹ of P during tuber initiation stage significantly increased potato total and marketable yield compared to no liquid P application in 2019. Despite relatively high initial soil P levels, added fertilizer enhanced yields, contradicting current recommendations. These findings suggest a need to reassess Mehlich-3 interpretations and further validate in-season liquid P use for broader application.