Critical phosphorus dilution curve and the phosphorus-nitrogen relationship in potato

Besides nitrogen (N), phosphorus (P) is the most limiting nutrient to potato growth. The P acquisition and utilization by potatoes is affected by the N supply. Accurately estimating the crop P sufficiency level is critical from economic and environmental standpoints. Critical P concentration (Pc), the minimum plant P concentration needed to achieve maximum crop biomass (total weight), is a suitable analytical tool to assess the crop P sufficiency level. Our objectives were to; (i) compare (Pc) curve based on the biomass (DM) of the entire potato plant (vines + tubers) with critical P curves recently developed in Argentina and Colombia ; (ii) analyze P dilution (the decline of P concentration as the plant gets larger) in vines and tubers, and to develop (Pc) curves for vines and tubers; and (iii) analyze the relationship between N and P concentrations in vine, tuber, and total biomass along with the changes in the N:P ratio with increasing biomass. Five P rates were applied to potatoes on soils located in four Canadian provinces from 2016 to 2018. Vine, tuber, total biomass, and N and P concentrations were measured every week for five consecutive weeks starting at 50 days after planting, and tuber yield was measured at harvest. The (Pc) in total biomass was below that developed in potatoes from Argentina and Colombia. The P and N concentrations of vine, tuber, and total biomass as well as the N:P ratio declined with increasing biomass. P dilution was less prominent in vines and tubers than in the total biomass. Strong relationship between N and P concentrations was observed in vine, tuber and total biomass. Phosphorus sufficiency in potato can be diagnosed early by analyzing vines alone. Indicators to assess P sufficiency in potato crop represent a promising alternative or a complement to the soil P tests traditionally used for fertilizer recommendations.