Soil and leaf phosphorus thresholds for modern potato production systems in tropical Oxisols

Precise diagnosis and prognosis of phosphorus (P) nutrition are essentials to improve P use efficiency and sustainability in potato cropping systems. Here, variable potato crop responses of 13 field experiments (2011–2022) were assessed to determine critical soil P-resin (SP_resin) and potato leaf P (LP) concentrations to achieve maximum tuber yield in tropical Oxisols. The study comprised four experiments with the factorial design of potato cultivars in response to P fertilization rates and nine experiments with P fertilization rates as fixed effects. Relationships between initial SP_resin test, LP measured at the third or fourth expanded leaf stage (i.e., 29–37 days after emergence, DAE), and relative total fresh tuber yield (RY) (yield of control/yield at highest P rate) were analyzed using linear-plateau, Mitscherlich, and quadratic-plateau regression models. A wide range of total fresh tuber yield (3.2–59 Mg ha^-1) and LP (1.3–5.7 g P kg^-1) were observed across experiments. The LP values in control plots was positively related with initial SP_resin, reaching a maximum LP of 3.8 g P kg^-1 at an initial SP_resin of 80 mg P dm^-3 (averaged across models). The relationship between RY and initial SP_resin was significant in the three regression models (p < 0.05; R² = 0.71–0.74). Maximum tuber yield was reached with the SP_resin value of 93 mg P dm^-3 (averaged across models). Across experiments and P fertilization rates, relationships between RY and LP were significantly described in the three regression models (p < 0.05; R² = 0.55–0.67). The critical LP of 4.5 g P kg^-1, obtained from the average across models, is proposed as the optimum indicator of potato P nutritional status to achieve maximum tuber yields in tropical Oxisols. These are the first critical P thresholds on a soil and environmental-specific conditions base available for tropical conditions in Brazil, timely informative in terms of optimization of P management to maximize tuber yield and P use efficiency, and minimize the risk of environmental P contamination.