Abstract

Precise diagnosis and prognosis of phosphorus (P) nutrition are essentials to improve P use efficiency and sus-tainability in potato cropping systems. Here, variable potato crop responses of 13 field experiments (2011-2022) were assessed to determine critical soil P-resin (SPresin) 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 SPresin 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 SPresin, reaching a maximum LP of 3.8 g P kg-1 at an initial SPresin of 80 mg P dm-3 (averaged across models). The relationship between RY and initial SPresin was significant in the three regression models (p < 0.05; R2 = 0.71-0.74). Maximum tuber yield was reached with the SPresin 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.