Testing critical phosphorus dilution curves for potato cropped in tropical Oxisols of southeastern Brazil

One of the challenges of potato (Solanum tuberosum L.) production is to minimize phosphorus (P) fertilization without negatively affecting the yield progress. Therefore, critical P dilution curves [P-c = a(c)W(-b); where P-c is the critical P concentration (%); a(c) is the critical plant P concentration (%) for a total dry matter (DM) biomass of 1 Mg ha(-1); W is the total DM biomass expressed in Mg ha(-1); and coefficient b is dimensionless and represents the ratio between the relative decline in plant P concentration and the relative crop growth rate] have been developed recently to improve P fertilization management in potatoes. The aim of this study was to test critical P dilution curves for potato cultivated in Sao Paulo State, southeastern Brazil. Nine field experiments were conducted in Oxisols with P-resin values ranging from 8 to 70 mg dm(-3) (very low to high). In each experiment, treatments were different P rates (ranging from 0 to 448 kg P ha(-1)) or the combination of different cultivars and P rates. Wide ranges in tuber DM yield (0.7-7.9 Mg ha(-1)) and plant P concentration (0.13-0.36 %) were observed before vine killing in response to P rates, cultivars, and site-years. Tuber DM yields were related to total DM biomass (R-2 = 0.98), while P uptake was related to both total DM biomass and total plant P concentration (p < 0.01). Relative tuber DM yields at harvest were closely related to P nutrition index (PNI) (p < 0.01, R-2 = 0.82) calculated with the critical P dilution curve previously reported for potato under higher yielding environments. These results validate the critical P dilution curve (P-c = 0.391W(-0.304)) as a useful diagnostic tool for improving the P fertilization of potato crops systems in the tropical region of Brazil.