Phosphorus (P) fertilizers are an essential input for economically sustainable crop production but they may represent a significant problem for water quality if managed incorrectly. Appropriate evaluation of soil P availability is a prerequisite for ensuring the productivity and long-term sustainable management of agroecosystems. A long-term trial at Agroscope-Changins in Switzerland has been conducted in a clay Gleyic Cambisol (FAO classification system) for 40 years to analyze the effect of P fertilization (0 to 60 kg P ha-1 yr-1) on soil and plant P status, and crop yields. Soil analyses (0-20 and 20-50 cm depth) included total, organic, inorganic and available-P assessed by a process-based approach and different chemical extractions. Shoot biomass and plant P concentration of wheat in 2011 and corn in 2012 were measured approximately weekly during the growing season (7 sampling dates) and the P nutrition index [PNI: 100 × (Pmeasured/PC)] was determined using a critical P concentration (PC) based on whole plant shoot biomass [PC = α × (DM)β]. After 40 years of cultivation, cumulative P (applied minus exported P) ranged from -567 to +1554 kg P ha-1, respectively for 0 and 60 kg P ha-1 yr-1. As a consequence, P-fertilization significantly affected, except organic P, all other measured soil P parameters for the 0-20 cm soil layer. Thus, the total P ranged from 0.78 to 1.14 g P (kg soil)-1 while the concentration of phosphate ions in soil solution varied from 0.06 to 0.75 mg P l-1, respectively for 0 and 60 kg P ha-1 yr-1. Phosphorus fertilization also significantly increased wheat and corn grain P concentration but did not affect grain yield. The PNI ranged at harvest from 97 to 166 % for wheat and 98 to 128 % for corn, showing that P was not crop-limiting even after 40 years of cultivation without P fertilization. This study highlights the interest of plant-based diagnostic methods alongside soil analyses for the optimization of P fertilization practices for croplands in Switzerland.Read less <