Updating phosphate fertilizing practices in carrot crops

Vegetable species are generally classified in the category of plants with high phosphorus (P) requirements. Such is the case for carrot, and the no-fertilization threshold is 70 mg P2O5 (Olsen)/kg soil for crops in sandy soil. Current practices are based on that value, but there has been no validation of the initial hypothesis and the ensuing practices. Four trials were conducted in the Aquitaine region (southwest France), a major growing area characterized by organic sandy soils with acid pH, in order to analyze the crop?s response to a wide range of P levels in the soil. The resulting response curves show that the current P2O5 (Olsen) threshold is too high in relation to the actual requirements of carrot crops. New indicators of phosphorus bioavailability, based on water-soluble P dynamics, were evaluated in spring and summer crops, and experimental references were established. As a result, the minimum P concentration of the soil solution, defined by the Cp indicator, is evaluated at 1 mg P/l. Above said value, carrot crops show no loss of yield. This response threshold, currently under validation for the diversity of agronomic situations, indicates true potential for progress in phosphate fertilization practices. Furthermore, the trials have made it possible to determine the optimum P consumption level, i.e. 26 kg P/ha or 60 kg P2O5/ha (for 50 t of commercial production); excess P will not enhance crop yield or quality. Finally, soil reserves represent a significant source of P. For instance, in soil considered as phosphorus-poor (20 mg P2O5 Olsen/kg soil), more than half of the phosphorus used by the crop to ensure optimum yield is supplied by the soil?s own resources. The newly acquired knowledge and technical references offer a means to update P fertilising practices in carrot crops which, based on the results of this study, may be used as a model for extension to other species. ? Sources Updating phosphate fertilizing practices in carrot cropsRaynal Lacroix C.(1), Denoroy P.(2)(1) CTIFL, Centre de Lanxade, Prigonrieux F-24130(2) INRA UMR TCEM, Domaine de la Grande Ferrade, Villenave d?Ornon F-33883Carrot and other Apiaceae International Symposium, 17-19 September 2014, Angers, Francehttp://www.symposium-carrot-apiaceae2014.fr/ The picture is by rampages.us ? Key wordsZanahoria?? ??? ?carrot?? ?wortel?? ?????? ?????? ?karoto?? ?carotte?? ????????? ??????? ??? ?carota?? ?marchew?? ?cenoura?? ?????????? ?havu砠 ??????? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ????