THERMAL TIME EVALUATION METHODS FOR DETERMINING PLANTING DATE OF POTATOES FOR AGROINDUSTRY

Abstract

In Northern Chile, Coquimbo Region, potato planting for agro-industry takes place in Autumn-Winter. Every year, growers have to reschedule the planting date to meet the potato delivery schedule on a pro-rata basis. Compliance with this requirement is subject to great uncertainty due to climatic variability, mainly between planting closure and harvest; therefore, in this study it is proposed to evaluate three methods based on thermal time to optimize the planting date. Using a four-year database with information on yields, quality, ambient temperature, days to harvest, dates of phenological stages and management, the following methods were evaluated: 1) mean temperature method or heat units with base temperatures of 4 and 7 °C, 2) degree days (°D) model with temperature range between 2 and 29 °C, and 3) Potato days (P-days) or phenological potato days with base temperatures of 4 and 7 °C. The best method for these conditions corresponded to P-days with 4 °C; however, and unlike other studies, it was determined that the relevant moment to start the accumulation of physiological time (Biofix) should be at plant emergence and not the planting date. A total of 723 P-days to harvest and an oscillation between planting and emergence of 34 to 66 days were recorded, with a close relationship with final crop yields.