Sugar beet response to N fertilization as assessed by late season chlorophyll and leaf area index measurements in a semi-arid environment

In a 3-year experiment (2002-2004), five N rates (0, 60, 120, 180, 240 kg N ha-1) were applied to sugar beets arranged in a Randomized Complete Block design with six replications. Experimentation took place under the semi-arid, irrigated conditions of central Greece. The aim of this work was to study the late season response of sugar beet crop to N fertilization as assessed by non-destructive measurements of chlorophyll (SPAD) and Leaf Area Index (LAI). Physiological measurements were conducted from early August to mid-September, every two weeks. Sugar yield response to N fertilization was evident only in 2004. The highest root and sugar yields were found in 2002 as a result of the unusually high, for Mediterranean conditions, rainfall during summer. The highest petiole NO3-N concentrations and the lowest sucrose content in root fresh weight were also recorded in 2002. In 2003, sugar beets were water stressed at late August and thus LAI was minimum. Thus, the lowest root and sugar yields were found in 2003. In 2004, SPAD and LAI values were related with root and sugar yields. SPAD readings of ca 38.00 were the optimal for maximum yield. Optimal LAI values for root and sugar yields were 3.99 and 3.88, respectively. SPAD was, also, related with petiole NO3-N concentration and α-amino N in roots. A healthy and green canopy at the late stages of the growing season can contribute to high sugar beet yield. Optimal N rate for maximum root and sugar yield was close to or higher than 200 kg ha-1 N. Chlorophyll (SPAD) and LAI determination by instruments could be a sensitive tool in revealing sugar beet response to N fertilization and non-destructively assessing sugar beet N nutrition status.