Autumn-sown sugarbeet (Beta vulgaris L.) responses (sugar yield, plant N-uptake and juice quality)
were studied in relation to the residual NO3−-N in a soil of southwestern Spain which, for the previous
five years (1989–93), had received high N rates, in accordance with conventional fertilization
schedules used by farmers in the area. Three different combinations of fertilizers, supplying equal
amounts of N, were used during the fertilization period (1989–93): a mineral fertilization treatment
(MF, a complex 15N-15P2O5-15K2O) and two organo-mineral fertilization treatments (an olive mill
wastewater sludge compost, AC, and a depotassified concentrated beet vinasse, V). All these
treatments also received a top-dressing with urea (46% N). A control treatment (C), without
fertilization was included for comparison.
During the major part of the beet growing season, the presence of almost four times as much
mineral N in the 0·100 cm soil layer of previously fertilized plots (AC, V and MF) than in the
unfertilized one (C), led to a significant increase (P<0·05) in total fresh weight yield and N-uptake,
but also to a significant decrease (P<0·05) in sugar content and beet processing quality. The time
course of NO3−-N concentration in sugarbeet petioles and the evolution of the nutritional state of
leaf-blades gave advance information about the final response of the crop to the different fertilization
treatments. Besides N, Na was the element which, due to the repeated and high fertilization rates
applied, had a major effect in reducing the technological quality of the sugarbeet.