Effects of genotypes, plant density and nitrogen rates on yield and quality of spinach

Nitrate is the principal source of nitrogen for most higher plants. Particularly leafy vegetables require large quantities of nitrate fertilizer to attain maximal yields. The crop yield and quality as well as nitrate accumulation in leafy vegetables depends upon many preharvest factors such as genetic materials, agronomical and environmental factors. Three greenhouse experiments were carried out in order to assess the effects of preharvest factors (cultivars, plant density and N dose) on yield and quality of spinach (Spinacia oleracea L.). In the first trial four spinach cultivars were compared in terms of yield and quality attributes. The marketable yield of the four cultivars tested was in the following order: ‘Tasman’ = ‘Kookaburra’ > ‘Platypus’ = ‘Regiment’. No significant differences among cultivars were observed for the βcarotene, vitamin C and nitrate contents. In the second trial, treatments were defined by four plant densities (800,000; 1,000,000; 1,200,000; 1,500,000 seeds ha-1). The lowest marketable yield was observed under the lowest plant density, whereas no significant difference was recorded between the other treatments. The highest leaf dry matter, K, and nitrate contents were recorded at 1000000 seeds ha-1. In the third experiment we evaluated the effects of four N fertilizer doses (0, 75, 150 and 225 kg ha-1) on crop performance. Marketable yield increased quadratically with increasing N application with the highest values recorded at both 150 and 225 kg ha-1 indicating a luxury consumption of the nutrient at 225 kg ha-1. Finally, the highest protein and nitrate contents were observed at 225 kg ha-1 of N.