Nitrate accumulation in petiole and blade of different spinach cultivars and its relation to plant growth

Pot experiment was carried out in greenhouse, with 30 spinach cultivars widely grown over northern China as test crops, to study nitrate accumulation in petiole and blade of different spinach cultivars and its relation to plant growth. Fertilization rate was P 0.13 g/kg and N 0.60 g/kg soil. Results showed that there was a significant variation of the shoot biomass and nitrate N concentration in shoot over these 30 spinach cultivars. The process of petiole in reflecting the variation of plant growth increment and nitrate accumulation among spinach cultivars was not coincided with that of blade. Leaf blade accounted for higher proportion to fresh shoot weight than petiole, and variation of the fresh blade weight over cultivars was higher than that of petiole too. Further more, a significant positive correlation was found between fresh weights of blades and shoots. Being different from the case of biomass, nitrate N concentration and the total nitrate N accumulated in petiole were significantly higher than those in blade. The petiole was the dominant organ for nitrate accumulation in leafy vegetables obviously. The variation of nitrate N concentrations in petioles was significantly higher than that in leaf blade and its correlation is more significant than that of leaf blade as well. Further analysis showed that nitrate N concentration in petiole was significantly correlated with the fresh shoot weight, dry shoot weight and the total amount of water over different cultivars. However this relationship was not found for the blade.