Characteristics Of Nitrate And Ammonium Nutrition And Thier Effect On Nitrate Accumulation In Spinach Plants

Hydroponic experiments were carried out to study the effects of different ratios of ammonium to nitrate (0/100, 5/95, 10/90, 15/85, 25/75, 50/50 and 100/0) and nitrogen supply rates (5moml/L,10mmol/L,15mmoml/L and 20mmoml/L) on growth and quality of four spinach cultivars (Ribendayebocai, Bozaguanneng, Shandongchangyidajianbo and Suzhoudajianbo). The results obtained were showed as follows:The growth and quality of spinach plants could be significantly affected by different ratios of ammonium to nitrate. Fresh weight, dry weight and water content of spinach plants were increased with increasing proportion of nitrate in nutrient solution. The dry weight of spinach plants was the highest when the ratio of ammonium to nitrate was supplied as 0 /100, which was nearly as similar as the ratio of ammonium to nitrate of 5/95 and 10/90 in most cultivars of spinach. Considering the highest dry mass, there was no difference existed between 0/100 and 5/95 and 10/90 of NH₄⁺ /NO₃^- ratio. However, 5/95 and 10/90 of NH₄⁺ /NO₃^- ratio was economically accepted and could decrease significantly the nitrate content of the plants. Nitrate accumulation of spinach plants including shoots and roots was reduced with increasing proportion of ammonium-nitrogen in the nutrient solution, while content of soluble sugar increased. Furthermore, there was no obvious change in the content of vitamin C (Vc) of spinach plants when the supply of NH₄⁺ /NO₃^- ratio was changed. The response tendency in Vc content of spinach plants was different among the cultivars, and the optimal NH₄⁺ /NO₃^- ratio was different in order to obtain the highest content of Vc. Therefore, quality of spinach could be improved by enhancing the proportion of ammonium in the nutrient solution. NH₄⁺ /NO₃^- ratio supplied as 5/95and 10/90 could improve higher quality ofspinach plants than that supplied as 0/100.There also existed an apparent effect of different nitrogen supply rates on growth and quality of spinach plants. Fresh mass of spinach plants including shoots and roots was increased with increasing concentration of nitrogen supplied in the nutrient solution. The optimal level of nitrogen supply was 15mmol/L. Nitrate content of spinach plants was increased with increasing concentration level of nitrogen supplied in the nutrient solution, while content of soluble sugar was reduced, which showed that different cultivars ofspinach yield could be improved by optimal nitrogen supply rate in the nutrient solution whereas lower concentration of nitrogen supply could improve the quality of spinach plants.Enhanced ammonium could increase the activity of nitrate reductase and glutamine synthetase in leaves, roots and stem of cultivars both in Ribendayebocai and Bozaguanneng.In the experiment, considering the higher biomass and better quality, the recommended ratio NH₄+/NO₃^- was 5/95 and 10/90, and the optimal supply level of nitrogen was 15mmol/L.