The uptake of nutrients by sunflower plants (Helianthus annum) growing in a continuous flowing culture system, supplied with nitrate or ammonium as nitrogen source

Abstract Sunflower plants (Helianthus annuus) were grown in a continuous flow nutrient system, in which nitrogen was supplied, under controlled pH conditions, in either the NO3‐or NH4‐form. Nutrient uptake and distribution, as well as dry matter production of the plants, was followed over the growth period. The results obtained may be summarized as follows: 1. At all stages in development, growth was somewhat greater in the plants of the NO3‐treatment, but the difference between the two treatments was not large. The similarity in the behaviour of plants in the two nitrogen treatments is discussed in relation to the maintenance of a high pH in the nutrient medium. 2. The mean rates of uptake of Ca, Mg, K, and Na, expressed per unit root length, were all higher in the NO3‐fed plants. For P, the mean rate of uptake was higher in the NH4‐fed plants. 3. The levels of K, Ca, Mg, and Na, per unit dry weight, were higher in the NO3‐fed plants, but for P the converse was true. 4. The higher uptake of Ca and Mg by NO3‐fed plants was reflected in the higher concentrations of these elements in the leaves. In the case of K, accumulation occurred in the roots. 5. From the results of selected harvests, it was found that total nitrogen uptake was higher in the NO3‐fed plants.