Effects of plant age on nitrogen uptake and distribution by greenhouse plants

Abstract

Water‐soluble nitrogen (N) fertilizer is intensively used in greenhouse crop production. Any N not used by a crop is subject to leaching as nitrate (NO3‐N), which may pollute groundwater. A close correlation between N supply and N uptake by plants would increase the efficiency of N fertilization and minimize the possibility of NO3‐N pollution. The objectives of this study were to measure N uptake by American marigold (Tagetes erecta L. ‘First Lady') and New Guinea Impatiens (NGI) (Impatiens hawkeri Bull. ‘Selenia') during growth, to determine the effect of plant age on N uptake, to determine if the two species have a preference for NO3‐N or ammonium (NH4‐N), and to determine the total N required for 70 days of growth.The plants were grown in solution culture using solutions supplying 120 mg each of NO3‐N and NH4‐N. At ten day intervals, six cultures were chosen at random for nutrient solution analysis and plant sampling for dry weight and tissue analysis. Nitrate‐N uptake was greater than NH4‐N uptake throughout the experiment for both marigold and NGI. Total N uptake by marigold was greater during the first 50 days after transplanting with maximum N uptake during the period 30 to 50 days. In contrast, N uptake by NGI was greater during the period 40 to 70 days after transplanting. Maximum N uptake for NGI occurred during the period 60 to 70 days. Results of this study suggest that early N fertilization of marigold could be more important for their growth and quality than N applied later. For NGI, N fertilization later in the crop's development appears to be more important than early on. The total N absorbed by marigold during the experiment was 1.1 gm N plant‐1; for NGI the quantity was 0.5 gm N plant‐1.