Effect of increasing ratios of urea-N in the nutrient solution on growth of Pelargonium (Pelargonium x Hortorum)
2012
Amberger-Ochsenbauer, S. | Taylor, M. | Lohr, D. | Meinken, E.
Fertilizers containing urea-N are recommended for horticultural crops because of the lower EC of the nutrient solution compared to solutions with ammonium or nitrate fertilizers, but high supply of urea raises the risk of plant damage and of gaseous N loss. Plants of Pelargonium × hortorum ‘Merkur’ were potted in partially decomposed peat with low nutrient supply from a complete water soluble fertilizer (0.75 g L-1, N+P2O5+K2O = 14+16+18). Plants were fertigated in an ebb-flow-system with nutrient solutions containing (mg L-1): 100 N, 16 P, 83 K, 8 Mg plus micronutrients. Nitrogen was applied as urea and ammonium nitrate at ratios of 0+100, 33+67, 67+33 and 100+0 per cent. The experiment was a factorial design with deionized water and tap water (electrical conductivity 0.7 dS m-1, acid capacity 5.8 mmol L-1, equivalent to 290 mg CaCO3 per litre) used with each fertilizer treatment. Increasing ratios of urea caused pH to increase and EC to decrease in the nutrient solutions. There was only a small effect (with tap water) or no effect (with deionized water) of urea on salt content and pH of the growing medium. Even with 100% urea in the nutrient solution, urea was rapidly decomposed in the growing medium. The fresh mass of plants was significantly impaired with increasing ratios of urea, if deionized water was used for fertigation. Even with 33% urea, plant growth was reduced compared to plants fertilized with 100% ammonium nitrate. In the tap water treatments urea only had a small negative effect on plant growth. Although the use of urea is an effective way to reduce EC in nutrient solutions, there is little or no influence on the content of soluble salts in the growing medium and even small amounts of urea may have a negative effect on growth of pelargonium.
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