Nitrogen Fertilization as Ammonium or Nitrate-N on <i>Hippeastrum hybridum</i> Bulb Growth

Abstract

Hippeastrum ( Hippeastrum hybridum ), a native of Central and South America, is a bulbous ornamental flowering plant in the Amaryllidaceae family. However, the correct balance of NH 4 to NO 3 -nitrogen in a fertilizer mix for Hippeastrum plants is largely unknown. Nitrogen was applied 2x weekly following irrigation at either 0.6 g (high), 0.3 g (medium) or 0.15 g (low) total N every four months. Nitrogen was supplied in different combinations of NO ₃ and/or NH ₄ . Nitrate:NH ₄ -N ratios were either 100% NO 3 :0% NH 4 (100NO 3 ), 70% NO 3 :30% NH 4 (70NO 3 ), 50% NO 3 :50% NH 4 (50NO 3 ) (second group only), 30%NO 3 :70%NH ₄ (30NO 3 ), or 0% NO 3 /100% NH 4 (100NH 4 ). Growth in bulb diameter after one year of fertilizer treatments not only increased from 0.15 to 0.6 g N (low to high level), but also differed with the form of N supplied to the plant. The largest diameter bulbs were produced in the 70NO 3 and 50NO 3 high N treatments. Within any NO 3 /NH 4 -N ratio grouping, fertilization at the high N rate resulted in larger diameter bulbs. No significant differences existed between treatments in the number of bulbs produced. Bulb growth was greater with a portion of N supplied as NO 3 than with NH 4 -N alone. These results indicate that application of N as a mixture of NH 4 and NO 3 at 0.6 g per 4 months produces the largest increase in bulb diameter.