Irrigation scheduling at specific growth stages of onion (Allium cepa L.) under variable fertilizer rates in different soil types in Gumselassa (Tigray), Ethiopia

Irrigated agriculture demands high consumption of water. However, the amount of water required and fertilizer utilization varies with specific crop and its specific developmental stages. In 2009–10 an experiment was conducted in Adigudem, Northern Ethiopia to determine the effects of nitrogen (N) and phosphorus (P) on yield and yield components of onion with specific developmental stages of irrigation water in different soil types. Factorial combination of Randomized Complete Block Design (RCBD) with three replications was used. Treatments consisted of four nitrogen levels (0, 46, 92, and 138) kgha⁻¹ and four levels of phosphorus (0, 46, 92 and 138 kg ha⁻¹ P₂O₅) in two different dominant soil types of the area. The gross experimental plot size was 1.5 x 1.6 (2.4 m²), 1.5 m between replication and 0.50m between plots within a block. The spacing used was 30 × 10 cm. Total bulb yield (t ha⁻¹), plant height (cm) significantly (p = 0.0001) increased with increasing N rates. However, unmarketable bulb yield (t ha⁻¹) was significantly (p = 0.01) decreased as N fertilizer increased. The rate of 138 kgha⁻¹ N increased yield and water use efficiency compared to the control. Total bulb yield and marketable bulb yield (t ha⁻¹), harvest index, crop water use efficiency, plant P concentration significantly increased with P fertilization. However, application of P did not show significant difference (p = 0.08) in unmarketable bulb yield.