Irrigation and nitrogen requirement of onion

An experiment was conducted during 2004 to 2007 at the Research Farm of Punjab Agricultural University, Ludhiana on sandy loam (Fine loamy, Typic Haplustept) and loamy sand (Coarse loamy, Typic Haplustept) soils to evaluate the effect of different levels of irrigation and fertilizer N, with and without FYM on onion bulb yield, bulb size and water use efficiency. FYM incorporation improved the bulb yield by 3.3 and 3.5 t ha⁻¹ on loamy sand (LS) and sandy loam (SL) soils, respectively compared to unmanured plots. Highest bulb yield was recorded where most frequent irrigations were applied based on IW/PAN-E=2.0 although irrigation based on IW/PAN-E = 1.5 and 1.0 saved 10 and 22.5 cm water, respectively. The crop irrigated at IW/PAN-E = 2.0 and 1.5, respectively produced 2.7 and 1.01 ha⁻¹ higher bulb yield on LS and 4.2 and 2.01 ha⁻¹ on SL soils compared to IW/PAN-E = 1.0. Onion responded significantly to application of 100 kg N ha⁻¹ on SL and 125 kg ha⁻¹ on LS soils, respectively. Improvement in plant height and leaf area index (LAI) was recorded both with FYM incorporation as well as fertilizer N application. Contribution of larger size bulbs towards yield was more with FYM incorporation (37 and 42% on LS and SL soils, respectively) compared to 27 and 28% without FYM. Frequent irrigation as well as fertilizer N application improved the percent contribution of larger size bulbs. Irrigation water use efficiency increased by 6.9 and 7.8 kg ha⁻¹ mm⁻¹, respectively with FYM on SL and LS soils, compared to no FYM plots.