RESPONSE OF ONION TO DIFFERENT LEVELS OF IRRIGATION WATER AND FERTILIZATION: (II) BIOMASS, YIELD, SIZE CLASSES, QUALITY, AND WATER USE

Abstract

An experiment was conducted to study the effect of different levels of irrigation water and NPK fertilizers on bulb yield and quality of onion (Allium cepa L.). Four levels of irrigation (65, 75, 85, and 100% of ETc) and four rates of NPK fertilizers (0, 50, 75, and 100% of the applied recommended rate of NPK) were arranged in a randomized complete block design, replicated three times. Onion yield, marketable yield, dry bulb yield, total dry biomass, WUEy of total yield, WUEm of marketable yield, WUEd of dry yield, TSS, N, P, and K were determined under trickle irrigation on a clay loam soil in 2011 and 2012. High yields were observed for the 100 and 85 % ETc with 100 and 75 % NPK treatments. The increase in applied water level significantly decreased the percentage of dry matter and total dry biomass in the onion bulb and the increase in NPK rates increased significantly the percentage of dry matter in the onion bulb in both years. There were no significant effect on WUEy and WUEm when decreasing the water level from 100% ETc to 85 % ETc and decreasing the NPK rate from 100 % to 75 %. The interaction between applied water levels and NPK application rates showed that the maximum significant increase in TSS, N, P, and K was with low water levels and higher levels of NPK rates in both 2011 and 2012 seasons.