DEFICIT IRRIGATION AND PLANT DENSITY IMPACT ON GROWTH, YIELD, QUALITY AND QUERCETIN OF SHORT-DAY ONION

This study evaluated growth, yield, quality and quercetin concentration in response to planting density and deficit irrigation of onion (Allium cepa L.) in southwest Texas over two years. Onion seeds (cv. TG 1015) were direct seeded in the field on November 11, 2007 and October 30, 2008 at two planting densities (PD), 397 (standard PD) and 494 (high PD) ×1000 seeds•ha-1. Three irrigation rates were imposed after plants were fully established, 100, 75, and 50% crop evapotranspiration rates (ETc). Overall, there were consistent trends for bulb size, yield and quality parameters in both seasons. The number of bulbs and total marketable yields significantly increased (7-14%) at high PD; however, high PD decreased bulb size as compared to standard PD. Deficit irrigation at 50% ETc decreased most growth components. Similarly 50% ETc rate decreased marketable yield by 27% and 19% in 2008 and 2009, respectively; while 75% ETc decreased only 8% in 2008 and 13% in 2009. Soluble solids content, pungency, and quercetin were not affected by irrigation or planting density in both seasons. These results suggest that growers in water-limited conditions could adjust planting densities and implement water conserving practices (e.g., 75% ETc rate) to target high-price bulb sizes without reducing flavor or nutritional components.