Response of Sunflower to Limited Irrigation and N Rate.

A field experiment was conducted at the Southwestern Colorado Research Center to determine the response of sunflower to irrigation scheduling and N rate.  Irrigation application at R-1 (start of the reproductive growth stage) through flowering (R-6) produced as much seeds/acre as the full irrigation treatment (I-2) and was similar to I-4 (irrigation during flowering).  Similarly, seed oil content was in the order (highest to lowest): I-2 ≥ I-3 ≡ I-4 > I-5 > I-1 (Table 3).  Sunflower plants averaged 116 cm in height with the treatment that received the least amount of irrigation water (I-1) and with I-4, and 131 cm with I-2, I-3, and I-5.  Thus, restricting irrigation mostly to the flowering period (I-4) reduced plant growth but it did not negatively impact seed yield or oil content compared to I-3.  Treatment I-4 produced more seeds/inch of irrigation water plus rain than I-2, I-3, and I-5.  The addition of 56 Kg N/ha increased seed yield and oil content significantly compared to the check.  Seed oil content decreased as N rate was increased from 56 to 112 kg N/ha.  The irrigation by N rate interaction had no significant effect on seed yield or oil content at α = 0.05, although there was a large increase (394 kg/ha) in seed yield with 112 kg N/ha compared to 0 and 56 kg N/ha at I-3.  These results indicate that sunflower yield and use efficiency can be increased substantially with limited but well targeted irrigation application.  Applying water mostly during flowering increased seed yield by 55% compared to early-season irrigation. Water (irrigation+rain) use efficiency (kg of seeds/cm of water/ha) increased by 70% compared to full irrigation. Seed yield also increased significantly with the application of 56 kg N/ha.