Three high-yielding and three low-yielding grain sorghum hybrids were grown for a full season for grain yield and total dry weight of forage with two levels of irrigation (dry and wet) and two levels of nitrogen (0 and 100 lbs /acre). The experiment was conducted at the University of Arizona Marana Agricultural Center. The combined high nitrogen fertilizer and high water irrigation increased grain yield and total dry matter of sorghum over the dry moisture condition and no nitrogen fertilizer application more than the applied increases of nitrogen fertilizer or irrigation water alone as expected. Both high- and low-yielding groups of sorghum hybrids had the same basic relative percentage potential for increased grain yield from additional nitrogen fertilizer under either wet or dry conditions.

Three high yielding and three low yielding grain sorghum hybrids were grown for grain yield and total dry weight in late planted simulated double-crop after barley or wheat harvest with two levels of irrigation (dry and wet) and two levels of nitrogen fertilizer (0 and 100 lbs/acre). The experiment was conducted on the University of Arizona Marana Agricultural Center. Nitrogen fertilizer and the interaction between nitrogen fertilizer and water irrigation had no significant effect on the grain yield of sorghum hybrids. Additional nitrogen fertilizer applied under dry conditions reduced both grain and total dry matter production, and when applied under wet conditions produced gains in grain or dry matter production of only 1% to 4% for the high and low yielding groups. Additional irrigation water produced 61% to 77% additional grain under low and high fertilizer levels for high and low yielding sorghum groups. Additional irrigation water produced 8% to 38% more plant dry matter under low and high fertilizer levels.