Crop growth rate (CGR) response of three warm season C4-grasses (cereals) namely: corn (Zea mays L., cv. Hybrid-5393 VT3), grain sorghum (Sorghum bicolor L. Moench, cv. Hybrid-84G62 PAT), and foxtail millets (Setaria italica, cv. German Strain R) grown in pure and mixed stands under low and high water levels was investigated at one month interval namely: 30, 60 and 90 days after emergence (DAE), in pot experiment at Dryland Agriculture Institute, West Texas A&M University, Canyon, Texas, USA during spring 2010. The corn CGR in the mixed stands was 22, 11 and 9% higher than in pure stand at 30, 60 and 90 days after emergence (DAE), respectively. The corn plants in pure stand had 91, 66 and 84% higher CGR than the average CGR of both sorghum and millets at 30, 60 and 90 DAE, respectively. Grain sorghum in pure stand had 72, 30 and 40% higher CGR than that of millets in pure stand at 30, 60 and 90 DAE, respectively. The CGR of the three crops in mixed stand was 10 and 12% higher than the average of two crops mixed stand at the two early stages; but the CGR was reduced by 42% in the three crops mixed stand than the average of two crops mixed stand at 90 DAE. Corn mixed stand in two crops (average of corn + sorghum and corn + millets) had 78, 75 and 74% higher CGR than the mixed stand of sorghum and millets at 30, 60 and 90 DAE, respectively. Corn and millets mixed stand had 16, 9 and 38% higher CGR than the corn and sorghum mixed stand at 30, 60 and 90 DAE, respectively. Corn had higher CGR under high water at 30 DAE. There was no difference in the CGR of sorghum under low and high water levels at different growth stages. Millets had higher CGR under high water level at 30 DAE, but had lower CGR under high water level at 90 DAE. Among the three crops, corn plants had the higher CGR due to the highest total dry matter accumulation in both shoots and roots and was considered the best competitor in all the mixed stands. Grain sorghum ranked second, while foxtail millets ranked in the bottom in terms of competitiveness in the mixed stands.
Key words: Zea mays, Sorghum bicolor, Setaria italica, competition, water levels, crop growth rate.
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