|Hoffman, Melinda - IOWA STATE UNIVERSITY|
|Owen, Micheal - IOWA STATE UNIVERSITY|
Submitted to: North Central Weed Science Society US Proceedings
Publication Type: Proceedings
Publication Acceptance Date: December 12, 1996
Publication Date: N/A
Technical Abstract: Seedling growth of domesticated and weedy Sorghum species germinated in a range of N concentrations in the laboratory was compared. Treatments consisted of KNO3 solutions containing 0, 10, 30, 50, 300, or 3,000 ppm N. Separate experiments were conducted for cultivated S. bicolor, wild type S. bicolor (shattercane), and S. halepense (johnsongrass). N at 3,000 ppm slowed germination of all three taxa. In both annual species, root weight was reduced by N at concentrations greater than 30 ppm but 3,000 ppm N was necessary to inhibit root growth of the perennial species. Trial by treatment interactions were significant so the effects of N on shoot growth varied with trial. Shoot weight of cultivated S. bicolor was reduced by 3,000 ppm N or by 300 ppm or greater N depending on trial. Depending on trial, shoot weight of wild type S. bicolor was increased by 10, 30, and/or 50 ppm N compared to 300 and 3,000 ppm N and lower concentrations of N also increased shoot growth compared to 0 N. S. halepense shoot weight was increased by 300 ppm N in one trial and by 30, 50, and 300 ppm N in another. Dry combustion methods were used to measure N in root and shoot tissues and N use efficiency (NUE) was calculated as the ratio of total dry matter per unit of N contained in the dry matter. Compared to lower concentrations of N, 300 ppm N reduced NUE in roots of both S. bicolor species. This was likely due to decreased dry weight. A similar effect occurred in shoots of cultivated S. bicolor. The response of shoots grown under these controlled conditions to N varied with time, although general trends were similar. Based on these results, it is likely that above-ground growth of these Sorghum taxa in nature would respond to N in an unpredictable manner .