NITROGEN USE EFFICIENCY AMONG DIVERSE SORGHUM CULTIVARS

Genetic diversity for N use efficiency (NUE) has been demonstrated in sorghum [Sorghum bicolor (L.) Moench] with some of the most efficient types being cultivars that evolved from low-fertility environments. Th e objectives of this study were to compare diverse sorghum cultivars f or their ability to cope with limited supplies of N. A Nigerian landra ce (SC566), an Indian improved line (M35-1), two U.S. pure Lines (CK60 and Martin), and a commercial sorghum hybrid (Dekalb E59+) were compa red in solution culture and under two levels of limited N availability in a Nebraska held environment. Dry matter production and NUE (grams of dry matter per gram of N) were determined among all environments. I n the held environments, the vertical canopy profile was divided into three layers and repeated observations were made of leaf morphology, i nternal leaf anatomy, N content, and CO2 gas exchange rates under ligh t saturating and dark conditions. As the nature of N stress changed an d increased among environments, SC566 and M35-1 became superior to all U.S. cultivars in NUE. Conversely, U.S. cultivars were among the most responsive in total dry matter production and grain yield as N supply increased. In general, traits related to high NUE included larger can opies comprised of fewer but larger leaves with low N concentration, t hicker leaves, larger leaf phloem transsectional area, rapid solubiliz ation and remobilization of N from older to younger leaves, and lower dark respiration rates. These characteristics did not necessarily seem related to the level of domestication or origin of a cultivar, though M35-1 was found superior in NUE among all environments. Unique and po ssibly useful traits were found among both landrace and domesticated c ultivars.