Nitrogen efficiency in grain sorghum

Grain sorghum, Sorghum bicolor (1.) Moench has not been fully evaluated for its variability in nitrogen efficiency. A 2‐year study using 12 hybrids was conducted and nitrogen efficiency was calculated as: 1. total dry matter (DM) per unit N uptake (NE₁), 2. total grain yield per unit N uptake (NE₂), and 3. the product of NE₂ and the grain N:stover N ratio (NE₃). NE₁ values increased with plant age and were significantly different among hybrids at all stages of growth. A 20% difference in NE₁ was found between the least and most efficient hybrids at maturity. A significant hybrid x year interaction showed that the environment strongly influenced hybrid ranking. Hybrids which ranked high in one year often did poorly the other year and visa versa for NE₁, NE₂, or NE₃. Each N efficiency criterion ranked the hybrids differently, although NE₁ and NE₂ appeared to be the most closely related. Hybrids generally maintained satisfactory values for NE₃ if one parent (either male or female) had a high NE₃ value in hybrid combination. Differences were more dramatic for partitioning of N between grain and stover than for NE values among hybrids. Due to environmental influences, it appears that at least 3 or more years of data may be needed in order to establish consistent trends for N efficiency in grain sorghum.