Abstract:
The results indicated that four general N use strategies are exemplified in the IBM RIL population. The primary strategies include high yield at low N accompanied by a small yield response to applied fertilizer N (Group 1; 31% of hybrids evaluated), and low yield at low N accompanied by a large yield response to fertilizer application (Group 2; 32% of hybrids evaluated). Group 1 hybrids produced 1.0 Mg ha-1 more grain than group 2 at low N (0 kg N ha-1) while Group 2 hybrids had a 1.0 Mg ha-1 greater response to applied fertilizer N (252 kg N ha-1). As a result both groups produced similar yields (6.9 Mg ha-1) when N was not limiting. Group 1 hybrids were characterized by higher than average genetic N utilization (grain yield per unit of accumulated N under unfertilized conditions) resulting in greater kernel number at low N, while Group 2 hybrids had higher NUpE and NUtE. An additional underrepresented group of germplasm in the IBM RIL population (16% of hybrids evaluated) is that which has a high yield under N limiting conditions and a large response to fertilizer N. This group appears to achieve high grain yield at low N through a combination of increased kernel number and kernel weight, while minimizing the decrease in kernel weight that typically results from fertilizer N associated increases in kernel number.
Parallel research to this project indicates that the majority of maize hybrids currently available in the marketplace fall into the two main groups demonstrated by the IBM RIL population. Further research should strive to understand the genetic and physiological mechanisms by which the two main groups of hybrids acquire and utilize N so that breeding programs can combine favorable traits from both groups.