Brace Root Contribution to Variation in Post-Silking N Uptake in Corn.

Improved post-silking nitrogen uptake by corn is one of the key components of nitrogen use efficiency contributing to increased yield potential in modern corn hybrids.  In a study of variation in nitrogen use efficiency components among six Dekalb commercial corn hybrids, we observed a positive relationship between increased post-silking nitrogen uptake and increased brace root number.  We hypothesized that increased brace root number led to an improved capacity to acquire N.  To test this hypothesis, we measured the effect of brace root pruning on N use efficiency components (determined by the budget method) of two hybrids with high (hybrid 1) and low (hybrid 2) brace root number, and of hybrid 1 subject to brace root pruning at V12.  Brace root pruning of hybrid 1 decreased post-silking N uptake, but only to a value intermediate between unpruned hybrid 1 and hybrid 2.  Increased post-silking N uptake by hybrid 1 relative to hybrid 2 may be driven by increased functional stay-green in hybrid 1, rather than solely by increased brace root numbers.  Brace root pruning decreased grain weight in hybrid 1, but did not affect R2 shoot biomass, indicating that root pruning likely had the largest effects on plant C allocation during grain-filling.  Brace root pruning strongly decreased N remobilization to levels below both unpruned hybrids, presumably due to strong effects on grain-filling in hybrid 1 combined with only moderate effects on post-silking N uptake.