STEM INFUSION OF N-15 TO QUANTIFY NITROGEN REMOBILIZATION IN MAIZE

Nitrogen (N) use efficiency (NUE) of fertilizer N can be accurately es timated by tracing the fate of soil applied labelled fertilizer, but t he quantity of N remobilization from non-kernel components into kernel s in maize (Zea mays L.) plants is difficult to determine. A field exp eriment involving stem infusion with labelled N-15 solution was conduc ted at Ottawa, Ontario (45 degrees 22'N, 75 degrees 43'W) for two year s to determine whether stem infused N-15 could be used to quantify N r emobilization and the contribution of remobilized N to the grain. A cu rrent stay-green commercial hybrid was grown at three fertilizer N rat es and infused with 30 mt N-15 solution [35.7 mmol N as (NH4NO3)-N-15- N-15 at 99.2 N-15% atom enrichment(a.e.)] into the internode below the primary cob at anthesis. The control plants were infused with distill ed water. Sampling occurred at 3 d, 2 wk and 5 wk after anthesis and a t physiological maturity. Each plant was subdivided into ten component s. Dry weight, total N concentration and N-15% a.e. were determined fo r each component. Thirty mt of dilute N solution plus 10 mt of distill ed water was taken up within 4 to 6 hours after infusion. At 3 d after infusion, infused N-15 moved out of the internode where it was infuse d, into dominant sinks, with more than 40% in the reproductive compone nts (cob, husk, and kernels), 30% in leaves above the ear, and another 15 to 20% in the upper stem. By physiological maturity, 65 to 75% of infused N-15 was deposited in the kernels. Between 59 and 82% of kerne l N was remobilized from non-kernel components, whereas 18 to 41% was derived from N uptake during grain fill. These findings indicate that stem infusion is a useful technique to study N remobilization.