Nitrogen uptake and partitioning in stay-green and leafy maize hybrids

Nitrogen requirement, uptake, and remobilization patterns have been extensively studied for normal maize (Zea mays L.), but there is limited published work for the stay-green (SG) and Leafy hybrids. Under controlled greenhouse conditions, growth, N uptake and partitioning patterns of three contrasting maize hybrids (a conventional, 'Pioneer 3905', one bearing the SG trait 'Pioneer 39F06 Bt', and one with Leafy trait 'Maizex LF850-RR') were investigated. Individual plants grown in 6-L plastic pots were subjected to five different N fertilization regimes: (i) no N supply from seeding to V8, (ii) withholding N supply after V8, (iii) withholding N supply after silking, (iv) withholding N supply from 3 wk after silking to physiological maturity, and (v) continuous N supply from emergence to physiological maturity (control). Leaf chlorophyll content, dry matter, N uptake, and accumulation in different plant parts were measured. The Leafy hybrid had a greater number of leaves and total plant dry matter while kernel yield was similar to that of the other two hybrids. There were no differences in total N uptake and partitioning among the hybrids studied across all five N treatments. The SG hybrid (Pioneer 39F06 Bt) remained green until physiological maturity only when there was a continuous N supply in the growing medium. For all hybrids, N supply was more critical before silking than after silking as limiting N supply reduced ear size, kernel yield and N uptake. Restriction of N supply from seeding to V8 caused an irreparable reduction in ear size and kernel yield (30%). Withholding N supply from V8 to maturity reduced kernel yield by 22% and N uptake by 53%. There was no yield reduction when N was restricted from silking, or 3 wk after silking to physiological maturity. The results indicate that stay-greenness in maize was exhibited only when there is an adequate supply of N in the growing medium and is not associated with greater N acquisition or remobilization than the conventional hybrids even with full N fertilization.