Effects of N-deficiency and timing of N supply on the recovery and distribution of labeled 15N in contrasting maize hybrids

Little information exists on the pattern of nitrogen (N) uptake, remobilization and N use efficiency (NUE) in Leafy and stay-green (SG) maize (Zea mays L.) genotypes. A pot experiment was conducted under controlled nutrition and growing conditions to determine the response of Leafy and SG maize genotypes to different levels of N-deficiency and timing of N supply. Three contrasting maize hybrids, ‘Pioneer 3905’ (a conventional hybrid with moderate SG characteristics), ‘Pioneer 39F06 Bt’ (with a high score of SG trait) and ‘Maizex LF850-RR’ (with a Leafy trait) were grown in 6 L plastic pots. Five different N treatments [no supply of N until V8 (N1), no supply of N after V8 (N2), no supply of N after silking (N3), no supply of N beyond 3 weeks after silking (N4), and continuous N supply from emergence to physiological maturity (N5; standard check)] were imposed through modified Hoagland solution applied manually. Labeled 15N of 5% 15N2–NH4NO3fertilizer was applied at 3 g per pot at the start of each schedule N treatment. Total amounts of N applied in different treatments were 3.13, 1.32, 1.90, 2.63 and 3.40 g, respectively in N1, N2, N3, N4 and N5. Dry matter, N concentration, 15N (atom% enrichment) and NUE were determined in roots, stalk, leaves and grains at crop maturity. The three contrasting hybrids did not differ in grain yield, total N acquisition, partitioning of 15N and NUE. Restriction of N supply until V8, and from V8 to physiological maturity significantly reduced grain yield and N-uptake in all hybrids. Irrespective of the level of N-deficiency in plant and timing when the labeled fertilizer was applied, the amount of 15N recovered in the matured plant was the same in all N treatments. It has been evident that maize continued to take up N beyond 3 weeks after silking and the later N was applied during the development, the higher proportion of it was partitioned to grains. Of the total 15N uptake, 78% was partitioned to kernels in the N4 treatment compared to only 61% in the control. Our data showed no evidence of differential N uptake, remobilization and NUE in the SG or Leafy hybrids tested, but the timing of N application and level of N-deficiency in plant significantly influenced N uptake, remobilization and N-dynamics in maize.