Utilization of Previously Accumulated and Concurrently Absorbed Nitrogen during Reproductive Growth in Maize

A prolific maize (Zea mays L.) genotype was grown to physiological maturity under greenhouse conditions to examine the effects of reproductive sink demand on (a) the remobilization of N accumulated during vegetative growth, and (b) the partitioning of N accumulated concurrent with ear development. One- and two-eared plants were treated with either a NO(3) (-) or NH(4) (+) source of (15)N-labeled N during reproductive growth. Plants with two ears enhanced grain production, N remobilization from the stalk and roots, and N translocation to the grain from concurrently assimilated N. But, remobilization of leaf-N was unaffected by ear number. In addition, N uptake and total dry matter accumulation during the reproductive period were also unaffected, although P uptake was greater in the two-eared plants. Less than 15% of the total K(+) uptake was accumulated after silking while during this time more than 40% of the total N and more than 50% of the total P were absorbed. The data also indicate that with NO(3) (-) nutrition, internal recirculation of K(+) between shoots and roots may play a prominent role in the transport of nitrogenous solutes during grain development. N source had no effect on dry matter production and N uptake of both one- and two-eared plants. However, slightly greater partitioning of labeled-N from the NH(4) (+) source to the grain was observed in the two-eared plants.