|Harrell, D - UNIV OF NEBRASKA/LINCOLN|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 10, 2002
Publication Date: September 30, 2002
Citation: WILHELM, W.W., MCMASTER, G.S., HARRELL, D.M. NITROGEN AND DRY MATTER DISTRIBUTION BY CULM AND LEAF POSITION AT TWO STAGES OF VEGETATIVE GROWTH IN WINTER WHEAT.. AGRONOMY JOURNAL. 2002. 94(5):1078-1086. Interpretive Summary: Technical Abstract: Understanding the distribution of N and dry matter, over time, to individual leaves and internodes of wheat can aid in developing more effective cultural practices and enhance usefulness of comprehensive crop growth models. We collected field-grown (Ft. Collins, CO) winter wheat plants during two seasons and identified and separated the stems (culms). We subdivided each culm into phytomer units (leaf blade, leaf sheath, and internode attached to one node). Each component was identified and labeled following a nomenclature system that named all plant part uniquely. This allowed comparison of components of different plants over time and space. The weighed and the N concentration of all components were determined. As the canopy developed, older tissue contributed more of the total dry weight. As a result, N concentration decreased, but N mass and dry weight increased. Dry weight and N mass was greatest for the main stem (the first culm to emerge), less for primary tillers T1 and T2 (tillers formed in the axil of the first and second leaves on the main stem, respectively), and least for secondary tiller T11 (tiller formed in the axil of the first leaf on the first tiller of the main stem). The opposite was found for N concentration. Initial growth of all components had N concentrations greater than 50 ppm; at senescence concentrations declined to less than 10 ppm. Identical phytomer positions on different culms had similar N concentrations. However, identical phytomers on primary tillers had greater dry weights than those on the main stem and secondary tiller.
Technical Abstract: Detailed knowledge of partitioning and distribution of N and assimilates to individual components of wheat improves crop management efficacy and aids development of crop growth models. We examined N concentration, N mass, and dry matter content during vegetative growth of individual blades, sheaths, and internodes on four culms during two seasons at the Colorado State University Horticultural Farm. As the canopy developed and older tissue contributed more of the total tissue, N concentration decreased, even though N mass and dry weight increased. Dry matter and N mass decreased from MC to primary tillers T1 and T2 and was least for secondary tiller T11. The inverse relationship was found for N concentration. Dry weight and N mass decreased as culm order increased (culm age decreased) because fewer phytomers were present on younger culms and the phytomers that were present were smaller. Nitrogen concentration had the opposite trend because new tissue contained high N concentrations (about 40 g N/kg) but declined steadily as the tissue aged. Initial growth of all tissues had N concentrations greater than 50 g N/kg; senescence concentrations declined below 10 g N/kg. Identical phytomer positions on different culms tended to have similar N concentrations while identical phytomers on primary tillers tended to have greater dry weights than those on the MC and the secondary tiller. Phytomers tended to increase in N concentration and mass and dry weight acropetally on a culm. This study shows that we can increase our understanding of canopy N dynamics and dry weight distribution patterns when we view the canopy as the interplay of the appearance, growth, interaction, and senescence of either culms or phytomers.