Nitrogen and Dry Matter Distribution by Culm and Leaf Position at Two Stages of Vegetative Growth in Winter Wheat

each plant component (Klepper et al., 1983; Wilhelm and McMaster, 1996), researchers can now communiKnowledge of N and assimilate partitioning in wheat (Triticum cate with greater detail and precision about phenomena aestivum L.) improves management efficacy and crop model development. Our purpose was to describe N and dry matter distribution occurring during wheat growth and development. The during vegetative growth of blades, sheaths, and internodes on four basic tissue types of leaves, stems, and kernels can now culms. Winter wheat grown at the Colorado State University Horticulbe partitioned as part of individually identified culms or tural Farm was sampled at Haun Stage 5 and jointing. Samples were as parts of phytomers. Phytomers are the fundamental dried, weighed, and analyzed for N. As the canopy developed and building block of culms consisting of a node and tissues older tissue contributed more of total tissue, N concentration dedeveloped from it, including the blade, sheath, intercreased although N mass and dry weight increased. Dry matter and node, and axillary bud (Wilhelm and McMaster, 1995). N mass decreased from MC to T1 and T2 to T11, while the reverse An advantage of this approach is that the canopy can be order was found for N concentration. Dry weight and N mass deconsidered a dynamic population of culms or phytomers creased as culm order increased (culm age decreased), because phyappearing, growing, interacting, and senescing over time, tomers were smaller and fewer existed. Nitrogen concentration had the opposite trend because new tissue contained about 40 g N kg 1 with the final result determining crop yield (Harper, but declined as the tissue aged to 30 g N kg 1. Initial growth of all 1977; McMaster, 1997). tissues had concentrations 50 g N kg 1 and at senescence declined In addition to the fact that little attention has been to 19 g N kg 1. Phytomer positions on different culms tended to have paid to N distribution within the wheat canopy, most similar N concentrations while identical phytomers on primary tillers work has emphasized distribution of N and assimilate tended to have greater dry weights than those on the MC and secondduring the reproductive phase and their effects on yield ary tillers. Phytomers tended to increase in N concentration and mass (Badaruddin et al., 1999; Demotes-Mainard et al., 1999). and dry weight acropetally. Results show that viewing the canopy as Unfortunately, far fewer reports exist on the content the interplay of appearance, growth, interaction, and senescence of and distribution of N and dry matter in winter wheat culms or phytomers can increase understanding of canopy N and dry during vegetative growth, the period during which most weight dynamics. of the yield potential is established (Gregory et al., 1979, 1981; Waldren and Flowerday, 1979). Translocation of assimilates (Demotes-Mainard et al., 1999; Rawson and N has long been recognized as a critical nutriHofstra, 1969; Wardlaw, 1967) and N (Bauer et al., 1987; ent for wheat (Miller, 1939). Work establishing adeDemotes-Mainard et al., 1999; Jeuffroy and Bouchard, quate nutrient levels for crops has usually involved 1999; McNeal et al., 1966) into wheat grain during grain whole-canopy analysis (Baker and Tucker, 1973; Melfilling is well documented. During grain filling, N consted et al., 1969), but researchers have increasingly rectent of nongrain tissue decreases while grain N content ognized the importance and utility of analyzing indiincreases (Bauer et al., 1987; Boatwright and Haas, 1961; vidual plant components at various stages of growth to Campbell and Davidson, 1979; Karlen and Whitney, better understand how wheat develops and grows (Baker 1980; Spratt and Gasser, 1970). Although studies exist and Tucker, 1973; Karlen and Whitney, 1980; McMaster, on the distribution of photosynthate in winter wheat 1997). Analysis of individual plant components, when (Thorne, 1982) and barley (Hordeum vulgare L.; Lauer done, has almost exclusively been based on pooling baand Simmons, 1985, 1988) canopies, more specific inforsic tissue types such as leaves, stems, and kernels from mation on dry matter and N partitioning is needed to all shoots within the canopy. With the development of understand wheat canopy growth and development durmorphological naming schemes that uniquely identify ing the vegetative phase. Descriptions of N distribution and dry weights among W.W. Wilhelm, USDA-ARS, Soil and Water Conservation Res. Unit, and within precisely identified culms and phytomers over Univ. of Nebraska, Lincoln, NE 68583; G.S. McMaster, USDA-ARS, the growing season would be useful in developing and Great Plains Systems Res. Unit, P.O. Box E, Fort Collins, CO 80522; testing simulation models of wheat development and and D.M. Harrell, School of Natural Resource Sci., Univ. of Nebraska, Lincoln, NE 68583 (formerly, USDA-ARS, Soil and Water Conservation Res. Unit, Univ. of Nebraska, Lincoln, NE 68583). Joint contribuAbbreviations: GDD, growing degree-days; MC, main culm; SE, stantion of USDA-ARS and Nebraska Agric. Res. Div. Published as Jourdard error of the mean; T1, primary tiller arising from the axillary nal Series no.13482, Agric. Res. Div., Univ. of Nebraska. Received bud of the first leaf on the MC; T2, primary tiller arising from the 25 Sept. 2001. *Corresponding author ([email protected]). axillary bud of the second leaf on the MC; T11, secondary tiller arising from the axillary bud of first leaf on primary tiller T1. Published in Agron. J. 94:1078–1086 (2002).