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Studies of Intact Shoot-Root Systems of Field-Grown Winter Wheat. II. Root and Shoot Developmental Patterns as Related to Nitrogen Fertilizer¹

Root development and growth for winter wheat (Triticum aestivum L. em. Thell.) influence seasonal water and nutrient uptake. Root location and function with time in the field are needed to understand the role of roots in plant growth and tiller survival. Fertilizer timing was used to modify root and tiller growth in a field experiment. Objectives were to observe appearance and measure distribution with depth and time of identified roots during the growing season. Field plots on a Walla Walla silt loam (mixed, mesic Typic Haploxeroll) were fertilized once with (NH₄)₂SO₄ in October, February, or April or left unfertilized. Square metal tubes, forced into the soil after emergence, enclosed shoots and developing root systems of six to eight plants. Tubes were extracted at beginning and mid-tillering, jointing, and anthesis. Roots were washed, separated, and identified. Length, condition, order of branching, and number and length of lateral roots was measured on each. Leaf development rates were the same in tubes and plots only for February-applied fertilizer. Denitrification from transient waterlogging occurred in some tubes. Seminal roots remained intact and grew until anthesis. Crown roots explored the soil in order of their appearance with older axes branching more and penetrating deeper. Seminal root distribution with depth was more nearly linear than that of nodal and tiller roots, which were exponentially distributed. Magnitude of rooting at all depths was increased by N which increased branching. Leaf and root development were closely correlated, but root development or lack thereof on tillers did not appear to be the major factor controlling tiller survival.

Key Words: Root length density • Seminal roots • Crown roots • Root depth • Tillers • Tiller roots • Triticum aestivum L. em Thell.

² Crop physiologist, A.F.R.C. Letcombe Laboratory, England (presently with the Dep. of Agriculture, Jarrah Road, South Perth 6151, Western Australia), and plant physiologist and soil scientist, respectively, USDA-ARS, Pendleton, OR 97801.

Received for publication September 9, 1985.