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Planting Date and Mater Deficit Effects on Development and Yield of Irrigated Winter Wheat¹

Major variability occurs in yield response of irrigated winter wheat (Triticum aestivum L. em Thell.) to water deficits and irrigation in the Southern High Plains. Evaluation of plant growth and development and yield components are needed to better understand water relations and to develop and test growth and yield models. The study was conducted to evaluate the effects of three planting dates, four to six water deficit treatments during stages of plant development, and two short wheats, ‘TAM W-101’ and ‘Vona,’ differing in yield components. Planting dates were early (15 September), normal (12 October), and late (7 November). Water deficits were established by withholding irrigation and were terminated at selected plant stages by applying irrigation to level border plots. The study was conducted on a slowly permeable Torrertic Paleustoll (Pullman clay loam). We evaluated development stages, tillering, plant water potential, grain and dry matter yields, and yield components of heads per m² spikelets per head, grain per spitelet, grain weight and number per m².

Early to normal planting, as compared with late planting (i) advanced the dates of phenological development, (ii) lengthened the time in the vegetative period, (iii) lengthened the time from floral initiation to inflorescence, (iv) increased tillering during vegetative growth and tiller senescence during jointing, and (v) increased dry matter and grain yields. Plant water deficits reduced yields by increasing tiller and stem senescence, which reduced harvested heads, and by reducing grain numbers (spikelets per head and grain per spikelet). Vona produced more secondary tillers and grains per head, but tiller-stem senescence and smaller grain size resulted in harvested head numbers and grain yield similar to those of TAM W-101.

High yields (5,580 kg/ha) were associated with adequate fall-tillering and irrigation during spring vegetative growth that minimized stress-associated tiller-stem senescence and reduction in spikelets per head. TAM W-101 was more resistant than Vona to severe desiccation and tillerstem senescence under severe water deficits. A fall irrigation applied before winter dormancy delayed the need for a spring irrigation until jointing. Irrigation just before a period of above average rainfall did not affect yields. Yields comparisons of TAM W-101 and Vona indicate that similar he yields can be produced by varieties having large differences in seed size and number per m², suggesting that specific yield components may not be closely correlated with high yield potential.

Key Words: Tillters • Yield components • Plant water stress • Dry matter accumulation rates • Southern High Plains

² Agricultural engineer and agronomist, respectively, USDA Southwestern Great Plains Research Cxnter. nushland, TX 79012.

Received for publication May 18, 1979.

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