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Barley, Wheat, and Triticale Grain Yield in Relation to Solar Radiation and Heat Units¹

High grain yields (6 to 10 t/ha) of spring habit small grain cultivars are typically obtained in the Tulelake Basin of northern California (41°58'N, 121°28'W, 1230 m elevation) in the April to September growing season. In an attempt to identify environmental factors important in attaining high grain yields, a 3-year study with four dates of planting (17 April to 7 May) and four seeding densities (100 to 400 seeds/m²) were used to modify the crop growth cycles of seven cultivars or populations of barley (Hordeum vulgare L.), wheat (Triticum aestivura L.) and triticale (X Triticosecale Wittmack). Solar radiation and heat units (maximum air temperature –5°C) were computed for each of three growth periods: early vegetative (EVP), early reproductive ERP), and late reproductive (LRP). Grain yields declined later planting dates; wheat and triticale were more strongly affected than barley. There was little effect of seeding densities on grain yields. Path coefficient analysis revealed the following relationships: Solar radiation, while strongly and positively cor. related with the length of early vegetative period (EVP) in all three crops, was negatively related to grain yield per day, while heat units positively affected the rate of grain yield formation during EVP. Both solar radiation and heat units were positively related to the length of the late reproductive period (LRP) all three crops. For barley there was a strong negative effect of solar radiation and heat units during the LRP on grain yield per day, in contrast to the strong positive effect of these parameters on wheat and triticale. These results suggest that barley required less solar and heat unit energy than wheat and triticale to produce maximum grain yield. Higher temperature and lower solar radiation during the early vegetative period appeared to be beneficial for all three crops.

Key Words: Date-of-planting • Seeding density • Correlation • Path analysis • Environmental factors • Hordeum vulgare L. • Triticum aestivum L. • X Triticosecale Wittmack

² Respectively specialist in agronomy; professor of agronomy, Dep. of Agronomy and Range Science; statiscian, Div. of Statistics, Univ. of California, Davis, CA 95616; farm advisor (retired), Univ. of California Cooperative Extension, Tulelake; and former research associates (present addresses, research geneticist, USDA, ARS, Dep. of Agronomy, North Dakota State Univ., Fargo, ND 58102; and Istituto di Biologia Agraria, Univ. degli Studi della Tuscia, Via Riello, 01100 Viterbo, Italy).

Received for publication June 4, 1984.