Effects of Air Temperature and Fertilizer Nitrogen on Spike Development in Spring Barley

Spring barley (Hordeum vulgare L.) grain yield levels are determined in part by kernel numbers per spike. Planting dates affect grain yields, in part, because of variation in air temperature; hence, there is a need to understand the effects of air temperature during initiation and development of the barley spike. The objectives of this study were to determine the effects of air temperature on the plant development stage, duration of apex differentiation, and number of spikelets per spike. ‘Bowman’ (two-rowed) and ‘Azure’ (six-rowed) were grown in controlled environments at constant air temperatures of 18, 22, and 26 °C from seedling emergence to awned-spikelet stage of spike development of the main stem at fertilizer N levels of 0, 70, and 200 kg N ha⁻¹. Mean Haun stage at apex double ridge was 3.5 for Bowman and 3.8 for Azure; at awned spikelet it was 5.4 for Bowman and 6.0 for Azure. Haun stage of both cultivars at double-ridge and at awned-spikelet stage was greater at 26 than at 18 and 22 °C. Days from seedling emergence to double ridge averaged 10.8 d for Azure and 11.7 d for Bowman; to awned spikelet 21 d for Azure and 23 d for Bowman. Duration of spikelet development for Azure was similar (avg. 11 d) at all temperatures, but for Bowman, duration was 7.8, 12.0 and 18.7 d at 18, 22, and 26 °C, respectively. The main stem spike of Bowman deformed and aborted when grown at 26 °C. Kernel numbers of both cultivars were highest at 18 °C. Based on the combined data from the controlled-environment study and a related field study, kernels per spike decreased by 1.5 for Azure and 0.6 for Bowman for each degree increase in mean daily maximum air temperature during spikelet development. This relationship has utility to predict kernel numbers per spike, and, along with plant population and tiller number, has practical application for predicting grain yield potential 25 to 30 d after seedling emergence.