Plant development and solar radiation interception of four annual forage plants in response to sowing date in a semi-arid environment

Annual forage crops attract more attention to researchers for it can be used as both forage in animal production and ethanol production in industry. Sowing date are critical to increase crop yield potential in semi-arid environments. Successful establishment and canopy develop are two key aspects ensuring the final yield of forage crop. Therefore, emergence time, leaf appearance and solar radiation interception by the canopy were measured with four annual forage grasses [maize (Zea mays), Sudan grass (Sorghum sudanense Stapf., S), foxtail millet (Setaria italic) and Japanese millet (Echinochloa crus-galli var. frumentacacea)] during the period of 2011-2013 in the western Loess Plateau of China. The results showed that a delay of sowing date could decrease the time for crop emergence. In addition, a decrease in the final leaf number (FLN) and the individual leaf area (ILA) (maize, foxtail millet and Japanese millet) from delayed sowing resulted in less light interception (RI). The variation FLN was closely related to day length (DL) and initial soil water and rainfall at flowering (W-s + R-f) for maize and foxtail millet, thermal time (TT), DL and W-s + R-f for Sudan grass and Japanese millet. Changes in leaf area per plant (LA(single)) in Sudan grass, foxtail millet and Japanese millet were caused by leaf area elongation rate (LAER). Sowing date did not affect leaf appearance rate (LAR) in Japanese millet while decreased in Sudan grass and increased in foxtail millet when the sowing date was delayed, mainly due to changes in DL, TT and W-s + R-f. Variations in individual leaf area (ILA) and LAER indicated the strong plasticity of the four crop species. Therefore, the results of this study improved the understanding of the relationship between sowing date and canopy development and provide important information in crop management and breeding to increase the crop yield.