The effects of early season soil temperatures on emergence of summer crops on the north-western plains of NSW

Abstract

The influence of early season soil temperatures on the extent and rate of emergence of five summer crops was examined using four sowings at weekly intervals between late September and late October. The crops were maize, grain sorghum, pearl millet, and two forage sorghums. Increasing soil temperature reduced the interval between sowing and first emergence, and gave variable results for the interval between first and final emergence. Percentage emergence of maize was high at all sowings, whereas that of all three sorghums was low at sowings with soil temperatures at 4 inches of below 65¦F, but did not differ significantly between sowings at temperatures above 65¦F. Emergence of pearl millet improved with each later sowing, but differences were not significant. Rate of emergence was accelerated by rising soil temperatures in the four days after first emergence, but subsequent effects after four days were generally minimal. Maize appeared to have a lower temperature requirement for emergence than grain and forage sorghums, which, in turn, showed a lower temperature requirement than pearl millet. From the results and other related data, it seems that maize can be sown with reasonable safety when four inch depth soil temperatures are 59¦ to 64¦F (expected in late September), sorghums (both grain and forage) when this temperature is 65¦ to 69¦F (expected in early- to mid-October), and pearl millet when it is 68¦ to 72¦F (expected in early- to mid-November). The results support the concept of soil temperature being the best criterion to determine a safe time for early season sowing of summer crops.