OVER-RIDING EFFECTS OF TEMPERATURE AND SOIL STRENGTH ON WHEAT SEEDLINGS UNDER MINIMUM AND CONVENTIONAL TILLAGE

Soil temperature and soil strength are the most important soil factors affecting the germination and emergence of seedlings when soil moisture status and aeration are not limiting. Wheat cultivars Hartog and Rosella were sown in six experiments on conventional and minimum tillage treatments in the central-west of NSW in 1987-1988. Measurements of soil temperature, soil water content and soil strength in the vicinity of the seeds were taken for 20 days during seedling growth. Correlations were obtained between the maximum rate of elongation of the coleoptile, length of the shoot (first leaf) and soil temperature and soil strength when all environmental factors were changing and interacting. Times to first seedling emergence and to median emergence were delayed by 7 and 9 days, respectively, as soil temperature decreased from 17 to 5-degrees-C, whereas the median emergence time was delayed by an extra 5 days for a two-fold increase in soil strength. The use of such information to derive a predictive model for wheat emergence is discussed.