I. Wheat seedling emergence under controlled climates

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Abstract
Experiments to determine the effects of the machinery and techniques used in creating direct-drilled seed grooves, and of covering the seeds, on wheat seed fate and soil physical characteristics are described. Comparisons were initially made in soils at either end of the available moisture range, and under contrasting controlled climatic conditions. Three coulter types were compared—an experimental chisel coulter, and commercially available triple-disc and hoe coulters. The technique used steel tillage bins containing dry, undisturbed fine sandy loam. In dry soil the seedling emergence count was significantly superior when the chisel coulter was used (58.4%) compared with the hoe coulter (31.3%), which was itself significantly superior to the triple-disc coulter (10.5%). In a moister soil the chisel and hoe coulters gave similar emergence counts (mean 68.8%), but both were superior to the triple-disc coulter (42.0%). A significant increase in seedling emergence was observed when the seeds were pressed into the base of the hoe and triple-disc coulter grooves before bar harrowing, compared with pressing the soil and cover over the seeds after bar harrowing. This appeared to be a result of improved seed-soil contact. In dry soil biological failure within the hoe coulter grooves was mainly at germination. With the triple-disc coulter seeds germinated but died before emergence. Seedling emergence was significantly improved when the controlled relative humidity was increased from a low to a high regime in dry soil, but had no effect with moist soil.