Investigation of the Effect of Direct Drilling Methods and Planting Depth on Seed Uniformity Indices and Some Agronomic Indices in Rainfed Wheat Cultivation

An experiment was conducted during 2017-2018 and 2019-2020 (the land was followed between two intervals) as a split-split plot in a randomized complete block design with three replications to investigate the effect of using the no-tillage method in different residues and variable planting depth in rainfed conditions. In this experiment, the main plots were crop residue levels with two levels (1- retaining only standing stubble and 2- retaining all residues), and subplots were opener types (1- Narrow shovel, 2- wide shovel, and 3- disc opener), and sub-sub-plots were planting depths with two levels (4-6 cm and 6-8 cm). This study used common direct drilling employed in the Markazi province for rainfed wheat cultivation (Hamedan Machine Barzegar, Jeiran Sanat Arya, and Taka Companies). Conventional tillage and planting methods (moldboard plow+cultivator+deep seeder) were also considered controls in each subplot. The planting depth uniformity coefficient, horizontal seed distribution uniformity coefficient, field germination percentage, and crop yield were measured in all treatments. The results showed that the effect of opener type and planting depth on the yield was statistically significant (p<0.5). The effect of residue in two years of cultivation on yield and measured traits was  insignificant and confirmed that the effect on yield and measured factors was no different. The direct seeding technique demonstrated a lower yield, while the conventional planting method with a deep seeder using the conventional common opener had the highest yield. The uniformity coefficient of vertical seed distribution is statistically significant (p<0.01), which indicates that the type of furrow opener can be effective in seed depth placement. With increasing planting depth, seed germination percentage and grain yield decreased. The findings also showed that employing the direct drilling method while reducing operation time has saved the amount of fuel consumption by an average of 75% compared to the conventional cultivation methods.