The Effect of Soil Moisture Content (in Primary Tillage) and Travel Speed during Disking Operation on Performance of Disk Harrow as a Secondary Tillage Tool

This study was conducted to investigate the effect of soil moisture content in primary tillage and travel speed during disking operation on the performance of an offset disk harrow in a silty clay loam soil. At first, the effect of three soil moisture content ranges of (12-14), (14-16) and (16-18) percent (dry basis) on soil clod size (left from moldboard plowing) was investigated. Then, the performance of disk harrow as a secondary tillage tool was evaluated at three speed ranges of (3-5), (5-7) and (7-9) km/h and three clod size mean weight diameters (31, 41 and 47 mm) resulted from moldboard plowing. The experiment was of a Randomized Complete Block Design, (a factorial experiment) of three replications. The performance parameters evaluated were: draft per unit width, drawbar power requirement, tractor drive wheel slip and degree of soil pulverization. Results indicated that, draft and drawbar power requirements of disk harrow increased significantly with increase in the travel speed. Tractor drive wheel slip was highly influenced by travel speed, clod sizes and as well by their interactions. Soil moisture content was an important factor primarily affecting the size and hardness of soil clods made by plowing operation, and secondly, it played an important role in soil pulverization through disk harrowing. Overall, the optimum soil moisture content for conducting primary tillage using a moldboard plow was determined as about 16 to 18%(dry weight basis), which corresponds to 91% of lower plastic limit of the experimental field. Meanwhile, the optimum speed range for disk harrowing was determined to be 5 to 7 km/h.