Document Type : Research Paper
Abstract
No tillage systems can reduce operating costs, enhance soil organic matter, ameliorate soil structure and prevent environmental damage caused by stubble burning. However, the lack of an appropriate direct drill for the hardened soil of arid areas reduces adequate soil-seed contact and, thus, the system has shown contradictory results in past tests. Developing a direct drill to place the seed and fertilizer at different depths, then cover the seed with a layer of fine soil without incorporating stubble into it is the first step in applying the no tillage system in pilot experiments. In this study, an active notched coulter (PTO driven) acting as a circular saw that cuts a groove on the soil surface was installed on a grain drill and was evaluated in hardened soil covered by wheat residue mulch. The active coulter operated at different rotary speeds in the forward and backward directions (with or against the rotation of the tractor wheels). Preliminary experiments showed that the backward rotation of the coulter cut a deeper groove at a given speed and left a relatively clean, empty groove than did the forward rotation, which nearly refilled the groove. A cutting unit, therefore, was designed based on the backward rotation of an active coulter at 580-700 rpm. The coulter cut a 15 mm wide groove to an average depth of 55 mm as it moved forward, throwing the soil forward and upward. This necessitated placement of a mudguard over the coulter to prevent or redirect the upward flow of soil toward the end of the cutting unit. The soil particles thrown off of the end of the mudguard then refill about 20% of groove depth, the amount of soil required to create a layer of soil between the fertilizer and seed. The fertilizer tube was installed immediately behind the coulter (50 mm above the soil surface) before the soil flow partly refilled the groove. The seed pipe was then installed far enough behind the cutting unit along the groove to allow the seeds to be placed on the partially-filled groove. Finally, a fork coverer filled the groove with fine particles of cut soil spread alongside the groove. Evaluation of the procedure showed that the direct drill equipped with such a cutting unit was able to place the fertilizer granules about 20 mm beneath the seeds in a hardened dry soil covered with stubble while cutting less than 10% of the soil surface.
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