Deep may not be meaningful: Cost and effectiveness of various ripping tine configurations in a plantation cultivation trial in eastern Australia

Deep ripping (subsoiling) is one of the more significant costs of establishing tree plantations on ex-pasture sites with compact soils. Ripping cost increases with depth, but the appropriate ripping depth required for successful tree establishment and growth is rarely clear. Tine modifications such as winged shanks and shallow leading tines have been shown to improve the work efficiency (volume soil loosened per unit drawbar pull) of deep ripping. We investigated whether increased work efficiency also translated to greater cost efficiency (volume soil loosened per unit cost), and whether additional depth and volume of loosened soil improved tree growth on a compact, medium clay, soil. We measured the operating costs for nine different ripping tine configurations, applied in conjunction with bed mounding, and compared early tree (Eucalyptus pilularis Sm.) growth and survival between the nine treatments and a no-cultivation control. Tine variations included presence or absence of wings, presence or absence of shallow leading tines, and depth (0.8 m, 0.6 m and 0.4 m). In most cases, increasing ripping depth or adding wings to the main tine increased operating cost but also tended to increase cost efficiency. The most cost efficient arrangement was for a winged main tine operating at 0.6 m with no leading tines. All cultivation treatments greatly enhanced survival and more than doubled growth to age 19 months compared to the control, but no cultivation treatment resulted in significantly better growth or survival than any other. Our provisional conclusion is that, when performed in conjunction with mounding, ripping beyond 0.4 to 0.6 m is not needed for satisfactory establishment on similar sites.

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