Comparison of Conventional and Minimal Tillage for Low-Input Pasture Improvement

In forage-based production systems farmers are frequently confronted with a decision of when, or whether, to reseed pasture in order to maintain or improve productivity. At its simplest such a decision would be guided by evaluation of the costs of improvement in relation to the benefits accruing from the newly-sown pasture but, in practice, costs may be difficult to define. In addition to labor, equipment, and material costs of the field operations necessary for planting, there are less obvious costs that result from production losses during the period of ground preparation and establishment of a new crop. While it is generally assumed that these production losses may be compensated over time by increased productivity in a reseeded pasture, the period of amortization may be prolonged (75,80). Hopkins et al. (51) found that yield benefits deriving from reseeded compared with continuous pasture were largely eliminated when establishment-year production shortfall of the reseed was considered. Lack of persistence, slow establishment of reseeds, and periodic stand failure will further compromise the long-term productivity of reseeded pastures and the economic viability of a reseeding program (6,9,77). Much has been published on the effectiveness of seeding by minimal-tillage methods, but the focus of work has been on minimal tillage as an alternative to conventional cultivation and sowing for establishment of annual crops (67). Less attention has been given to its impact on pastures or on its value in low-input pasture systems, where resource constraints make reduced cultivation and infrequent reseeding especially desirable. Seeding pasture by minimal tillage offers several potential advantages over conventional methods, including cost savings resulting from reduced cultivation, reduced risk of soil erosion, improved trafficability of land, and reduced damage by grazing animals (67). However, the potential of minimal tillage to reduce establishment-phase production loss by minimizing damage to existing pasture has not been specifically addressed. Nor is it clear whether the savings in cultivation and planting effort that use of minimal tillage permits are offset by longer-term impacts of reduced pasture productivity, reduced persistence and a need for more frequent pasture renewal. This literature review assesses the value of minimum tillage for pasture improvement and its particular application in lowinput systems. Presentation of data. For comparison of performance parameters (emergence or yield), "minimal tillage" has been interpreted to mean seeding by no-till or conventional drill into ground undisturbed except for the passage of the seeder, or by broadcasting onto untilled or frost-tilled ground [pre-plant tillage 0 to 3 on the 0 to 10 scale used by Wolf et al., (95)]. Data sources were selected to provide direct comparison between minimal tillage and conventional seeding practices, and parameter values have been expressed as a percentage of no-till drill values (= 100) unless otherwise noted, to allow comparison among disparate experiments and crop types. Four main categories of minimal-tillage seeding were identified: cool-season grass sown into cool-season grass (CSGCSG); cool-season grass sown into warm-season grass (CSG-WSG); cool-season legume sown into cool-season grass (CSL-CSG); and cool-season legume sown into warm-season grass (CSL-WSG). Some instances of cool-season grass sown