Effectiveness of narrow tyne and double-discs openers to overcome shallow compaction and improve soybean yield in long-term no-tillage soil

Compaction adversely affects the soil physical quality and crop yields in no-tillage (NT) systems. No-tillage seeders equipped with narrow tyne openers may be a cost-effective option to overcome shallow compaction in NT soil and reduce the reliance on tillage for seedbed preparation and crop establishment. This study was conducted to: (1) quantify changes in soil physical quality indicators and determine the crop response to the use of a NT seeder equipped with either narrow tyne or double-disc openers, and (2) evaluate the potential of seeding tynes to overcome shallow compaction in NT soils of southern Brazil. Soil compaction was induced by applying 0, 3, 6, and 9 tractor passes equivalent to 84 %, 89 %, 94 %, and 99 % of the degree of compactness. In each treatment, a narrow tyne opener was used for the deposition of fertilizers compared to double discs. Undisturbed soil samples were taken from the 0-0.10 and 0.10-0.20 m depths and used to measure soil bulk density, soil water and air storage capacity, and the Least Limiting Water Range (LLWR). Soil penetration resistance and soybean (Glycine max L., Merr.) yield were also measured during the 2014/2015 cropping season. Soil bulk density and soil water storage capacity increased while air storage capacity and the LLWR decreased with an increase in the degree of compactness. The use of narrow tyne openers reduced soil penetration resistance in the 0.0-0.10 m layer by up to 66 % compared with the use of discs, and increased soybean yield by an average of 600 kg ha-1 (or US$ 227 per ha). By contrast, the use of double-discs on previously compacted soil resulted in yield penalties of up to 1200 kg ha-1. Soybean yield was more strongly correlated with LLWR (r = 0.97) than with any other measured soil physical quality indicator. Overall, these results supported the hypothesis that the use of NT seeders equipped with narrow tyne openers was effective in overcoming shallow compaction in NT soil.