After making a presentation at the SSCA Annual Conference in February 2000 on the Opener/Rotation Study at Aneroid, I received several questions regarding why the weed populations with the knife opener was so high in 1999 as compared to the higher disturbance openers. I should clarify this situation and provide some more background that may shed some light on what is likely happening in this situation. Previous to the start of this study (three years ago), the field was seeded using sweeps for four years and hoe drills before that. This resulted in a significant weed seed bank population in the soil. Although the knife is a low disturbance opener, the hard fact is that it still disturbs the soil to some degree, depending on soil condition. In 1998, under very dry soil conditions, the sandy loam soil was totally fractured, even the subsoil, which stimulated weed growth. In 1999, under rather wet conditions, the surface was disturbed somewhat, but not the subsoil. However, the knife still produced high weed populations in '99. The rationale for this is that although it is a low disturbance opener, it apparently is going to take time before the weed populations from the existing weed seed bank in the soil are reduced. In addition, there is little weed control from the light tillage effect of the knife as compared to the sweep or even the spoon. The angle disc has so little soil disturbance that annual weed population reductions are immediate.
The next obvious question is "How long will it take before the weed populations become reduced using the knife?" That is difficult to answer. It will depend on soil zone and soil texture. In the Dry Brown Soil Zone of southwest Saskatchewan, it will likely take at least three or more years. In other areas, annual weed population reductions could be much sooner. The problem for farmers is this transition time from converting from a conventional or even high disturbance direct seeding system, to a low disturbance system using a knife. The benefits from going to that opener won't occur for a few years and the costs for weed control are still high. Hopefully, the farmer can hang in there during this period of transition because the benefits will certainly occur; not only in lower weed populations, but if using a diverse, extended rotation, the soil quality will also increase.
Another two years left in this study. The first weed count has just been completed at the time of this writing but the results have not been compiled. I will provide a further update on this project later in the year.