Tillage, Soil Health, and Weeds: WSU Organic Transitions Project

Project Details

With recent funding acquired from WSU’s BIOAg Grant Program, we initiated an experiment this spring to evaluate the impact that tillage has on soil health metrics, weed populations, and crop growth. To evaluate this, we utilized a field at WSU Mount Vernon Northwestern Research and Extension Center that had not been tilled for about 10 years. Previously it was planted into alfalfa, but over time that planting became less and less competitive and eventually was altogether non-present. This offered a unique opportunity to re-introduce tillage back into this field and monitor changes in soil health and weeds. To this end, we decided to initiate two experiments in the field.

Figure 1. Dandelion taproot unearthed during weed seedbank sampling.

The first experiment involved two treatments: 1.) full tillage then planted with orchardgrass (Dactylis glomerata) and 2.) no-till overseeded with orchardgrass (Figure 2a and 2b). The goals of this experiment are to see the impacts of a single tillage event on soil and whether that single disturbance leads to changes in the weed population. Pastures commonly need to be renovated, so this trial compares two methods for renovating a pasture/grassland.

Figures 2a and 2b. No-till drill overseeding orchardgrass into non-tilled plots adjacent to full till plots.

Figure 3. Orchardgrass after one mowing 6/19/21.

The second experiment looks at the conversion of a non-tilled field into row crops comparing two different tillage tools: 1.) rototiller and 2.) power harrow. A section of the field was chisel plowed (to alleviate compaction) running at a consistent depth, then either of the two implements were used. Within a few days ‘Black Magic” lacinato kale was transplanted using a two-row transplanter. You’ll notice a visible surface residue difference between the two PTO implements (FIG 4).

Figure 4. Power harrow plots with visually more residue on the surface.

Prior to tillage we utilized glyphosate to knock back the remaining alfalfa but have since followed organic production standards. These trials explore two different transitions: 1.) conversion to organic production and 2.) conversion of a pasture/grassland to row crop production.  

We hope this project provides improved knowledge about the ongoing processes during pasture renovation and the conversion of pasture/grassland to row crops, elucidates the impacts that different types of tillage have on soil health, and helps us develop better strategies for weed management during the transition to organic production. 

We will be documenting the journey of this project in this blog over the next several years so stay tuned for more!