No-till and the Soil

Driving around the state in recent days I see still a lot of tillage. You may think this is not a big deal. However, we have to consider what we are doing to our soils over the long run. Tillage moves soil downslope in undulating landscapes like our Pennsylvania terrain – this is called Tillage Erosion. Although reduced tillage like chisel plowing or disking doesn't move as much soil as moldboard plowing, it still moves some soil downslope.

A study done a few years ago showed that in the Corn Belt, the topsoil (A-horizon) was completely gone on 35% of the acreage due to tillage erosion. This is only in parts of the field but those parts of the field will have lower productivity. Other Midwestern studies showed 16-26 bu/A corn yield reduction due to the loss of the A-horizon. This is a significant yield reduction. Once gone, it is very difficult to build the A-horizon back up (even if you use all the soil health practices possible). 

Let's avoid soil degradation in the first place by using no-till practices for crop establishment. Now, water erosion is another form of erosion we are more familiar with. When I started working at Penn State in 2000, we were wondering if no-till was really necessary for soil conservation. A lot of work was done to determine the reductions in crop residue achieved with different tillage implements, aiming to achieve at least 30% crop residue after planting. Why 30%? Well, rainfall simulation studies showed that with 30% residue cover, sheet and rill erosion are already reduced 70% (See Figure 1), so 30% residue cover was set as the threshold to be considered 'conservation tillage'.

Now we've found that it's very difficult to meet that threshold if you do any type of tillage. In 2010, crop residue surveys were done in 7 counties in the southcentral and southeast of PA (Adams, Cumberland, Dauphin, Franklin, Lancaster, Lebanon, and York). The survey noted that very rarely was the 30% residue threshold reached when tillage was used, but almost all the no-till fields had more than 30% crop residue. That is the reason why we recommend no-tillage for soil erosion protection. 

Today, there is vertical tillage equipment that can leave more than 30% crop residue when used after corn grain harvest (but not after other crops), where all the residue is left in the field. However, in reality, farmers mostly use this equipment, and it is set aggressively to ‘move some dirt’. The result is that even with these tools, we can easily reduce crop residue cover below 30%, while research has shown no yield improvement or other substantial benefits for weed control, nutrient management, or seedbed preparation. One thing you may notice when you compare a crop like corn planted in tilled soil with no-till side-by-side is that the corn comes up more quickly in tilled soil and looks greener. This is a temporary effect due to slightly lower soil temperatures in no-till (See Figure 2). The reason is, the crop residue acts as an insulating blanket and this keeps the soil cooler while also conserving moisture.

Therefore, later, when temperatures inch up more, you will notice that the no-till crop catches up to the tilled crop and actually may surpass the corn in the tilled soil due to moisture conservation. Research in Kentucky showed that in heavy stover, evaporative soil water loss was about 1 inch more per month in tilled soil than in no-till soil until canopy cover. This can make a world of difference if you only get 3 inches or less in a month. Hopefully, this will convince you to stick with no-till and to try to improve this system instead of going back to tillage.

References 

T.E. Fenton, M. Kazemi, M.A. Lauterbach-Barrett, 2005. Erosional impact on organic matter content and productivity of selected Iowa soils. Soil Tillage Res. 82:163-171

Evan A. Thaler, Isaac J. Larsen, and Qian Yu, 2021. The extent of soil loss across the US Corn Belt. Proceedings Nat. Acad. Sci. Vol. 118 No. 8 e1922375118