By Sjoerd Willem Duiker
What is the reason to do tillage? Read on for a review of possible pros and cons.
Soil tillage decisions should not be made lightly, because of the increased exposure of soil to erosion, increased runoff potential, reductions of surface tilth and organic matter, and negative effects on soil life, fuel use, and labor needs.
It is important to evaluate all the reasons, options, and consequences of a tillage decision.
The most important reason for tillage has traditionally been weed control. However, with the advent of effective herbicides, this reason has largely disappeared. Weeds developing herbicide resistance may change this, but for now we can still obtain excellent weed control with available herbicide options and without any tillage in most situations. How do I know this? Well, in a Penn State study that was started in 1978, we continue to have excellent weed control after 44 years of no-till (first 22 years in corn, then 22 years in a corn-soybean-small grain/legume cover crop rotation). Does this mean no-till farmers use excessive amounts of herbicide? No—they may use an extra 'burndown' herbicide to kill existing vegetation prior to planting, but from then on, they use mostly the same herbicides as "tillage farmers." So that puts that question to bed.
So then, why do farmers till? The case could be made in the past that planting equipment could not accurately place seed at the right depth or properly close the seed slot in untilled fields. But that reason has also disappeared with the availability of excellent no-till planters and drills and an abundance of specialty attachments that can help customize your planter for your local conditions. Some will say this doesn't matter when you have to plant into 300 bu/A corn stover, but again, this argument can be easily destroyed by talking to one of our leading no-till farmers who are doing so, successfully. We even have farmers successfully planting 'green' into 6 feet tall rye cover so excessive residue is not a valid reason for tillage.
So then, why do farmers till? Is it to alleviate soil compaction from heavy machinery? If this was a valid reason for tillage, all farmers with large equipment would be tillage farmers, but instead we see many large farms use continuous no-till. In fact, we are seeing that with tillage ruts caused by heavy equipment are much worse than in continuous no-till. This causes a downward spiral of tillage and compaction.
So again, why do farmers till? Is it because they need to mix nutrients into the soil? If nutrient stratification were a problem agronomically, we would see a dramatic effect in our 42-yr no-till plots at Penn State, but we are not seeing that at all. So again, this argument is a no-starter. It may be, however, that ammonia volatilization from surface applied manure or urea-based fertilizer is a problem. This argument would hold water if farmers immediately incorporate the manure or fertilizer. Instead, often the tillage is done 2 or three days when all the ammonia volatilization has already happened. Injection of manure, banded application of nitrogen fertilizer, or using a urease inhibitor are other ways to reduce ammonia volatilization. Now from an environmental point of view there might be an argument to plow highly stratified phosphorus into the soil to reduce soluble phosphorus loss in runoff. In my view, this calls for some pretty serious inversion tillage – not a little mixing and stirring of the surface soil. Another reason for tillage may be odor problems. This is probably the most valid reason for tillage, but manure injection would be much more effective than tillage because the manure is immediately covered.
But then, why do farmers till? Perhaps it is because crop yields are better if they till. But this is another empty argument when we compare crop yields from our long-term tillage trial where we get lower yields with moldboard plowing and similar yields in no-till and chisel/disked plots. This exhausts my reasons for tillage, so the justification for it seems pretty slim.
Now you might respond with, "what is the big deal about tillage?" Well, tillage is the major reason for soil erosion in our state and we are still losing way too much productive topsoil. Tillage increases runoff because of the sealing of surface soil due to raindrop impact on bare soil. Tillage also destroys surface aggregates and reduces surface organic matter content, the major factor in producing favorable soil tilth. Soil tillage also has a negative effect on soil life and uses up fuel and time. These are the reasons why a tillage decision should not be lightly made.
Source : psu.edu