You've asked a very loaded question. Lots to consider there, and you'll get many different opinions. When you say 'soil health', what particular aspects are you considering: Compaction? Maintaining moisture? Keeping organic mater content as high as possible? Reducing spray use for better microbe & micro-nutrient preservation? All important, and unfortunately every tillage method (or lack of) has advantages in one area and disadvantages in another. I don't pretend to be an expert, but here are just a few points to consider:
- Greater depth is better for breaking up compaction, which can have significant results on yield (especially with modern equipment being so large/heavy. It wasn't so much of a concern back in our Grandfathers' time). A deeper tillage pass every now and again also helps bring some of the deeper nutrients and OM from deeper root systems to the surface.
- Moldboard plowing can create a hard pan along the bottom of the share that's bad for compaction in heavier soils.
- Deeper moldboard plowing is the best mechanical weed control you can get. If it allows you to avoid a spray pass, the benefits to soil health are huge. I don't want to sound like a tree-hugging hippy (I'm quite the opposite), but the years from about 1960 to 2000 saw some of the worst practices for soil health and sustainability. Only in recent years are folks are finally realizing there's more to yields and soil sustainability than just your basic NPK credits and organic matter content. Microbe action is huge for soil health and yield, as well as for converting and preserving micronutrients. And pretty much every common pesticide/herbicide out there harms your microbes. Because the last few decades have seen so much ravaging of the soil, these days you hear more and more about different nutrient deficiencies than you did, say, 30 years ago.
- A disc plow like you're thinking of (or a more modern offset disc) typically won't get quite as deep as a moldboard plow, nor bury the trash quite as effectively. But does do reasonable jobs of both. And often results in a smoother surface. So not as good for weed suppression and may result in more herbicide use being necessary. But it may allow fewer additional tillage operations being necessary, and thus can be beneficial for some other aspects, because of:
-- Every tillage pass does some damage to the organic matter content, and is the equivalent of removing 1/2" to 1" of rain. Obviously you want to keep organic matter content as high as possible. But if you need to dry out your fields, some extra tillage passes can help. But if you have dry growing seasons (especially dry early growing seasons - which we seem to be seeing more and more of) the last thing you want to do is lose that residual moisture. I was a huge fan of my old Dearborn disc plow for this reason: A good happy medium between moldboard plowing and minimal till. It does a reasonable job of burying the trash and weed suppression for many conditions, but also leaves a much smoother field. Often a single pass with a harrow is all that's required after the disc plow. With a moldboard plow, it requires at least two or three additional operations afterwards, which don't do an favours to the OM content or moisture retention. Unfortunately my piddly little disc plow is far too small to use at any kind of a large scale. It's even too small for my pokey little antiquated operation.
- Disc rippers, chisel plows, and more modern one-pass tillage systems typically have deeper penetration and are much better than conventional methods for breaking up compaction. But often quite poor for weed suppression and burying trash.
It's a 'pick your poison' scenario. A good mix of methods is probably the best: And I certainly don't pretend to be an expert.
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