It is a shame that the direct drilling thread has stopped. It was just getting to an interesting stage. A few contributors were challenging that a seed drill could influence crop yield. Let me tackle that question by asking if those readers believe that tillage influences crop yield? Of course it does. Everyone knows that poor tillage will result in lower yields that good tillage. When you undertake no-tillage, almost everything that an array of tillage tools would have been doing is now required to be done by a single implement, the drill. A huge amount of scientific research was devoted to finding out exactly what influence a no-tillage drill could/should have on (1) stand establishment and (2) crop yield. The results are all wriiten up in a book that was commission by FAO (United Nations) because FAO thought is was sufficiently important for other people to know about it. The book is called "No-Tillage Seeding in Conservation Agriculture" and will be published by CABI, Oxford. shortly. In summary:
(a) Drill openers have a big influence on the microenvironment that seeds and seedlings experience in untilled soils (tillage tools rather than drills have most influence on the microenvironment in tilled soils).
(b) This microenvironmental influence is itself largely determined by where the surface residues end up relative to the slot (there are no surface residues in tillage).
(c) The microenvironment is also influenced by depth of seeding. Consistency of depth is more important and difficult to maintain in no-tillage than in tillage and drill design has a major influence on how well this is achieved (in tillage, because the soil is made uniformly soft and smooth the drill has a simpler job to do).
(d) Drill openers have a major influence on compaction around the seed (tillage eliminates the influence of opener compaction by unformly loosening the soil). Compaction, in turn influences growth of seedling roots.
(e) Drill openers have a major influence on how seeds derive water for germination. In no-tillage, vapour-phase water (in other words soil humidity) becomes an important germination resource whereas in tillage it is less important and even virtually non-existent in loose seedbeds. Liquid water is the only thing available in most tilled seedbeds.
(f) Similarly no-tillage drill openers have an important influence on areation around the seed and seedling roots (tillage does this instead in conventional seedbeds).
(g) Drill openers influence how well the slots are closed, which is harder to achieve than in tillage because the soil is less friable. But it influences how much drying and bird damage occurs.
(h) Finally seed drill openers determine if and where fertilizer is placed during the drilling process (fertilizer placement is not very important in tillage but has a major influence on crop yield in no-tillage).
I hope the doubters can now understand that they have simply not thought deeply enough about the topic to be able to comment with any basis of knowledge. Of course genetic content and available nutrients are also major determinants of yield. But even these fundamental resources are useless unless the drill positions seeds, seedlings and growing plants to take full advanatge of them. I guess another way of looking at it is that poor drill design can negate the positive things that genetics and fertilizers offer.
Cross Slot drills did not just appear from under a gooseberry bush. They are probably the only drills in the world that were the result of 30 years of detailed scientific research designed to find out exactly what influence drills could have on yield in no-tillage before a single piece of steel was cut. That is why they have taken so long to come to fruition and why they are relatively expensive to produce.