There are pros and cons to both...
1. The evenness on the spread sowed beans is better..the air seeder tends to get stacking, alot of clumps of 3 seeds together...I'm very happy with how the spread ones are spaced.
2. The spread ones need around 4" of loose dirt to incorporate into, I tried doing 2" but it left to many on top, these get destroyed by birds and what does grow may not anchor well and rapid growth sperts or high wind will blow them over.
3. I don't suffer from not enough moisture here...but if I was at toolondo still, when going into the bean rotation I would be discing them in, you loos a bit of moisture when discing in but when you do get winter rain it soaks into that 4" alot better, spring rain is critical for beans...cereals can tolerate alot more...
4. The double disc seeder leaves the seedbed more compressed, I could still drive over my block in a two wheel drive ute, it's amazing, greatly helped by drainage, levelling and incorporating stubbles last two years. We sprayed pre em after seeding and I rolled that in with my roller filled with water...instead of being untouchable for 3 months I might have 4-6 weeks where I can't get on...straw incorporation has changed this place...so I guess in summary when I get a semeato or a bar with disc units on it, that will be my first choice...on new lease ground it will be spread and disc method.
5. Speard method, germination is uneven due to depth of seed from on top to 4" deep, I assume they will level out, this might be an advantage? Or disadvantage not sure..
I know alot of guys have bought discs up around st.arnaud due to chemical resistance and ground getting hard after continuous direct drilling...so doing a pass before beans would be the shot in my book..so once every 4-7 years depending on rotation and how soil is going..I know they say soil life will solve all of this but this dirt ain't the best, was never the best, and will never be the Nile delta...
Ant...