Seeking out experiene in which nitrogen fixing plants will grow through 4 inch straw (from rolls) when sown on top of unworked soil just before applying the straw, and which ones will grow when sown on top of the straw after it has been put down?
Looking for ways to grow peppers, tomatoes, cucumbers, aubergines ... even melons in a field without cover high in the short season, cold night alps.
I use straw as a mulch on my raised beds and I grow fava beans, english peas, snow and snap peas as well. I mulch about 3-4 inches thick, and none of the aforementioned will poke thru straw that dense. I carefully pull/push the straw aside when sowing my seeds in the soil so as soon as they sprout, they have sunlight. Once they're 6 inches tall I then push the straw snugly back up around the plants. They have serious difficulty poking thru straw that thick because of the shape of the sprout, being nubby and immediately growing small flat leaves. The only thing I currently grow that I can sow and then cover in straw and forget about is garlic. The shape of the emerging tip is needle like, and will weave its way thru the straw looking for sunlight.
I have no experience casting seeds on top of straw so I can't speak of results. One thing I can comment on when sowing seeds is to make sure there is good soil to seed contact so the seeds absorbs water, don't dry out, and there is moist soil immediately available for the acrospire to grow into. Good luck, I hope this helps!
"Study books and observe nature; if they do not agree, throw away the books." ~ William A. Albrecht
None of the mentioned seeds will push through 4 inches of straw mulch.
That much mulch, regardless of what that mulch is will keep the sun's warmth from reaching the soil until far after the time most people want their seeds to sprout.
Mulch that thick will create far more resistance than a young sprouting shoot can break through.
The accepted method for such thick mulch is to either let the seeds sprout prior to laying the mulch layer down or thinning the mulch layer at the planting site so the sprout can make it through.
Once the plant is up and growing you can spread mulch to just below the primary leaves, as the plant grows taller, you can add more mulch if desired.
As James mentioned, seeds rarely sprout directly in thick straw mulch, the exception I know of is well seasoned straw bales. These have added nitrogen and some soil watered in to them during the seasoning period.
That added soil is normally where you would direct plant seeds in the straw bales. The usual method though is to plant seedlings started elsewhere so they are already growing well when put into the bales.