The digestion is a good hint: Since about one year ago, when having problems with seeds, I put them in my mouth first. I wet them well. It is supposed to give the seeds bacteria which will stimulate soil biology around the seed. I read somewhere that plants can stimulate the bacteria they need for good health and growth. Since I started dowing this, I have more seedlings when direct sowing. Whether that is because of better germination or healthier plants that are not attacked by slugs I dont know. When I red this at first, I thought it was really weird, but it wouldn't hurt to try. I still giggle when somebody catches me with a mouthful of seeds... you have to find a method: I use my left hand to poke a hole in the ground with my finger, and than take a seed out of my mouth with the right hand, so I wont have to eat soil. Because it was so succesfull, iI pay a lot more attention to the soil biology in my garden. Any addition of bacteria has a positive effect (on weeds as well). Good luck!