I always found that establishing a cover crop or grain crop is a difficult task since either germination will be bad or germinated seeds does not push through mulch. Initially when I started natural farming, I never used to spend more time in preparing field. Later I understood that more time and care has to be spent in preparing a field. In conventional farming where they do tilling, they spend lot of time in making field uniform and they prepare bunds and field will look really nice. May be since I am new into the farming, I didn't observe these things closely.
First few trials, when I tried to establish sunhemp, I just broadcasted sunhemp and then cut the grass, in some places mulch were very thick and some places grass was not cut properly and ultimately sunhemp was not established uniformly and lot of grasses also grew along with it. The issue is that when you want to grow a grain crop after sunhemp, that also won't get established uniformly.
Another problem was, the germination won't happen uniformly. Later I found that this is some thing even Fukuoka san had experienced. In one straw revolution in the chapter 'Farming Among Weeds' it says
"White clover is sown about one pound per quarter acre, winter grains 61⁄2 to 13 pounds per quarter
acre. For inexperienced farmers or fields with hard or poor soil, it is safer to sow more seed in the beginning. As the soil gradually improves from the decomposing straw and green manure, and as the farmer becomes more familiar with the direct seeding non-cultivation method, the amount of seed can be reduced"
"Between mid-November and mid-December is a good time to broadcast the pellets containing the rice seed among the young barley or rye plants, but they can also be broadcast in spring. Rice is sown 41⁄2 to 9 pounds per quarter acre. Toward the end of April Mr. Fukuoka checks the germination of the fall-sown seed and broadcasts more pellets as needed"
So ultimately it is better to use more seeds in the beginning and also check if germination has happened otherwise some more seeds can be sown. This is very practical and that is what I like about Masanobu Fukuoka and he was a complete farmer.