A Queensland, Australia author explains the Nitrogen issue well: The presence of undecomposed organic matter in the soil stimulates an explosion in the populations of the micro-organisms that rot it down. This explosion makes a heavy demand on soil nitrogen, to form the body proteins of the organisms. When decomposition is complete, the population returns to normal levels, releasing nitrogen back into the soil.
If crops are planted before the decomposition process is complete, they usually suffer from a deficiency of nitrogen and are more vulnerable to attack from the higher population of plant-pathogenic soil micro-organisms. The usual diseases that occur are seed rots or damping-off of young plants. Losses are often so heavy that replanting is necessary, resulting in high establishment costs and a delayed harvest.
Take care that you do not mix the subsoil (usually a lighter colour) with the topsoil, but add plenty of organic matter to both.
After digging, leave the soil to settle. Ideally, you should dig over a new border [planting area] in autumn and leave for the winter. But gardeners do not always have control over time-scales, are busy and frequently impatient to get going with planting! Do try to let the earthworms do their stuff though, and leave the newly dug border for [at least] a few weeks. You can remove annual and perennial weeds that emerge over the coming weeks, further cleaning the border.
Great! So have patience. It will be worth the wait. This would apply after you have turned under winter ground covers, chopped and dug in green manure favas, or added manures unless it’s bunny poop, which can be used instantly. My favas have already flowered and I’ve dug them in, last week of January, so that soil will be ready to go mid March! Dig in, watch, weed, wait, weed, plant!