It is a well-known fact that Germany suffered from food shortage during World War I, and that there were several causes of this, including in no particular order:
- The blockade restricting food imports
- The blockade restricting fertilizer imports
- Haber-process nitrate production diverted away from fertilizer to explosives
- Labor shortage because so many men had been sent to the front lines
- Shortage of horses for similar reasons
- Late and poorly designed food rationing measures
What seems to be much more difficult to obtain is any kind of numerical estimate for the relative importance of each of these causes. https://everydaylivesinwar.herts.ac.uk/2015/04/food-and-the-first-world-war-in-germany/ confirms that it wasn't just loss of imports:
As men and horses were called up, farmers’ wives took over the running of the farm, but lack of equipment, fertiliser and manpower, even though some 900,000 prisoners of war worked on the land, saw substantial falls in crop yields, which almost halved by the war’s end.
Right now I'm trying to get an idea of the importance of labor shortage. The time of year when labor is most needed for food production is harvest. In medieval times, pretty much the entire population, at least everyone able to walk, would help gather the harvest. By 1913, this was no longer necessary. But what happened during World War I? Sure, the men were on the front lines, or buried under them. But there were cities full of women and children who would be perfectly capable of harvesting crops. Were they employed in that capacity? If so, why was there still a labor shortage? If not, why not?
So to ask a specific factual question:
What percentage – or what absolute number – of the German population worked on gathering the harvest in 1917? (I would also be interested in figures for other years. But I pick 1917 in particular because by then, there had surely been enough time to make whatever changes from the peacetime economy, needed to be made.)