I'm not an expert in the situation, but I'd guess that:

• Animal manure. We're wealthy enough that we don't think about it much, but meat is calorie inefficient, something for the wealthy. North Korea is pretty poor, has had recent problems just feeding the population, has seen famine. Unless you're part of the regime -- I suspect, looking at his figure, that Kim Jong Un is getting a healthy dose of calorie-rich foods -- I doubt that a lot of meat consumption is happening in North Korea. If you're having a hard time getting enough calories produced, you aren't going to be targeting luxuries like meat.

  kagis

  https://archive.ph/osH3s/again?url=https://www.nknews.org/2022/04/how-north-korea-tried-and-failed-to-boost-consumption-of-the-other-white-meat/

  North Korea has never been a nation of meat eaters, even considering an increase in consumption under Kim Jong Un, but that does not mean the country’s people do not like meat. On the contrary, meat has always been a desirable and prestigious delicacy in the DPRK, as it is throughout East Asia.

  The problem has always been that high population density has required the use of nearly all available flat land for rice paddy fields, since an acre of agricultural land produces roughly ten times the calories of an acre of pasture.

  This says that meat consumption did increase somewhat under Kim Jong Un:

  https://www.38north.org/2023/09/north-koreas-animal-protein-farming-expansion-status-and-challenges-2/

  Prior to 2000, except for North Korea’s elites, the country subsisted principally on vegetarian diets. To have meat as few as two to three times a year was the apparent norm. Under Kim Jong Il, that began to change as efforts to expand the availability of animal protein to more of the population began around 2005.

• Ashes. I don't think that this is a substitute, don't think that nitrogen at least is provided, which is the most-critical thing that fertilizer normally provides.

  kagis

  Sounds like it.

  https://gardening.usask.ca/articles-and-lists/articles-how-to/using-wood-ash-in-the-garden.php

  Is wood ash a good fertilizer? 

  Wood ash adds nutrients to your soil, but the amount varies according to the kind of wood burned. Generally, the largest ingredient in wood ash is calcium carbonate (about 20%). This is followed by potassium (less than 10%), phosphorus (1%) and trace amounts of micro-nutrients such as iron, manganese, boron, copper and zinc. Wood ash does not contain nitrogen. 

  Used in moderation, wood ash helps to fertilize your soil. However, since wood ash has no nitrogen at all, it is not a complete fertilizer. Adding compost to your soil will help meet the other nutrient needs of your plants.

  https://en.wikipedia.org/wiki/Fertilizer

  Nitrogen-fixing chemical processes, such as the Haber process invented at the beginning of the 20th century, and amplified by production capacity created during World War II, led to a boom in using nitrogen fertilizers.[2] In the latter half of the 20th century, increased use of nitrogen fertilizers (800% increase between 1961 and 2019) has been a crucial component of the increased productivity of conventional food systems (more than 30% per capita) as part of the so-called "Green Revolution".[3]

• Bones. Bones come from animals. See above point about meat.