The Nazi's were very concerned about German food sustainability. A big factor in Germany's WWI loss, was the Allied blockade leading to starvation in Germany. By the end of 1918, 763,000 German civilians died from starvation and disease. This was followed by 15 years of economic devastation and poverty for many.
Nazi's believed that the US standard of living, which they envied, was directly proportional to its agricultural production. Hitler wanted a better living standard for Germans. They also believed that German agricultural productivity was maxed out by the 1930s. That German agriculture could make no big gains in productivity.
Hence, before WWII, Germany secretly proposed to Poland, no less than eight times, a join German-Polish invasion of the Soviet Union because the Nazis wanted to annex the Ukraine for Germany. German farmers would then colonize the Ukraine; one of the most fertile agricultural regions, close to Germany.
This belief in the absoluteness of limits to the economy, we can call it neo-Malthusianism, is central to Green thinking.
Leading Nazis were vegetarians too. Not because they loved animals, but because they considered it morally repugnant to eat meat. Because arable land can support 15 times the population that pastoral land does. Eating meat, while other Germans starved was morally repugnant to them.
Revealed in Black Earth, by Timothy Snyder.