Isn't agricultural production much more efficient when you don't kill all the farmers?
https://en.wikipedia.org/wiki/Organization_of_Ukrainian_Nationalists
https://en.wikipedia.org/wiki/Ukrainian_Insurgent_Army
Part of that depends on which areas of Ukraine you mean. The UPA had it's support in the areas west of the Dniepr, so theoretically they could feed their people and organize a government based in Kiev, giving surpluses to the Germans, while then starving the pro-Russian/Soviet populations east of the Dniepr. People with a Ukrainian identity then had a major split geographically much as they do now:
It isn't inconceivable that to eliminate potential sources of resistance to their rule they'd use food as a weapon to deal with Russian identity civilian populations to create their visions of a 'mono-ethnic state'. Given that people that considered themselves Ukrainian, not Russian, was probably less than half the population of geographic Ukraine, there are a lot of people that the UPA would see as threats to their regime and potentially disposable in the search for food for the war effort. Besides it is not like they couldn't ration either.
That says little about Ukraine's capacity to assist the Germans unless if it is married to where agricultural production originated. The principal benefit that the Germans expected and desired from Ukraine was her agricultural capacity. This is not, and was not, distributed evenly throughout Ukraine. I have not thus far, been able to find a map of Ukrainian agricultural output relevant to the era, but soil maps to the time period under discussion - which would be broadly similar - do exist.
For commentary upon this (from a different map:
http://www.fao.org/ag/agp/agpc/doc/counprof/Ukraine/ukraine.htm )
The north-west has a wide belt of soddy (dern or dernovo)- podzolic soils with mainly light texture on sand-clay strata. These soils form some 70 percent of the total cover, are characterised by low humus content, increased acidity and therefore need application of mineral fertilizers and organic manures, as well as lime to yield a rich harvest. Thirty percent of the territory is occupied with sod (dern), meadow, meadow-bog and peat-bog soils with slight soddy (dernor dernovo) sands on elevated pine-clad terraces. Over 600,000 hectares(60 percent) of Ukrainian peat lands are concentrated here.
A wide belt of grey forest soils, as well as podzol and typical chernozems with a 1.2-1.5 m thick humus bed, running from south-west to northeast, is located somewhat to the south. These soils are formed on loess strata. In addition to these, small areas are occupied with bog, meadow and meadow-chernozem soils, often of solonetz type.
Further to the south, encompassing a considerable part of the territory of Odessa, Kirovograd, Dnipropetrovsk, Zaporizhia, Donetsk and Lugansk regions, typical chernozems stretch, with the thickness of their humus bed up to 80-90 cm, formed on moist-loamy strata.
The southern part of Prychernomorie lowlands contains dry southern chernozems, which are replaced along the coastlines of the Black Sea and the Sea of Azov with a rather narrow strip of dark-chestnut and then chestnut soils combined with solonetz and soloth.
Carbonatic chernozems and brown forest (often with gravel) soils prevail in the Crimean Mountains, while the Carpathians are characterised with short-profile mountain-forest and sod-brown soils with low content of humus, leached and heavy acid soils (pH=3.6 - 5).
[Note: The classification applied in this paper is the Russian Soil Classification (Ivanova and Rozov, 1967) or a variant thereof. The terms dern(ovo) and sod are typically Russian and not easily translatable. Dernovo is used as "pseudo" in podzol-like soils. "Sod" refers to the topsoil horizon. Many of these soils correspond with the Albeluvisols (or FAO Podzoluvisols) which are characterized by a dark surface horizon, a bleached eluvial horizon and a horizon in which clay has accumulated. They are normally acid and sandy textured.
Western Ukraine can be broadly summarized thus as having soils which are worse in quality than their Eastern Ukrainian equivalents. Of course, agricultural productivity might vary beyond the soil productivity, but I would doubt that Western Ukraine would have any great advantage over their Eastern Ukrainian equivalents, or would be the inverse. The debilitating problems of collectivization would be avoided, such is true (although collectivization also makes it much easier to collect the farmers' agricultural surplus), but Poland's economic growth during the Interwar was lower than their Soviet equivalent, and investment and productivity gains in Eastern Poland - which became much of Western Ukraine - would be lower still. I think it highly doubtful that Western Ukraine produces anything in regards to an agricultural surplus given its poverty and poor soils. Starving Russians in Eastern Ukraine is what happened originally; all that the change in policy does is spare Western Ukraine from the same treatment and decrease the amount of food that can be taken from the region.
Rationing furthermore is not an option, not on the scale that is needed by the Germans. The agricultural surplus generated in the region is not enough to simultaneously ensure a healthy working population (especially important for the hard labor which unmechanized farming implies), while also providing for the food needs of the Germans. Thus, the question will be; who is to suffer? The Germans, or the Ukrainians?
No German government will ever choose the latter, and if they choose that then any policy seeking Ukrainian collaboration will be greatly reduced in effectiveness.
An obvious long term option is to starve the Russians in the East and replace them with peasants from the West who are loyal. But this is a long term option and either actively harms or at least does nothing to help agricultural production in the short term. If this is a long term policy, then it falls into the regular problem of German ideology; settling Ukrainian peasants there instead of Germany peasants is alien to German ideological and strategic plans.
Isn't agricultural production much more efficient when you don't kill all the farmers?
Isn't industrial production much more efficient when you don't starve all the workers?
The choice, in the short term, is whether to prioritize calorific consumption for Germans and industrial workers or for Eastern European farmers. Providing production does not increase - difficult to conceive in wartime Europe outside of temporary increases due to good harvests - the only option is to reduce consumption. The obvious target is the Ukrainians, and the only people who have the supplies of food the Germans need is the Eastern European/Ukrainian peasants. Germany will inevitably squeeze them, and this will make any attempts at cooperation meaningless.
From what I understand this only became true in late 42 and 43 . Before that Germany was able to feed it self, but the harsher winters caused a lower harvest.
The military crisis of the winter of 1941-2 frustrated Herbert Backe's
immediate aim of bringing about a massive rearrangement of the food
balance in the Eastern territories. But at the same time it confirmed his
deepest anxiety. Backe had not been bluffing in 1941. In light of the
extension of the war into the indefinite future, Germany was facing a
severe food problem.78 The German grain harvest in both 1940 and
1941 had been well below average and imports from the occupied
territories had not made up the difference.79 For lack of feed the swine
herd had been reduced by 25 per cent since the start of the war, triggering
a cut in meat rations as of June 1941.80 Bread rations had only been
sustained by making severe inroads into grain stocks. By the end of
1941, these were nearing exhaustion. When the order to ship large
numbers of Eastern workers to Germany for work was first given by
Goering in November 1941, Backe protested vigorously.
81 The 400,000Soviet prisoners of war already in Germany were more than he could
provide for. Goering had spoken casually of feeding the Eastern workers
on cats and horse-meat.82 Backe had consulted the statistics and reported
glumly that there were not enough cats to provide a ration for the
Eastern workers and horse-meat was already being used to supplement
the rations of the German population.83 If the Russians were to be given
meat, they would have to be supplied at the expense of the German population.
The official ration that was settled on for Soviet prisoners and Ostarbeiter
in December 1941 was clearly inadequate for men
intended for hard labour. It consisted of a weekly allocation of 16.5
kilos of turnips, 2.6 kilos of 'bread' (made up of 65 per cent red rye,
25 per cent sugar beet waste and 10 per cent straw or leaves), 3 kilos of
potatoes, 250 grams of horse- or other scrap meat, 130 grams of fat and
150 grams of Naehrmittel (yeast), 70 grams of sugar and two and a
third litres of skimmed milk. The appalling quality of the bread caused
serious damage to the digestive tract and resulted in chronic malnutri-
tion. The vegetables had to be cooked for hours before they were palat-
able, robbing them of most of their nutritional content. Though this was
a diet that was, relatively speaking, high in carbohydrates, providing a
nominal daily total of 2,500 calories, it was grossly deficient in the fat
and protein necessary to sustain hard physical labour. It was certainly
not enough to restore half-starved Soviet prisoners to good health. To
make matters worse, in the vast majority of camps nothing like this
official ration was ever delivered to the inmates.
Exhausted grain stocks and such major decreases in the animal reserves does not speak of the agricultural economy in 1940/1941 being in good health. Even marginal decreases in calories are going to have major effects upon the growing foreign labor supply, which will stunt armaments increase further.