Something that would/could have improved german food stituation considearbly : Give Falkenhayn a wee bit more "belief" in his own believes about the duration of the war and some more serious talks with his brother, who run the ... "family estates".
He as the War Minister knew quite well about the "material" preparedness or better unpreparedness of Germany for a longer war (6 months plus). Therefore he jumped happily on the occasion, when Rathenau offered him to "run" the raw material management for (mostly military) industrial production.
Somehting achieved with quite remarkable good results. Esp. if you keep in mind, that such a task on a "reichsweit" (nation-wide) scale was something completly new and heavily opposed by almost every other industrialist and industrial economist by that time in Germany.
Unfortunatly for Germany :
Falkenhayn wasn't able to adapt his thinking of the needs and duration of the war to food and agriculture sector as well. ... Though Rathenau proposed to apply the by that time only thought of methods for industry to agriculture as well.
Couriosly Falkenhayn rejected this offer made by Rathenau in late August/beginning September 1914 (again), referring to the then assumed shortness of the war as well as an assumed sufficient capability of the existing agricultural sector ( a position as unfortunatly also taken by Falkenhayns 2nds in charge at the War Ministry Franz von Wandel and Wild of Hohenborn).
For the OP :
If you look for a suitable POD let Falkenhayn give Rathenau also the agriculture to "reorganize" in late summer/early autumn 1914.
You will get a much more efficient agricultural production with effective allocation and use of fertilizers, man and horse power, transportation etc. in accordance with the needs of the industrial sector as well and a much more efficient buying of food-stuff in the neutral neighbour-countries than OTL. You might even see some "forced" reorganisation of agricultural land-ownerships for more effectiveness (Flurbereinigung).
I am quite sure, that something as catastrophically felt like the turnip-winter wouldn't have occured (I am as sure, that the usage of turnip would have been implemented much earlier but in a much more ... "relaxed" way than OTL).