You could try Handbook of the German Army, compiled by British Army observers in about 1906 and updated just before the outbreak. It's available as a joint publication with the Imperial War Museum and someone else. I've got the Handbook of the Belgian Army, and it goes into just that kind of detail (although a lot less complicated, since Belgium had only one type of field gun and no howitzers)
There are loads of books on the subject. I'm sure there'll be something on the Net about a topic of such great interest.
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"Sometimes things that are not true are included in Wikipedia. While at first glance that may appear like a very great problem for Wikipedia, in reality is it not. In fact, it's a good thing." - Wikipedia.
A 1914 German field artillerie batterie was composed of six guns. Regular army infantry divisions also had light field howitzers. Their ratio to guns was 1:3. Foot artillerie batteries were composed of heavy guns and howitzers. This included all guns of 9cm or larger, and howitzers of 15cm or larger. Foot artillerie batteries were typically under Korp control.
Later, when the numbers of field artillerie were expanded they were reduced to 4 gun batteries.
