In 1973, Robert Warren Tissing, Jr. completed his Baylor University Master's Thesis: "Utilization of Prisoners of War in the United States during World War II: Texas, A Case Study".

It's available online courtesy of the Robertson County Historical Commission.

From the conclusion:

The availability of prisoners for farm labor enabled farmers to save time and money by planting more crops and harvesting them faster. The German prisoners of war were well-treated during their stay in Texas. Almost all of the farmers enjoyed being around the prisoners and described them as being most cooperative and well-mannered. Many of the prisoners wrote letters to the farmers and expressed their desire to return to Texas.