What is the title of Cato the Elder's handbook on agriculture?

The title of Cato the Elder's handbook on agriculture is indeed "De Agricultura." This work, written in the 2nd century BCE, is one of the earliest examples of a Roman agricultural treatise. It serves as a comprehensive guide covering a wide range of topics related to farming, soil management, and agricultural practices. Cato's manual is significant not only for its practical advice but also for its insights into Roman rural life and economy.

The other options do not represent the correct title. "De Agri Cultura," while appearing similar in translation, is not the title that Cato used for his work. "De Hortis" translates to "On Gardens," which does not encompass the broader agricultural practices Cato discusses. "De Arboribus," meaning "On Trees," focuses specifically on a limited aspect of agriculture, rather than the entirety of farming and cultivation that Cato explores. Thus, "De Agricultura" correctly reflects the title and scope of Cato's influential agricultural manual.