Ask a question before reading for an answer
A question gives reading a purpose. Before opening an explanation of a process, ask what changes, what causes the change or why the sequence matters. The question directs your search without requiring you to know the answer already, and it gives the resulting note a clear reason to exist.
Go deeper
Turn a topic into something you want to resolve
The topic soil is broad. The question why some soils hold water longer than others gives the reading a more specific direction.
A pre-reading question creates a target for understanding. As you read, you can identify which passages answer it and which provide background.
The question is allowed to change. A source may reveal that your original wording combines two different processes or assumes something inaccurate. Revising the question is part of learning, not a failure to follow the plan.
When writing the note, keep the resolved question visible. This helps prevent the result from becoming a collection of attractive but disconnected facts copied simply because they appeared on the same page.