This is an example of a type of question you can get, where sometimes examiners put together some of the 'outlying' elements in a unit's syllabus (minor points mentioned in the indicative content but which aren't as 'core' to the topic perhaps as understanding NPK or soil texture) to make up a complete question.
If it had been anything other than Question 1 it probably wouldn't have been so daunting to candidates. It's a reminder to read through all the questions before you begin answering, and don't be put off right at the beginning of the exam if you don't think you can recall much for the first question.
If you can't think of something to put down immediately, leave it, answer the ones you know well and and then go back and apply common sense if you can't recall many hard facts!
Janet