I propose you a little listening exercise:
1. Fill in the blank as you listen to this sentence:
_____________ is material spread over soil. (The mp3 has been adapted / cut from VOA SPECIAL ENGLISH)
2. Answer key: above
3. More:
The word mulch can be defined as a shelter, as of vegetal or plastic material over the soil to protect plants from soil erosion, water loss etc.
Some bilingual dictionaries do not give the right translation of the term. (I will omit the wrong Spanish translation).
When it comes to translate so technical terms, I recommend specialized dictionaries, such as this one:
ISBN: 84-7114-818-8
By the way, the proper translation of mulch into Spanish is: acolchado (or mulch, I´m sorry, as I see it it´s not worth fighting against Anglicisms) .
Have a nice weekend!
Alonso