guano vs mulch

guano

noun
  • Coccothrinax borhidiana, a variety of palm tree indigenous to Cuba. 

  • Dung from a sea bird or from a bat. 

mulch

noun
  • Any material used to cover the top layer of soil to protect, insulate, or decorate it, or to discourage weeds or retain moisture. 

verb
  • To apply mulch. 

  • To turn into mulch. 

How often have the words guano and mulch occurred in a corpus of books? (source: Google Ngram Viewer )