Possible Clues:

• Fertiliser from seabirds
• Fertiliser from birds
• Eco-friendly fertilizer
• The dung of sea-fowl, used as manure
• Manure from birds — artificial fertiliser from fish
• Dung of sea birds
• Fertiliser applied a month after turning
• Islander not opposed to old type of fertiliser
• Perhaps Robin's dropping some fertilizer
• A ground prepared, but it's not right day for fertiliser