Perhaps you should try some spelling variations:
"Migrant agriculture soil Mexico." » "Migrant agriculture crop Mexico.", "Migrant agriculture _ Mexico."
"migrant agricultural laborers mexico." » "migrant agricultural labor mexico.", "migrant agricultura laborers mexico."
soil mexico » social mexico, seel mexico, civil mexico

Try widening your search to All Fields.

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (("migrant agricultural laborers mexico.") or ("Migrant agriculture soil Mexico."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("migrant agricultural laborers mexico.") OR ("Migrant agriculture soil Mexico.")).
• Removing quotes may allow a broader search: (( migrant agricultural laborers mexico. ) or ( Migrant agriculture soil Mexico. )).
• Adding a wildcard symbol may retrieve word variants: (("migrant agricultural laborers mexico.") or ("Migrant agriculture soil Mexico."))*.