A tool grated in the gravelly soil.
Mr.Duke was no doubt using his night turn at the water on his corn instead of turning it on the hay-land as was the custom.

He would inquire of him about Carlia.
As he approached the light, the scraping ceased, and he saw a dark figure dart into the shelter of the tall corn.

When he reached the lantern, he found a hoe lying in the furrow where the water should have been running.

No man irrigates with a hoe; that's a woman's tool.

Ah, the secret was out! Carlia was 'tending' the water.