The most common and most likely answer to this crossword clue is the 4 letter word LOAM
I've seen this crossword clue in The Guardian
L
O
A
M
Buddy explains!

The straight part
We know that "his" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case his = loam.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does LOAM mean?
LOAM noun- A type of soil; an earthy mixture of sand, silt and clay, with organic matter to which its fertility is chiefly due.
- A mixture of sand, clay, and other materials, used in making moulds for large castings, often without a pattern.
- To cover, smear, or fill with loam.
- Made of loam; consisting of loam.