1) Dirt expert 2) Expert 3) Expert in soil management 4) Soil-management expert 
• (n.) One versed in agronomy; a student of agronomy.
A·gron'o·mist noun One versed in agronomy; a student of agronomy. 
[n] - an expert in soil management and field-crop production
agronomist, agronome 1. Someone engaged in the study of agronomy; a rural economist. 2. A person who studies or is an expert in crop production and soil science.
Qualified person who inspects crops and advises growers on agronomy, varieties, herbicides etc.
noun an expert in soil management and field-crop production