This is what a good agriculture dictionary says.

And from the web:
https://www.trenchers.co.uk/what-is-trenching.html
What is Trenching
Trenching is a technique which is often used in agriculture and sports fields to basically prevent the ground from becoming water logged.

Agricultural Trenching
Trenching has been widely used in agriculture for centuries to prevent the soil from becoming saturated. This is the best way to get the maximum yield of crops from ground which is prone to becoming waterlogged, the deep, narrow trenches are positioned to collect excess water and transport it away from crops allowing the soil to produce the maximum possible and the crops to flourish with just the right amount of moisture.