Here are just a few more thoughts that are relatively random suggestions compared to Hai-Etlik's excellent analysis
Heavy agriculture isn't a term I'm familiar with. I think more of intensive farming and extensive farming. The former being characterised by market gardening, which is found more around cities or on good soil where there is space to build huge greenhouses and use hydroponic growing systems, while extensive farming is usually stereotypically characterised more by hill farming livestock that roam across unfenced moorland pastures.
To represent intensive farming (and depending on scale) I would draw the greenhouse systems, or lots of contrasting plots and strips in a close packed pattern. (intensive farming also includes those horrible sheds where animals are kept in tiny cages!)
To represent the extensive farming I would draw a map showing little farmsteads dotted quite a distance apart from one another, and maybe give some indication of paths worn by livestock passing through bottlenecks like gates from area to area, and add a couple of winter feeding sites where the ground has become puddled to mud around the drop point for bales of winter fodder. Also any water pumping sheds associated with water troughs, and the tracks leading to and from the troughs.