Create New folder and copy the map zip file you want to add corn texture to
extract the files to that folder

Copy the foliage_maize_diffuse to "textures/foliage" replace the file


Open map.i3d with notepad or notepad++
Search for:
<FoliageSubLayer name="maize"

then edit following with following numbers
numBlocksPerUnit="1.42"
width="2"
horizontalPositionVariance="0"

Save the file...Put everything back into zip
Copy back to My documents/mygames/farmingsim/mods
and enjoy
Have fun