Should I enter a farm expense of a new drainage field for the house under assets to be deducted over several years or just under other expenses?

This is an improvement to your property that must be depreciated as a capital expense (page 25, no. 9 under Capital Expenses).  Tile drainage systems have a property class life of 15 years. This is more commonly referred to as the useful life of the asset.

Farmer's Tax Guide: https://www.irs.gov/pub/irs-pdf/p225.pdf