This quality-of-life mod simply expands the area where a water block may be in order to hydrate (water) a farmland block.

It adds an additional, 3x1x3 layer below the crop block where water may reside. This makes it possible to create "fields" where water is hidden under the block.

More specifically, it changes the water scan area. Assuming (0, 0, 0) is the position of the farmland block, the scan ranges from:

vanilla:  (-4, 0, -4) to (4, 1, 4)
mod:      (-4, 0, -4) to (4, 1, 4)  +  (-2, -1, -2) to (2, -1, 2)