Does anything become incumbent upon me towards my other children due to my equipping my son's agricultural land with water-pumping equipment that cannot be separated from the land, the cost of which he cannot afford, and which I cannot compensate my other children for with an equivalent value?

The preponderant view is that it is obligatory to be just between children in gifts and donations. An exception to this is if some of the children have a special need that necessitates favoring them to the extent of their need.

So, if your assistance to your child is due to his need, then there is no harm. However, if it exceeds his need, then it is not permissible to single him out with that. And the fact that he helped you in developing your land and incurred debt does not justify favoring him. For either that was a voluntary act from him, which is an act of righteousness, and favoritism is not permissible because of it; or he did that intending recompense, in which case he is entitled to it accordingly, and should be given a sum similar to what his wages would be if he were a stranger.

Therefore, you must equalize your children in giving, either by retrieving what you gave to the son or by giving the other children a similar amount. If retrieval is not possible, then you must give the other children a similar amount to what you gave this child, unless they consent to their brother being favored, provided they are adult and of sound judgment. And if you do not find anything to give them, then resolve to do so whenever you are able.