I took a different reading from that, though it may be due to differences between the theatrical cut and the directors cut. I interpreted it not as him showing them how to irrigate, but organizing the work and directing it to be done.

The line "your father was important, his lands were not" suggests to me that this was not considered particularly good land worth capital improvements, hence why it had not had such a works built previously. Or, alternatively, it was badly administered land with an absentee landlord.