You can still see fields in England and persumably in Ireland too where they have ploughed up and down the field creating what is called ridge and farrow lines which are off contour. They tend to be pasture fields now and sometimes people plant trees on the ridge and the excess water collects and drains in the farrow. If Seimi could plough in a load of biochar at the same time with a horse (to minimise compaction) he would be increasing the water holding capacity and forming the earth works at the same time.