Got it!

My mind it goes back to the days of my childhood
When my footfall fell lightly on valley and hill
And later my seaweed cart rocked on the bright road
As I nourished black earth and each sciollain hole filled

Scoillain is Irish for a seed potato. The way of planting potatoes depended on the type of soil. But the wrack, seaweed, was a common fertiliser in costal areas. It was usually gathered after storms, but was actually 'farmed' in some places, for example Mill Bay on the shores of Carlingford Lough.