https://www.cambridge.org/core/journals/antiquity/article/scotlands-first-farmers-new-insights-into-early-farming-practices-in-northwest-europe/7C027B8A129F68533E558FAB47B63027
https://www.cambridge.org/core/journals/antiquity/article/abs/neolithic-timber-hall-at-balbridie-grampian-region-scotland-the-building-the-date-the-plant-macrofossils/D420E725469B2C8D55373400BE411024
The canny and thrifty Scots used materials that were cheap and plentiful in the land to fertilize their crops. Rocks.
Archeologists have found fields literally filled with rocks and made the obvious deductions.