A line trial is a method used in agriculture to determine the best seed-row spacing, plant population and other management practices for optimum crop yield. It involves planting multiple rows or plots with different combinations of row spacing, plant density, fertilizer application rates, irrigation levels, etc., and then comparing the results to see which combination yields the highest return. The term "line" refers to a single row or plot in the trial, while "trial" means an experiment conducted to test the effectiveness of different methods.