I need to p this test help please!?!?!?

None really put N back into the soil, but 3 would be the best... Since the others are mainly for erosion and irrigation. The first choices actually had legumes, which are beneficial for soils, as N depositors. But crop rotation seems the likely choice. That is what farmers do, to keep soils from losing all nutrients, many times, they will not even plant a certain field. Give the field some rest, to allow it replenish certain nutrients.