This is great information, Entwined, thank you for sharing about how deep rooted plants can bring nutrients up to the surface of the soil. The negative side is that your plant of choice, Convolvulus arvensis, Field bindweed is non-native, from Europe and Asia and is considered an invasive and noxious weed in 35 States of the USA. I would think twice before considering using bindweed as a soil enrichment plant and make sure it's not considered invasive in my area before planting it.