If you have visited the Wine Country in late winter or early spring, you have seen this in bloom, carpeting the vineyards with gold. Not planted to be picturesque, though--it is widely planted to control soil diseases and pests like nematodes and fusarium. Deep taproot helps break up clay, hardpan, and other problem soils. It is not a legume, and doesn't fix nitrogen; instead it enriches the soil with sulfur, an essential plant nutrient for disease resistance, strong roots, and good soil structure. A very popular cover crop in the West with cost-conscious farmers because a little seed goes a long way and it has such beneficial effects on the soil. You can also harvest the seeds to make table mustard.