I had to look this up, so I thought there might be others who hadn't a clue what sanfoin was. Here is what I found:
Sainfoin has been grown in parts of Europe and Asia for hundreds of years. Various strains have been introduced to North America since about 1900. Most of the early introductions originated in western Europe, and were low yielding and poorly adapted to North American conditions. Recent introductions from the USSR and Turkey have shown greater promise, and more farmers have been growing the crops since the release of improved cultivars in Canada and the United States.
Sainfoin is deep-rooted and very drought-resistant, provided the annual rainfall is 12 inches or over. It yields best on deep, well-drained soils, and will not withstand wet soils or high water tables. Tests show that it will not tolerate saline soils and that it is not as winterhardy as the locally-recommended cultivars of alfalfa.
Sainfoin grows taller than alfalfa, its stem is hollow, there are many leaflets (like a vetch) and its flowers, which are pink, are borne on a raceme. The "seed" used to establish this crop is, in fact, a pod which contains a single seed. Even without the pod, the true seed is large (for a legume); there are only 28,000 seeds per pound.