Persian clover (Trifolium resupinatum) is an annual which is widely used across Europe. It is less common in the UK but can be a useful forage plant. It grows on most soils, even heavy types, and on slighty acidic to alkaline pHs.
As a clover it is, of course, a nitrogen fixer. According to work in Canada (Thompson & Stout, 1997) grass and cereal crops grown with Persian clover yielded 95% of the yield obtained with 200kg N/ha.
If autumn sown it grows well in spring (see photo) and has good summer growth after cutting or grazing. It may also be sown in spring for grazing or cutting in the same year. It is compatible in seed mixtures with most grasses and legumes. We have spring sown Persian clover at our trials ground at Moreton in Marsh. Results were acceptable but poor soil quality and lack of rain restricted its yield. On soils that suit it - those with high fertility and plenty of rainfall - yields would approach that of red clover.
Protein content is similar to other clovers and in mixture with grasses this will increase around 2-3%. Seeds are not expensive and are usually priced similar to red clover. Remember that this is an annual plant but seedlings from seeds that shed can give the false impression of it lasting more than one year.
For a one year ley Persian clover is a very good option and will be more productive than red clover for a short-term nitrogen boost.