There are many nitrogen-fixing plants, some used for cover crops, some used for food, some are trees. Why talking only about clover and vetch?
And vetch is not considered as nothing or forgettable. Actually it fixes between 100 to 250 kg/ha (quite a bit more than the estimate you gave in your post), and is very often recommended in seed catalogs by itself or as part of a cover crop mix, commonly with winter rye, to be sown in the fall and plowed over or tilled-in in the spring.
Actually to correct myself, vetch can actually fix 60 to 120 lb/acre of nitrogen, and as much as 250 lb per acre under optimal conditions. I hadn't done the conversion from hectare to acre. Forgive the error.
There are many nitrogen-fixing plants, some used for cover crops, some used for food, some are trees. Why talking only about clover and vetch?
And vetch is not considered as nothing or forgettable. Actually it fixes between 100 to 250 kg/ha (quite a bit more than the estimate you gave in your post), and is very often recommended in seed catalogs by itself or as part of a cover crop mix, commonly with winter rye, to be sown in the fall and plowed over or tilled-in in the spring.
Actually to correct myself, vetch can actually fix 60 to 120 lb/acre of nitrogen, and as much as 250 lb per acre under optimal conditions. I hadn't done the conversion from hectare to acre. Forgive the error.