Barley as a green manure quickly gains green mass, suppresses most of the weeds and improves the quality of the soil. These features and properties are subsequently used to grow other garden plants.
Teeeeeeechnically... it's watered down poop. Heheheh It does include the urine though, which adds more calcium and phosphorus than the straight poop. (At least that's been my conclusion from reading)
Figured out why some folks claim the foliar acts as a pesticide. Turns out bugs die when they eat healthy, protein rich plants. Plants can absorb foliar nutrients and (when sufficient nutrients plus molybdenum, boron and calcium are available) convert ammonium to proteins in 24-48 hours. Bugs eating on those plants will either leave or die.