Fish emulsion, in its most basic form, is an organically decayed fish derivitive created through the heating and fermentation of fish scraps. The methods for applying fish emulsion can differ, but generally the absorption rate is universal.
Since the concoction has naturally-occurring nutrients, both from byproducts of benign aerobic bacteria and those found within the fish inherently, the plants can absorb them with less difficulty, and less nutrient loss. In homemade fish emulsion brews, gardeners use browns, or sticks, straw, sawdust, or dead leaves, which also provide the nutrients that remain in decaying plant matter. The nitrogen produced by the decay is similar in levels to various nitrogen fertilizers, but happens in a natural fashion.
Soil or Folial Fertilization
Some plants need folial fertilization, or spraying liquid fertilizer directly onto the plant so it can absorb the nutrients through the leaves. Others require soil fertilization, which will give the roots the nutrients. In particular cases, both processes can be used and be highly beneficial, but as this depends on the plant itself and its unique needs, it is best to follow directions included with the plant at purchase. There are gardening circumstances in which plant food is unnecessary, as usage of fish emulsions in hot composting piles can add most of the nutrients to the peat found in plant food. This makes fish emulsion, whether you buy it or make it yourself, a frugal and healthy choice for your garden.