Establishment scheme for official standards of liquid swine manure fertilizer

A more efficient use of nutrients can benefit both farmers and water quality. To propose an establishment scheme for official standards for liquid fertilizer from swine manure slurry, we evaluated previous and present data related to swine manure as well as analyzed 101 swine manure samples collected from 28 public livestock recycling centers throughout the nation. From these investigations, we found that the official standards for byproduct fertilizers set by the Rural Development Administration (RDA), especially for a liquid swine manure fertilizer, should be revised due to nutrient content requirements having to meet at least 0.3% content for the sum of nitrogen, phosphorus, and potassium. Otherwise, most of the swine manure cannot be utilized as a liquid fertilizer because the result of the 101 samples' analysis showed fewer than 28% of them met the minimum standard of ${\geq}0.3%$ content for the sum of nitrogen, phosphorus, and potassium, while the contents of heavy metals as indicators of toxicity met the standard requirements. Therefore, it is suggested that official standards for byproduct fertilizers set by RDA should be revised as follows: no limit for nutrient contents and addition of chloride as homogeneity. Also, NaCl should be changed to Na because NaCl cannot be analyzed by instrument.