Scientific Application of Organic Fertilizers to Solve Soil Problems

Organic fertilizers (here refers to rotted compost) have some other disadvantages besides the shortcomings of insufficient quick-acting nutrients and insignificant crop yield increase in the current season. For example, the problem of harmful substances in the rotted compost made from livestock manure is of most concern. In order to make better use of organic fertilizers, it is necessary to focus on source control, harmless treatment, etc., and to use organic fertilizers scientifically and rationally.

Based on the perspective of environmental protection, resource utilization and market acceptance, the current important organic fertilizer fertilizer sources are livestock manure from intensive farms, crop straw and agricultural processing offcuts, which are compounded with these three major components and then transformed into common organic fertilizer and other functional organic (type) fertilizer products with commercial properties after high temperature aerobic composting treatment. The harmful substances in commercial organic (type) fertilizer products mainly come from livestock and poultry manure, and their types and contents vary greatly. However, the harmful substances of general concern include two major categories, one is heavy metals (including metal-like, hereinafter referred to as heavy metals); the other is antibiotics and antibiotic resistance genes (ARGs).

Due to the ability to promote animal growth, improve feed efficiency and control and treatment of diseases, trace heavy metal elements (such as zinc, copper, arsenic, etc.) and veterinary antibiotics such as quinolones, β-lactams, macrolides, Juanamides and tetracyclines are added to feed for a long time and are widely used in intensive livestock and poultry farming around the world. However, the heavy metal elements and antibiotics added in the feed cannot be fully absorbed and metabolized in the animal's body, and most of them are excreted in their original form with the feces and urine. The content of silver, zinc, arsenic and other trace elements and antibiotics in livestock and poultry feces is directly related to the content of these elements and substances in the feed. Animal gut microorganisms naturally contain higher abundance and diversity of ARGs, and the use of antibiotics has the potential to promote the abundance or diversity of ARGs in the animal gut.

In order to achieve safe application of commercial organic fertilizers made from livestock manure, besides controlling the safe addition of heavy metal elements and antibiotics in farm feed at source, another effective way is to treat livestock manure before its agricultural use to maximize the removal or safe conversion of heavy metals and antibiotics and ARGs in livestock manure. The purpose is to gradually degrade and transform the unstable organic matter in the compost material into a stable, crop-friendly and soil-improving compost product through high-temperature aerobic fermentation.