Double roller press granulators are more suitable for dry inorganic fertilizers such as urea, ammonium phosphate, and potash. Processing well-rotted organic fertilizers presents several technological shortcomings; the forming effect, equipment wear and tear, and product quality all fall short of standards. This is the core reason why organic fertilizer plants prioritize disc granulators.

Firstly, there is a serious incompatibility in the moisture content of the raw materials. Well-rotted cow manure and chicken manure generally have a moisture content of 25%–32%, with a soft and sticky texture. Roller extrusion relies on high-pressure extrusion molding; high-moisture organic materials will stick to the roller grooves, continuously clogging the mold and requiring frequent shutdowns for cleaning. In contrast, inorganic fertilizers have a moisture content of less than 10%, making them less prone to sticking to the roller grooves—a completely opposite compatibility. Forcibly drying organic fertilizer to extremely low moisture content not only significantly increases drying energy consumption but also kills beneficial bacteria inside, negating the core value of bio-organic fertilizer.

Secondly, poor pellet formation and numerous product defects. Organic fertilizers have a high fiber content and high elasticity, resulting in significant internal stress after high-pressure extrusion. This makes them prone to springing back and breaking after exiting the rollers, leading to a high amount of broken powder and a granulation rate of less than 60%. This results in a large amount of recycled material, reducing production line capacity. The extruded granules are mostly flat and cylindrical, with a rough appearance and high dust content, making them far less appealing than the rounded granules produced by disc rolling, resulting in low market acceptance. Fibers can also clog the roller die slots, requiring frequent roller polishing over long-term production.

Furthermore, fertilizer produciton machine wear and maintenance costs are high. Organic fertilizers contain hard impurities such as straw and sand, which rapidly wear down rollers, bearings, and oil seals under high pressure. Worn rollers increase the forming gaps, resulting in loose and poorly formed granules, and replacing roller parts is costly. High-moisture organic materials also easily corrode roller shafts and sealing structures, leading to material leakage, bearing corrosion, and a significant increase in downtime for maintenance.

Finally, the process technology is incompatible. Extrusion granulation requires extremely fine materials and a large amount of binder. Adding too much bentonite to organic fertilizer will dilute the organic matter, resulting in the finished product having insufficient organic matter content and failing to meet national standards for organic fertilizer. Disc granulation relies on rolling and bonding to form the material, which has a higher tolerance for moisture and fiber in the raw materials, resulting in better forming effect and lower loss. Therefore, it has become the mainstream forming equipment for organic fertilizer.