A Poly(Acrylamide-co-Acrylic Acid)-Encapsulated Nitrification Inhibitor with Good Soil-Loosening, Phosphorous-Solubilizing, and Nitrogen Fixation Abilities and High-Temperature Resistance

3,4-dimethylpyrazole (DMPZ), when used as a nitrification inhibitor, exhibits volatility, poor thermal stability, high production costs, and limited functionality restricted to nitrogen fixation. To address these limitations and introduce novel phosphorus-solubilizing and soil-loosening abilities, herein, a poly (acrylamide-<i>co</i>-acrylic acid)-encapsulated NI (P(AA-<i>co</i>-AM)-<i>e</i>-NI) is synthesized by incorporating linear P(AM-<i>co</i>-AA) macromolecular structures into NI systems. The P(AA-<i>co</i>-AM)-<i>e</i>-NI demonstrates an obvious phase transition from a glassy state to a rubbery state, with a glass transition temperature of ~150 °C. Only 5 wt% of the weight loss occurs at 220 °C, meeting the temperature requirements of the high-tower melt granulation process (≥165 °C). The DMPZ content in P(AA-<i>co</i>-AM)-<i>e</i>-NI is 1.067 wt%, representing a 120% increase compared to our previous products (0.484 wt%). P(AA-<i>co</i>-AM)-<i>e</i>-NI can effectively reduce the abundance of ammonia-oxidizing bacteria and prolong the duration during which nitrogen fertilizers exist in the form of ammonium nitrogen. It can also cooperatively enhance the conversion of insoluble phosphorus into soluble phosphorus in the presence of ammonium nitrogen (NH₄⁺-N). In addition, upon adding P(AA-<i>co</i>-AM)-<i>e</i>-NI into soils, soil bulk density and hardness decrease by 9.2% and 10.5%, respectively, and soil permeability increases by 10.5%, showing that it has a good soil-loosening ability and capacity to regulate the soil environment.