A Novel High Temperature Resistant and Multifunctional Nitrification Inhibitor: Synthesis, Characterization, and Application

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-co-acrylic acid)-encapsulated NI (P(AA-co-AM)-e-NI) is synthesized by incorporating linear P(AM-co-AA) macromolecular structures into NI systems. The P(AA-co-AM)-e-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-co-AM)-e-NI is 1.067 wt%, representing a 120% increase compared to our previous products (0.484 wt%). P(AA-co-AM)-e-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-co-AM)-e-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.

Synthesizing a Water-Soluble Polymeric Nitrification Inhibitor with Novel Soil-Loosening Ability

Nitrification inhibitor is essential for increasing the nitrogen utilization efficiency of agricultural plants, thus reducing environmental pollution and increasing crop yield. However, the easy volatilization and limited functional property is still the bottleneck of nitrification inhibitors. Herein, a novel water-soluble polymeric nitrification inhibitor was synthesized through the copolymerization of acrylamide and bio-based acrylic acid, which was synthesized from biomass-derived furfural, and the complexation of carboxyl groups and 3,4-dimethylpyrazole. The results showed that the nitrification inhibitor was an amorphous polymer product with a glass transition temperature of 146 °C and a thermal decomposition temperature of 176 °C, and the content of 3,4-dimethylpyrazole reached 2.81 wt%, which was 115% higher than our earlier product (1.31 wt%). The polymeric nitrification inhibitor can inhibit the activity of ammonia-oxidizing bacteria effectively, thus inhibiting the conversion of ammonium nitrogen to nitrate nitrogen and converting the insoluble phosphate into soluble and absorbable phosphate. By introducing a copolymer structure with a strong flocculation capacity, the polymeric nitrification inhibitor is further endowed with a soil-loosening function, which can increase the porosity of soil to improve the soil environment. Therefore, the nitrification inhibitor can be used in water-soluble and liquid fertilizers, as well as in high tower melting granulated compound fertilizers.