Phosphorus (P) availability is widely assumed to be limited by the formation of metal (Ca, Fe, or Al) phosphate precipitates that are modulated by soil organic matter (SOM), but the SOM–precipitate interactions remain uncertain because of their environmental complexities. Here, we present a model system by quantifying the in situ nanoscale nucleation kinetics of calcium phosphates (Ca-Ps) on mica in environmentally relevant aqueous solutions by liquid-cell atomic force microscopy. We find that Ca-P precipitate formation is slower when humic acid (HA) concentration is higher. High-resolution transmission electron microscopy observations demonstrate that HA strongly stabilizes amorphous calcium phosphate (ACP), delaying its subsequent transformation to thermodynamically more stable phases. Consistent with the formation of molecular organo–mineral bonding, dynamic force spectroscopy measurements display larger binding energies of organic ligands with certain chemical functionalities on HA to the initially formed ACP than to mica that are responsible for stabilization of ACP through stronger HA–ACP interactions. Our results provide direct evidence for the proposed importance of SOM in inhibiting Ca-P precipitation/transformation. We suggest that similar studies of binding strength in SOM–Fe/Al–P may reveal how both organic matter and metal ions control P availability and fate, and thus the eventual P management for agronomical and environmental sustainability.

Phosphorus (P) is a nonrenewable resource with low availability in soils and thus can be a yield-limiting factor for food production. Alginate from brown algae has been proved to be a promising fertilizer additive to promote P utilization efficiency so as to achieve sustainable P management. However, there has been a lack of direct observation of how alginate promotes P availability due to the complexity of the soil system. Here, by combining in situ atomic force microscopy (AFM) and Raman spectroscopy, we in real time observed the nanoscale phase transformation kinetics of amorphous P-bearing minerals (APM) (Fe−P and Ca−P) prepared with the addition of alginate before (treatment II) and after (treatment I) the synthesis of APM. The surface of crystalline P-bearing minerals (CPM) derived from the phase transformation of APM without alginate addition showed obvious nanoscale etch pits after exposure to alginate-bearing solutions at mineral−water interfaces, indicating the solubilization of coprecipitated P, which was then quantified through batch dissolution experiments. Overall, the results revealed that alginate delayed the phase transformation of APM and enhanced the dissolution of CPM in a concentrationdependent or polymerization degree-dependent manner to retain plant-available forms of P. In addition, treatment II could more significantly delay the phase transformation than treatment I. AFM-based dynamic force spectroscopy (DFS) suggested that, consistent with the formation of molecular organomineral bonding, alginate with a higher polymerization degree had a higher binding energy to P-bearing minerals, which would contribute to APM stabilization and CPM dissolution through stronger alginate− mineral interactions. These findings provide direct evidence for the P availability-promoting effect of alginate as an additive as well as some guidance for the better design of P fertilizer additives to achieve sustainable P management in agriculture.

Phosphate (P) adsorption systems featuring metal-based adsorbents have claimed to achieve ultralow P removal. However, little is known about the micron- and molecular-scale energetic knowledge of P-adsorbent interactions including the...

As a potential phosphorus (P) pool, the enzymatic hydrolysis of organic phosphorus (Po) is of fundamental importance due to the release of bioavailable inorganic phosphate (Pi) for agronomic P sustainability....

Changes in the secondary structure of phytase, particularly the conserved active catalytic domain (ACD, SRHGVRAPHD) are extremely important for the varied catalytic activity during hydrolyzing phytate in the presence of...