ABSTRACT: Phosphorus (P) is a limiting macronutrient that regulates plant growth and development based on the bioavailability of its inorganic form, i.e., orthophosphate (Pi). P plays a critical role in cell development, and it is a key component of ATP, DNA, lipids, and cell signaling machinery. Without the exogenous application of P fertilizers, the yield of crops will not meet the ever-growing demand in today's world. However, due to the non-renewable nature of natural P reserves and simultaneous rapid human population growth, food crops must be ultimately produced more than ever by using a lower P fertilizer input. Hence, the strategy of preparing nano-fertilizers was conceptualized and demonstrated with great success. For example, nano-diammonium phosphate (n-DAP) performed far better than the commercial granular DAP (c-DAP). However, nano-fertilizers, including n-DAP, cannot be produced on a large scale using the available processing methods. Herein, a novel processing strategy, namely cryo-milling, is demonstrated to prepare n-DAP on a kg-scale without altering DAP's bonding structure. Cryo-milling involves milling at liquid N2 temperatures and therefore helps in brittle fracture of coarser DAP particles into n-DAP particles. Cryo-milled n-DAP, with particle size ∼5000 times smaller but specific surface area ∼14 000 times greater than that of c-DAP, enhanced the growth of monocot (wheat) and dicot (tomato) plants due to improved bioavailability of Pi even for a far lower input than c-DAP. Phenotypic observations such as higher leaf biomass, longer shoots, shorter roots, and less anthocyanin pigmentation manifested the extraordinary efficacy of cryo-milled n-DAP for 75% lower input than c-DAP.
