To supply adequate food, the ongoing and unrestrained administration of nitrogen fertilizer to agricultural fields is polluting the climate and living organisms. On the other hand, the agriculture sector urgently needs a technological upgrade to effectively confront hunger and poverty. Here, we report a rapid synthesis of zinc and magnesium-doped hydroxyapatite-urea nanohybrids for slow release and delivery of nitrogen to wheat and rice crops. Nanohybrids slowly release nitrogen for up to six weeks compared to the burst release of nitrogen from urea, and their use substantially reduces, by at least 3.8 times, ammonia emissions into the environment compared with that of urea fertilizer. A half‑nitrogen dose applied as multi-nutrient complexed nanohybrids maintained crop growth, yield, and nutritional compositions in wheat and subsequent rice crops. Nanohybrids enhanced the wheat crop yield and nitrogen uptake by 22.13% and 58.30%, respectively. The synthesized nitrogen nanohybrids remained in the soil for two continuous crop cycles, reduced ammonia volatilization, and achieved nitrogen delivery to the crops. Additionally, soil dehydrogenase activity (534.55% above control) and urease activities (81.82% above control) suggest that nanohybrids exhibited no adverse impact on soil microorganisms. Our comprehensive study demonstrates the advantages of 'doping' as a method for tailoring hydroxyapatite nanoparticles properties for extended agricultural and environmental applications. The use of nanohybrids substantially reduced greenhouse gas emissions and enabled the reduction, by half, of nitrogen inputs into the agricultural fields. This study, therefore, reports a novel nano-enabled platform of engineered hydroxyapatite-urea nanohybrids as a nitrogen fertilizer for efficient nitrogen delivery that results in improved crop growth while minimizing environmental pollution.

The ongoing and unrestrained application of nitrogen fertilizer to agricultural lands has been directly linked to climate change and reductions in biodiversity. The agricultural sector needs a technological upgrade to adopt sustainable methods for maintaining high yield. We report synthesis of zinc and magnesium doped and undoped hydroxyapatite nanoparticles, and their urea nanohybrids, to sustainably deliver nitrogen to wheat. The urea nanohybrids loaded with up to 42% nitrogen were used as a new source of nitrogen and compared with a conventional urea-based fertilizer for efficient and sufficient nitrogen delivery to pot-grown wheat. Doping with zinc and magnesium manipulated the hydroxyapatite crystallinity for smaller size and higher nitrogen loading capacity. Interestingly, 50% and 25% doses of urea nanohybrids significantly boosted the wheat growth and yield compared with 100% doses of urea fertilizer. In addition, the nutritional elements uptake and grain protein and phospholipid levels were significantly enhanced in wheat treated with nanohybrids. These results demonstrate the potential of the multi-nutrient complexes, the zinc and magnesium doped and undoped hydroxyapatite-urea nanoparticles, as nitrogen delivery agents that reduce nitrogen inputs by at least 50% while maintaining wheat plant growth and nitrogen uptake to the same level as full-dose urea treatments.