Fertilizers Containing Balanced Proportions of NH 4 + -N and NO 3 − -N Enhance Maize ( Zea mays L.) Yield Due to Improved Nitrogen Recovery Efficiency

The current study aimed to improve the nitrogen recovery efficiency (NRE) of maize under the application of balanced proportions of ammoniacal-nitrogen (NH 4 + -N) and nitrate-nitrogen (NO 3 − -N) (1:1), as well as to determine economic impacts of such fertilizers on maize productivity. A 3-year field study was carried out in Sahiwal, Punjab, Pakistan during the 2018–2020 growing seasons with autumn maize. In parallel, multi-location field experiments were conducted at farmer’s fields in Sahiwal during the same growing seasons with autumn maize. The trials compared the effects of different fertilizers like urea, calcium ammonium nitrate (CAN), Sarsabz nitrophos (NP), nitrphos plus (NP Plus), and di-ammonium phosphate (DAP) on maize growth and yield, as well their economic efficiency. The results revealed that the application of Sarsabz NP and CAN increased the maize grain yield by 30%, 13%, 15%, 19%, 15%, and 9% as compared to the control, NP + urea, NP Plus + CAN, NP Plus + urea, DAP + urea, and DAP + CAN, respectively. In addition, the combined application of NP and CAN increased the total N and NO 3 − -N concentrations, whereas it decreased the NH 4 + -N concentrations in the soils. By contrast, NP + CAN increased the NH 4 + -N concentrations in maize leaves as compared to NO 3 − -N concentrations. Overall, the NRE of maize plants and the net return were higher under combined application of NP and CAN. In conclusion, CAN fertilizer increased the soil NO 3 − -N concentrations, which thus assimilated in the plants as NH 4 + and improved the NRE of maize. Improved NRE thus enhanced maize yield and resulted in the maximum net return as compared to all other fertilizer combinations.