Transitioning From Soil‐Based to Soil‐Foliar Hybrid Application for Nitrogen Fertilizers Offers Energy‐Saving and Use‐Efficiency Benefits

ABSTRACT Nitrogen (N) is the most important nutrient for crop plants to achieve their yield potential, yet it is also recognized as a major pollutant of the environment due to often‐excessive N‐fertilizer use. The world has been struggling for decades to improve N use efficiency (NUE) beyond 50%. Nano‐nitrogen, a nanoparticle‐based liquid N‐fertilizer, has been reported to improve crop yield, yet any gain in NUE is uncertain. Field and controlled tests on the usage of nano‐nitrogen in rice(scented)‐wheat systems and its impact on crop yield, growth responses, and NUE were conducted to ascertain this. The study included 10 strategies for the integration of nano‐nitrogen with the conventional practice of prilled urea, including four with varying degrees of replacement of soil‐applied prilled urea by foliar applied nano‐nitrogen (33%, 50%, 66%, and 100%), two with augmentation using additional inputs (micronutrients, and sea‐weed fertilizer), and two with sensor‐based fertilizer scheduling using leaf color chart (LCC) and greenseeker (GS). The controls included ‘100% prilled urea’ (R0; no replacement) and ‘no N fertilizer at all’ (No‐N). Replacing prilled urea with foliar applied nano‐nitrogen up to 33% in the rice‐wheat system [2 soil applications of prilled urea (2/3rd of currently recommended fertilizer) and 1 foliar application of nano‐nitrogen (3 mL per liter)] was found to significantly improve achievable NUE. Up to 33% replacement of conventionally used prilled urea by nano‐nitrogen (2 soil‐1 foliar scenario) did not significantly affect grain yield as well as N yield for the rice‐wheat cropping system; however, it saved 80 kg N application, which translates to 4848 MJ energy saving per hectare in the rice (scented)‐wheat cropping system. Augmentation with seaweed fertilizer, biofertilizer, and micronutrients further improved yield and energy efficiency (13% higher) compared to 100% N via prilled urea. With 13.5 M ha of area under the rice‐wheat system in the Indo‐Gangetic plain, a saving of at least 65 PJ of energy is achievable from the region. More sustainable N use in rice (scented)‐wheat systems can be achieved by transitioning from soil‐based to soil‐foliar hybrid application technique.