Optical Sensing and Arbuscular Mycorrhizal Fungi for Improving Fertilizer Nitrogen and Phosphorus Use Efficiencies in Maize

Application of fertilizer nitrogen (N) and phosphorus (P) in excess of crop requirement causes nutritional imbalances in soil along with economic and ecological losses. The optical sensors (leaf color chart, chlorophyll meter, and GreenSeeker) help guide real-time N topdressing decisions and arbuscular mycorrhizal fungi (AMF) further improve nutrient uptake from soil. A four-year field study was conducted to improve N- and P-use efficiencies in maize using different optical sensing tools and coating seeds with AMF. The AMF seed coating improved mycorrhizal colonization in soil. Higher mycorrhization was observed in no-P treatment; however, P fertilization and mycorrhiza inoculation diminish the effect as growth progressed from 30 to 60 days after sowing. The mycorrhizal inoculation increased grain yield by 17.1% in no-N treatment; however, the response diminishes with N fertilization. The optical sensing–based N management sustained grain yield, total N uptake, and root and plant dry weight equivalent to the soil test–based fertilizer N recommendation with the less use of 30 kg N ha−1. The respective improvement in agronomic and recovery efficiencies of applied fertilizer N up to 38.6 and 34.9% highlights the potential of optical sensing tools and the inability of soil test–based N recommendation for precision N management. Mitigated greenhouse and nitrous oxide emissions respectively by 30.7% and 29.7% further underline the prominence of replacing soil test N recommendations with optical sensing–guided N top-dressings. Sufficient inherent soil P restricts the AMF benefits in improving P-use efficiencies in maize.