Optical sensing for precision Nitrogen management in wheat

Fertilizer nitrogen (N) is the major input for food production. Excessive and untimely fertilizer N topdressings to achieve high yields are common among the farmers in the major food producing regions of Asia. A four year field study was conducted to validate precision N management strategies in wheat (Triticum aestivum L.; variety PbW 550) through optical sensing with leaf colour chart (LCC), chlorophyll meter (SPAD), and GreenSeeker (GS) optical sensor for achieving high N use efficiencies. The study consisted of five treatments--no-N control, soil test based N application, and precision N application using LCC, SPAD meter and GS optical sensor. The precision N management techniques sustained grain yield, N assimilation and root dry weight equivalent to the soil test based fertilizer N application with 16.7 to 25.8 percent less use of fertilizer N during different years. The optical sensing techniques improved agronomic and recovery efficiency of applied N up to 40.5 and 35.3 per cent, respectively in comparison with the soil test based fertilizer N recommendation. The optical sensing based N topdressings promisingly synchronized fertilizer N supply with the plant N demand and are thus more useful in improving N use efficiency, reducing cost of production and mitigating escape of reactive N from soil system to atmosphere.