Efficient management of fertilizer nitrogen in spring maize using spad chlorophyll meter and greenseeker optical sensor

Over-application of fertilizer nitrogen (N) in spring maize results in low fertilizer N use efficiency. Site specific need-based fertilizer N management in spring maize using chlorophyll meter (SPAD meter) and GreenSeeker optical sensor was compared with soil-test recommended N applications in field experiments conducted for two years during 2017 and 2018. Treatments consisted of different rates of N application based on SPAD and GreenSeeker sufficiency index approaches and soil-test based recommended N applications. The results showed that N application using SPAD based on sufficiency index of 0.95 and GreenSeeker based on 0.90 sufficiency index criteria not only produced significantly higher yields but also increased total N uptake by 10.7% to 15.0% than soil-test based fertilizer N recommendation with fertilizer N dose of 120 kg N ha⁻¹. Significantly higher N recovery and agronomic efficiencies were observed when N was applied using SPAD and GreenSeeker based sufficiency index approaches. The results of this study suggested that to avoid over application of N and to obtain high yields and N-use efficiencies in spring maize fertilizer N application should be guided by sufficiency index approach that indicate N deficiency or sufficiency for the crop.