The historic Knorr-Holden experimental site near Scottsbluff, Nebraska, US, established in 1912 is the oldest irrigated maize plot in North America. Over years, the treatment has been revised a few times to reflect and address contemporary practices. The N fertilization is found to be capable of restoring most of production capacity of the soil. After a full century of the experiment, in 2014, N treatments were revised again. Now, the experiment is a split-plot randomized complete block design with four replications. The main factor is manure treatment (0 and 67 Mg ha-1) and the sub-plot is N treatment, which includes 0, 56, 112, and 168 kg urea-N ha-1. There are additional N treatments of 224 and 280 kg urea-N ha-1 in non-manured plots and urea-N treatments based on spring soil test (SST) and crop sensing at V6 (CS) in manured plots. Manured plots received 67 Mg ha-1 of cattle manure in 2014 and will continue at same rate every four year. Collection of crop vegetative indices for all N treatment plots at several growth stages was initiated using a passive sensor, Crop Circle® in 2017. The normalized difference red edge index (NDRE) at different maize growth stages (V6, V8, V10, and R1) were correlated with urea-N rates and maize grain yield. Grain yield in manured plots were greater than in non-manured plots. Grain yield in the control treatment was the lowest of all in 2017. When N treatments in manured and non-manured plots were analyzed separately, no significant effect of N treatment was observed in manured plots. Among N treatments in non-manured plots, the control treatment had the lowest grain yield among all. The 56 kg N ha-1 treatment had significantly lower grain yield compared to the 280 kg N ha-1. The NDRE at all growth stages were significantly correlated to urea-N treatments in non-manured plots only. The regression relationship between NDRE and corresponding grain yields was the best at growth stage V10. The NDRE had poor correlation with urea-N treatments in manured plots, highlighting the importance of accounting for N supply from other N input such as manure while using crop sensor data and need for calibration of sensor for manured fields.