Assessing flue-cured tobacco crop growth and biomass Response to nitrogen application levels using canopy Reflectance

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Visual seedling health monitoring can be done through the use of optical sensors that rely on light to assess the physiological status either at the leaf or canopy level using vegetation indices. Plant reflectance properties that are indicative of crop N status can be useful for directing in-season variable-rates of N applications and help interpret if there are any nitrogen related problems. In this study a multispectral Radiometer (MSR5) was used to monitor tobacco varieties response to N application levels. A 3 x 4 factorial experiment in a Randomized Complete Block Design, with four replications was used. Three tobacco varieties and four N levels were established in a conventional seedbed experiment at Kutsaga research station in Harare. MSR 5 readings, biomass and total nitrogen data were collected and analysed to investigate Normalised Difference vegetation Index (NDVI) response to these canopy characteristics. The results showed a significant two way interaction between fertiliser and varieties (P <0.05). Significant differences (P <0.05) were recorded on KE1, differing from both KRK 26 and T66 and also on all the N treatments. Crop biomass and total nitrogen were also highly correlated to NDVI (R2>0.8), in an N dependent pattern. The NDVI values increased with an increase in N levels up to, and above the recommended rates. The results indicated that NDVI can be a useful tool in N management in tobacco. The fact that different varieties showed differing NDVI values makes the application of this technique variety-specific.