Abstract
An experiment on a 50 ha center pivot field was conducted to determine the Vegetation Indices (VI’s) that were helpful in assessing the in-season performance of wheat crop treated with graded levels of irrigation water and fertilizers. The irrigation levels were at 100, 90, 80 and 70% evapotranspiration (ETc); however, the fertilizer levels of N: P: K kg-1ha included 300:150:200 (low); 400:250:300 (medium) and 500:300:300 (High). The crop was sown on January 1st and harvested on May 9th, 2012. Temporal data on biophysical parameters and reflectance of the crop in hyper spectral bands (350-2500 nm) were collected at booting and ripening growth stages (February 17th and April 5th, 2012). Results of the study revealed that many of the tested spectral indices showed significant response to irrigation levels. Out of those, only two spectral indices (Plant Senescence Reflectance Index ’PSRI’ and Photochemical Reflectance Index ’PRI’) also exhibited significant response to fertilizer levels. The Middle Infrared-Based Vegetation Index (MIVI) showed a significant response to the irrigation levels for both sampling dates. Among the tested spectral indices, Normalized Difference Infrared Index (NDII) and Normalized Difference Nitrogen Index (NDNI) exhibited the highest correlation to crop Leaf Area Index (LAI). Five indices showed the most response to wheat grain yield. These indices included Near Infrared band (NIR), Water Band Index (WBI), Normalized Water Index-1 (NWI-1), Normalized Water Index-3 (NWI-3) and Normalized Water Index-4 (NWI-4).
Highlights
The fact that crop phonological stages and growth period vary in different areas and cropping seasons and
Remote sensing based on various vegetation indices (VI) is expected to provide important information that will help in the efficient assessment of within-field spatial variability of various agronomic parameters (Hatfield and Prueger, 2010)
Spectral vegetation indices were calculated from the measured spectral reflectance values of wheat crop samples representing four irrigation levels and three fertilizer levels on two sampling dates (February 17th and April 5th, 2012)
Summary
The fact that crop phonological stages and growth period vary in different areas and cropping seasons and. The analysis of hyper-spectral data, to clearly interpret plant response to management practices, is crucial (Stellacci et al, 2012) Spectral vegetation indices, determined mathematically at various spectral bands, are considered as semi-analytical measures of vegetation activity and appropriate for the assessment of spatial variability in agricultural fields (Vina et al, 2011). These vegetation indices will enhance the interpretation process of the crop spectral reflectance measured at different growth stages and will help in understanding the response of agricultural crops to management practices. Remote sensing based on various vegetation indices (VI) is expected to provide important information that will help in the efficient assessment of within-field spatial variability of various agronomic parameters (Hatfield and Prueger, 2010)
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