Ground-based radiometric measurements in the red and infrared bands were used to monitor the growth and development of wheat under irrigated and stressed conditions throughout the 1987-88 and 1988-89 growth cycles. Spectral data were correlated with plant height, leaf area index, total fresh and total dry biomass, plant water content and grain yield. The radiance ratio (R) and normalized difference vegetation index (NDVI) were highly and linearly correlated with yield, establishing the potential which remote sensing has for predicting grain yield. The correlation for R and NDVI was at a maximum between 75 and 104 days after sowing, corresponding with maximum green crop canopy cover. The differences in spectral response over time between irrigated and unirrigated crops allowed detection of water stress effects on the crop, indicating that a hand-held radiometer can be used to collect spectral data which can supply information on wheat growth and development.Efectos de lafalta de agua en el trigo RESUMEN Se utilizaron mediciones radiometricas del suelo en las banda roja e infrarroja para monitorizar el crecimiento y desarrollo de trigo bajo condiciones de irrigation y de escasez de agua durante todo el transcurso de los ciclos de crecimiento de 1987-88 y 1988-89. Los datos espectrales fueron correlacionados con la altura de planta, indice de superficie de hoja, total de biomasa fresca y seca, contenido de agua en la planta, y rendimiento de grano. La intensidad de radiation (R) y el indice de vegetation con diferencia normalizada (IVDN) fueron correlacionados en forma lineal y elevada con el rendimiento, estableciendo el potencial de la detection remota para predecir el rendimiento de grano. La correlation de R y IVDN estuvo en un maximo de entre 75 y 104 di'as a partir de la siembra, correspondiendose con el maximo de cobertura verde de la cosecha. Las diferencias en la respuesta espectral de las zonas irrigadas y las no irrigadas con el paso del tiempo permitio detectar los efectos de la falta de agua en la cosecha, lo cual senalo que se puede utilizar un radiometro de mano para recolectar datos espectrales que pueden suministrar information relacionada con el crecimiento y desarrollo del trigo.
Wheat growth profile based yield models for 12 districts of Punjab State and 16 districts of Haryana State have been developed using the normalised difference vegetation index (NDVI) derived from NOAA-11 AVHRR data of the 1993-94 cropping season. Atmospheric normalisation of AVHRR data was performed prior to deriving district-level area weighted average NDVI (AWANDVI). The invariant growth profile model suggested by Badhwar was fitted and spectral emergence date, maximum vegetative vigour, peak day value of profile, growth rate and senescence rate, area under the curve, etc. were derived. These parameters were related to the reported district-level wheat yields using multiple regression analysis. A field study was also conducted using a handheld spectro-radiometer at the research station of Punjab Agricultural University (PAU), Ludhiana. From this field experimental data, wheat growth profile parameters were derived which were compared with satellite based parameters. Inversion of the models was carried out to evaluate the results by comparing the reported and predicted wheat yields. The results indicate highly significant fitting of the NDVI profile to the Badhwar model as indicated by multiple linear correlation coefficients and Fisher test. A significant relationship between district-level wheat yields and fractional area under the curve was also observed. The overall correlation of 0.82 for Punjab and Haryana states was obtained between reported yield and growth profile derived parameters. Atmospheric normalisation resulted in improvement of prediction model statistics (R increased from 0.42 to 0.86). Evaluation of the models indicated that 10 out of 16 districts of Haryana State and 9 out of 12 districts of Punjab State showed relative deviations within 10% between reported and model predicted wheat yields.
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