Relationship between Tobacco Crop Evapotranspiration and the Normalized Difference Vegetation Index

Monitoring crop consumptive water use by applying recent remote sensing techniques has become a topic of research interest in water resources management and planning. In irrigated agriculture, conventional methods of estimating water use are costly. This study aims at estimate the relationship between tobacco crop evapotranspiration (ETcrop) and the normalized difference vegetation index (NDVI) during the crop development stage at Chedgelow irrigated farm in Zimbabwe. Tobacco ETcrop was estimated as a product of reference evapotranspiration (ETo) and crop coefficient (Kc). The Penman-Monteith model was applied to estimate ETo using climate data from Kutsaga research station, some 2 km away from the farm. Kc values were extracted from FAO tables. Five cloud-free MODIS images for the month of October in 2000, 2001, 2002, 2003 and 2007 were processed extract the NDVI values using ILWIS GIS. The results show significant (p = 0.000) differences between tobacco NDVI values over the years studied. The results also show a strong and significant positive relationship (r2 = 0.8061, p = 0.047) between ETcrop estimated using Penman Monteith model and NDVI. Research findings show that satellite derived NDVI is a good and reliable predictor of tobacco crop water evapotranspiration. Therefore, remotely sensed NDVI can be used to monitor crop water use in irrigated tobacco fields in areas where resources do not permit field measurements.