Comparison of NDVI seasonal trajectories and modelled crop growth dynamics

Abstract

Wheat growth in south-eastern Australia shows a strong seasonal pattern associated with a variable ‘break’ of season, a dry and usually warm season finish, and poor buffering from limited soil water storage. Our main aim was to interpret seasonal growth trajectories using Normalised Differential Vegetation Index (NDVI) time series for the period April 1998-August 2007 in selected locations in South Australia. Secondary aims were to (a) assess the sensitivity of APSIM simulations (b) upscaling from point to landscape to provide insights into a range of issues including spatial water stress. The method applied to this analysis combined three independent approaches. These were (a) an examination of spatial crop class overlays to examine the spatial and temporal variability of classes in the case study region; (b) a comparison of spatial class information and APSIM modelled data; and (c) curve fitting approach to explain the peak and the amplitude. The combination of these three approaches allowed simulated growth variables from APSIM, including green cover, biomass, soil water uptake, leaf area index and yield to be compared with NDVI. Strong correlations between NDVI and simulated crop growth parameters allowed to attempt benchmarking APSIM sowing rule, as an example.