Abstract:
The objective of this study was to assess the accuracy, spatial variation and potential value of remote sensing (RS) estimates
of evapotranspiration (ET) and biomass production for irrigated sugarcane in Mpumalanga, South Africa. Weekly ET and
biomass production were estimated from RS data from 2011 to 2013 using the Surface Energy Balance Algorithm for Land
(SEBAL). Ground estimates of canopy interception of photosynthetically active radiation (FPAR) and aerial biomass were
compared to RS estimates. ET was estimated with a surface renewal (SR) system in one field. Evaporation coefficient (Kc)
values were calculated from ET and reference grass evaporation. Remote sensing FPAR and biomass estimates compared well
with field measurements (R2 = 0.89 and 0.78). SEBAL ET estimates exceeded SR estimates by 5 mm/week, while full canopy
Kc values for SEBAL compared better with literature values than with SR Kc values. SEBAL estimates of ET and biomass were
regarded as reliable. Considerable spatial variation was observed in seasonal RS ET (1 034 ± 223 mm), biomass (45 ± 17 t/ha)
and biomass water use efficiency (WUEBIO, defined as dry biomass produced per unit of ET) (4.1 ± 1.0 kg/m3). About 32%
of sugarcane fields had values below economic thresholds, indicating an opportunity to increase productivity. Actual yields
correlated well with WUEBIO values, suggesting that this may be used for monitoring crop performance and identifying areas
that require remedial treatment.
