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Actual evapotranspiration (mm/week) is the quantity of water that is removed from a land surface. This includes transpiration and evaporation from the soil and water intercepted by plants. Evapotranspiration is commonly estimated by multiplying reference evapotranspiration with a crop factor. Sugarcanelook provides actual estimates of evapotranspiration estimated using the Surface Energy Balance Algorithm for Land (SEBAL) model.

Totale werklike verdamping (mm/week) - Die total werklike verdamping is die hoeveelheid water wat van 'n opervlakte verlore gaan deur transpirasie, verdamping van water in die grond en van water wat deur plante onderskep is. Daar word ook hierna verys as evapotranspirasie. Waar 'n grondoppervlak total en al (of hoofsaaklik) met plante of 'n gewas bedek is, is die waarde ekwivalent aan transpirasie of gewas waterverbruik. Waar 'n stuk grond braak le, verwys die waarde na verdamping vanuit die grond. Werklike verdamping waardes is in die verlede gereeld bepaal deur of A-pan verdamping of verwysing gewas verdamping met 'n gewas faktor te vermenigvuldig.

Evapotranspiration deficit (mm/week) is calculated as the difference between the crop potential and actual evapotranspiration. It is an indicator of plant water stress since it reflects and evapotranspiration shortfall from the potential evapotranspiration rate. Potential evapotranspiration refers to the upper limit of evapotranspiration of a specific plant or crop type.

Verdampings- of evapotranspirasie tekort (mm/week) - Die verdampings tekort word bereken as die verskil tussen die potensiele evapotranspirasie van die gewas (of plant) en die werklike total verdamping of evapotranspiration. Dit is 'n indikasie van die moontlike plant stress wat ondervind word. Die potensiele evapotranspirasie verwys na die boonste limiet van evapotranspirasie van 'n spesifieke plant.

Biomass production (kg/ha/week) refers to the growth of total living plant material expressed as dry weight. It includes living material above and below the ground (such as stems, leaves, roots, fruits and grains). Biomass production is the main indicator of the growth vigour. Biomass Production reflects biomass production over a period of a week and not the total crop biomass.

Biomassa produksie (kg/ha/week) verwys na die toename in plant material, insluitend material wat bo of onder die grond geproduseer is (blare, stamme, wortels, vrugte). Biomassa produksie is 'n indikator van hoe aktief 'n plant / gewas groei. Die biomassa produksie verwys na die biomassa produksie (droe gewig) oor 'n periode van 'n week en nie die totale plant biomassa nie.

Biomass water use efficiency (kg/m3) refers to the total biomass produced per cubic meter of water used.

Biomassa water verbruiks doeltreffendheid (kg/m3) verwys na die totale hoeveelheid plant material wat geproduseer is per kubieke meter water gebruik in die proses.

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A new project co-funded by the Water Research Commission (WRC) and the Department of Agriculture, Forestry & Fisheries (DAFF) 'Water use efficiency of irrigated agricultural crops determined with satellite imagery' started on 1 April 2011.

This project wants to build on research conducted in South Africa in recent years where the accuracy of models that use remote sensing data to estimate evaporation (ET) was evaluated (Jarmain et al., 2010a) and use of spatially explicit data products generated with the Surface Energy Balance Algorithm for Land (SEBAL) model have been evaluated (e.g. Klaasse et al, 2008; Jarmain, et al., 2010a, Jarmain et al., 2010b; Jarmain et al., 2011).

The project wants to address the need in South Africa for information on the water use efficiency of irrigated crops. The information is required both spatially and at frequent intervals so it can be used operationally. The water use efficiency (WUE) information can be used at different levels (field, farm, irrigation scheme, catchment) in water resources management. This spatial, frequent updates in information can assist in evaluating the WUE across farms, irrigation schemes, etc. - problems can be detected and addressed swiftly and crop WUE and other resource use (fertilizer, electricity, etc.) optimized and wastage minimized.

In this project we will illustrate how spatially explicit information provided at frequent intervals can be used to assess and potentially improve WUE within irrigated agriculture, though two case studies. In the first case study the focus will be on irrigated sugarcane produced in parts of the Inkomati basin and in the second case study the focus will be on grain crops produced in parts of the Vaal and Orange river catchments. This project will aim at conclusively confirming the degree of accuracy of the SEBAL model for estimating evaporation (crop water use) and WUE of the selected agricultural crops. This project should pave the way for future operational near-real time application of remote sensing data in agricultural water management.

The four objectives of the project are:

  • Confirming the degree of accuracy of total evaporation (ET), biomass, yield production and WUE estimated using the Surface Energy Balance Algorithm for Land (SEBAL) model (for selected crops and different spatial and temporal scales),
  • Showing how spatially explicit ET and yield data generated using the SEBAL model can be used by different users (researchers, farmers, irrigation advisors, water users associations) to assess and improve WUE at different spatial scales (field, farm or larger) and for selected irrigated agricultural crop,
  • Developing spatial (WUE) information generated with the SEBAL model to the point of operational use in SA and
  • Building capacity (in students, researchers, extension officers, farmers, etc.) in the use of field and remote sensing based methods for improved WUE.

Case study 1: Water use efficiency of irrigated sugarcane

In case study 1, the SEBAL model will be used to produce maps of actual evapotranspiration, evapotranspiration deficit and biomass production for areas under irrigated sugarcane in the Inkomati catchment for the period 1 November 2011 to 31 October 2012. This data is disseminated to users through the Sugarcanelook website.

The accuracy of the SEBAL estimates will be assessed against field measurements. The SEBAL total evaporation estimates will be compared against estimates using micrometeorological and site soil water balance data and data generated using the MyCaneSim and SAPWAT models. The SEBAL estimates of biomass production will be compared to the biomass and stalk mass estimates over the study period and also against the Leaf area index estimates.

Funders and collaborators

This project is co-funded by the Water Research Commission and the Department of Agriculture, Forestry and Fisheries. A number of institutions are contributing to this project, including the University of KwaZulu-Natal, WaterWatch, South African Sugarcane Research Institute, University of Pretoria, University of the Free State, University of Stellenbosch, University of Limpopo and Griekwaland-Wes Korporatief.

Contact

For more information on this research project, please contact Dr Caren Jarmain at jarmainc@ukzn.ac.za

Related articles and projects

Improved water use only a satellite away - WaterWheel September/October 2011. PDF

This project is conducted in close collaboration with the Spatial Earth Observation Monitoring for Planning and Water Allocation in the International Incomati Basin (WATPLAN) project conducted in the Incomati catchment. WATPLAN is funded by the European Union and focus on providing information for spatial, near-real time catchment water management for the entire Incomati catchment management area. WATPLAN will provide information for irrigated crops, sugarcane, forest plantations and natural vegetation. See http://www.watplan.eu and http://www.watplan.com.

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