Energy flux and water use efficiency measurements in a maize and soybean cropping system

The agricultural sector is one of the crucial sectors heavily impacted by the consequences of water scarcity. Improved water resources management in croplands is important as available water resources become scarcer. Evaporation and transpiration are important processes in the hydrological cycle. Their quantification remains one of the important challenges for the agricultural and environmental sciences. Eddy covariance, a direct method of measuring fluxes, was used for estimating total evapotranspiration (ET) over maize and soybean crops in the KwaZulu-Natal midlands. Observed ET coupled with maize and soybean yields were used to determine water use efficiency for each crop for the entire growing season (2012/13). Thereafter, observed ET and crop yields were compared to the total ET and yield from simulations done using the FAO AquaCrop crop model. AquaCrop simulates attainable yields of several crops as a function of water use under rainfed, deficit of full irrigation conditions. The observed ET, yield and water use efficiency for each crop showed good agreement with model outputs. The skills to operate instruments such as those used in flux measurements are rare and the cost of instrumentation is too much for routine use. Where there is limited budget and shortage of skill to operate flux instruments to determine water use efficiency or other parameters, the FAO AquaCrop model may be used to give comparable results.