Modelling the soil water balance of canola Brassica napus L (Hyola 60)

Abstract

Soil Water Balance (SWB) is a generic crop growth and irrigation-scheduling model. It improves on traditional methods of irrigation scheduling using evaporative demand by mechanistically and dynamically, quantitatively considering the soil–plant-atmosphere continuum. However, it needs specific crop growth parameters, which are not readily available for canola. The objective of this study was to determine crop growth parameters specific to canola and to identify the effect of water stress at different stages of growth on seed and oil yield. The study was conducted on the experimental farm of the University of Pretoria, South Africa, under a rain shelter during 2002 and in an open field during 2003. Weather data were recorded with an automatic weather station, phenological stages monitored frequently and growth analyses carried out every two weeks. Soil water content was measured with a neutron water meter weekly during 2002 and once every five days during 2003. Fractional interception of PAR was also measured with a sunfleck ceptometer. Specific crop parameters including specific leaf area, the leaf stem partitioning parameter, maximum rooting depth and thermal time requirements for crop development were generated from field measurements. These data form the backbone for accurate mechanistic simulations of the soil-water balance. The model was successfully calibrated and evaluated, proving its potential to be used as a generic crop irrigation-scheduling tool. Highest seed and oil yield was harvested from the unstressed treatment and lowest from the treatment stressed during the flowering stage.