Modelling competition for water in intercrops: theory and comparison with field experiments

A knowledge of plant interactions above and below ground with respect to wa ter is essential to understand the performance of intercrop systems. In thi s study, a physically based framework is proposed to analyse the competitio n for soil water in the case of intercropped plants. A radiative transfer m odel, associated with a transpiration-partitioning model based on a modifie d form of the Penman-Monteith equation, was used to estimate the evaporativ e demand of maize (Zea mays L.) and sorghum ( Sorghum vulgare R.) intercrop s, In order to model soil-poor water transport, the root water potential of each species was calculated so as to minimise the difference between the e vaporative demand and the amount of water taken up by each species. A chara cterisation of the micrometeorological conditions (net radiation, photosynt hetically active radiation, air temperature and humidity, rain), plant wate r relations (leaf area index, leaf water potential, stomatal conductance, s ap flow measurements), as well as the two-component root systems and water balance (soil-root impacts? soil evaporation) was carried out during a 7-da y experiment with densities of about 4.2. plant m(-2) for both maize and so rghum. Comparison of the measured and calculated transpiration values shows that the slopes of the measured versus predicted regression lines for hour ly transpiration were 0.823 and 0.778 for maize and sorghum, respectively. Overall trends in the variation of volumetric water content profiles are al so reasonably well described. This model could be useful for analysing comp etition where several root systems are present under various environmental conditions.