Implementing microscopic water uptake in soil-plant interaction modelling for assessing effects on crop growth

Crop transpiration is one of the most important processes in simulating soil-water-plant-atmosphere interactions. Roots perform a crucial role by taking up water and thus contributing to transpiration and enabling crop growth. Shortage of water or oxygen in the root zone results in transpiration reduction as well as reduced crop yield.

In the Netherlands we use SWAP (Soil Water Atmosphere Plant) for simulating effects of hydrology on transpiration and agricultural production. Within SWAP we have now implemented several concepts for root water uptake including two published different versions of so-called microscopic root water uptake.

These microscopic concepts consider water fluxes in a soil column around roots towards and through the roots which results in a water flux to the leaves considering hydraulic characteristics of both soil and plants. Water flow in the soil towards the root is determined by a gradient in the matric flux potential, and the flux into the root and towards the leaves is determined by the hydraulic conductivity of the root wall and hydraulic conductance of the path root-stem-leaves and the gradient in pressure heads of the root system and leaves. Transpiration reduction occurs as a function of the leaf water potential.

For all units of the Dutch Soil Physical Units Map simulations were peformed with these microscopic root water uptake concepts and the results were compared with the simulation results using the more traditional macroscopic root water uptake concept of Feddes. We found that the microscopic concepts both produced more reliable results than the traditional concept. In our presentation we will explain the concepts, show the differences in simulated crop yields, discuss the sensitivity of the microscopic models for the choice of their input parameters, and elaborate on which concepts we would propose for future studies to evaluate the effects of the soil-water system on crop production.