Simulation of tropisms of root system growth based on feedbacks between functions and structures

It is very important to quantitatively study spatial growth and distribution of root system in precision agriculture, which can optimize the use efficiency of soil water and nutrient，and minimize the impacts of fertilizer to ecological environment. However, the spatial growth and distribution of root system were influenced mainly by the growth direction of root individual which was induced by geotropism, hydrotropism and nutrient-tropism. The growth process of root system in 3D soil space was implemented using the root functional-structural model developed by the principles of GREENLAB. The regions in which root system grows and develops were discretized by 3D spatial voxels. Having defined the voxels, the soil moistures and nutrients of local area which surrounded the root segment could be calculated by spatial collision detection technique. After obtaining the soil moistures and nutrients, the electro-impedance functions were used to adjust the sinks, while the growth direction of each root segment generated in current growth cycle was recalculated by the adjusted functional and structural parameters. With the help of multi-needle data structure, the dynamic storing of new root segment and visiting of all root system in each growth cycle was implemented. Finally, given some scenarios of spatial moisture and nutrient distribution, the geotropism, hydrotropism and nutrient-tropism of growth and development of root system were realized in the homogenous soil using the visual way, in which the parameters were from literatures.