Hidden Half Network Model: A Prototype for Simulating Soil Pore Space, Root Architecture, and Water Movement.

Interactions among soils, roots, and water may be modeled using the concept of networks. Many models have been developed to study soils, roots, water, and their interactions. However, it is still a challenge to show the real-time feedback loops among the three features. This study attempts to develop a comprehensive model, called the Hidden Half Network Model (HHNet), to investigate the dynamics and feedbacks among soils, roots, and water. The HHNet model consists of three main modules: 1) Soil structure module: Soil aggregates are presented by different spatial distribution of soil grains, which illustrated by little balls, and their clusters with specific features. The micropores are represented by the tiny space between the grains inside the clusters. While the macropores are represented by the network of pore space between clusters generated based on the Cahn-Hilliard method; 2) Water movement module: Subsurface flow is simulated using the Lattice-Boltzmann method. The mobility and stability of water perform differently in the micropores and macropores; 3) Root architecture module: Guided by scale-free network theory, roots are branching in the given conditions of soil and water. Soil horizons are simulated by stacking layers of soils with distinct properties, e.g. porosity, pH, nutrient concentration and so on, by which root branching and water flow are influenced. Meanwhile, the root growth would also change the soil properties as well as the water distribution. These three module are functioning simultaneously to reveal the real-time feedback loops among soils, roots, and water. Preferential flow have been observed in the model due to the heterogeneous soil and root growth. HHNet model provides an opportunity to study the complex network systems in the underground world.