Simplified Measurement-Based Simulation Model of Soil-Plant Phosphorus Cycles in Long-Term Agro-Systems.

Actual phosphorus models are created in conventional tillage system. In addition, most simulation models are process-based, which need mathematical descriptions of fundamental physio-chemical mechanisms. The small time-step e.g. daily might not fit long-term simulation. In this study, a P model based on measured data was created to simulate the evolution of soil P status along soil profile in long-term. In P model, a soil zone was divided into 30 grids according to vertical (0-5, 5-10, 10-20, 20-30 and 30-40 cm) and lateral (0-10, 10-20 and 20-30 cm for two sides into inter-row) coordinates. For each grid, P stock was defined as total amount of phosphate ions in solid and liquid phases. The P inputs and P outputs of each grid such as fertilizer, uptake, runoff and leaching were estimated with measured data in every time-step (yearly). The P status (phosphate ion concentration in soil solution) was calculated from P stock and P budget in each time step. The simulation was conducted with two tillage systems [moldboard plough (MP) and no-till (NT)].The P model managed to simulate the evolution of P status along soil profile in MP and NT during 25 years; while it was a homogenous distribution of soil P within 0-20 cm in MP. The simulated results indicated that higher accumulation of soil P in upper layers might lead to a lower use of soil P stocked in sub-soil by crop uptake. However, the model still needs validation and adjustment of parameters to form more accurate results.