| Simultaneous distributions of water and nitrogen from a point source were measured in laboratory. In the experiments, the application rate was varied from 0.6 to 7.8 L/h, the input concentration from 100 to 700 mg/L, and the applied volume from 6L to 15L. The results showed that the ultimate saturated radius on the surface increased with the application rate. Surface wetted radius and vertical wetted depth were proportional to the applied water volume with power values of about 0.29 and 0.44, respectively. An increase in rate resulted in an increase in the wetted horizontal area and decrease in the wetted soil depth. A uniform distribution of nitrate concentration in the soil was found 17.5 cm around the point source for a given concentration. The average concentration of this area increased with the input concentration and application rate. For any input concentration, the accumulation of nitrate at the boundary of the wetted volume was observed. There existed an extremely high ammonium concentration in the proximity of the point source (about 2.5 to 7.5cm from the source), which increased with the input concentration. Results also demonstrated that the influence of fertigation on the ammonium distribution was restricted in a small volume, about 10 cm around the point source. Results demonstrated the input concentration is the main factor that affects nitrogen distribution in soil.The commercial software, namely HYDRUS-2D, was used to simulate water and nitrogen transport in the soil under drip fertigation. The code simulated the water movement in the soil successfully. Somehow, it is unable to simulate the moving wetted boundary condition. The code needs to be improved in simulating nitrogen transport and transform in soil under surface drip fertigation. Fertigation strategy has much of an influence on solute distribution in soil, and there remain more solute within the root zone under strategy 1/4-1/2-1/4(1/4 of the total irrigation time apply water, then solute applied during the next 1/2 of the total irrigation time, and apply water during the last 1/4 of the total irrigation time). |
