Description:
Microirrigation systems cause a spatially rather heterogeneous distribution of water in the root zone and the timing of irrigation and fertilizer injection has implications for where in the soil nutrient concentrations will be high. This tool was developed to demonstrate the effect of irrigation and fertilizer injection timing on the distribution patterns of nitrate and soil moisture in the root zone. The tool shows results of simulating a single irrigation event on a moderately dry soil. Simulations do not account for water or nutrient uptake of roots and evaporation from the soil surface and were done using the software HYDRUS 2D/3D (Šimunek et al., 2012), which numerically simulates the movement of water and solutes under unsaturated conditions in soils. The work was funded by the Specialty Crop Block Grant Program (SCBGP) and the Fertilizer Research and Education Program (FREP) of the California Department of Food and Agriculture (CDFA).
Instructions:
1. Select the variable to be displayed:
- Soil moisture change: Change in soil moisture relative to the initial soil water content
- Matric potential
- Nitrate concentration: Nitrate concentration of the pore water
- Nitrogen concentration: Nitrogen concentration of the pore water
- Nitrate content: Mass of nitrate per volume of soil
2. Select the irrigation system. For Fan-Jet (microsprinkler), a larger wetted area is assumed than for drip whereas the volume of water applied is the same.
3. Select the irrigation duration (between 3 and 24 hours).
4. Select the flow rate.
5. Select whether fertilizer should be injected continuously throughout the irrigation event or as a pulse. When selecting pulse, fertilizer injection can be started at different times after the start of the irrigation event (6. Fert. Start Time). Pulse duration (7. Fertigation Duration) can be either one or three hours. Only those timing options are available that allow the injection to stop at least one hour prior to the end of the irrigation event.
8. Select the amount of N to be applied.
9. Select the soil type by either selecting a soil texture or a soil series (soil series may have several horizons with different textures). Texture information of the soil series was obtained from SoilWeb (California Soil Resource Lab).
10. Select either centimeters or inches as length unit for the plot.
11. Click the submit button to generate the graph.
Axis options:
- Optimal for current settings: Cutoff values of the legend are selected based on the current graph to optimally show the spatial distributions.
- Fixed for current soil and irrigation system (works for soil moisture and matric potential, only): Legend remains the same when changing timing parameters.
- Custom: Enter custom cutoff values into the boxes next to the legend and click apply.
- Isolines can be added to the plot by specifying the desired values at which lines should be drawn in the box, separated by a comma (e.g. "0.03, 0.05, 0.1").
References:
California Soil Resource Lab. “SoilWeb.” SoilWeb: An Online Soil Survey Browser. California Soil Resource Lab, casoilresource.lawr.ucdavis.edu/gmap/.
Šimunek, J., Van Genuchten, M. T., & Šejna, M. (2012). HYDRUS: Model use, calibration, and validation. Transactions of the ASABE, 55(4), 1263-1274.