Table D.1.
Comparison of the irrigation methodologies in different frameworks
| General topic | FOCUS surface water (FOCUS, 2001) | New FOCUS groundwater (European Commission, 2014) and PEC soil (EFSA, 2017) | Internal PRZM irrigation routines (Carsel et al., 2003; Suárez, 2005) | |
|---|---|---|---|---|
| Calculation of soil moisture deficit and irrigation threshold | Measure | Total plant‐available soil water, summed up over the root zone | Soil moisture deficit (= difference field capacity (FC) – current water content, summed up over the root zone) | Total plant‐available soil water, summed up over the root zone |
| Meaning of ‘root zone’ | Calculated to max. root depth or current root depth? | Calculated to current root depth (since FOCUS PELMO v.4.4.3)a | Calculated to maximum root depth in winprzm.exe (v.4.63) included in the latest official FOCUS surface water PRZM release. However, the code was recently changed to use current root depth | |
| Remarks | Water balance calculated with ISAREG model; unclear quantities ‘effective precipitation’ and ‘deep percolation’b | Routines poorly documented in manual code is better documented, but difficult to read for non‐programmers | ||
| Irrigation period and triggering | Checking | Continuous checking | Check every week on a fixed weekday | Continuous checking |
| Trigger | Total plant‐available soil water storage drops to Rmin (point where the plant starts to reduce transpiration) | Soil moisture deficit > 15 mm | Irrigation is triggered if (1 − PCDEPL) of the total plant‐available water volume in the root zone have been depleted and it does not rain on the day of concern | |
| Questions/remarks | Rmin = (1 − p) Rmax; p = 0.4 for all scenario/crop combinations (except for grass in D3 where p = 0.3) | Start of senescence is a model parameter in FOCUS groundwater, but does not exist in FOCUS surface water. If once‐a‐week checking is meant to reflect farmers’ behaviour, how do they determine the soil moisture deficit? 15 mm should result in quite frequent irrigation events | PCDEPL is user‐input (according to comments in source code, the range 0–0.9 is allowed. However, PRZM accepts also PCDEPL = 1) and independent of the internal trigger for evapotranspiration reduction (0.6 × potential plant‐available water in the root zone) | |
| Irrigation modes, volumes and occurrence of surface run‐off | Modes | Sprinkler (but technically added to rainfall file) | Flood and sprinkler | Flood, furrow, various types of sprinkler |
| Irrigation volume | Always 30 mm | Fill up the root zone to field capacity (FC) | Fill up the root zone to field capacity (FC), also surplus can be applied (saline soils, parameter FLEACH); for options 3–6, upper limit of irrigation volume given by RATEAP parameter; for option 7, irrigation volume is fixed by RATEAP parameter | |
| Can irrigation cause surface run‐off? | Yes, every time in irrigated R scenarios (given the application as rainfall and the chosen CN parameterisation) | No | Yes and no (depends on the selected option) | |
| Questions/remarks | ISAREG has many different options, not only the one used in FOCUS (2001) |
Test simulations with winprzm v.4.63 and examination of the code suggested that most PRZM options do not exactly correspond to their descriptions in the manual and also have bugs Mark Cheplick replaced option 5–7 with new, bug‐free options Option 5 (new): sprinkling over canopy, without run‐off Option 6 (new): sprinkling under canopy, without run‐off Option 7 (new): sprinkling under canopy, user‐defined rates, without run‐off |
a
Current root depth vs. maximum root depth will not make a difference in PRZM/PELMO if maximum root depth is ≤ evaporation depth ANETD. However, most crops root deeper than ANETD.
b
cf Discussion in Reichenberger (2015).