Water mode

Exercise objective:

       ·  Running ORYZA2000 with a water balance; file control.

Suggested reading:

Chapters 7.1 and 7.3 (the part on water management) of the book, ORYZA2000: modelling lowland rice.

Running ORYZA2000 with a water balance requires parameter input in the crop and the experimental data file. Additionally, a new data file is needed that contains properties of the soil. This soil data file is specified in the control file CONTROL.DAT.

Exercise:

In the ‘water’ mode, ORYZA2000 takes into account the effect of water availability on growth and development of rice. This water availability is expressed as soil water content and as soil water tension. Soil water tension is linked to (reduction in) crop growth processes, such as leaf development, leaf rolling, photosynthesis, spikelet sterility and death rate of leaves. Crop parameters are specified in the crop data file to define a variety’s sensitivity to soil water tension on these growth processes. Soil water tension is the resultant of the water balance in the soil, i.e. the daily balance of all water inflows and all water outflows. The inflows of water in the soil are rainfall and irrigation. Irrigation management is specified in the experimental data file. The outflows of water from the soil (such as seepage and percolation) are determined by its hydrological properties. These properties are specified in the soil data file.

Ex-IV.1. Start up the Shell FSEWinRunOnly. Open project C:\COURSE\WATER\ORYZAWin. Study CONTROL.DAT and verify its contents:

FILEON = 'RES.DAT'                       ! Output file

FILEOL = 'MODEL.LOG'                     ! Log file

FILEIT = 'C:\COURSE\WATER\EXPLORE.DAT'   ! Experimental data

FILEI1 = 'C:\COURSE\WATER\IR72.D92'      ! Crop data

FILEIR = 'C:\COURSE\WATER\RERUNS.DAT'    ! Rerun file

*   FILEI2 = 'C:\COURSE\WATER\PADDY.DAT'    ! Soil data

Read the crop data file IR72.D92 and scroll to Section 9 ‘Drought stress parameters’ at the bottom. These parameters specify the sensitivity of the specific rice variety to soil water tension. So-called upper and lower limits indicate at what tension a certain crop growth process starts to be negatively affected, and at what tension the reduction is 100%, respectively. Soil water tension is expressed in kilo Pascal (kPa; 1 kPa = 10 mbar = 10 cm water). For example, at a soil water tension of 74 kPa, leaves of cv. IR72 start rolling (thus intercepting less light, leading to lower photosynthesis) and at 794 kPa, all leaves are fully rolled.

Scroll through the experimental data file (EXPLORE.DAT) and note that the simulation mode is still set to POTENTIAL. Run ORYZA2000, and verify the results in column Sim1 of Table IV.1.

Table IV.1.

View ANSWERS from the Tutorial_answer_sheet.pdf file. 

Ex-IV.2. Set ORYZA2000 to the water mode in the experimental data file by selecting PRODENV = 'WATER BALANCE'. ORYZA2000 has three water balance modules and we must select one of them: WATBAL = 'PADDY'. The model PADDY is the standard module for flooded lowland conditions. SAWAH is a more detailed and complex module and can be used for both lowland and aerobic or upland conditions. SAHEL is a simple water balance module for free-draining aerobic or upland soils. Each of the three modules requires specific soil parameters that need to be provided in a soil data file. In these exercises, we will only illustrate the use of PADDY. Run ORYZA2000 and examine the results. The error message is cryptic and does not give a clue to what is wrong…. Open CONTROL.DAT and note the line *FILEI2 = 'C:\COURSE\WATER\PADDY.DAT'. When ORYZA2000 is run in the water mode, a soil data file must be supplied as FILEI2. Remove the * , so that the file FILEI2 is ‘activated’. Open PADDY.DAT and note that this file contains various soil characteristics. In the top of the file we find a definition parameter SCODE = 'PADDY'. This is a check that the data provided in the file are those for the soil water balance module PADDY. For the water balance modules SAHEL and SAWAH, other parameters have to be provided. We will deal with the soil data file in more detail in “Chapter V: Water-limited production; soil properties”. For now, run ORYZA2000 and note that the model runs without any errors.