Crop parameters

Introduction

The crop parameters used are fundamental to using WOFOST. They can be difficult to navigate because there are so many of them (48 in the current version). Here we present them all, so you can evaluate which parameters are of most relevance to you. Unless you are a specialist, you should use default values for most parameters for a crop of interest. However, you could consider using different values for the phenology parameters.

List of crops

Here is a list of the default crop parameter sets that come with Rwofost

library(Rwofost)
## Warning: package 'Rwofost' was built under R version 4.3.1
crops <- wofost_crop()
cat(crops, "\n")
## barley, cassava, chickpea, cotton, cowpea
## fababean, groundnut, maize_1, maize_2, maize_201
## maize_202, maize_203, maize_204, maize_205, maize_fra
## maize_spa, millet, mungbean, pigeopea, potato_701
## potato_702, potato_703, potato_704, rapeseed_1001, rapeseed_1002
## rapeseed_1003, rapeseed_1004, rice_501, rice_hybds, rice_hybws
## rice_ir64d, rice_ir72, rice_ir72d, rice_ir72w, rice_ir8a
## sorghum, soybean, soybean_901, soybean_902, soybean_903
## soybean_904, soybean_905, soybean_906, sugarbeet_601, sugarbeet_602
## sugarbeet_603, sugarbeet_604, sugarcane, sunflower_1101, sunflower_fra
## sunflower_spa, sweetpotato, tobacco, wheat_fra, wheat_spa
## winterwheat_101, winterwheat_102, winterwheat_104, winterwheat_105, winterwheat_106
## winterwheat_107

You can get parameters for a single crop (variety) by like this.

crop <- wofost_crop("barley")

You can also provide a filename to wofost_crop to read parameters from a file you created yourself. Have a look at the files in the Rwofost package. On your computer they are installed on what is returned by R if you run this: system.file("wofost/crop", package="Rwofost")

The object crop is a list with 48 elements (some of the parameters are used to compute nutrient limitation but that has not been implemented yet — so these can be ignored for now).

class(crop)
## [1] "list"
length(crop)
## [1] 48
str(crop[1:5])
## List of 5
##  $ TBASEM: num 0
##  $ TEFFMX: num 30
##  $ TSUMEM: num 110
##  $ IDSL  : num 0
##  $ DLO   : num -99

Most are single numbers, but there are also two-row matrices (referred to as tables in the context of WOFOST). The names of these matrix-parameters end on TB (for table). Here is an example.

crop$FOTB
##      [,1] [,2] [,3] [,4] [,5]
## [1,]    0  0.8    1 1.01    2
## [2,]    0  0.0    0 0.85    1

You can get some (but not very informative) meta-data about the parameters by using the argument describe=TRUE.

crop <- wofost_crop("barley", describe=TRUE)
## BARLEY, SPRING
## Regions: Whole of the European Communities
## Sowing date varying from 9 Feb in Greece and southern Spain,
## to 26 Mar in southern Germany.
## Mean date of flowering varying from 1 May in the south to
## 19 June in the north.
## Mean date of maturity varying from 20 June in the south to
## 15 Aug in the north.
## Calibrated for use in WOFOST model at the Centre for Agrobiological
## Research (CABO-DLO) for the simulation of crop growth and yield on the
## basis of daily weather data.
## Purpose of application: Crop growth monitoring with agrometeorological
## model in the EC.
## Developed in the framework of JRC Agriculture Project Action 3.

Parameters

Emergence

These parameters help determine how long it takes for the crop to emerge. This is only relevant when the simulation of the crop starts at sowing, and not at emergence. For emergence to occur, a thermal time TSUMEM has to be reached, but summing up the daily difference in between the average temperature and TBASEM — if the temperature is > TBASEM; and by capping the average temperature at TEFFMX.

variable	description	unit
TBASEM	lower threshold temp. for emergence	°C
TEFFMX	max. eff. temp. for emergence	°C
TSUMEM	temperature sum from sowing to emergence	°Cd

The default parameters for barley are:

crop$TSUMEM
## [1] 110
crop$TEFFMX
## [1] 30
crop$TBASEM
## [1] 0

Initial conditions

variable	description	unit
TDWI	initial total crop dry weight	kg ha-1
LAIEM	leaf area index at emergence	–
RGRLAI	maximum relative increase in LAI	d-1

Phenology

Phenology parameters are very important as they determine the “maturity type” (early, late) of the variety, and hence the length of the growing season. This can have a very strong effect of crop yield potential, but also on the risk to encounter drought stress. You can easily change the maturity type by changing the values for TSUM1 and TSUM2

variable	description	unit
IDSL	development depends on temp: 0, daylength: 1, both: 2	–
DLO	optimum daylength for development	hr
DLC	critical daylength (lower threshold)	hr
TSUM1	temperature sum for vegatative phase	°C d
TSUM2	temperature sum for generative phase	°C d
DTSMTB	increase in temp. sum as function of avg. temp (°C)	°Cd

Other WOFOST implementations may also have DVSI, the initial development stage (DVS), and DVSEND development stage at harvest; but Rwofost does not have these.

Green area

variable	description	unit
SLATB	specific leaf area as a function of DVS	ha kg-1
SPA	specific pod area	ha kg-1
SSATB	specific stem area as function of DVS	ha kg-1
SPAN	life span of leaves growing at 35°C	d
TBASE	lower threshold temp. for ageing of leaves	°C

Assimilation

var iab le	description	unit
KDI FTB	ext. coefficient of diffuse visible light as function of DVS	–
EFF TB	light-use effic. single leaf as function of avg. temperature	kg ha-1 hr-1 J-1 m2 s
AMA XTB	maximum leaf CO2 assimilation rate as a function of DVS	kg ha-1 hr-1
TMP FTB	red. factor of AMAX as function of average temperature	–
TMN FTB	red. Fact. of gross assim. rate as function of low min. temp.	–

Conversion of assimilates into biomass

variable	description	unit
CVL	efficiency of conversion into leaves	–
CVO	efficiency of conversion into storage organ	–
CVR	efficiency of conversion into roots	–
CVS	efficiency of conversion into stems	–

Maintenance respiration

variable	description	unit
Q10	relative increase in respiration rate per 10°C temp increase	–
RML	rel. maint. resp. rate leaves	kg CH2O kg-1 d-1
RMO	rel. maint. resp. rate storage organ.	kg CH2O kg-1 d-1
RMR	rel. maint. resp. rate roots	kg CH2O kg-1 d-1
RMS	rel. maint. resp. rate stems	kg CH2O kg-1 d-1
RFSETB	red. factor for senescence as function of DVS	–

Partitioning of biomass

variable	description	unit
FRTB	fraction of total dry matter to roots as a function of DVS	–
FLTB	fraction above-ground biomass to leaves as a function of DVS	–
FSTB	fraction above-ground biomass to stems as a function of DVS	–
FOTB	fraction above-ground biom. to stor. org. as a function of DVS	–

Death rates

variable	description	unit
PERDL	max. relative death rate of leaves due to water stress	–
RDRRTB	relative death rate of stems as a function of DVS	d-1
RDRSTB	relative death rate of roots as a function of DVS	d-1

Water use

variable	description	unit
CFET	correction factor transpiration rate	–
DEPNR	crop group number for soil water depletion	–
IAIRDU	air ducts in roots present (=1 or TRUE) or not (=0 or FALSE)	–

Roots

variable	description	unit
RDI	initial rooting depth	cm
RRI	maximum daily increase in rooting depth	cm d-1
RDMCR	maximum rooting depth	cm

CO₂

varia ble	description	u n i t
CO2AM AXTB	mult. factor for AMAX as a function of CO2 concentration	–
CO2EF FTB	mult. factor for EFF as a function of CO2 concentration	–
CO2TR ATB	mult. factor for max transp rate TRAMX as a function of CO2 conc.	–