Dear Crop Modelers,
Below, please find a summary of some of the activities of the cassava
crop modeling team. If you are interested in cassava and especially if
you have experimental data for model evaluation and improvement, we
would like to invite you to join the team. Please contact Ms. Patricia
Moreno at CIAT for further information ([log in to unmask]) or visit
the DAPA-CIAT web site (http://dapa.ciat.cgiar.org/cassava-cmit/)
Gerrit
*The last months the group has been quiet, but we have moved forward in
the improvement of the cassava model. We would like to share some news
related with the development of the cassava model. Please review the
attached file or the next bullets:*
vA second meeting was held in April at CIAT headquarters with
researchers experienced in cassava physiology and modeling (James Cock,
physiologist and first developer of a cassava model; Anthony Hunt,
physiologist and plant breeder, co-developer of the GUMCAS cassava model
(Matthews and Hunt, 1994), and developer of the most recent prototype
cassava model (CROPSIM-cassava) in DSSAT, Gerrit Hoogenboom DSSAT
coordinator, Myles Fisher ecophysiologist with broad experience in crop
modeling; John Hargreaves, CSIRO crop modeler and developer of the APSIM
cassava model; Attachai Jintrawet, Associate Professor, Chiang Mai
University; Vinai Sarawat from the Khon Kaen Field Crop Research Center;
Clair Hershey, Cassava Program Leader, International Center for Tropical
Agriculture (CIAT); Andy Jarvis, Program Leader-Decision and Policy
Analysis (DAPA), CIAT; and Patricia Moreno, cassava modeler, CIAT.
·In the meeting some processes were modified in the current cassava
model on DSSAT:
oDelete phenological phases and definition of branching parameters
o*/Code modification in nitrogen distribution:/*The model now has the
leaf nitrogen growth restriction working, together with a growth
restriction on stem, crown, and root to prevent the N concentration
falling below the minimum. With the minimums as now set, this had quite
an effect on stem growth. This characteristic is probably important in
enabling cassava to produce well in low fertility soils
o*/Initial changes with photosynthesis:/*Calculation of a VPD running in
the daily time-step. There is a VPD photosynthesis factor (VPDFP) with
a multiplicative effect to calculate the daily carbon assimilation. This
factor is estimated from a threshold (5 kPa) and a linear decline, with
coefficients defined in the species file (-0.35 fr/kPa).
/VPDFP=1-0.35*VPD1000-5/
oAdjustment of species parameters
üPHINT now changes with growth stage factor to represent the observed
changes in the rate of leaf appearance;
üDeleted the leaf petiole fraction (it is now included with the lamina);
üAdded a coefficient for the fraction of stem assimilates left as
reserves (RSFRS);
üAdded a coefficient to limit the leaf growth according with N content
(NLLG) to represent the high observed N concentrations of cassava leaves;
üAdded minimum concentrations of soil NO_3 and NH_4 below which the
plant cannot take them up;
üIncluded a coefficient that controls the size of the second shoot
relative to the first (SGRO2). The coefficient is used to change shoot
growth rate as the plant ages.
oImproved representation of leaf area as a function of thermal time.
vThe model will be included also in APSIM.
vThe cassava Crop Model Improvement Team (CMIT) has established short,
medium and long term objectives (For more
info:http://dapa.ciat.cgiar.org/wp-content/uploads/2013/05/Cassava-crop-model-improvement-team.pdf).
vIn August, we met with Reinhardt Howeler, a soil scientist with broad
experience on the nutritional requirements of cassava:
o We discussed the need to work on the effects of nutrients on branching
(we do not have data on how nutrients affect the number of branches and
node development) and leaf duration (K increases the leaf duration).
oNutrients in cassava are less mobile in response to stress than in many
species.
oDr Howeler has some datasets available for model development, which we
will organize for distribution to those developers who need them. He is,
however, fully commited until the end of the year.
oFor more
information:https://docs.google.com/a/cgxchange.org/file/d/0Bz8XnYCCMibIZXN4ekcxYllqbnc/edit?usp=docslist_api)
vMost of the available data about growth and development for cassava are
in the tropics. It is therefore necessary obtain data from the sub
tropics to represent photoperiod effects for inclusion in the model in
the future.
vWe are developing a non-destructive system for monitoring cassava
growth. This will simplify data collection for adding new features to
the model and for model testing
vOur next steps are:
oDocument the processes, equations and algorithms used in the current
cassava model.
oIncorporate the VPD hourly effect in the model
oInvite people/institutions to be part of the cassava CMIT through model
evaluation or contribution with processes improvement.
oCassava modeling workshop (tentatively December 2013) with data
collectors and modelers for model development and evaluation.
vFuture aspects to review:
oThe need to add root quality to the model, which is lacking at present
in most models. We will probably have to develop this ourselves rather
than use a plug in from DSSAT or APSIM.
--
Gerrit Hoogenboom
Director, AgWeatherNet, and
Professor of Agrometeorology
Washington State University
24106 North Bunn Road
Prosser, Washington 99350-8694, USA
1-509-786-9371; Fax: 1-509-786-9370
[log in to unmask]
www.weather.wsu.edu
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