Hello Muhammad,
Very briefly, CERES-Maize first calculates daily root growth rate (GRORT, g/plant), according to the C balance rules. Then that root dry mass is converted into root length by using a root-length-to-weight-ratio parameter (RLWR). The resulting variable RLNEW is the calculated root length (cm/m2 ground) to be added today to the root system. To distribute RLNEW among the various soil layers the model calculates a per-layer variable, RLDF, as a function of the most limiting stress (water or N), soil hospitality factor (SHF), and layer thickness. Soil hospitality factor is read per-layer from the soil file (SRGF).

In summary, SRGF is an indication of the relative adequacy of the soil environment for root growth, but other factors also contribute to root length density calculation.

Hope this was useful.
Best regards,
Jon

Jon I. Lizaso
Dpto. Producción Vegetal. Fitotecnia
ETS Ingenieros Agrónomos
Senda del Rey s/n
28040 Madrid, SPAIN
email: [log in to unmask]
Tel: 34 91 549 1122
________________________________________
From: DSSAT - Crop Models and Applications [[log in to unmask]] On Behalf Of muhammad anjum iqbal [[log in to unmask]]
Sent: Monday, May 04, 2009 7:49 AM
To: [log in to unmask]
Subject: HI.PLEASE

Hi, All DSSAT users,
  Would you like to help me for the following questions?
How is root distribution specified in DSSAT? Our objective is to define an exponentially decreasing distribution of roots (of root lenght density) as frequently used in other models. We used an exponentially decreasing SRGF in the soil file. However, the plant growth output file gives a root lenght density in the different layers (RL1D, ...) that doesn't follow the distribution that was defined according to the SRGF in the soil file. Are there some environmental modifiers (as stated in the book "Understanding options for Agricultural Production", p. 94 "The root weighing factor from the soil file is multiplied by a soil water factor to obtain the actual root depth distribution.") and how can this modifiers be disabled? Or are there also some other root parameters to be defined in relation to distribution, e.g. in the cultivar, ecotype or species file?

Could you provide us some paper or references where to find the details on root growth and distribution used in DSSAT/Ceres-Maize.
MUHAMMAD
DEPARTMENT OF WATER , ATMOSPHERE & ENVIRONMENT
UNIVERSITY OF NATURAL RESOURCES & APPLIED LIFE SCIENCES
VIENNA -AUSTRIA