root growth paramterization

[Sebastian]

Dear Per,

I use DS_Depth in the rootdens module where the relative root density is a function of the soil depth. In an irrigation experiment with Maize, I want to investigate the root growth over time and use this to parameterize the root in Daisy.

I was now wondering what data I need to collect. The model description states that relative values of the root density distribution are scaled to match the current total root mass. Is it therefore sufficient to "simply" determine the ratio of dry root biomass in different depths to the overall dry root biomass and use this value in DS_Depth or do I have to determine the length of the roots in different depths instead and refer them to the total root length?

One might think a thick root has a high mass therefore a high ratio compared the total root mass but only little length and thus little effect on root water uptake whereas fine roots have little mass but higher total root length and therefore greater impact on root water uptake.

Thank you for you help,

Sebastian

[Per Abrahamsen]

Daisy assumes all the roots have the same length per mass ratio (SpRtLength), so no thick or fine roots.

Apart from that, I'm not quite sure what you are asking. Are you trying to parameterize Daisy based on direct root measurements, and asking which measurements would be most useful?

Regards,

Per

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[Sebastian]

Right, this is exactly what I was asking. Which measurements are most useful, mass or length measurements of roots?

[Per Abrahamsen]

Root length measurements are most useful. Root length is what matters for water and solute, not root mass.

[Sebastian]

Thanks for your help.