## How to calculate the root water uptake of a certain soil depth range

A discussion forum for Hydrus-1D users.
liumg
Posts: 3
Joined: Tue Feb 09, 2021 4:21 am
Location: China

### How to calculate the root water uptake of a certain soil depth range

Dear sir,
I'm studying the water uptake amount of a deep root crop at different depths.I want to know how to determine the actual amount of water uptake by roots within a certain depth range with hydrus-1d. I tried to sum and integrate sink terms of different depths, and I found that their results were the same. All of them (12.9cm) were significantly lower than the total root water absorption (56cm).I used the trapz() function in the caTools package of R software for integration (Trapezoid Rule Numerical Integration).
Thank your!

Minguo Liu

Jirka
Posts: 5216
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

### Re: How to calculate the root water uptake of a certain soil depth range

The root water uptake from different depths, Sink [1/T] (e.g., 1/day), is reported in the Nod_inf.out file. If you integrate this value over a root zone (multiply by lengths associated with each node of the root zone), you will get the actual transpiration rate [L/T] (e.g., cm/d; T_a=integral(Sink*dx)). This value should be equal to the value vRoot [L/T] reported in T_Level.out. If it is not, you do it wrong. If you integrate this only over a certain soil layer, you get root water uptake from this layer.

If you integrate T_a over time, you get cumulative actual transpiration rate [L] (e.g., cm). J.

liumg
Posts: 3
Joined: Tue Feb 09, 2021 4:21 am
Location: China

### Re: How to calculate the root water uptake of a certain soil depth range

Dear Jirka,

I used the the Sink , is reported in the Nod_inf.out file, to calculate Ta with T_a=integral(Sink*dx) at different time points, and the result was consistent with vRoot item (corresponding time point) in T_Level.out file. However, i still have a problem. Although the root water uptake is similar at the corresponding time point bewteen vRoot and Ta, why the vRoot drawing fromT_Level.out file and sink drawing with integral have completely different results.I submit the two figures as attachments.Can`t I directly integrate Ta over Time to calculate the cumulative root water uptake?
Thank you!

Minguo Liu
Attachments
vRoot.png (7.47 KiB) Viewed 628 times
Ta.png (7.92 KiB) Viewed 628 times

Jirka
Posts: 5216
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

### Re: How to calculate the root water uptake of a certain soil depth range

You will need to figure this out yourself. It is all pretty simple. I know that it is simpler to ask for help than to try to resolve it yourself, but you should at least try. J.

liumg
Posts: 3
Joined: Tue Feb 09, 2021 4:21 am
Location: China

### Re: How to calculate the root water uptake of a certain soil depth range

Thank you for your help and advice. I have tried hundreds of times this week, and I enjoy it. I will continue to try. I think it may be that I don't understand how each index of the model is calculated. Tomorrow is China's traditional festival. With very best wishes for your happiness in the New Year.