Solute transport initial boundry conditions

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Muhammad Tahir
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Joined: Fri Nov 05, 2010 12:32 pm
Location: Pakistan
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Solute transport initial boundry conditions

Post by Muhammad Tahir » Fri Dec 03, 2010 5:27 pm

Hay all,

I have two questions
Question-1 is regarding: Solute transport boundry conditions: initial conditions:
I am simulating NO3 leaching of applied urea in a field trial using Hydrus 1D (solute Transport with Nitrification Chain).While simulating NO3 uptake by roots using Hydrus-1D, when I put initial conditions for NO3 as immobile zone concentration [MM-1], output shows no uptake, but it shows uptake only when I put as [ML-3]. I have initial NO3 conc. as mg/kg soil but I have also moisture contents in soil profile. Can I change my initial boundry condition to [ML-3] on the base of soil water contents (ug of NO3/cm3 of water present in field upto respective depth).
2nd Question: What should be value of “Maximum allowed conc. of passive root water uptake” for maize and wheat crop for NO3 uptake while using feddes model when I am applying pulse input of urea, i.e., 7.5 cm irrigation depth having 35 and 100 ug/cm3 conc. of urea for wheat and maize , respectively. It was followed by 40 cm and 500 cm irrigation depth of water only to wheat and maize crop, respectively.
Thanks in advance

Muhammad Tahir

Jirka
Posts: 4759
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Post by Jirka » Thu Jan 20, 2011 10:42 pm

Muhammad,

This question belongs to the Discussion forum about HYDRUS-1D. Not about the Soil Physics with HYDRUS book.

1. Root water and nutrient uptake is only from the liquid phase in the mobile zone. It is not from the immobile liquid phase (where the concentration should be in the same units, i.e., [M/L3]), nor from the sorbed phase (here the units are indeed [M/M]. I do not see why you would not be able to specify the liquid phase concentration. You can also specify the total concentration and let HYDRUS to distribute solute between different phases - See the Solute Transport - Boundary Conditions command.

2. Since this is the maximum allowed concentration for passive uptake, I would recommend to simply specify a large number (larger than you encounter during the simulation). Roots likely take up all Nitrogen dissolved in water during the passive uptake, i.e., there is no exclusion of N from the uptaken water.

Jirka

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