Hello all,

bulk density, how to measure it and what data to enter into the model may become a complicated issue when smaller stones / gravel are abundant in the soil.

First of all, it may be tricky if not impossible to get a reasonable value of BD by undisturbed 100cm3 core sampling.

But, as BD also related directly to porosity and (water-filled) pore space, other soil parameters, such as field capacity or permanent wilting point, are automatically affected and should be modified accordingly. Otherwise, water and nutrient movement in the soil will not be simulated correctly.

Then, how about soil moisture readings by e.g. small capacitance or TDR probes? How many of such readings do you need to get a representative water content of a stony soil? I guess quite a few.

Just some thoughts.

Regards,
Rolf


> -----Original Message-----
> From: DSSAT - Crop Models and Applications
> [mailto:[log in to unmask]] On Behalf Of Jans Bobert
> Sent: Thursday, April 19, 2012 08:31
> To: [log in to unmask]
> Subject: Re: Bulk density
>
> Dear Maria,
>
> you should use the density including the > 2 mm fraction. This is the
> standard method we use in Germany. If you take a look at the DSSAT
> documentation (in the DSSAT folder), you find a description of the method
> for the determination of the bulk density on page 226 pp. (Volume 4):
>
> BULK DENSITY
> Core Method
> A core sampler can be a single cylindrical tube or a tube with several
> cylindrical rings of known dimensions. The sampler can be driven
> mechanically or manually into the soil either horizontally or vertically.
> Extruded soil from core sampler or soils and rings are weighed and oven-
> dried to constant weight at 105°C. The oven-dry weight divided by the
> volume of the core sampler or cylindrical ring is the bulk density
> usually expressed in g/cm3. This method should not be used for wet (e.g.,
> aquic,
> histic) or
> dry, sandy soils.
>
> As reference the authors mention -> SCS, USDA. 1984. Soil survey
> laboratory methods and procedures for collecting soil samples. In Soil
> Survey Investigation Report No. 1. U.S. Gov. Print. Office, Washington,
> D.C..
>
> Hope this clarifies.
>
> Jans
>
>
> Am 4/19/2012 4:38 PM, schrieb maria soldevilla:
> > Thank you very much for the quick responses.
> >
> > In fact, I took the cilinder samples and measured the dry weight, but
> > I also measured the weight of the coarse fraction so I can subtract it
> > from the total and and get the density (without stones) dividing by
> > the volume of the cylinder, as it is common to give the density on
> > that way. My question was which of the two densities should I
> > introduce in the soil file, but I guess it is the total one (including
> stones).
> >
> > Thank you again
> > Maria
> >
> > 2012/4/19 Jorge Batlle<[log in to unmask]>
> >
> >> Soil bulk density is measured in undisturbed soil samples (ussually
> >> token by insertion of a cilinder of knwon volume, and dividing the
> >> dry weight of this soil content by the volume of the cylinder). This
> >> measurement can be related to total volume porosity if the real
> >> density of soil particles is measured also by picnometer method.
> >> If you separed coarse fragments>2 mm and fine fraction<  2 mmm, it
> >> means that you already disturbed your sample.
> >> I hope this help.
> >> Jorge Batlle
> >>
> >>> The bulk density of a soil, is the ratio between the mass and volume
> >>> of a
> >> fraction of soil, the most important is that the volume fraction have
> >> included soil air. This is very important because in the porous part
> >> is where there is water movement and more movement of the roots
> >> becoming root penetration, among other things, like the movement of
> >> nutrients or nutrient uptake by the roots.
> >>> -----Mensaje original-----
> >>> De: DSSAT - Crop Models and Applications
> >>> [mailto:[log in to unmask]]
> >> En
> >> nombre de fyy0201
> >>> Enviado el: Jueves, 19 de Abril de 2012 08:15 a.m.
> >>> Para: [log in to unmask]
> >>> Asunto: 回复: Bulk density
> >>>
> >>> Dear colleage,
> >>> I am not familiar with the content mentioned by you.So I am sorry
> >>> and
> >> can not
> >> help you.
> >>> Best regards,
> >>> Lily
> >>> 2012-04-19
> >>>
> >>>
> >>>
> >>> fyy0201
> >>>
> >>>
> >>>
> >>> 发件人：maria soldevilla
> >>> 发送时间：2012-04-19 21:10
> >>> 主题：Bulk density
> >>> 收件人："DSSAT"<[log in to unmask]>
> >>> æ  送：
> >>>
> >>> Dear colleages.
> >>>
> >>> I have a question and may be somebody can help me. The Bulk density
> >> coefficient ( SBDM ) in the soil file, is the soil density including
> >> coarse elements or without them? I'm not sure which density I should
> write.
> >>> Thank you very much
> >>> Best regards
> >>> Maria
> >>>
> >>>
>
>
> --
> ____________________________
>
> Jans Bobert
> Stavangerstrasse 23
> 10439 Berlin
> Germany
> phone: ++49 (0)30 6923768
> email: [log in to unmask]