Agriculture Reference
In-Depth Information
Box 3.1
(continued)
of a laboratory result for “available” P in the top 0.15 m of soil,
C
p
(milligrams per
kilogram) to an amount per ha per 0.15 m depth becomes
(B3.1.3)
Amount of P per ha
≅
2
C
p
kg P/ha.0.15 m
If the soil depth of interest is more than 0.15 m, as it would be for mineral N,
the conversion factor is correspondingly greater.
Element concentrations are sometimes expressed as a percentage of the dry
weight (g/100 g). For example, a soil N concentration of
C
percent converts to an
amount per hectare as
C
g
g soil
001
.
kg
kg soil
C
(B3.1.4)
C
%
=
=
100
001
.
kg
kg soil
C
Amount of N per ha
=
×
2 000 000
,
,
(B3.1.5)
=
20 000
,
C
kg N/
ha.0.15 m
Analysesofmanuresandbiosolidsareoftenquotedasapercentageofthe
elementinthefreshor“wet”weight.Toconverttoadrymatter(DM)basis,divide
the element concentration in the fresh weight (
C
f
percent) by the percentage of
DMinthefreshweightasfollows:
C
f
100
g fresh weight
g DM
(B3.1.6)
=
×
×
C
% (DM)
100
100
g fresh weight
a
The concentration
C
of an element is an example of a variable. Symbols for variables are
written in italics.
b
Units of measurement and their abbreviations are given in appendix 1.
to H
2
CO
3
and the strength of this acid. Carbonic acid is a weak acid because it
does not completely dissociate into H
+
and HCO
3
−
in solution. Ions that carry
one or more positive charges (+) are called cations, and those carrying one or more
negative charges (-) are called anions.
Sources of the Elements
In sunlight, vine leaves and green stems absorb C and O
2
as carbon dioxide (CO
2
)
from the atmosphere for the synthesis of sugars. Oxygen and H are also supplied
in water (H
2
O) derived from the atmosphere and soil. Chlorine (Cl) is abundant
