Agriculture Reference
In-Depth Information
580
Aug.24, 2006
range = 51m
570
560
550
540
550
580
Nov. 7, 2006
range = 27m
570
560
550
540
550
570
580
590
600
610
620
630
640
easting (abbreviated) in m
0
4
8
12
16
20
24
mg per kg
32
Fig. 9.8
Contour lines of nitrate-N in a field at the date of wheat harvest (
top
) and about 10 weeks
later (
bottom
) as created by the sensing technique shown in Fig.
9.6
.
Darker colors
indicate higher
amounts of soil nitrate N. For details see the scale. The
plus signs
designate the respective sample
locations, the
numbers above them
stand for the identification of samples and the
numbers
below
them indicate the respective nitrate N level in mg per kg. The first four numbers of the northings
and eastings have been deleted (Extracted from Sibley
2008
, altered)
The soil minerals can store a variety of plant nutrients. But there are no minerals
that contain nitrate N. Reserves of nitrate N in soils primarily depend on the decom-
position of organic matter and the conversion of ammonium that results from this.
For the actual plant supply, the main
reserves
of nitrate N are in the soil water. And
since the soil water is a very
transient property
, so is the nitrate N in the soil. When
soil water moves away from the rooted soil zone -
e.g.
into the groundwater region
- the nitrate N goes with it.
On-the-go soil nitrate sensing allows to track the supply in a site-specific mode,
at least for the depth range from which samples are taken. Based on the technique
of Fig.
9.6
, contour lines about the site-specific nitrate N supply of a field in Nova
Scotia, Canada, were mapped several times during the year (Sibley
2008
; Sibley
et al.
2010
). Figure
9.8
shows an extract of the results from the time of wheat har-
vest to late autumn.
