Agriculture Reference
In-Depth Information
Another concept of a site-specific adjustment for the slope of the control line
would be to take into account the effect of different soils. It is well known that -
ceteris paribus
- the efficiency of nitrogen use also depends on the
texture of soils
(Tremblay et al.
2012
). On sandy soils, the nitrogen use efficiency often is not as
good as on soils with more clay or silt. And since a surrogate of texture - the soil
conductivity - can rather easily be mapped, a feasible approach would be to orient
the slope of the control line on site-specific field maps of this soil property. The
result would be a site-specific
soil conductivity based slope
of the control line.
This approach is not state of the art, but it would be rather easy to implement such
an additional control mode.
9.4.9.3
Controls for Improving the Quality of Products
A completely different situation arises for small cereals when it comes to a
late
dressings
that might be applied after heading,
i.e.
after BBCH stage 50. The objec-
tive of such late applications is not to increase the yield mass, which hardly is pos-
sible at this stage any more. Instead, the application of small amounts of nitrogen in
this developmental period aims at raising the protein content of the kernels.
Accordingly, this rather late application is denoted as “quality-dressing”. However,
this “quality-dressing” needs biologically active plants. Therefore, the more dark
and green the canopy is, the more effective this late application can be, and the
higher the nitrogen rate beyond BBCH 50 should be. This explains why, for quality-
dressing, the basic controlling mode goes in the opposite direction: with rising red
edge inflection point or red edge ratio index, the application rate is increased
(Thiessen
2001
,
2002
; Reckleben and Isensee
2004
). Hence, compared to earlier
dressings, the slope of the control line is inverted (Fig.
9.37
, bottom).
Proper quality-dressings of nitrogen for small cereals result in a higher protein
contents, which can improve the value of the grain if it is used for bread or for feed.
The advantage of applying this quality-dressing in a site-specific mode instead of a
uniform way for the whole field is that this can provide for less
variation in the
protein content
of the harvested grain. This holds especially for small cereals from
fields with varying soil texture (Reckleben
2003
).
Still another situation exists if the objective is to produce
malting barley
for
beer breweries. For this product, the ideal crude protein concentration is not high,
but rather low, namely about 10.7 % of the dry matter. Site-specific nitrogen appli-
cation too can assist in getting close to this protein content. Any late dressings after
heading can be left out completely, since high levels of protein content deteriorate
the quality in this special case. The approach for keeping the protein content at this
rather low level is reflectance sensing for the control of nitrogen application at the
earliest possible growth stage,
i.e.
at about BBCH 30 - BBCH32 (Hopkins et al.
2007
; Pettersson and Eckersten
2007
; Söderström et al.
2010
). The site-specific
control provides the means for limiting the application and for evening out varia-
tions in the protein content within a field that - without using this technique - might
develop as a result of differences in soil texture.
