Agriculture Reference
In-Depth Information
georeferencing of combine and fertilizer spreader by GPS
mapping the site-specific yield
of the previous crop
in t of grain per ha
8
10
4
7
9
11
12
site-specific control of fertilizing
according to crop's removal
in kg P 2 O 5 per ha
13
46
58
41
23
52
64
70
75
Fig. 9.1 Concept of site-specific fertilizing according to nutrients removed in the previous har-
vest. The inserted numerals are based on the harvest of wheat in tons of dry matter - straw not
considered - as well as on a removal of 5.8 kg of P 2 O 5 per ton (From Swedish Institute of
Agricultural Engineering 1988 /89, supplemented and altered)
9.1
Fertilizing Based on Nutrient Removal
by Previous Crops
Harvesting crops always results in a removal of mineral nutrients from fields. The
concept that these nutrients should be replaced in order to avoid depletion of soils
has been accepted in the agricultural sciences since long. However, in the past,
removal and replacement respectively referred to whole fields. The yields as well as
the fertilizing had a whole field basis.
Modern georeferencing, fertilizing and harvesting techniques (see Chap. 12 )
have changed the situation. If during harvesting, the yields in units of mass are
recorded and georeferenced with a high spatial resolution for e.g. grid areas of
100 m 2 , the removal of nutrients for these small areas can be determined. Because
knowledge about the gravimetric nutrient content of the harvested products is avail-
able. Consequently, a georeferenced distribution of the fertilizer for the next crop
can be controlled in such a way that precisely this amount of nutrients is applied in
a site-specific way (Fig. 9.1 ). The result is a site-specific maintenance application ,
since the nutrients removed by the harvest are replaced.
This concept for detecting the site-specific nutrient need is reasonable if the sup-
ply of the previous crops was adequate, hence the soil not deficient in nutrients. A
second prerequisite is that the removal by the plants is the only factor or at least the
dominating criterion for the nutrient depletion of the soil.
The first prerequisite mentioned above can be met approximately by starting the
system with careful conventional manual sampling, traditionally analysing the supply
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