Agriculture Reference
In-Depth Information
Table 9.1
Removal of phosphate and potash per ton of dry matter of harvested crop parts
a
Crop Phosphate in kg P
2
O
5
Potash in kg K
2
O
Winter wheat, only grain 5.8 7.6
Winter wheat, straw plus grain 4.0 18.6
Winter barley, only grain 6.5 8.8
Winter barley, straw plus grain 4.6 19.7
Maize, only grain 6.8 4.8
Soybeans, only grain 14.0 22.0
Rape or canola, only grain 18.4 9.2
Grass, leys, parts aboveground 8.0 30.0
a
Extracted from International Fertilizer Use Manual (
2007
) and Soil Science Society of
America (
2008
), data partly converted
necessary. But large amounts of fertilizers that contain these chemical elements
might be needed to maintain a specific acidity level of soils (pH value) that pro-
motes growth. Site-specific sensing of this acidity level is dealt with is Sect.
9.2.2
.
In principle, also the removal of
micronutrients
such as copper, zinc, manga-
nese, boron and molybdenum by the harvest can be recorded via yield sensing.
For doing this, the information about the micronutrient content within crops and
parts thereof is available (International Fertilizer Association
2007
; Osmond and
Kang
2008
). Especially for micronutrients, recording the site-specific situation
via removal by yield sensing appears highly attractive, since no other methods are
available. Because the laborious traditional soil sampling plus analysing in labo-
ratories is by far too expensive on a site-specific basis. However, with micronutri-
ents - as with macronutrients - sensing the situation via removal might not be the
only factor that defines the need of a crop. Leaching as well as the release of
micronutrients by soils must be considered. Both might depend on the respective
ion and the pH of the soil. Up to now, recording the removal of micronutrients via
site-specific yield sensing is not state of the art. Research directed to this topic is
urgently needed.
Summing up, phosphorus as well as of potash - with exceptions in the latter case
(see above) - are candidates of application. Removal rates of these nutrients are
listed in Table
9.1
. They depend on crop species and on the harvested crop parts.
The more the harvested crop parts are composed of vegetative- instead of reproduc-
tive plant matter, the higher the ratio of potash units to phosphate units is.
It should be noted that the
removal rates
in Table
9.1
are per ton of dry matter.
Removal rates per ton of harvested product that are based on moist plant material
and not on its dry matter can be very misleading since the water content can vary
widely with most crops. As an extreme example: when forage in harvested from
grasslands or leys, the water content of fresh material can be 85 %, but with dry hay
it may be 15 %. With all crops, the water content of the harvested product changes
steadily due to varying weather. And the water does not contain any nutrients.
Hence for exact records, the respective
site-specific dry matter
content at har-
vest time must be taken care of. For several crop species, yield sensing instruments
