Agriculture Reference
In-Depth Information
Humic Nitosols, and Orthic Acrisols. Sixty farms, located in the three sublocations,
were selected by Tittonell et al. (2005). Together, they represent much of the bio-
physical and socioeconomic variability observed in the highlands of western Kenya
where cultural backgrounds differ widely (e.g., tribes). This led to the differentia-
tion of five farm types, referred to here as T1 to T5, where T1 farms have the high-
est assets and T5 the lowest. A consistent trend of decreasing input use from farm
types T1 to T5 was generally observed by Tittonell et al. (2005); however, nutrient
resources and land management practices (e.g., fallow) differed markedly between
sublocations. Maize (
Zea mays
L.) yields on Nitisols were slightly higher than those
on Acrisols and Ferralsols; however, nutrient balances were dominantly negative
and self-sufficiency in maize production was achieved by <40% of farmers in all
sublocations—ecosystem service 1, thus, is only partially met in the area.
The case for western Kenya and the earlier cases reviewed here illustrate the very
high variability in soil fertility management that is associated with the “soilscape,”
such as the location of land along hillslopes, and with differences in soil fertility
management as a function of household wealth. This will be reflected in different
gradations of achievable soil security; however, usually, soil security is low. Many
studies report a high variability of fertility within farmer's fields, which is based
on samples for chemical analyses of surface soil. However, variability of soil types
within farms is usually much smaller as they are correlated with landscape position,
and this is one reason to use soil type classifications as “carriers” of information.
2.3.5 S
aPric
h
iStoSolS
in
the
w
eStern
P
art
of
the
n
etherlandS
Sapric Histosols, located in the lower reaches of the European Rhine-Meuse Delta,
contain large amounts of nitrogen (N), and peat decomposition is a substantial con-
tributor to the mineral N supply of crops. For grasslands on nonfertilized poorly
drained peat soils in the Netherlands, an average N uptake of 252 kg/ha
was reported
(Vellinga and André 1999). Despite the large supply of N from the soil, applica-
tion of fertilizer N was about 205 kg N/ha per year for dairy farms on peat soils
in the west of the Netherlands in the 1990s (Reijneveld et al. 2000). This largely
corresponded with common fertilizer guidelines: 195-230 kg N/ha per year for well-
drained and 235-275 kg N/ha per year for poorly drained peat soils. Together with
relatively large inputs from concentrates (102 kg N/ha per year on average) and rela-
tively low exports of N through milk (68 kg N/ha per year) and animals (13 kg N/ha
per year), this resulted in N surpluses at farm level of 270 kg N/ha per year on aver-
age for a dairy farm on peat soil at the end of the 1990s (Reijneveld et al. 2000).
These surpluses are distributed over various environmental fluxes, such as gaseous
losses to the atmosphere, because of denitrification and export of N to surface waters
(Van Beek et al. 2004).
Following EU Directives, environmental policies were introduced to reduce N
losses and increase farm nutrient efficiencies. One farmer in the area, owning a farm
of 37 ha, was able to remain economically viable without the input of fertilizer N
(Sonneveld et al. 2008) by large and long-term inputs of organic N sources, such as
dung, ditch sludge, farmyard manure, cow slurry, and nonharvested herbage. Thus,
average N uptake under nonfertilized conditions increased to 342 kg/ha, with only
