World’s Soil Resources

a Kenyan district. N deficits in excess of -1 00 kg ha -1 yr -1 were found for maize, sugar cane, and pyrethrum. P
deficits in excess of -1 0 kg ha -1 yr -1 were found for sugar cane, pyrethrum, and beans, but P excesses occurred
in tea and maize-bean plots. Except for coffee, tea and seasonal fallow, K deficits in excess of -50 kg ha -1 yr -1
occurred in all systems. These observed differences reflect differences in the use of (in-)organic amendments,
but also nutrient transfers across LU types. In the case of coffee for instance, mulching is recommended, which
is done by using residues from other crops (e.g. bananas) or grasses from fallow land.
In Asia, both strongly positive and strongly negative balances have been reported. K deficits have been
reported for rice-based systems across several Asian countries ranging from -25 to -70 kg ha -1 yr -1 . also reported
K deficits in 71 paddy farms in south China, but found N and P surpluses. Based on negative nutrient balances
for Bangladesh, Vietnam, Indonesia, Myanmar, the Philippines, and Thailand, and positive balances for Japan,
Malaysia and Korea, it has been argued that lower-income countries with large and growing population were
more likely to present negative balances whereas higher income countries with stable populations tended to
have positive balances. In sub-Saharan Africa, the larger the population density, the more negative the N and
P balances.
For similar systems, differences in nutrient balances may also arise from variable access of farmers to
external inputs. In the Sudanian zone of west Africa, cultivated plots near hamlets tended to have less negative
or more positive balances than plots near larger villages because farmers in hamlets cared better for their
crops, earned more income from sales and therefore could invest more in fertilizers. Generally, cultivated plots
near hamlets and villages benefit from greater additions of household refuse and human and animal faeces.
However, social inequality in access to resources has been found to have an equally large or even larger effect
on nutrient balances than distance from the village. For instance, positive N, P and K balances were observed
for Fulani cropland because their large herds supply them with abundant manure. Likewise, nutrient budgets
ranging from strongly negative to strongly positive were reported for banana-based systems in Tanzania
depending on access to cattle and cattle management (Roy et al., 2003). Especially in small-holder agriculture,
site-specific management may also induce large fertility gradients over short distances.
(Peri-)urban agriculture is characterized by large excesses in nutrients, especially N. This is commonly driven
by the market-oriented nature of this production system, which allows farmers to invest in external inputs. In
addition, these systems often rely heavily on the re-use of urban solid waste and waste water. Hence, (peri-)
urban production systems exemplify another form of large scale fertility transfer, from rural areas to urban
areas. Food produced by nutrient mining in rural areas is consumed in cities, leading to strong soil enrichment
of urban soils, especially at urban vegetable production sites (see Box 6.2).
6.8.5 | What does the future hold?
Soil nutrient budgets depend on the local socio-economic conditions but also on market prices of inputs and
on policies. In Western Europe for instance, rising prices of fertilizers and the strengthening of environmental
policies has led to reductions in N and P inputs into farmland, and this trend is expected to continue. Dwindling
P resources and climate change may further affect soil nutrient balances, in managed but also in natural
ecosystems.
Status of the World’s Soil Resources | Main Report Global soil status, processes and trends
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