Agriculture Reference
In-Depth Information
production was achieved by bringing additional land into cultivation (extensifica-
tion). Over time, as the available arable land decreased, these systems were not
sustainable, largely because the inputs used were low in nutrient content. Another
contributing factor was poor soil conservation practices, with some exceptions such
as the dike and pond fields in southeastern China. Even as late as the 1930s in the
United States, approximately one-third more land was being cultivated than in the
late 1990s; however, yields were only a fraction of what they are today. The damage
to the environment from these practices was substantial owing to the large areas of
land, including fragile lands, required for such extensive agriculture (Byrnes and
Bumb 1998).
The Haber-Bosch process (first commercialized in 1913) revolutionized agri-
culture and proved to be the major contributor to food security. The chemical pro-
cess allowed the conversion of nitrogen from air to a form that could be taken up
by the plant to produce more grain and biomass. This discovery, combined with
the development of phosphate fertilizers from phosphate rock, the commercial
mining of potash-bearing minerals, and improved farm management practices,
has allowed food production to keep pace with rapidly expanding population
growth.
As mentioned earlier, mineral fertilizers are responsible for substantial increases
in agricultural and land productivity. While fertilizer use is primarily focused on
the major plant nutrients—nitrogen, phosphorus, and potassium—there is increasing
recognition of the importance of balanced nutrients, including secondary nutrients
(i.e., sulfur) and micronutrients, in yield increases (i.e., zinc, boron, etc.) (Figure 3.7).
Recent work in East Africa indicates that deficiencies of sulfur and boron are limit-
ing maize (Zea mays) and wheat (Triticum aestivum) yields in smallholders' fields
(Figure 3.8a and b). Micronutrients are also important in human nutrition, and one
option to include these nutrients in the human diet may be through crops.
Elements deficient
Food grain production (Mt)
400
350
Mb
B
Mn
S
K
P
Zn
Fe
N
300
250
Mb
B
Mn
S
K
P
Zn
Fe
N
B
Mn
S
K
P
Zn
Fe
N
B
Mn
S
K
P
Zn
Fe
N
200
150
Mn
S
K
P
Zn
Fe
N
K
P
Zn
Fe
N
100
50
Fe
N
N
0
1950
1960
1970
1980
1990
2000
2010
2025
FIGURE 3.7
Relationship between balanced nutrition and yield over time. (From VFRC.
2012.
Global Research to Nourish the World
. International Fertilizer Development Center.)
