Agriculture Reference
In-Depth Information
50
40
30
20
10
0
40
30
20
10
0
Y = 16.4687 + 18.56X - 0.00027X
2
R
2
= 0.6082**
Y = 13.7996 + 0.1256X - 0.00017X
2
R
2
= 0.8279**
50
40
30
20
10
0
5
4
3
2
1
Y = 9.1850 + 0.1947X - 0.00027X
2
R
2
= 0.8920**
Y = 4.5921 - 0.0049X + 0.0000039X
2
R
2
= 0.5952**
0
100 200 300 400
Nitrogen applied to soil (mg kg
-1
)
500
600
FIGURE 1.3
Relationship between N and yield and yield components of dry bean.
High quantities of inorganic fertilizer, particularly N, have been used to increase the world food
production (Follett, 2001).
The increased crop productivity has been associated with a 20-fold increase in the global use of
N fertilizer application during the past five decades (Glass, 2003), and this is expected to increase
at least threefold by 2050 (Good et al., 2004). Although the N fertilizer use increased globally, this
increase was not uniform in all countries or geographical regions (Vitousek et all 2009) (Table
1.1). N use in North America and China increased significantly during the past few decades. In
contrast, Denmark recorded a decrease in fertilizer use, and Africa is underusing N fertilizers (Liu
et al., 2008; Malik and Rengel, 2013). Conventional breeding efforts in the past few decades have
significantly increased crop yield and, as a corollary to this, also improved N use efficiency (NUE)
(Kant et al., 2010). For example, a comparison between corn hybrids from the 1970s and the 1990s
has shown that hybrids from the 1990s exhibited a higher yield response to increasing N supply
(O'Neill et al., 2004).
N has long been recognized as a critical nutrient for the productivity of annual crops (Miller,
1939). In tropical America, N deficiency is a major soil constraint over 93% of the region occu-
pied by acidic soils (Sanchez and Salinas, 1981). N fertilizer, along with irrigation, dramatically
increased food production in developing countries during the green revolution (1960-1980) (Follett,
2001). Stewart et al. (2005) reported that the average U.S. corn yield was predicted to decline by
41% without N fertilizer, or in their words, N fertilizer was responsible for 41% of corn yield.
Furthermore, the importance of N fertilization has been proved by the response of upland and
lowland rice (
Oryza sativa
L.) (Fageria, 2001, 2013, 2014; Fageria and Baligar, 2001, 2005; Fageria
