Agriculture Reference
In-Depth Information
8.4.2 a
doptInG
a
pproprIate
C
rop
r
otatIon
Crop rotation is defined as a planned sequence of crops growing in a regularly recurring succession
on the same area of land, in contrast to a continuous culture of one crop or growth of a variable
sequence of crops (Soil Science Society of America, 2008). Growing crops in rotation has many
positive effects that are responsible for higher and/or sustainable yields. These effects are control
of diseases, insects, and weeds, increase in nutrient use efficiency, improve in water use efficiency
(WUE), improvement in soil fertility, and control of allelopathy. In an appropriate crop rotation,
legumes are rotated with cereals. For example, in the Brazilian central part locally known as the
“Cerrado” region, growing soybean, upland rice, dry bean, and corn rotation is a common practice.
Legumes in rotation with cereals are beneficial in many ways (Yau et al., 2003; Krupinsky et al.,
2006). In addition to enhancing soil N status and suppression of cereal diseases and pests, there
is an N-sparing effect (Chalk, 1998), and growth-promoting substances released from decaying
legume residues give healthier wheat roots (Stevenson and Van Kessel, 1996). Jones and Arous
(1999) and Jones and Singh (2000) reported that shorter and earlier-maturing legumes enhance the
yield of the subsequent cereal crops grown in rotation.
Including legumes in rotation with cereals is an appropriate rotation. However, many studies have
shown that even growing cereals in rotation or including oil crops in rotation with cereals has posi-
tive effects on yields compared to growing cereals in monoculture (Yau and Ryan, 2012). Yau and
Ryan (2012) reported that growing safflower (
Carthamus tinctorius
L.), an oil crop, before barley
increased barley yields and was comparable to or better than after some legumes. In the northern
Great Plains, growing wheat and barley following safflower increased wheat yield by 30% and barley
yield by 23% (Krupinsky et al., 2004), while flax (
Linum usitatissimum
L.) yield was increased one-
fold (Tanaka et al., 2005). Wheat in Western Australia is generally grown in rotation with pastures,
lupins, and other cereals. The supply of N for wheat is mostly from biological fixed N from previous
legume (Angus et al., 1993). Campbell et al. (1995) reported that sweet clover used as green manure
in rotation with wheat increased wheat yield compared to fallow-wheat rotation, probably a result of
N fixation, as evidenced by a 57% higher N supplying power in the soil under green manure.
Crops grown in rotation or with shorter fallow periods often have higher annualized biomass
N than monocrop systems or those with longer fallow periods (Copeland and Crookston, 1992;
Halvorson et al., 2002). Including pea in rotation with spring wheat and barley can not only sustain
their yields by efficiently using soil water but also reduce N fertilization rates by supplying supple-
mental N from the pea residue due to its higher N concentration (Miller et al., 2002; Sainju et al.,
2009, 2013). The increase in WUE is a result of less soil water use by pea than spring wheat and
barley, thereby leaving more water available for succeeding crops and increasing their yields (Miller
et al., 2002). Other benefits of crop rotation compared to monoculture include control of weeds, dis-
eases, and pests (Vigil et al., 1997; Miller et al., 2002), reduction in farm inputs, and improvement
in economic environmental sustainability (Gregory et al., 2002).
8.4.3 I
mprovement
In
w
ater
u
se
e
ffICIenCY
Although one-third of the earth's surface is occupied by water, only about 2.5% of the total water
on earth is freshwater (Shiklomanov, 1993). The water shortage on a global scale may be arguable
(Heumesser et al., 2013). Some sources consider that there is no serious threat of water shortages
in the future (Bruinsma, 2003), whereas others estimate that taking environmental water require-
ments into account, serious water shortages are likely to occur (Smakhtin et al., 2004; Heumesser
et al., 2013).
Globally, agriculture is the most extensive and by far the largest area of human management eco-
systems (Monfreda et al., 2008; Foley et al., 2011). The FAO estimates that about 1.53 billion ha of
land, 11% of the world's total land area, is currently used for crop production, 80% of which is rain-
fed (Gebremedhin et al., 2012). Furthermore, in the last few decades, the main threats to agricultural
