Agriculture Reference
In-Depth Information
production system in which two or more species develop simultaneously during part or the entire
growing season and compete with each other for available resources (Fukai and Trenbath, 1993).
Such type of a cropping system improves the efficiency of resources such as water and nutrients in
comparison with their sole crop counterparts (Andrews and Kassam, 1976; Ofori and Stern, 1987;
Caviglia et al., 2004; Echarte et al., 2011; Coll et al., 2012; Andrade et al., 2012). In addition to the
improvement in resource use efficiency, other mechanisms that can contribute to the increased yield
observed in intercropping systems include increased ecological stability and resilience (Reddy and
Willey, 1981; Tilman, 1996; Trenbath, 1999; Szumigalski and Van Acker, 2008). Indeed, there are
many examples of intercropping systems that have demonstrated greater grain or forage yield as
compared to monoculture systems on an equivalent land area basis (Ikeorgu et al., 1989; Chen et al.,
2004; Agegnehu et al., 2006; Ghosh et al., 2006; Wortman et al., 2012).
Sunflower and soybean are two species that can be intercropped (Calvino and Monzon, 2009).
Andrade et al. (2012) reported higher yields of sunflower-soybean intercrops in the southern Pampas
of Argentina compared to sole crops. The greater intercrop yield was associated with an increase
in capturing the resource use efficiency (Andrade et al., 2012). Intercropped sunflower and soybean
complement each other in the use of the resource because critical periods for yield determination
occur at different times during a period of low resource demand by the other component (Coll et al.,
2012). The critical period for yield determination of a crop is defined as the stage where a reduction
in resources availability (water, nutrients, and solar radiation) determines the greater grain yield lost
(Cantagallo et al., 2004; Egli and Bruening, 2005). In the southern Pampas of Argentina, sunflower
sown in mid-October has its critical period for yield determination when soybean (sown in mid-
November) is still in its vegetative stages, and soybean critical period takes place close to sunflower
maturity (Andrade et al., 2012).
Intercropping soybean and palisadegrass (
Bracharia brizantha
Hochst. Ex A. Rich) favors
soybean production as it reduces weeds and breaks the pest disease cycle (Silva et al., 2006). In
addition, palisadegrass has an aggressive root system that favors nutrient cycling, increased soil
biological activity, and increased organic matter content (Dabney et al., 2001; Nacent and Crusciol,
2012). Furthermore, palisadegrass produces a high amount of dry matter, which provides good
ground cover in no-tillage system, with greater persistence in the soil surface (Crusciol et al., 2012).
Borghi et al. (2007) also reported that soybean can supply N to the palisadegrass from the biological
fixation of soybean.
2.10 CONCLUSIONS
N is the most essential plant nutrient for crop production. Soils cultivated with crops are always
deficient in N and the use of chemical N fertilizers is a prerequisite to obtaining a higher yield. N
cycle in soil-plant system is very dynamic and influenced by soil, plant, and climatic factors. In
modern agriculture, the major source of N is chemical fertilizers. The major part of N applied to
plants is lost through leaching, volatilization, denitrification, surface erosion, and loss of NH
3
from
plant foliage. Among these processes of N loss, the major part of N loss occurs through leaching
and denitrification. These two processes can constitute about 50% of the total N loss from the soil-
plant system. N loss through ammonia volatilization can be significant if N is not incorporated into
the soil and no irrigation and/or precipitation occurred after N fertilization was applied to the soil
surface. Factors affecting N losses from soil-plant system are precipitation, temperature, soil pH,
soil texture, methods of N application, N source and particle size, and plant factors. A discussion on
these factors is provided in this chapter.
Some practices that can be adopted to reduce N losses are irrigation immediately after N fertil-
izer application, incorporation of applied N fertilizers into the soil, and the use of a slow-release
source of N fertilizer such as polymer-coated or sulfur-coated urea. The use of adequate rate, source,
and timing of N application can also reduce N losses. In addition, the use of gypsum, use of biochar,
and intercalation of urea in montmorillonite can also reduce N losses and improve N use efficiency
