Agriculture Reference
In-Depth Information
1.2.3 I
mprovement
In
G
raIn
p
roteIn
C
ontent
Nitrogen is an important nutrient for improving N contents in the grain of cereals and legumes.
Protein content in grains of cereals and legumes is an important index in determining the quality of
grain for human consumption. For example, grain protein is a key quality measure for bread wheat,
affecting gluten strength and bread loaf volume (Wall, 1979; Mallory and Darby, 2013). Mallory
and Darby (2013) reported that ensuring adequate available N for grain protein development is a
primary challenge for organic production of winter bred wheat (
Triticum aestivum
L.). Generally,
wheat grain must have a protein concentration of 120 g kg
−1
(12%) or greater to be considered suit-
able for bread flour (Mallory and Darby, 2013). Wheat grain that does not meet the acceptable
level either receives a discounted price or must be sold into alternative, often lower-value markets.
McKenzie et al. (2010) also reported that the most important wheat quality parameter is the grain
protein concentration because it affects the milling and backing quality of the grain and because
wheat growers generally receive a premium for high protein concentration.
Farmaha and Sims (2013) reported that because of higher protein concentration, hard red spring
wheat is mainly used for blending with lower protein wheat for milling and baking in the state
of Minnesota, USA. Farmers sometimes receive a premium payment if the protein concentration
exceeds 140 g kg
−1
(14%) but more frequently receive a discount payment if the protein content is
<140 g kg
−1
. The most critical factors controlling grain protein are genotypes and N availability
(Peltonen and Virtanen, 1994; Wooding et al., 2000). Protein concentration depends on the plant's
ability to translocate already accumulated N from vegetative plant parts to the developing grain or
the ability to accumulate N, which may be mobilized directly to the developing grain near or soon
after anthesis (Banziger et al., 1994). Some cultivars translocate a relatively high percentage of N
to the developing grain during the reproductive period (Bhatia and Rabson, 1976). Therefore, the
timing and amounts of N availability during the growing season of hard red spring wheat could have
significant impacts on the N uptake amount and timing at which N is used to generate grain yield
and protein (Farmaha and Sims, 2013).
In conventional systems, splitting applications of N fertilizer to include in season topdress appli-
cations has been shown to increase grain protein content and baking quality (Randall et al., 1990;
Knowles et al., 1994; Peltonen and Virtanen, 1994; Mallory and Darby, 2013) as well as reduce N
losses (Sowers et al., 1994). Randall et al. (1990) reported that topdressing N at heading increased
grain protein, dough properties, and baking quality for irrigated wheat grown in Australia. Similarly,
Nass et al. (2002, 2003) reported that topdressing N at stem elongation in wheat grown in eastern
Canada improved protein content and met a milling standard of 13.5% protein.
The eating quality of rice is a multifaceted characteristic associated with many physiochemi-
cal properties (Chung et al., 2012). Protein, starch, and lipids are considered to be the main grain
components that affect the cooking and eating quality of rice (Zhou et al., 2002). In particular,
protein is believed to play a significant role in the palatability and grain quality of rice (Lin et al.,
2005; Butt et al., 2008). The application of N in the late reproductive growth stage or at the grain-
filling growth stage does not improve the grain yield but improves the protein content of rice grain
(Fageria, 2014).
Conceptually, controlled-release N fertilizers may provide the synchronized supply of N for
plant uptake, and therefore, increase protein concentration without reducing yield (Shaviv, 2001).
The idea is that preplant applied N fertilizer will release N to the pool of available N throughout the
growing season. Polymer-coated urea, a controlled-release N fertilizer, regulates the release of N to
the soil solution (Salman, 1989). Differences in osmotic potentials between the inside and outside of
the polymer coating cause water to diffuse through the polymer coating and dissolve urea, and the
liquid urea diffuses through the polymer coating to the soil solution (Fujinuma et al., 2009). The N
release from polymer-coated urea is mainly affected by the soil moisture and temperature with the
release rates increasing as soil moisture and temperature increase (Gandeza et al., 1991; Fujinuma
et al., 2009). McKenzie et al. (2010) and Farmaha and Sims (2013) found that the delayed N release
