Agriculture Reference
In-Depth Information
Because of the importance of both S and N in protein synthesis, these nutrients are intimately
linked and are often considered to be colimiting. It has been established that for every 15 parts of N
in protein, there is approximately 1 part of S (i.e., 15:1 ratio of N:S) (Norton et al., 2013). However,
this general guide will vary for different crops. For example, wheat grain has an N:S ratio of around
16:1, while the N:S ratio for canola seed is around 6:a (Norton et al., 2013). An inadequate S supply
will not only reduce yield and crop quality but it will also decrease NUE and enhance the risk of N
loss to the environment. Studies have demonstrated that supplying S to deficient pastures increased
yields and NUE, and lowered N losses from the soil (Norton et al., 2013). Owing to the close linkage
between S and N, Norton et al. (2013) reported that one unit of S deficit to meet plant demand can
result in 15 units of N that are potentially lost to the environment.
Nitrogen and sulfur interaction is synergistic to affect crop grain yield (Wang et al., 1976; Randall
et al., 1981), grain protein and grain quality (Randall et al., 1990), and N utilization efficiency
(Malhi and Gill, 2002, Salvagiotti and Miralles, 2008). Optimizing S nutrition increases NUE,
mainly by increasing N uptake efficiency in grass species (Brown et al., 2000; Salvagiotti et al.,
2009). In brassica crops, yield and oil content (Ahmad et al., 1999), glucosinolate (Kim et al., 2002;
Schonhof et al., 2007), and isothiocyanate (Gerendas et al., 2008) concentrations are influenced
by relative supplies of N and S (Pan, 2012). The field observation of N and S fertility interactions
are well reflected at the cellular and root levels (Reuveny et al., 1980; Hesse et al., 2004). Mineral
nutrition studies have revealed that the uptake and assimilation of N and S are coregulated by the
substrate ions and their assimilatory products (Clarkson et al., 1989; Koprivova et al., 2000; Hesse
et al., 2004; Pan, 2012). Sulfate uptake and assimilation are regulated by
O
-acetylserine, a cysteine
precursor that is in itself regulated by N availability and assimilation (Koprivova et al., 2000; Pan,
2012). Excess cysteine production when S is high or N is limiting will repress S uptake and assimi-
lation (Zhao et al., 1999). Conversely, N uptake and assimilation is depressed during S starvation
(Clarkson et al., 1989; Prosser et al., 2001) as arginine and asparagine accumulated with reduced
cysteine and methionine production (Thomas et al., 2000; Prosser et al., 2001; Pan, 2012).
6.3 INTERACTION OF NITROGEN WITH MICRONUTRIENTS
Micronutrients are required by plants in small amounts compared to macronutrients. Overall, the
concentration of macronutrients (except C, H, and O) in plant dry matter at maturity varied from 1 to
12 g kg
−1
(0.1-1.2%) (Fageria et al., 2011a). Micronutrients essential for plant growth are Zn, Fe, Mn,
Bo, Cu, Mo, Ni, and Cl. The deficiency of micronutrients is not as widespread as that of macronutri-
ents. However, whenever it occurs, it can result in a significant reduction in the yield and quality of
crops and utilization efficiency of other nutrients and water (Aulakh and Malhi, 2005). For example,
the deficiency of Zn is very common in upland rice in the central part of Brazil locally known as the
“Cerrado region.” Addition of about 10 kg Zn ha
−1
with zinc sulfate can correct the deficiency and
improve the yield and nutrient use efficiency (Fageria, 2009, 2013; Fageria et al., 2011a).
6.3.1 n
ItroGen
versus
z
InC
Zinc deficiency is one of the main problems in crop production around the world (Fageria et al., 2002,
2012; Alloway, 2008). Graham (2008) reported that half of the world's soils are intrinsically deficient
in Zn. Zinc deficiency in annual crops is reported in Brazil (Fageria and Stone, 2008), Australia
(Graham, 2008), India (Singh, 2008), China (Zou et al., 2008), Turkey (Cakmak, 2008), Europe
(Sinclair and Edwards, 2008), the United States (Brown, 2008), and Africa (Waals and Laker, 2008).
Fageria and Baligra (1999) reported that liming of acid soils is one of the main factors creating Zn
deficiency in crop plants (Figure 6.9). Hence, it can be concluded that the knowledge of factors affect-
ing Zn uptake (including interactions with other nutrients) is important to its adequate management.
Nitrogen application improved crop growth, which may create Zn deficiency in soils having low
Zn content. Such interaction of N × Zn has been observed by Fageria (2013) in upland rice grown on a
