Agriculture Reference
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Average of two
soil depths
3000
2000
1000
Y = 555.44 + 1035.0900X
R 2 = 0.4719**
0
10-20 cm
3000
2000
Y = 1456.21 + 847.3017X
1000
R 2 = 0.2237**
0
0-10 cm
3000
2000
Y = 676.42 + 784.1896X
1000
R 2 = 0.5550**
0
1
2
3
Potassium saturation (%)
FIGURE 8.6 Relationship between potassium saturation and grain yield of dry bean. (From Fageria, N. K.
2008. Commun. Soil Sci. Plant Anal. 39:845-857. With permission.)
8.2.2.3 Controlling Soil Salinity and Alkalinity
Soil salinity and alkalinity problems exist in many regions of the world. There are more than 800
million hectares of land that suffer from salinization and alkalinization in the world (Lv et  al.,
2013). The control of soil salinity and alkalinity is an important strategy in efficient N management
in crop production. A large part of world's agricultural land is affected by salts and this imposes
serious limitations on crop growth and productivity (Lauchili and Luttge, 2002; Flexas et al., 2007;
Guo et al., 2013) and consequently on N use efficiency (Fageria, 2013). In naturally saline soils, the
predominant ions are Na + , Ca 2+ , Mg 2+ , K + , Cl , SO 2− , CO 2− , and NO 3 and the main salts responsible
are NaCl, Na 2 SO 4 , NaHCO 3 , and Na 2 CO 3 (Lauchli and Luttge, 2002). Many studies suggest that
saline soils present two distinct forms of stress, that is, salt stress (principally NaCl and Na 2 SO 4 ) and
alkali or pH stress (NaHCO 3 and Na 2 CO 3 ) (Guo et al., 2013). High pH conditions not only damage
the plant directly but also cause deficiencies of micronutrients (Fageria, 2013).
In addition, salt stress induces an osmotic stress and direct ion injury by disrupting ion homeo-
stasis and the ion balance within cells (Niu et al., 1995; Ghoulam et al., 2002; De-Lacerda et al.,
2003). Salinity- and alkalinity-tolerant plant species have the capacity to absorb and utilize N more
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