Agriculture Reference
In-Depth Information
high leaching as a result of
NH
4
+
displacement on the soil exchange complex by Ca
2+
(Koenig and
Pan, 1996). The increase in
NH
4
+
concentration in soil solution due to application of gypsum can be
beneficial for plants due to the high absorption of
NH
4
+
as compared to
NO
3
−
. The absorption of
NH
4
+
requires less energy by plants as compared to absorption of
NO
3
−
(Fageria et al., 2011). Leaching is
the main process by which
NO
3
−
is transported soil to water (Smith et al., 1990). For
NH
4
+
, losses by
leaching are lower than those for
NO
3
−
(Piovesan et al., 2009) due to the adsorption of
NH
4
+
to the
soil particle surfaces (Sparks, 1995).
In addition, gypsum application improves soil structure in heavy-textured soil, so that water infil-
tration and the ability of roots to penetrate the soil are enhanced (Viator et al., 2002). The improve-
ment in the root growth of upland rice and soybean with the application of gypsum in Brazilian
Oxisols has been reported by Fageria (2013). Improved root growth may absorb a higher amount
of N that may reflect in increasing crop yields (Fageria, 2013). Improvements in the yield of wheat
and sorghum with the addition of gypsum have been reported by Thomas et al. (1995). Gypsum
application in irrigation water increased the sugar yield and juice extraction percentage of sugarcane
(Kumar et al., 1999). Gypsum also increased the yield in corn and alfalfa up to 50%. This yield
response was partially attributed to higher exchangeable Ca and S, and a complementary reduction
in exchangeable Al (Toma et al., 1999). Reduction in exchangeable Al may improve root growth and
consequently higher N uptake and efficiency of use. For some crops, gypsum is effective in reducing
the incidence of soil-borne diseases (Kao and Ko, 1986). The decrease in disease infestation may
improve N use efficiency in crop plants.
Subsoil acidity is one of the major yield-limiting factors in acid soils because they restrict root
growth (Toma et al., 1999). Surface application of gypsum is an effective technique to ameliorate
the effects of subsoil acidity (Ritchey et al., 1980; Hammel et al., 1985; Shainberg et al., 1989;
Alcordo and Rechcigl, 1993; Sumner, 1993, 1995; Saigusa et al., 1996; Toma et al., 1999). Vigorous
root growth in the soil profile may improve water and nutrient uptake, higher yield, and a higher N
efficiency of use. Toma et al. (1999) concluded that the gypsum effect is so long lasting; its use as
a subsoil acidity ameliorant becomes highly economic because the initially high cost can be amor-
tized over an extended period of time.
2.9.8 u
se
of
C
rop
G
enotYpes
p
roduCInG
h
IGh
r
oot
B
Iomass
The use of crop genotypes producing high root biomass is an important strategy in reducing N loss
from soil-plant systems. Johnson et al. (2006) summarized the contributions of different plant parts
from different plant species to soil organic carbon and gave guidelines, including the contribu-
tions of plant roots and rhizodeposition to the total C cycle when analyzing changes in soil organic
carbon. The belowground deposition of fixed C in structural root biomass, exudates, mucilage, and
sloughed cells may be a major source for soil organic carbon accumulation (Bottner et al., 1999;
Allmaras et al., 2004). Benjamin et al. (2010) reported that the contribution of the crop root system
to the formation and increase of soil organic carbon is important when considering the selection of a
crop rotation in a cropping system. Fageria (2013) discussed the variation in crop species and geno-
types within species in root biomass production. Crop plants having C4 photosynthetic pathway
(corn, pearl millet, and sorghum) produced more vigorous root system as compared to crop plants
with C3 (rice, barley, wheat, and dry bean) photosynthetic pathway (Fageria, 2013). Glass (2003)
reported that nutrient uptake by plants is a function of root biomass, root morphology, root age, root/
plant growth rates, and root proliferation in regions of abundant nutrients, in addition to the roots
physiological capacity for nutrient uptake (Glass, 2003).
The author studied root growth of 12 lowland rice genotypes. The maximum root length was sig-
nificantly influenced by N rate and genotype treatments (Table 2.2). However, N × G interaction was
not significant for this growth parameter, indicating that each of the 12 genotypes reacted similarly
to changes in N rates. Maximum root length varied from 21.17 to 29 cm, with an average value of
24.84 cm. Root length was significantly higher at a low N rate as compared to a high N rate. When
