Soils as Driver and Victim of Climate Change in Egypt
119
of soil from sandy loam to fine clay, showed that the effects of biochar on the three
GHG emissions were affected by other soil properties, especially soil C and N forms,
soil reaction (pH), bulk density, and porosity (aeration), all of which were mainly
also affected by soil texture. Furthermore, it was stated that in the coarse-textured,
low-buffer Ultisol, cumulative CO 2 and CH 4 emissions increased with increasing
volatilized carbon (VC) content of biochars; however, CO 2 emission significantly
decreased at 83 mg VC g
−1 soil [19]. By increasing VC values in the fine-textured,
high-buffer Oxisol, cumulative CO 2 emission increased.
On the other hand, clayey soils tend to show greater N 2 O emissions than sandy
soils, and N management may increase the emission of N 2 O, particularly in soils of
fine texture before showing N 2 O emissions induced by the applied soil management
and by rain which were greater by four times in a fine textured soil than in the
course-textured one [20, 21].
In the clayey soil, the small amount of large pores would increase anaerobic conditions which enhancing N 2 O emissions. It was reported that emissions in coarsetextured soils occur with soil moisture higher than that necessary for the same emissions in a clayey soil [22]. Another study was conducted on GHG fluxes from cornsoybean cropping systems across 35 Wisconsin soil series different in their textures
[23]. Their results suggested that soil texture is an important variable in controlling
a range of N 2 O emission characteristics and is critical for projecting future N 2 O
emissions from agricultural fields. Silt loam soils showed the largest N 2 O emissions
among the other soil types, exhibiting higher mean emissions (80–158%) and 100–
282% greater emissions when compared to loamy sand and sandy loam soils, respectively. They suggested that denitrification may explain the most variation (74–98%)
in total N 2 O emissions in the different soil textures and locations.
Also, a study on heavy clay and gravelly loam soils in eastern Canada [24] concluded that the annual fluxes of N 2 O were exceptionally high in the heavy clay soil,
varying from 12 to 45 kg N 2 O–N ha
−1 during the 3 years of the study. This high
fluxes may be not associated with N-fertilizer inputs but rather with denitrification
maintained by the decomposition of relatively large contents of soil organic matter
(192 Mg C ha
−1 in the top 0.5 m). It was found that the optimal soil moisture for
NO emission differed significantly between the various soil textures, and ranged
between 15% water-filled porosity (WFPS) in sandy Italian floodplain soil and 65%
in loamy Austrian beech forest soils (Fig. 4) [25]. Thus, each soil had its own optimum
condition probably owing to differences in other soil characteristics [26].
3.1.2 Soil pH
Soil pH is a variable that supervised soil productivity and plays a significant role in
controlling the chemical and biological activity in soil and consequently soils GHG
emissions. Previous work has shown that liming acid soils could enhance [27] or
depress N 2 O emission [28]. Nitrous gas N 2 O emissions may increase when soil pH
was close to being at neutral value but decreased when pH exceeded the neutral value
[29]. It was found that N 2 O flux declines with increasing pH within the range 5–7
119
of soil from sandy loam to fine clay, showed that the effects of biochar on the three
GHG emissions were affected by other soil properties, especially soil C and N forms,
soil reaction (pH), bulk density, and porosity (aeration), all of which were mainly
also affected by soil texture. Furthermore, it was stated that in the coarse-textured,
low-buffer Ultisol, cumulative CO 2 and CH 4 emissions increased with increasing
volatilized carbon (VC) content of biochars; however, CO 2 emission significantly
decreased at 83 mg VC g
−1 soil [19]. By increasing VC values in the fine-textured,
high-buffer Oxisol, cumulative CO 2 emission increased.
On the other hand, clayey soils tend to show greater N 2 O emissions than sandy
soils, and N management may increase the emission of N 2 O, particularly in soils of
fine texture before showing N 2 O emissions induced by the applied soil management
and by rain which were greater by four times in a fine textured soil than in the
course-textured one [20, 21].
In the clayey soil, the small amount of large pores would increase anaerobic conditions which enhancing N 2 O emissions. It was reported that emissions in coarsetextured soils occur with soil moisture higher than that necessary for the same emissions in a clayey soil [22]. Another study was conducted on GHG fluxes from cornsoybean cropping systems across 35 Wisconsin soil series different in their textures
[23]. Their results suggested that soil texture is an important variable in controlling
a range of N 2 O emission characteristics and is critical for projecting future N 2 O
emissions from agricultural fields. Silt loam soils showed the largest N 2 O emissions
among the other soil types, exhibiting higher mean emissions (80–158%) and 100–
282% greater emissions when compared to loamy sand and sandy loam soils, respectively. They suggested that denitrification may explain the most variation (74–98%)
in total N 2 O emissions in the different soil textures and locations.
Also, a study on heavy clay and gravelly loam soils in eastern Canada [24] concluded that the annual fluxes of N 2 O were exceptionally high in the heavy clay soil,
varying from 12 to 45 kg N 2 O–N ha
−1 during the 3 years of the study. This high
fluxes may be not associated with N-fertilizer inputs but rather with denitrification
maintained by the decomposition of relatively large contents of soil organic matter
(192 Mg C ha
−1 in the top 0.5 m). It was found that the optimal soil moisture for
NO emission differed significantly between the various soil textures, and ranged
between 15% water-filled porosity (WFPS) in sandy Italian floodplain soil and 65%
in loamy Austrian beech forest soils (Fig. 4) [25]. Thus, each soil had its own optimum
condition probably owing to differences in other soil characteristics [26].
3.1.2 Soil pH
Soil pH is a variable that supervised soil productivity and plays a significant role in
controlling the chemical and biological activity in soil and consequently soils GHG
emissions. Previous work has shown that liming acid soils could enhance [27] or
depress N 2 O emission [28]. Nitrous gas N 2 O emissions may increase when soil pH
was close to being at neutral value but decreased when pH exceeded the neutral value
[29]. It was found that N 2 O flux declines with increasing pH within the range 5–7