4. Discussions
4.1 Changes in SOC following LU
The exact quantification of SOC is very important for detecting and
predicting the changes in response to altering global climate (Negi and
Gupta, 2010). The present study showed that FL had a negative effect on
SOC over other LU (BL/CL/GL/HL/PL), and the findings of meta-analysis,
which is similar to the present information that LUC from FL to other LU
may lead to decrease in SOC (Kolambukattu et al ., 2013). However,
these results were not the universal condition for all the LUC because
this test of heterogeneity showed noteworthy variability among studies.
Large annual addition of OM in the form of leaf litter, SOC is highest
in the FL, which exists in the soil due to the non-disturbance of any
tillage activities and also slow decomposition rate due to prevailing
low temperature in the forest resulted higher soil carbon values
(Haynes, 2005; Baker et al ., 2007; Kolambukattu et al .,
2013) whereas in other LU the SOC was lower as when compared to FL is
due to interference of human activities or tillage practices and higher
temperature in these LU due to direct exposure to radiation increases
the rate of mineralization resulted higher decomposition of organic
matter. The decomposed organic matter releases CO2 in
the atmosphere and causes loss in SOC (Ramzan et al ., 2019).
Similarly in case of CL, scarce of OM addition, removal of crop residues
and rigorous cultivation activities increase C losses from the soil
system (Lal and Kimble, 1997; Yang et al ., 2004; Baker et
al ., 2007; Smith, 2008 and Sharma et al ., 2014). The lost SOC
increased the CO2concentration of atmosphere which
further resulted in global warming and climate change.
To manage climate change, it is essential to store SOC in the
terrestrial ecosystem. In the terms of quantity, the change in SOC
content due to LUC from FL to other LU if tried to regain can be helpful
to sequester more C in the terrestrial system. The study shows that the
scope of improvement of SOC in other LU (BL/CL/GL/PL/HL) to become C
equivalent to FL can be possible by increasing SOC by 27.3% in BL,
31.1% in CL, 36.1% in GL, 35.5% in PL and 11.5% in HL as when
compared to FL. This change can be possible through proper management
strategy in other LU.
4.2 Changes in SCS following LU
LUC is one of the influential factors which bring changes in SCS build
up. Several studies suggest that the conversion of LU from FL to other
LU led to decrease in the soil quality owing to the reduced SCS. LUC
from FL into other LU may act as a C source (De Blécourt et al .,
2013; Guillaume et al ., 2015; Fan et al ., 2016; Iqbal and
Tiwari, 2016) and concurrently affect soil characteristics (Abera and
Wolde-Meskel, 2013). Based on study about 350 m.ha. of FL has been
converted to other LU (ITTO, 2002) and leads to biodiversity loss
(Ahrends et al ., 2015) and SCSt losses of 20–40%(De Blécourtet al ., 2013 and Guillaume et al ., 2015).A Meta-analysis
reported that SCS decreased 13% to 42% when native FL was converted to
PL and CL, respectively (Guo and Gifford, 2002). Similarly in this study
the negative effect of SCS on other LU was observed in comparison to FL.
The lower SCS for PL and HL was recorded in this study as compare to FL
might be because of the absence of deep rooted trees and fewer canopy
covers. The potential for soils to restore C from the atmosphere is
affected by the balance between rate of deposition of the photosynthetic
materials and rate of respiration to decompose the C inputs (Mathieuet al ., 2015). In addition, as root tissue is recalcitrant for
degradation and mineralization than the top soil litters therefore root
derived C has long residence time (Rasse et al ., 2005). More
accumulation of organic matter can reduce the leaching (Kenye et
al ., 2019). Also, absence of canopy covers, the exposure of direct
solar radiation thereby increases the rate of mineralization.
The present study shows that the scope of improvement of SCS in other LU
(BL/CL/GL/PL/HL) to become C equivalent to FL can be possible by
increasing SCS by 34.0% in BL, 41.2% in CL, 1.47% in GL, 33.5% in HL
and 47.9% in PL as when compared to FL. The changes of SCS can be
supported by the study depth-wise on SCS. However this change is more in
depths as compared to surface soil is due to LUC leads to difference in
SCS is more at subsurface soil over the surface soil. Regaining the lost
SCS amount under different LU is a tedious work. If this can become
possible through management practices, a large amount of atmospheric
CO2 can be restored in the soil and problems of climate
change can be mitigated. Integration of organics with chemical
fertilizer in cultivated soil can be one of the better LUM strategies
for restoring C in the soil and improving the crop productivity and thus
managing soil health and ensuring food security.
4.3. Improving SOC through nutrient management strategy
Intensive monocropping system, fertilizer-responsive varieties and
continuous imbalanced chemical fertilization have caused losses in SOC
(Singh et al. , 1999) and soil health (Anwar et al. , 2005;
Kumar et al ., 2017 and Kumar et al. , 2018), that leads to
unsustainable crop production. Organic matter (OM) addition usually acts
as a “revolving nutrient fund” and as an agent to improve soil
structure, maintain tilth and minimize erosion
(www.fao.org) and thus converts the
unsustainable to sustainable crop production system. The OM addition
rapidly gaining favor but, owing to the problems related to the lack of
supply of a good quality and quantity of the added materials, the system
may not be sufficient to achieve and sustain the crop production for
food security (Kumar et al ., 2018). Therefore, it is essential to
maintain quality OM for good produce.
Balanced and INM can maintain OM levels in the soil have been well
established. The INM system improves soil health through building up SOC
and improving soil properties. Integrating organic and inorganic sources
can help in the sustenance of farming for a longer period than chemical
fertilizer alone (Sharma et al ., 2019).The present study observed
that in case of INM over the inorganic alone, as the SOC status
increases in the soil it helps to improve the yield of rice and wheat
crop. The finding directs that SOC improves the soil physical, chemical
and biological quality that provides suitable conditions for crop growth
and result into good crop. Rice and wheat are the major staple food of
India and main source of energy. Achieving its optimum yield level based
on soil, climate and atmospheric condition will help to meet out the
food security for ever growing population of India.
4.4. Effects of SOC on soil health and food security
Greenhouse gases (GHG) are the main player to maintain the global energy
balance. A small change in their amount in the atmosphere can affect the
climatic conditions on earth. Anthropogenic emissions of
CO2 are likely to increase as in the future human
population increases. Human led LUC can result into significant
exchanges of CO2 between the soil and air (Lal,
2000).Therefore, restoration of C in the soil can only be option to
counteract the effect of climate change and the problems created due to
climate change. Since OM plays a multifaceted role in several soil
processes (Gregorich et al ., 1994) hence, SOC is the panacea for
sustaining soil health and food security by the maintenance of
production system (Anantha et al ., 2018).
The findings suggest SOC is related to different soil properties like
BD, CEC and Soil pH. Similar strong correlations has been reported in
several studies of different aspects (Pal and Pawar, 2013; Wang et
al ., 2014; Xu et al ., 2019). The result supports that LUC affect
not only SOC but also other soil properties. Some studies have derived
correlations between SOC and total nitrogen (TN) and other parameters
suggesting OM turnover influences these factors (Xu et al .,
2019).
Increasing attention is being focused on the role of managing and carbon
storage in the soil. However, it is a major challenge to maintain or
improve low level of SCS due to LUC. Proper management strategies can be
utilized to mitigate this problem.