4. Discussion
Growth and productivity of plants in ravines are adversely affected by
nutrient and moisture deficits, soil compaction, and high summer
temperatures as well as by biotic stressors. Consequently, vegetation in
ravine lands experiences multiple stresses. Despite these challenges,
there is a lack of extensive research focusing potential of resilient
perennial fruit crops and sustainable land management techniques to
enhance productivity and fruit quality in degraded ravines. Few fruit
crops identified for marginal lands near ravines; however, they have not
specifically addressed the unique challenges faced by ravine slopes in
rain-fed environments. The present results showed significant effect of
SMSTs on the tree growth and fruit yield of rain-fed sapota cultivated
in degraded ravine lands. The incremental changes in growth parameters
such as tree height, canopy spread and volume, collar diameter under
SWCMs viz., terraces and trenches shows positive influence of SWCMs in
or improving the various physical, chemical and biological properties of
soil (Dagnachew et al., 2020; Moradi et al., 2014; Ping et al., 2012;
Zhang et al., 2023; Yue et al., 2022; Mahajan et al., 2021). The two
crucial factors for the growth of any plant in general and more specific
under rain-fed cultivation are water and nutrients. SMSTs play
instrumental role in enhancing availability of essential soil nutrients
and moisture that results in the better photosynthesis, translocation of
photosynthates and other growth promoting physico-biochemical processes
that lead to higher plant growth. On the other hand, slope conditions
are deprived of these two precious resources from the soil root zone
(Panigrahi et al., 2009 & 2017; Hishe et al., 2017). The increased
availability of soil nutrient and moisture under field might be owing to
minimized runoff and soil loss, higher SOC under SMSTs. Lower runoff
generation might have enhanced deeper water infiltration and prolonged
soil moisture availability in post-rainy season (Panigrahi et al., 2009;
Tsui et al., 2004; Negi et al., 2012). These findings signifies the
SWCMs induced greater nutrient and water accumulation that have
positively influenced the plant growth parameters such as tree height,
canopy spread and stem diameter in harsh climates and degraded lands.
The improvement in plant photosynthesis rate under sufficient water
situations has already been reported in crops (Vu and Yelenosky, 1988;
Mpelasoka et al., 2001). Likewise, higher plant growth was achieved in
normal irrigation compared to deficit irrigation (Mpelasoka et al.,
2001; Hajlaoui et al., 2022). In the present experiment also SMSTs
enhanced soil moisture, SOC, availability N, P, K etc. under degraded
ravines. Therefore, higher vegetative growth of sapota plants under
SMSTs (Fig. 2a) in this experiment can be attributed to higher
availability of nutrients and moisture through reduction in runoff,
which are indispensable for plant growth and development.
Enhanced yield and RWP of sapota under degraded ravine lands through
SMSTs (SCCBT, followed by SBT, SSTS) can also be attributed towards
optimum water and nutrients availability in the soil. This might have
improved physiological activities of plants e.g. greater photosynthesis
and higher availability, translocation of photosynthates to fruits
(Zhang et al., 2023). As reported earlier, the decrease in
photosynthetic capacity of leaves exposed to water deficit during water
stress may results in the reduction of assimilates offered for fruit
growth and a stronger contest for assimilates between sink organs
(Moutinho-Pereira et al., 2004 and Hajlaouiet al., 2022). Another reason
could be improvement of micro-climatic conditions for fruit setting and
fruit development events including pollination and fertilization
activities resulted in to better fruit set, higher fruit number and
fruit growth. In the present study, as discussed above these SMSTs have
improved soil properties made soil conditions more favorable for plant
growth and development on ravines. Further, SMSTs induced enhancement of
soil moisture could be one of the crucial points for higher fruit
setting and fruit growth in rain-fed fruit cultivation (Huang et al.,
2014). Under rain-fed cultivation, fruit crops face water scarcity in
different growth phases; resulting in the reduction of plants growth,
mortality of young plants, hampered fruit set and fruit quality. Thus,
the utilization of SMSTs can mitigate the adverse effects of water
stress on plant growth during various stages of the growth cycle in
rain-fed conditions by increasing soil moisture. The crucial role of
water in rain-fed cultivation can be justified by its functionality in
enhancement of number of fruits, fruit weight and size, and yield
(Panighrahi et al., 2017; Wang et al., 2019; Mpelasoka et al., 2001;
Hajlaoui et al., 2022).
Present study observed positive influence of SMSTs (SCCBT and SBT) on
fruit quality parameters like fruit and pulp weight, and fruit diameter.
These three parameters are one of the decisive to make good fruit
quality, appealing and market value. Higher partitioning of
photosynthates towards fruits and availability of soil moisture produced
fruits with higher weight; on the contrary, moisture deficiency reduces
the fruit weight (Wang et al., 2019). Further, water stress (drought)
can lead to insufficiency of water necessary for enlargement of cells;
consequently reduces the fruit size (Yildirim et al., 2015). Current
study also showed that the SMSTs treatments (SCCBT and SBT) produced
fruits with higher moisture which lead to reduction in TSS and total
sugars; this might be due to the higher moisture dilution effect in the
fruits (Panighrahi et al., 2017; Davis & Albrigo, 1994). Whereas,
reduced fruit moisture, higher TSS, total sugars, reducing and
non-reducing sugars were observed in treatment without any SMSTs i.e.
SS. Water stress conditions enhances the TSS, soluble sugars, and
reduces TA in fruits. This may displays improved conversion of acids to
sugars in dehydrated juice sacs that is essential to sustain the solute
potential of fruit cells under modest moisture stress situations (Huang
et al., 2000; Navvaro, 2010). This also indicates the adaptation in
solute pathway stimulated by the plants in the degraded ravines under
moisture deficit. Many times light moisture deficit is recommended to
enhance the fruit quality (Mpelasoka et al., 2001; Wang et al., 2019).
Further, SMSTs enhanced vitamin C content in the sapota fruits compared
to control. Higher vitamin C under SMSTs has been earlier been observed
by Liu et al. (2012) and Panighrahi et al. (2017). It has been reported
that soil moisture regime is negatively and positively correlated with
vitamins and polyphenols, respectively in wolfberry (Wang et al., 2020).
Results of present study confirms the observation with respect to
organic acids, phenols however contradict with the vitamin C. We have
reported increase in vitamin C content under SCCBT and lowest under SS
on par with SST. Whereas, total phenol content in the fruits observed
more in control plot which received no SMST followed by SCCBT and lowest
when Sapota grown alone with bench terrace and trenches. Present result
revealed that the moisture deficit conditions improved the phenolic
compounds. This rise in phenolic concentrations can be attributed to the
activation of metabolic responses triggered by the moisture stress,
which aims to adapt to the unfavorable conditions (Buendia et al., 2008;
Guizani et al., 2022).
Present investigation showed that natural slopes produced highest
runoff, whereas terrace reduced run-off and the latter may be due to the
tillage activities and rainfall interception by both trees and crops.
Earlier studies have also reported that the steep slopes, reduced or no
tillage, poor organic matter, bare soils, and high rainfall intensity
etc., are the major factor responsible for generating the higher runoff
and consequently higher erosion risks in similar kinds of lands
(Barrena-Gonz´alez et al., 2020; Ben-Salem et al., 2018; García-Díaz et
al., 2016; Salom´e et al., 2016; Baiamonte et al., 2019). Therefore,
reduced slope, tillage operation and rainfall interception by tree
canopy cumulatively reduces runoff in the bench terrace (SCCBT and SBT)
compare to control (Fang et al., 2021; Keesstra et al., 2016). Further,
in terrace based SMSTs, the reduction in water velocity and subsequent
its more retention over surface leads to the greater water infiltration
into the soil that consequently reduced runoff generation (Zhnag et al.,
2014). Though SCCBT produced lowest runoff but caused highest soil loss
which could be due to the application of tillage operations during
cowpea and castor cultivation (Fig. 2c). On the other hand, the highest
runoff and moderate soil loss in SS was resulted from the generation of
greater runoff water velocity on the undisturbed slope (Bagagioloet al.,
2018; Keesstra et al., 2016). Since the development of agriculture,
tillage is the prime provoker of the soil erosion (Brevik and Hartemink,
2010; Nie et al., 2016). Tillage makes the soils bare, loose and
consequently makes it prone to higher soil erosion. Tillage is typically
regarded as the major factor responsible for soil erosion in rain-fed
agriculture (Kurothe et al. 2014) and is accountable for the
acceleration of sediment fluxes on all continents (Van Oost et al.,
2009). Despite this, tillage is considered a crucial factor in
agricultural production (Singh et al., 2014) because it alters soil
characteristics such as SOC (Hassan et al., 2014), biota habitat (Balota
et al., 2014), and chemical properties (Laudicina et al., 2015; Zornoza
et al., 2015). Therefore, findings showed that the despite the higher
soil loss recorded under SCCBT treatment, it also contributed greater
fruit yield as well as quality.
The present investigation revealed the improvement of availability major
nutrients under SMSTs measures, compare to natural slopes of degraded
ravine lands. These measures influenced improvement in status of soil
moisture, SOC, soil nutrients like N2O,
P2O5, and K2O could be
attributed to the erosion reduction under SMSTs. The higher SOC in the
SCCBT, SBT, and SST treatments could be the result of accumulation and
retention of organic matter in the soil. Conversely, lower levels of SOC
in SS may be due to the loss of decaying plant parts from the surface
soil through soil erosion because of inadequate physical barriers.
Improvement in SOC through different SMSTs has been reported previously
in different studies (Gu et al., 2017). Eroded soils lose a large amount
of surface SOC because of its preferential removal by the erosion
process and relatively low density of SOC (Lal, 2003). Further, Mahajan
et al. (2021) reports that continuous contour trenches and vegetative
barrier improved SOC (1.41% to 2.02%), SOC stock (44.9-57.8 Mg C
ha-1), rate of SOC sequestration (1.5 Mg C
ha-1 yr-1), soil microbial biomass
carbon (33.9 mg kg-1), and had lowest metabolic
quotient (0.52 mg CO2-C g-1 h-1),
compared to the control, which indicates improved soil biological
activity and reduced environmental stress on the soil microbes. Several
studies report the similar findings of loss of SOC under accelerated
soil erosion process (Rhoton and Tyler, 1990; Kimble et al., 2001; Zhang
et al., 2023). Further present study revealed that SMSTs improves
properties of soils one or other way. Likewise, Dagnachew et al. (2020)
reported that farmlands with SMSTs had significantly improved soil
physical properties such as silt and clay fractions, and volumetric soil
water content and chemical properties like pH, SOC, TN, C:N ratio, and
available phosphorus, compared with farmlands without SWC measures.
Numerous studies, including those by Hailu et al. (2012), Ademe et al.
(2017), Abay et al. (2016), Stahr (2010), and Zhang et al. (2023), have
reported that farmlands implementing SMSTs and lower slope gradients
tend to demonstrate considerably greater levels of SOC, total nitrogen
etc. when compared to non-conserved lands and having higher slope
gradients. Similar to our study, the higher availability of
P2O5 and K2O in case of
SMSTs and lower slopes were also observed by the previous researchers
(Dagnachew et al., 2020; Mengistu et al. 2016; Ademe et al., 2017).
Therefore, higher accumulation of SOC and soil nutrients like available
N2O, P2O5, and
K2O can be attributed towards positive effects on SMSTs
on sites.