Next Article in Journal
Wildfire Spread Prediction Using Attention Mechanisms in U2-NET
Previous Article in Journal
Development and Application of Tree Radial Measurement Device
Previous Article in Special Issue
Accumulation of Glomalin-Related Soil Protein Regulated by Plantation Types and Vertical Distribution of Soil Characteristics in Southern China
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Forests
Volume 15
Issue 10
10.3390/f15101709
forests-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Growing Jatropha curcas L. Improves the Chemical Characteristics of Degraded Tropical Soils

by
Renaud Massoukou Pamba
1,2,
Vincent Poirier
1,*,
Pamphile Nguema Ndoutoumou
3 and
Terence Epule Epule
1
1
Agriculture and Agri-Food Research and Development Unit, University of Québec in Abitibi-Témiscamingue, Notre-Dame-du-Nord, QC J0Z 3B0, Canada
2
Ministry of Water and Forests, Sea, Environment, in Charge of the Climate Plan and the Land Use Plan, Libreville P.O. Box 199, Gabon
3
Laboratory of Plant Biotechnology, Department of General Agronomy, Institute of Agricultural and Forestry Research, National Centre for Scientific and Technological Research, Libreville P.O. Box 2246, Gabon
*
Author to whom correspondence should be addressed.
Forests 2024, 15(10), 1709; https://doi.org/10.3390/f15101709
Submission received: 2 August 2024 / Revised: 13 September 2024 / Accepted: 18 September 2024 / Published: 27 September 2024
(This article belongs to the Special Issue Biogeochemical Cycles in Forests)
Browse Figures
Versions Notes

Abstract

:
Intensive agriculture in tropical regions is the main cause of soil impoverishment, reducing its productivity. Studies based on soil restoration methods are being implemented, including the use of plants such as Jatropha curcas L., which could have the capacity to improve the agronomic properties of degraded soils in the tropics. The aim of this study is, therefore, to demonstrate that J. curcas L. can improve the characteristics of degraded tropical soil. Between October 2019 and November 2022, we evaluated the effect of spacing, planting material type and age, as well as their interactions, on carbon (C) and nitrogen (N) concentrations and pH at two depths (i.e., 0–10 and 10–20 cm) in the soil. The results reveal that after three years of J. curcas L. growth, C concentration and soil pH increased significantly (p < 0.001) at both depths, while N concentration increased significantly between 0 and 10 cm only. Plants grown from cuttings improved soil pH at 10–20 cm depth more (p = 0.012) than those grown from seeds. Three years after planting, soil N concentration under J. curcas reached a value comparable to that of undisturbed adjacent soil. Overall, our results indicate that J. curcas is a plant that can contribute effectively to restoring degraded tropical soils, therefore contributing to limiting the deforestation of natural forests.

1. Introduction

Tropical soil degradation is either linked to anthropogenic activities or to natural causes such as climate change and other related factors [1,2]. It can be defined as the process that leads to the reduction in the production potential of these soils [3,4] and the destruction of natural resources [5,6]. Soil degradation is manifested by several factors such as (i) soil erosion by wind and water [5,7]; (ii) soil pollution [8]; (iii) soil compaction [9,10]; (iv) loss of soil biodiversity [11]; (v) impoverishment in soil nitrogen (N), carbon (C) and phosphorus (P) [12], (vi) loss of soil macro- and micronutrients [13,14] and increased metal toxicity due to soil acidification [2,15]. Numerous studies maintain that the problem of soil degradation affects all areas of the globe where humans are present [16,17]. However, the degradation of tropical soils remains poorly studied despite their global ecological importance. In the humid tropics, and particularly in Gabon, anthropogenic activities such as the intensive cultivation of cocoa (Theobroma cacao L.) and rubber (Hevea brasiliensis L.) contribute to soil degradation. Acid forest zones are generally deficient in P, calcium (Ca) and magnesium (Mg), and aluminium (Al) and manganese (Mn) toxicity are major constraints on plant growth [18]. This soil degradation leads farmers to abandon their land in search of new land, putting pressure on the forests by clearing them and practicing slash-and-burn agriculture. It is, therefore, urgent to examine how to restore these degraded soils, particularly in the tropics, where forests play a huge role in regulating the global C cycle [19]. Some of the methods available include the use of so-called “soil improvers” such as Jatropha curcas [20,21]. The use of this plant species has shown promising results for restoring degraded soils in dry tropical climates [22,23]. However, little is known about its ability to restore degraded tropical soils in humid environments.
Jatropha (Jatropha curcas L.) is a species native to tropical America and widespread in many tropical and subtropical areas of Africa and Asia [24,25,26]. It is a shrub of the Euphorbiaceae family that reaches 8 m in height [27,28] and can adapt to a wide range of ecological conditions [25]. As such, J. curcas can grow on nutrient-poor soils [22,23,29,30]. Several studies have shown the positive effects of J. curcas on soil chemical properties, such as soil organic C (SOC) [31,32,33], soil total N [31,34] and soil pH [35,36]. However, studies showing the cumulative positive effects of J. curcas on organic carbon (SOC), total nitrogen and soil pH are rare, as are those showing that J. curcas has positive effects on the chemical properties of nutrient-poor soil.
The J. curcas can be propagated generatively (seeds) or vegetatively (cuttings) [37,38]. Plants growing from cuttings have a shallower lateral root system than those growing from seeds, which generally have a deeper taproot [25,39]. However, [29] showed that the height of J. curcas growing from seeds was increased at lower plant spacing, while the opposite was observed for J. curcas growing from cutting. These results show that the type of material used for propagation and the spacing between them can influence above- and below-ground growth and, thus, could affect the properties of the soil that supports their growth. Still, how propagation material, plant spacing, and their interaction influence the way J. curcas affects the properties of degraded soils and the mechanisms leading to their restoration remains unknown, especially in the humid tropics.
The aim of this work is to assess the capacity of J. curcas to improve certain characteristics of a degraded tropical soil impoverished by the successive intensive cultivation of cocoa and rubber trees in northern Gabon. We aim to verify the three following hypotheses: (H1) after three years of J. curcas cultivation, SOC and total soil N concentrations and soil pH will be greater than before planting, and (H2) the positive impact of J. curcas will be visible primarily in the topsoil and (H3) the positive impact of J. curcas will depend on the density of these plants.

2. Materials and Methods

2.1. Description of the Study Site and Experimental Set-Up

The study was carried out in the village of Akam Effak, located 25 km from the town of Bitam in northern Gabon (Figure 1). According to the Köppen–Geiger climatic classification, the climate at this site is classified as a tropical rainforest (Af) [40,41]. It comprises four seasons, depending on the intensity of rainfall and drought: a short dry season (January and February); a long rainy season (March, April, May, June); a long dry season (July, August and September) and a short rainy season (October, November and December). According to Nguema Ndoutoumou et al. [42,43], relative humidity is around 92%, mean annual temperature is 23.3 °C and average rainfall varies between 1800 and 2300 yearly. According to the World Soil Resources Database (IUSS Working Group WRB 2022), the soil at the study site is a Ferralsol, as it contains a strong dominance of kaolinites and Fe and Al oxides [44].
To test our hypotheses, a three-year field experiment was conducted in which soils were sampled at 0–10 cm and 10–20 cm depth before and after planting J curcas seeds and cuttings at 2 m × 2 m, 2.5 m × 2.5 m and 3 m × 3 m distances. Soils were analysed for SOC, total soil N concentration and soil pH, and adjacent soil from an undisturbed natural forest was sampled as a reference for comparison.
Our experimental set-up was located on an abandoned plantation where intensive cocoa (Theobroma cacao L.) (1976–1999) and rubber (Hevea brasiliensis L.) (1999–2019) cultivation succeeded one another for over 43 years, leading to an impoverished and degraded soil [29]. Site preparation operations prior to planting J. curcas at the start of the experiment involved manually removing herbaceous vegetation, trees and stumps, and exporting plant residues outside the area where the treatments were installed (see [29] for details). No fertilizer was applied. The experimental set-up comprises three planting distances (i.e., 2 m × 2 m, 2.5 m × 2.5 m and 3 m × 3 m) and two types of material used for propagation (i.e., seeds and cuttings) of J. curcas. It includes four replicates, giving a total of 24 treatments, each attributed to an experimental unit. The latter consisted of a 144 m2 (12 m × 12 m) plot receiving between 16 and 25 plants depending on planting distance.

2.2. Soil Sampling and Analysis

Each experimental unit was sampled manually at two soil depths (0–10 and 10–20 cm) using a cylindrical tube measuring 5 cm × 5 cm × 10 cm. This yielded 48 soil samples, each one consisting of a composite of three sub-samples taken at the experimental unit level. The soils were sampled in October 2019 after site preparation operations but before J. curcas plantation. In each of the 12 m × 12 m plots, soil sampling was carried out in the same location as in 2019. The soil was sampled again in November 2022 after 40 months of growth at about 15 cm from plant collar. We also sampled soils with the same method in an undisturbed, natural forest located close (i.e., c. 500 m) to our experimental set-up to have a reference site where neither rubber nor cocoa had been grown before. At this reference site, seven sampling points spaced about 5 m apart were arbitrarily chosen where soil was sampled at two depths (i.e., 0–10 and 10–20 cm) for a total of 14 soil samples. Each sample consisted of a composite of three sub-samples taken at the sampling point level. Following sampling, soils were put in plastic bags, weighed, and air-dried for 7 d and sieved to 2 mm prior to analysis. The presence of coarse fragments >2 mm was negligible.
Six (6) grams of air-dried soil from each sample were crushed, and approximately 600 mg were taken for the analysis of total soil C and N concentrations by dry combustion using a vario MAX cube apparatus (Elementar Analysensysteme, Langenselbold, Germany). There was no inorganic C in the soil, and thus, total soil C was considered as soil organic C. The pH was obtained by suspending the air-dried soil samples in a 0.01 M CaCl2 solution at a soil-to-solution ratio of 1:2, as described by Hendershot et al. [45]. Soil texture was measured using the hydrometer method described by Kroetsch and Wang [46]. Soil nutrients (P, K, Ca, Mg, Na, Cu, Zn, Mn, Fe and Al) were extracted using the Mehlich III solution and measured by inductively coupled plasma optical emission spectroscopy (ICP-OES) apparatus (model 5110, Agilent Technologies, Santa Clara, CA, USA). Soil texture and nutrient concentrations were analysed on samples taken in October 2019 for characterization purposes, while soil C and N concentrations and soil pH were analysed on samples taken in October 2019 and November 2022 to evaluate the impact of J. curcas growth.

2.3. Statistical Analysis

We evaluated the influence of planting distances (i.e., 2 m × 2 m, 2.5 m × 2.5 m and 3 m × 3 m), propagation material (i.e., seeds and cuttings), time (i.e., October 2019 and November 2022) and their interactions on soil organic C and total soil N concentrations and soil pH. Two soil depths (i.e., 0–10 cm and 10–20 cm) were investigated and analysed independently from each other. The postulates of homogeneity of variance and normal distribution of residuals were evaluated with Shapiro–Wilk and Levene tests. Since the results from these tests showed that the postulates were not respected, we used a permutational analysis of variance (PERMANOVA) to evaluate if the treatments or their interactions influenced the dependent variables. This non-parametric analysis allowed us to analyse non-transformed data. The PERMANOVA and averaging were performed with the perm.anova package of the R software. We considered effects to be significant at p < 0.10. To illustrate significance, graphs were produced using the ggplot2 package of the R software. All analyses were performed with the R 4.0.3 software [47].

3. Results

Soil particle size distribution was 504, 470 and 26 g kg−1 of clay (i.e., <2 µm), silt (i.e., 2–50 µm) and sand (i.e., 50 µm–2 mm) particles and was similar at both soil depths (i.e., 0–10 and 10–20 cm). According to Ferret’s triangle for particle-size distribution, soil texture would be classified as silty clay. Analysis of soil nutrients of samples taken in October 2019 revealed high concentrations of Al and Fe (i.e., 896 and 121 mg kg−1 soil, respectively) and low concentrations of P, K, Ca, Mg, Na, Cu, Zn and Mn (i.e., 3, 17, 18, 5, 3, <1 and <1 mg kg−1 soil, respectively). As for soil texture, nutrient concentrations were similar at both soil depths. The effect of planting distance, propagation material, period and their interactions on total soil N and soil organic C concentrations and soil pH at both depths are shown in Table 1.
Our results indicate that the growth of J. curcas significantly increased soil organic C concentration. In November 2022, after 40 months of growth, soil organic C concentration was 15.6 and 14.0 g C kg−1 soil at 0–10 and 10–20 cm depths, respectively (Figure 2a,b). These values are greater than those of the soil sampled in October 2019 (i.e., 10.8 and 10.0 g C kg−1 soil at 0–10 and 10–20 cm depths, respectively) when there was no J. curcas crop yet (p < 0.001, Table 1 and Figure 2a,b). Growing J. curcas thus led to increases of 1.60 and 1.33 g C kg−1 soil yr−1 at 0–10 and 10–20 cm depths, respectively. Still, the values obtained under J. curcas cultivation in November 2022 remain below those of the undisturbed natural forest soil used as a reference (Figure 2a,b).
Results for total soil N concentration were similar to those obtained for soil organic C, except that the effect of the period (i.e., October 2019 vs. November 2022) was only significant at the 0–10 cm depth (p = 0.087, Table 1). In November 2022, total soil N concentration at 0–10 cm depth was about 1.6 g N kg−1 soil, which is 1.8 times greater than that measured in October 2019 (i.e., 0.9 g N kg−1 soil, Figure 3). After 40 months of growth of J. curcas, total soil N concentration in November 2022 in the 0–10 cm depth soil layer reached a value comparable to that of undisturbed natural forest soil used as a reference (Figure 3).
As noted for soil organic C and total soil N concentration, we also found that the growth of J. curcas increased soil pH over time. At 0–10 cm depth, soil pH significantly increased from a value of 3.61 before the establishment of our plots in October 2019 to a value of 4.15 in November 2022 (p < 0.001, Table 1 and Figure 4a). At 10–20 cm depth, the increase in soil pH was also significant and rose from a value of 3.61 before the establishment of our plots in October 2019 to a value of 4.05 in November 2022 (p < 0.001, Table 1 and Figure 4b). However, soil pH values at both depths under J. curcas in November 2022 remained below those of undisturbed natural forest soil (Figure 4a,b).
We also noted a significant effect of propagation material type on soil pH at 10–20 cm depth. At this depth, plots sown with J. curcas cuttings had higher soil pH than those sown with seeds but remained lower than that of the undisturbed natural forest soil (Figure 5).

4. Discussion

4.1. Soil Organic Carbon Concentration

The results obtained for soil organic C are consistent with our first hypothesis (H1) that its concentration would be higher after three years of J. curcas growth than before planting. They are also consistent with our second hypothesis (H2), according to which we expected this effect to be more pronounced at 0–10 cm than at 10–20 cm depth. However, results for soil organic C concentration did not support the third hypothesis (H3) as we found no effect on planting distance.
Our results show that soil organic C increased at rates equivalent to 1.60 and 1.33 g C kg−1 soil yr−1 at 0–10 and 10–20 cm depth, respectively, and an average of 1.47 g C kg−1 yr−1 across both depths. This is greater than the rate calculated from results presented by Wani et al. [33] in tropical India. These authors observed an increase in soil organic C of 3.10 g C kg−1 soil under J. curcas after four years, corresponding to a gain of 19% compared with adjacent grassland soil and an accumulation rate equivalent to 0.78 g C kg−1 yr−1. Our results are, however, comparable to those of Ogunwole et al. [31], who investigated J. curcas growth in degraded soils in India. The latter reported an increase in soil organic C of 4.49 g C kg−1 soil at 0–10 cm depth after 31 months when compared to adjacent soil under native vegetation, corresponding to a rate of 1.74 g C kg−1 yr−1.
Increases in soil organic C could be associated with important litter addition and root biological activities [48,49,50,51]. The increase in soil C over time can be explained by the addition of litter from leaf and stem fall, which can be rich in organic carbon [36,52,53,54]. Massoukou Pamba et al. [29] observed after one year of J. curcas growth a progressive drop in leaf production, which could be explained by the low fertility of the soil on which it was planted. This species is a xerophytic plant with deciduous leaves that fall when faced with certain nutrient deficiencies [29,30,55]. Leaves that accumulate on the soil add organic matter, which stimulates the growth and activity of soil microbial biomass [25,56,57]. An increase in soil microbial biomass resulting from the abundant fall of J. curcas leaves and stems can, thus, contribute to an increase in soil organic C concentration [33,58].
The increase in soil C concentration observed in our study can also be explained by the fact that we sampled the soil close to the stem, in the rhizosphere, where soil biological activity is intense [23,33,54,59]. The rhizosphere is enriched in C [59], and this enrichment may result from (i) the intense microbial activity that takes place there [22,23,54], (ii) root exudation [60] and (iii) superficial root development [34,38]. Our results corroborate those of Bazongo et al. [23,34] in Burkina Faso, who observed, over a relatively short period of time (i.e., 10 months), a greater increase in soil C concentration under J. curcas plant crowns and then further away from the plant [23]. The fact that we sampled at 15 cm from J. curcas collar likely shows that the root system of this plant has the capacity to increase soil organic C concentration in the short term.
The increase in average soil C levels can also be linked to the development of soil structure and aggregation mechanisms that protect C from decomposition. Indeed, Ogunwole et al. [31] report that the cultivation of J. curcas increased soil aggregate mean weight and microaggregate-associated organic C concentration compared to adjacent soil under native vegetation. These results concur with those of [36], who found a reduction in soil bulk density and an increase in water-holding capacity by 10% after three years of J. curcas growth. The authors attributed this effect to the positive impact of the J. curcas roots on soil structure and macroporosity [36]. Thus, it is probable that the positive impact of J. curcas on soil organic C concentration noted in our work could be caused by the influence of its roots. However, this would need to be demonstrated experimentally.

4.2. Total Soil Nitrogen Concentration

The results obtained regarding total soil N concentration partly confirm our first hypothesis (H1) since, after three years of J. curcas cultivation, the average N concentration increased significantly only at a 0–10 cm soil depth. This, however, confirms our second hypothesis (H2), according to which this effect should be more pronounced at this depth than at a 10–20 cm depth. However, as for soil organic C concentration, results for total soil N concentration did not support the third hypothesis (H3) since no effect of planting distance was found.
Our results concord with Ogunwole et al. [31], who reported an increase in soil N concentration after two years of J. curcas cultivation in degraded soils in India, particularly in the microaggregate fraction. The increase we noted (i.e., 1.8 times) was, however, greater than that of Ogunwole et al. [31] (i.e., 1.3 times for whole soil N concentration). The enrichment in soil N that we noted could be associated with leaves of J. curcas that fell from the plant and accumulated on the soil surface, as mentioned earlier. Leaves from this species are particularly enriched in N as compared with other parts of the plant [58], which facilitates their decomposition by soil micro-organisms and the consequent accumulation of N in the upper part of the soil profile.
Another possible explanation for the increase in soil N concentration could be related to the association between J. curcas roots and soil micro-organisms. This species can form a symbiotic association with arbuscular mycorrhizal fungi [61]. In addition, although J. curcas is not a legume nor an actinorhizal plant, its roots can be colonized by N-fixing endophyte bacteria of the Enterobacter species that are native to this plant [62]. The presence of arbuscular mycorrhizal fungi and/or endophytic bacteria can increase plant N availability [54,63], which can translate into N enrichment plant leaves [54,62]. The increased microbial activity under J. curcas [33] could have promoted the decomposition of N-rich leaves fallen to the ground and consequently enriched the soil with this element.
We sampled the soil close to the stem in the rhizosphere where biological activity is intense, and this could explain why we solely found an increase in soil N concentration at a 0–10 cm depth. The presence of arbuscular mycorrhizal fungi and/or endophytic bacteria can also increase soil nitrogen concentration in the rhizosphere [64,65]. In addition, [33] showed that the growth of J. curcas increased microbial biomass N concentration by 24% in the rhizospheric soil under this species compared to the control site. These observations concord with [58], wherein the authors concluded that J. curcas increased soil biological activity and led to more accumulated N relative to C (i.e., lower C-to-N ratio). Altogether, these results suggest that J. curcas has the capacity to improve soil fertility in the upper part of the soil profile.

4.3. Soil Acidity

The growth of J. curcas significantly reduced soil acidity and increased soil pH at both 0–10 cm and 10–20 cm depth, which confirms our first hypothesis (H1). Our second hypothesis (H2) is not verified since the effect observed was not more pronounced at a 0–10 cm than at a 10–20 cm depth. Our results did not support the third hypothesis (H3) since no effect of planting distance was found. Surprisingly, however, we noted a significant effect of propagation material.
Our results concur with others who showed increases of 0.2 to 0.4 pH units (i.e., the soil is 1.6 to 2.5 times less acidic) after growing J. curcas alone in tropical acid soils without amendments [58,66,67,68,69]. These studies, however, did not propose any mechanisms to explain how J. curcas could increase soil pH and reduce its acidity. Perhaps leaf fall is related to this process since the addition of plant material to the soil has the capacity to increase soil pH [70,71]. Possible mechanisms include the addition of litter-derived base cations, the association of organic anions from plant material with H+ or Al3+ in the soil and ammonification of organic N [70,71,72,73]. More work is needed to clearly identify which mechanism could be responsible for the observed increase in soil pH after three years of J. curcas growth in our study.
We also found that soil pH under J. curcas at a 10–20 cm depth was greater when the species was propagated with cuttings than with seeds. This could be associated with root development of the plant. The latter is superficial with multiple ramifications and has no taproot with cuttings compared with seeds [36,38,39,74]. Root systems with multiple branches absorb nutrients more easily and promote microbial and enzymatic activities [22,23]. Perhaps this translated into increased transformation of organic N in the rhizosphere through ammonification, a process that consumes H+ and reduces soil acidity [70,71]. The superficial and ramified root systems with cutting could have released more compounds through rhizodeposition that can form organo-mineral complexes with Al in soils [75,76], thereby reducing the negative impact that Al species have on soil acidification [76,77]. Again, more work is needed to clearly elucidate the mechanisms by which planting J. curcas with cuttings as opposed to seeds contributes to increased soil pH.

5. Conclusions

This study demonstrated that the cultivation of J. curcas can improve the chemical properties of soil impoverished by the successive intensive cultivation of cocoa and rubber trees in northern Gabon. Soil organic carbon concentration increased with time at both sampling depths (0–10 and 10–20 cm) but remained below the value obtained at the reference site. Total soil nitrogen concentration increased with time only at a 0–10 cm depth and reached a similar value as that obtained at the reference site. Soil pH also increased significantly with time at 0–10 cm and 10–20 cm depths but remained below the value at the reference site. We also observed that J. curcas plants sown with cuttings improve soil acidity better than those sown with seeds.
The J. curcas is a plant that responds effectively to current agricultural needs, both economically and environmentally, as it is a palliative to the use of chemical fertilizers thanks to its soil-enriching action. Growing J. curcas on degraded tropical soil thus seems a promising avenue to improve their fertility. This could reduce the pressure exerted on the natural forest by deforestation activities by farmers in search of new, more fertile soils to cultivate. However, further research is needed to ascertain whether growing this plant also improves soil properties over the medium- to long-term on the same soil.

Author Contributions

Conceptualization, R.M.P. and V.P.; methodology, R.M.P. and V.P.; software, R.M.P.; validation, P.N.N., V.P. and T.E.E.; formal analysis, R.M.P.; investigation, R.M.P. and V.P.; resources, R.M.P., V.P. and P.N.N.; data curation, R.M.P.; writing—original draft preparation, R.M.P.; writing—review and editing, R.M.P., V.P., P.N.N. and T.E.E.; visualization, R.M.P.; supervision, V.P. and P.N.N.; Project administration, R.M.P. and V.P.; Funding acquisition, R.M.P. and V.P. All authors have read and agreed to the published version of the manuscript.

Funding

Our most sincere thanks go to the Programme Canadien des Bourses de la Francophonie (PCBF) for providing us with a grant to R.M.P. (file number 20185529) and to the Fondation de l’Université du Québec en Abitibi-Témiscamingue for providing funds to V.P. (Projets courts FIRC/FUQAT) to finance this work. Please find in these few words all our gratitude.

Data Availability Statement

Data are contained within the article.

Acknowledgments

Our thanks go to SAMA Valérie EPSE MASSOUKOU PAMBA for the enormous financial sacrifices made for R.M.P. studies and during various data collections in the field. Our thanks also go to Richard PAMBA and Alix PAMBA for the logistical support that facilitated various field trips. We would also like to thank our colleague from the PCBF, Jules Hadé Wenkouni DARANKOUM, for his sincere collaboration since the beginning of our training, as well as technical and administrative staff at the Centre de l’UQAT du Témiscamingue in Notre-Dame-du-Nord.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Lal, R. Soil degradation as a reason for inadequate human nutrition. Food Secur. 2009, 1, 45–57. [Google Scholar] [CrossRef]
  2. Lal, R. Restoring soil quality to mitigate soil degradation. Sustainability 2015, 7, 5875–5895. [Google Scholar] [CrossRef]
  3. Chenu, C.; Klumpp, K.; Bispo, A.; Angers, D.; Colnenne, C.; Metay, A. Stocker du carbone dans les sols agricoles: Évaluation de leviers d’action pour la France. Innov. Agron. 2014, 37, 23–37. Available online: https://hal.science/hal-01173319 (accessed on 13 September 2024).
  4. Lal, R. Soil degradation by erosion. Land Degrad. Dev. 2001, 12, 519–539. [Google Scholar] [CrossRef]
  5. Benbrahim, K.F.; Ismaili, M.; Benbrahim, S.F.; Tribak, A. Land degradation by desertification and deforestation in Morocco. Sci. Chang. Planétaires/Sécheresse 2004, 15, 307–320. [Google Scholar]
  6. Lahmar, R.; Ruellan, A. Dégradation des sols et stratégies coopératives en Méditerranée: La pression sur les ressources naturelles et les stratégies de développement durable. Cah. Agric. 2007, 16, 318–323. [Google Scholar] [CrossRef]
  7. Rajot, J.L.; Karambiri, H.; Ribolzi, O.; Planchon, O.; Thiebaux, J.-P. Interaction entre érosions hydrique et éolienne sur sols sableux pâturés au Sahel: Cas du bassin-versant de Katchari au nord du Burkina Faso. Sci. Chang. Planétaires/Sécheresse 2009, 20, 17–30. [Google Scholar] [CrossRef]
  8. Khalid, N.; Majid, A.; Bilal Tahir, M.; Niaz, N.A.; Khalid, S. Carbonaceous-TiO2 nanomaterials for photocatalytic degradation of pollutants: A review. Ceram. Int. 2017, 43, 14552–14571. [Google Scholar] [CrossRef]
  9. Al-Awadhi, J.M.; Misak, R.F.; Omar, S.S. Causes and consequences of desertification in Kuwait: A case study of land degradation. Bull. Eng. Geol. Environ. 2003, 62, 107–115. [Google Scholar] [CrossRef]
  10. Walter, C.; Lemercier, B. Les sols bretons sont-ils menacés? Bretagnes 2008, 9, 30–35. Available online: https://hal.science/hal-02060271 (accessed on 18 September 2024).
  11. Ahononga, F.; Gouwakinnou, G.; Biaou, S.; Ahouandjinou, O.; Biaou, S.; Sonounameto, R. Facteurs d’affectation des terres et effets sur les services écosystémiques et la biodiversité: Synthèse bibliographique. Bull. Rech. Agron. Bénin 2020, 30, 1–9. [Google Scholar]
  12. El Mazi, M.; Hmamouchi, M.; Houari, A. Impact de l’évolution de l’utilisation des terres sur la dégradation des ressources en sols dans le Rif Central méridional, Maroc. Rev. Marocaine Sci. Agron. Vétérinaires 2021, 9, 567–572. [Google Scholar]
  13. Maier, C.; Kress, L. Soil CO2 evolution and root respiration in 11 year-old loblolly pine (Pinus taeda) plantations as affected by moisture and nutrient availability. Can. J. For. Res. 2000, 30, 347–359. [Google Scholar] [CrossRef]
  14. Thibodeau, L.; Raymond, P.; Camiré, C.; Munson, A.D. Impact of precommercial thinning in balsam fir stands on soil nitrogen dynamics, microbial biomass, decomposition, and foliar nutrition. Can. J. For. Res. 2000, 30, 229–238. [Google Scholar] [CrossRef]
  15. Calvaruso, C.; Blanchart, A.; Bertin, S.; Grand, C.; Pierart, A.; Eglin, T. Quels paramètres du sol mesurer pour évaluer les fonctions et les services écosystémiques associés? Étude Gest. Sols 2020, 27, 36–376. [Google Scholar]
  16. Eswaran, H.; Lal, R.; Reich, P. Land degradation: An overview. In Response to Land Degradation; Padmanabhan USDA Natural Resources Conservation Service: Washington, DC, USA; University of Puerto Rico: Mayaguez, Puerto Riuco; Universiti Technologi Sumber: Kuching, Malaysia, 2019; pp. 20–35. [Google Scholar]
  17. Eswaran, H.; Reich, P. Human impact on land systems of the world. Soil Surv. Horiz. 2007, 48, 11–15. [Google Scholar] [CrossRef]
  18. St. Clair, S.B.; Sharpe, W.E.; Lynch, J.P. Key interactions between nutrient limitation and climatic factors in temperate forests: A synthesis of the sugar maple literature. Can. J. For. Res. 2008, 38, 401–414. [CrossRef]
  19. Mitchard, E.T. The tropical forest carbon cycle and climate change. Nature 2018, 559, 527–534. [Google Scholar] [CrossRef]
  20. Patel, D.; Saraf, M. Influence of soil ameliorants and microflora on induction of antioxidant enzymes and growth promotion of Jatropha curcas L. under saline condition. Eur. J. Soil Biol. 2013, 55, 47–54. [Google Scholar] [CrossRef]
  21. Théodore, A.K.; Gnénakan, Y.; Justin, K.Y. Etude de l’influence de Jatropha curcas sur le rendement du maïs (Zea mays L.) en association culturale dans la région de Bingerville en Côte d’Ivoire. Int. J. Innov. Appl. Stud. 2021, 34, 532–542. [Google Scholar]
  22. Bazongo, P.; Ouattara, B.; Traore, K.; Traore, O. Effet de Jatropha curcas sur les propriétés physiques et chimiques des sols dans la zone sud-soudanienne du Burkina Faso. Int. J. Innov. Appl. Stud. 2021, 32, 35–42. [Google Scholar]
  23. Bazongo, P.; Traore, K.; Traore, O.; Bilgo, A.; Yelemou, B.; Sanon, K.B.; Hien, V.; Nacro, B.H. Caractérisation des systèmes de production de Jatropha dans les exploitations agricoles de la zone Ouest du Burkina Faso. Int. J. Biol. Chem. Sci. 2015, 9, 2432–2445. [Google Scholar] [CrossRef]
  24. Divakara, B.; Upadhyaya, H.; Wani, S.; Gowda, C.L. Biology and genetic improvement of Jatropha curcas L.: A review. Appl. Energy 2010, 87, 732–742. [Google Scholar] [CrossRef]
  25. Domergue, M.; Pirot, R. Jatropha curcas L. Rapport de Synthèse Bibliographique; CIRAD: Paris, France, 2008; 111p. [Google Scholar]
  26. Sunil, N.; Sivaraj, N.; Anitha, K.; Abraham, B.; Kumar, V.; Sudhir, E.; Vanaja, M.; Varaprasad, K. Analysis of diversity and distribution of Jatropha curcas L. germplasm using Geographic Information System (DIVA-GIS). Genet. Resour. Crop Evol. 2009, 56, 115–119. [Google Scholar] [CrossRef]
  27. Wang, X.-R.; Ding, G.-J. Reproductive biology characteristic of Jatropha curcas (Euphorbiaceae). Rev. Biol. Trop. 2012, 60, 1525–1533. [Google Scholar] [CrossRef] [PubMed]
  28. Yang, Q.; Peng, D.; Duan, Z.; Wang, Z.; Sun, Q. Study on pollination biology of Jatropha curcas (Euphorbiaceae). J. South China Agric. Univ. 2007, 28, 62–66. [Google Scholar]
  29. Massoukou Pamba, R.; Poirier, V.; Nguema Ndoutoumou, P. L’écartement de plantation affecte différemment la croissance végétative du Jatropha curcas L. en culture sur un sol surexploité au nord du Gabon. Int. J. Biol. Chem. Sci. 2022, 16, 158–172. [Google Scholar] [CrossRef]
  30. Minengu, J.d.D.; Mobambo, P.; Mergeai, G. Influence de l’environnement et des pratiques culturales sur la productivité de Jatropha curcas L. en Afrique subsaharienne (synthèse bibliographique). Biotechnol. Agron. Société Environ. 2014, 18, 290–300. Available online: https://hdl.handle.net/2268/171574 (accessed on 18 September 2024).
  31. Ogunwole, J.; Chaudhary, D.; Ghosh, A.; Daudu, C.; Chikara, J.; Patolia, J. Contribution of Jatropha curcas to soil quality improvement in a degraded Indian entisol. Acta Agric. Scand. Sect. B–Soil Plant Sci. 2008, 58, 245–251. [Google Scholar] [CrossRef]
  32. Srivastava, P.; Kumar, A.; Behera, S.K.; Sharma, Y.K.; Singh, N. Soil carbon sequestration: An innovative strategy for reducing atmospheric carbon dioxide concentration. Biodivers. Conserv. 2012, 21, 1343–1358. [Google Scholar] [CrossRef]
  33. Wani, S.P.; Chander, G.; Sahrawat, K.L.; Rao, C.S.; Raghvendra, G.; Susanna, P.; Pavani, M. Carbon sequestration and land rehabilitation through Jatropha curcas (L.) plantation in degraded lands. Agric. Ecosyst. Environ. 2012, 161, 112–120. [Google Scholar] [CrossRef]
  34. Singh, B.; Singh, K.; Rao, G.R.; Chikara, J.; Kumar, D.; Mishra, D.; Saikia, S.P.; Pathre, U.V.; Raghuvanshi, N.; Rahi, T. Agro-technology of Jatropha curcas for diverse environmental conditions in India. Biomass Bioenergy 2013, 48, 191–202. [Google Scholar] [CrossRef]
  35. Behera, S.K.; Srivastava, P.; Tripathi, R.; Singh, J.; Singh, N. Evaluation of plant performance of Jatropha curcas L. under different agro-practices for optimizing biomass–a case study. Biomass Bioenergy 2010, 34, 30–41. [Google Scholar] [CrossRef]
  36. Singh, K.; Singh, B.; Tuli, R. Sodic soil reclamation potential of Jatropha curcas: A long-term study. Ecol. Eng. 2013, 58, 434–440. [Google Scholar] [CrossRef]
  37. Achten, W.M.; Nielsen, L.R.; Aerts, R.; Lengkeek, A.G.; Kjær, E.D.; Trabucco, A.; Hansen, J.K.; Maes, W.K.; Graudal, L.; Akinnifesi, F.K. Towards domestication of Jatropha curcas. Biofuels 2010, 1, 91–107. [Google Scholar] [CrossRef]
  38. Achten, W.M.; Verchot, L.; Franken, Y.J.; Mathijs, E.; Singh, V.P.; Aerts, R.; Muys, B. Jatropha bio-diesel production and use. Biomass Bioenergy 2008, 32, 1063–1084. [Google Scholar] [CrossRef]
  39. Diop, B.; Samba, S.; Akpo, L.E. Caractéristiques morphologiques et croissance de jeunes plants de Jatropha curcas L. Int. J. Biol. Chem. Sci. 2012, 6, 677–691. [Google Scholar] [CrossRef]
  40. Geiger, R. Klassifikation der Klimate nach W. Köppen. In Classification des Climats d’après W. Köppen; Landolt-Börnstein—Zahlenwerte und Funktionen aus Physik, Chemie, Astronomie, Geophysik und Technik, Alte Serie; Springer: Berlin, Germany, 1954; Volume 3, pp. 603–607. [Google Scholar]
  41. Geiger, R. Überarbeitete Neuausgabe von Geiger, R.: Köppen-Geiger/Klima der Erde. (Wandkarte 1:16 Mill.); Klett-Perthes: Gotha, Germany, 1961. [Google Scholar]
  42. Nguema Ndoutoumou, P.; Bouanga, E.P.; Massounga, Y.C.; Boussiengui Boussiengu, G. Étude comparée de trois méthodes de multiplication de Jatropha curcas L. dans les conditions climatiques du sud-est du Gabon. J. Appl. Biosci. 2013, 65, 4989–4998. [Google Scholar]
  43. Nguema Ndoutoumou, P.; Ndong, A.N.; Anda, C.C.O.; Midoumbou, F.P.N.; Ognalaga, M.; Missang, C.E. Régénération du cacaoyer (Theobroma cacao L.) sur un substrat à base de compost de Jatropha curcas L. Int. J. Biol. Chem. Sci. 2019, 13, 1043–1053. [Google Scholar] [CrossRef]
  44. IUSS Working Group WRB. World Reference Base for Soil Resources. In International Soil Classification for Naming Soils and Creating Legends for Soil Maps, 4th ed.; International Union of Soil (IUSS): Vienna, Austria, 2022. [Google Scholar]
  45. Hendershot, W.; Lalande, H.; Duquette, M. Chapter 16—Soil reaction and exchangeable acidity. In Soil Sampling and Methods of Analysis, 2nd ed.; Carter, M.R., Gregorich, E.G., Eds.; CRC Press: Boca Raton, FL, USA, 2006; 8p. [Google Scholar]
  46. Kroetsch, D.; Wang, C. Particle Size Distribution. In Soil Sampling and Methods of Analysis, 2nd ed.; Carter, M.R., Gregorich, E.G., Eds.; CRC Press: Boca Raton, FL, USA, 2006; 16p. [Google Scholar]
  47. R Core Team. Platform: x86_64-w64-mingw32/x64 (64-bit); The R Foundation for Statistical Computing: Vienna, Austria, 2020. [Google Scholar]
  48. Block, R.; Van Rees, K.; Knight, J. A review of fine root dynamics in Populus plantations. Agrofor. Syst. 2006, 67, 73–84. [Google Scholar] [CrossRef]
  49. Chomel, M.; DesRochers, A.; Baldy, V.; Larchevêque, M.; Gauquelin, T. Non-additive effects of mixing hybrid poplar and white spruce on aboveground and soil carbon storage in boreal plantations. For. Ecol. Manag. 2014, 328, 292–299. [Google Scholar] [CrossRef]
  50. Marone, D.; Poirier, V.; Coyea, M.; Olivier, A.; Munson, A.D. Carbon storage in agroforestry systems in the semi-arid zone of Niayes, Senegal. Agrofor. Syst. 2017, 91, 941–954. [Google Scholar] [CrossRef]
  51. Sartori, F.; Lal, R.; Ebinger, M.H.; Eaton, J.A. Changes in soil carbon and nutrient pools along a chronosequence of poplar plantations in the Columbia Plateau, Oregon, USA. Agric. Ecosyst. Environ. 2007, 122, 325–339. [Google Scholar] [CrossRef]
  52. Atchada, C.C.; Zoffoun, A.G.; Akplo, T.M.; Azontonde, A.H.; Tente, A.B.; Djego, J.G. Modes d’utilisation des terres et stock de carbone organique du sol dans le bassin supérieur de Magou au Bénin. Int. J. Biol. Chem. Sci. 2018, 12, 2818–2829. [Google Scholar] [CrossRef]
  53. Lawrey, J.D. The relative decomposition potential of habitats variously affected by surface coal mining. Can. J. Bot. 1977, 55, 1544–1552. [Google Scholar] [CrossRef]
  54. Leye, E.; Ndiaye, M.; Ndiaye, F.; Diallo, B.; Sarr, A.; Diouf, M.; Diop, T. Effet de la mycorhization sur la croissance et le développement de Jatropha curcas L. J. Renew. Energy 2009, 12, 269–278. [Google Scholar]
  55. Anguessin, B.; Mapongmetsem, P.M.; Ibrahima, A.; Fawa, G. Effet de la fertilisation organique à base de litière foliaire de Jatropha curcas L. et Jatropha gossypifolia L. sur la culture de tomate (Lycopersicon esculentum Mill.) à Guider (Nord/Cameroun). Int. J. Biol. Chem. Sci. 2021, 15, 524–535. [Google Scholar] [CrossRef]
  56. Haynes, R.; Beare, M. Influence of six crop species on aggregate stability and some labile organic matter fractions. Soil Biol. Biochem. 1997, 29, 1647–1653. [Google Scholar] [CrossRef]
  57. Stäuble, N.I. Etude ethnobotanique des Euphorbiacées d’Afrique de l’Ouest. J. Ethnopharmacol. 1986, 16, 23–103. [Google Scholar] [CrossRef]
  58. Gbemavo, D.S.J.C.; Gnangle, P.C.; Azontonde, A.; Glele Kakai, R.L. Modélisation du stock de biomasse et dynamique de séquestration minérale et carbone de Jatopha curcas L. sous différent types de sol au Bénin. Ann. Sci. Agron. 2014, 18, 1–20. [Google Scholar]
  59. Paterson, E. Importance of rhizodeposition in the coupling of plant and microbial productivity. Eur. J. Soil Sci. 2003, 54, 741–750. [Google Scholar] [CrossRef]
  60. Chaudhary, D.R.; Saxena, J.; Lorenz, N.; Dick, L.K.; Dick, R.P. Microbial profiles of rhizosphere and bulk soil microbial communities of biofuel crops switchgrass (Panicum virgatum L.) and jatropha (Jatropha curcas L.). Appl. Environ. Soil Sci. 2012, 2012, 906864. [Google Scholar] [CrossRef]
  61. Koranda, M.; Schnecker, J.; Kaiser, C.; Fuchslueger, L.; Kitzler, B.; Stange, C.F.; Sessitsch, A.; Zechmeister-Boltenstern, S.; Richter, A. Microbial processes and community composition in the rhizosphere of European beech—The influence of plant C exudates. Soil Biol. Biochem. 2011, 43, 551–558. [Google Scholar] [CrossRef] [PubMed]
  62. Singh, A. Studies on arbuscular mycorrhizal fungi associated with Jatropha curcas L. Mycorrhiza News 2006, 18, 12–14. [Google Scholar]
  63. Madhaiyan, M.; Peng, N.; Te Ngoh, S.; Hsin, C.; Lin, C.; Lin, F.; Reddy, C.; Yan, H.; Ji, L. Improvement of plant growth and seed yield in Jatropha curcas by a novel nitrogen-fixing root associated Enterobacter species. Biotechnol. Biofuels 2013, 6, 140. [Google Scholar] [CrossRef]
  64. Afzal, I.; Shinwari, Z.K.; Sikandar, S.; Shahzad, S. Plant beneficial endophytic bacteria: Mechanisms, diversity, host range and genetic determinants. Microbiol. Res. 2019, 221, 36–49. [Google Scholar] [CrossRef] [PubMed]
  65. Gupta, G.; Panwar, J.; Jha, P.N. Natural occurrence of Pseudomonas aeruginosa, a dominant cultivable diazotrophic endophytic bacterium colonizing Pennisetum glaucum (L.) R. Br. Appl. Soil Ecol. 2013, 64, 252–261. [Google Scholar] [CrossRef]
  66. Patel, D.; Saraf, M. Comparative study of different soil amendments and microbes for integrated nutrient management and growth promotion of Jatropha curcas. J. Plant Nutr. 2014, 37, 2209–2226. [Google Scholar] [CrossRef]
  67. Kumar, C.M.; Ghoshal, N. Variation in Soil physicochemical properties in dry tropics: Effect of land-use change. Archives 2017, 17, 1404–1410. [Google Scholar]
  68. Silva, E.; Alleoni, L.R.F.; Santos, S.; Magalhães, S.; Farnezi, M. Response of physic nut trees to liming of acidic soils. Commun. Soil Sci. Plant Anal. 2016, 47, 1023–1032. [Google Scholar] [CrossRef]
  69. Santos, A.A.; Agustini, J.A.; Maltoni, K.L.; Cassiolato, A.M. Addition of residues and reintroduction of microorganisms in Jatropha curcas cultivated in degraded soil. Rev. Bras. Eng. Agrícola E Ambient. 2016, 20, 372–377. [Google Scholar] [CrossRef]
  70. Butterly, C.R.; Wang, X.; Sale, P.; Li, G.; Tang, C. Liming effect of non-legume residues promotes the biological amelioration of soil acidity via nitrate uptake. Plant Soil 2021, 464, 63–73. [Google Scholar] [CrossRef]
  71. Ritchie, G.; Dolling, P. The role of organic matter in soil acidification. Aust. J. Soil Res. 1985, 23, 569–576. [Google Scholar] [CrossRef]
  72. Butterly, C.R.; Baldock, J.A.; Tang, C. The contribution of crop residues to changes in soil pH under field conditions. Plant Soil 2013, 366, 185–198. [Google Scholar] [CrossRef]
  73. Serpantié, G.; Ouattara, B. Fertilité et jachères en Afrique de l’Ouest. La Jachère En Afr. Trop. 2001, 2, 21–83. [Google Scholar]
  74. Medza Mve, S.D.; Mergeai, G.; Baudoin, J.-P.; Toussaint, A. Culture in vitro de Jatropha curcas L. Biotechnol. Agron. Société Environ. 2011, 15, 567–574. Available online: https://hdl.handle.net/2268/138817 (accessed on 18 September 2024).
  75. Jones, D.L.; Nguyen, C.; Finlay, R.D. Carbon flow in the rhizosphere: Carbon trading at the soil–root interface. Plant Soil 2009, 321, 5–33. [Google Scholar] [CrossRef]
  76. Bojórquez-Quintal, E.; Escalante-Magaña, C.; Echevarría-Machado, I.; Martínez-Estévez, M. Aluminum, a friend or foe of higher plants in acid soils. Front. Plant Sci. 2017, 8, 1767. [Google Scholar] [CrossRef]
  77. Boyer, J. L’aluminium échangeable: Incidences agronomiques, évaluation et correction de sa toxicité dans les sols tropicaux. Cah. ORSTOM Sér. Pédol. 1976, 14, 259–269. [Google Scholar]
Forests 15 01709 g001
Figure 1. Location of Akam Effak village (a) within the province of Woleu-Ntem (b) in northern Gabon, West Africa (c).
Figure 1. Location of Akam Effak village (a) within the province of Woleu-Ntem (b) in northern Gabon, West Africa (c).
Forests 15 01709 g001
Forests 15 01709 g002
Figure 2. Comparison of soil organic carbon concentrations between October 2019 and November 2022 after 40 months of growth of J. curcas at 0–10 cm (a) and 10–20 cm (b) depths on a tropical soil that has been previously cultivated intensively during 43 years for rubber and cacao production. Means associated with different letters differ significantly from each other at p < 0.10. Vertical bars represent mean standard error. The horizontal red line presents the values of undisturbed natural forest soil used as a reference.
Figure 2. Comparison of soil organic carbon concentrations between October 2019 and November 2022 after 40 months of growth of J. curcas at 0–10 cm (a) and 10–20 cm (b) depths on a tropical soil that has been previously cultivated intensively during 43 years for rubber and cacao production. Means associated with different letters differ significantly from each other at p < 0.10. Vertical bars represent mean standard error. The horizontal red line presents the values of undisturbed natural forest soil used as a reference.
Forests 15 01709 g002
Forests 15 01709 g003
Figure 3. Comparison of total soil nitrogen concentrations between October 2019 and November 2022 after 40 months of growth of J. curcas at 0–10 cm on tropical soil that has been previously cultivated intensively for 43 years for rubber and cacao production. Means associated with different letters differ significantly from each other at p < 0.10. Vertical bars represent mean standard error. The horizontal red line presents the value of undisturbed natural forest soil used as a reference.
Figure 3. Comparison of total soil nitrogen concentrations between October 2019 and November 2022 after 40 months of growth of J. curcas at 0–10 cm on tropical soil that has been previously cultivated intensively for 43 years for rubber and cacao production. Means associated with different letters differ significantly from each other at p < 0.10. Vertical bars represent mean standard error. The horizontal red line presents the value of undisturbed natural forest soil used as a reference.
Forests 15 01709 g003
Forests 15 01709 g004
Figure 4. Comparison of soil pH between October 2019 and November 2022 after 40 months of growth of J. curcas at 0–10 cm (a) and 10–20 cm (b) depths on a tropical soil that has been previously cultivated intensively during 43 years for rubber and cacao production. Means associated with different letters differ significantly from each other at p < 0.10. Vertical bars represent mean standard error. The horizontal red line presents the values of undisturbed natural forest soil used as a reference.
Figure 4. Comparison of soil pH between October 2019 and November 2022 after 40 months of growth of J. curcas at 0–10 cm (a) and 10–20 cm (b) depths on a tropical soil that has been previously cultivated intensively during 43 years for rubber and cacao production. Means associated with different letters differ significantly from each other at p < 0.10. Vertical bars represent mean standard error. The horizontal red line presents the values of undisturbed natural forest soil used as a reference.
Forests 15 01709 g004
Forests 15 01709 g005
Figure 5. Comparison of soil pH at 10–20 cm depth between the two types of propagation material used to grow J. curcas on tropical soil that has been previously cultivated intensively for 43 years for rubber and cacao production. Means associated with different letters differ significantly from each other at p < 0.10. Vertical bars represent mean standard error. The horizontal red line presents the values of undisturbed natural forest soil used as a reference.
Figure 5. Comparison of soil pH at 10–20 cm depth between the two types of propagation material used to grow J. curcas on tropical soil that has been previously cultivated intensively for 43 years for rubber and cacao production. Means associated with different letters differ significantly from each other at p < 0.10. Vertical bars represent mean standard error. The horizontal red line presents the values of undisturbed natural forest soil used as a reference.
Forests 15 01709 g005
Table 1. Effects of different sources of variation on soil organic carbon (C) and total soil nitrogen (N) concentrations and soil pH at 0–10 cm and 10–20 cm depth.
Table 1. Effects of different sources of variation on soil organic carbon (C) and total soil nitrogen (N) concentrations and soil pH at 0–10 cm and 10–20 cm depth.
C N pH
Source of VariationF ValuePr (>F)F ValuePr (>F)F ValuePr (>F)
0–10 cm depth
D0.330.72010.800.45651.4580.2458
M2.110.15541.140.29200.0030.9555
P21.370.00013.080.087219.4260.0001
D × M0.300.74120.970.38860.1060.9002
D × P0.360.69760.640.53471.6140.2134
M × P0.090.76470.740.39430.1770.6758
D × M × P0.050.95490.860.43330.1470.8642
10–20 cm depth
D0.5170.60100.8900.41850.9340.4024
M1.7200.19750.9300.34136.9280.0123
P47.4460.00012.6280.114254.2060.0001
D × M0.0320.96881.0740.35232.2630.1184
D × P0.1220.88450.9210.40681.7540.1875
M × P0.0960.75880.7720.38630.6880.4121
D × M × P0.0320.96871.0120.37320.8540.4343
D = planting distance; M = propagation material; P = period.
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Massoukou Pamba, R.; Poirier, V.; Nguema Ndoutoumou, P.; Epule, T.E. Growing Jatropha curcas L. Improves the Chemical Characteristics of Degraded Tropical Soils. Forests 2024, 15, 1709. https://doi.org/10.3390/f15101709

AMA Style

Massoukou Pamba R, Poirier V, Nguema Ndoutoumou P, Epule TE. Growing Jatropha curcas L. Improves the Chemical Characteristics of Degraded Tropical Soils. Forests. 2024; 15(10):1709. https://doi.org/10.3390/f15101709

Chicago/Turabian Style

Massoukou Pamba, Renaud, Vincent Poirier, Pamphile Nguema Ndoutoumou, and Terence Epule Epule. 2024. "Growing Jatropha curcas L. Improves the Chemical Characteristics of Degraded Tropical Soils" Forests 15, no. 10: 1709. https://doi.org/10.3390/f15101709

APA Style

Massoukou Pamba, R., Poirier, V., Nguema Ndoutoumou, P., & Epule, T. E. (2024). Growing Jatropha curcas L. Improves the Chemical Characteristics of Degraded Tropical Soils. Forests, 15(10), 1709. https://doi.org/10.3390/f15101709

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop