Next Article in Journal
Circularity in the New Gravity—Re-Thinking Vernacular Architecture and Circularity
Previous Article in Journal
A Novel Model Based on DA-RNN Network and Skip Gated Recurrent Neural Network for Periodic Time Series Forecasting
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Sustainability
Volume 14
Issue 1
10.3390/su14010324
sustainability-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

Changes in the Physico-Chemical Properties of Degraded Soils in Response to the ReviTec Approach Applied at Gawel (Far-North Cameroon)

by
Pascal Blaise Tchida
1,*,
Albert Ngakou
1,
Raimund Kesel
2 and
Hartmut Koehler
3
1
Department of Biological Sciences, Faculty of Sciences, University of Ngaoundere, Ngaoundere 454, Cameroon
2
KeKo—Kesel, Koehler & Partner, 28359 Bremen, Germany
3
Department of Ecology, University of Bremen, 28359 Bremen, Germany
*
Author to whom correspondence should be addressed.
Sustainability 2022, 14(1), 324; https://doi.org/10.3390/su14010324
Submission received: 10 November 2021 / Revised: 20 December 2021 / Accepted: 23 December 2021 / Published: 29 December 2021
Browse Figures
Versions Notes

Abstract

:
A heavily degraded hardé area in the community of Gawel (Extreme Nord) was rehabilitated with a ReviTec approach. To evaluate the efficiency of introduced plants for rehabilitation, the site was monitored with the BioSoilPlot experiment over two years during the dry and rainy seasons (January 2018/2019, June 2018/2019, respectively). ReviTec was applied to accelerate ecological succession and improve the establishment of vegetation on these degradation-prone sites (Gawel 1 and Gawel 2). Growth volume, height and percentage cover of the herbaceous plants and soil physical and chemical parameters were assessed. Growth volume increased in both sites between 2018 and 2019 with Pennisetum pedicellatum exhibiting the highest values (Gawel 1: 3.41 dm3/m2 and 3.50 dm3/m2; Gawel 2: 3.47 dm3/m2 and 3.62 dm3/m2). Bunds were suitable for herbaceous growth, Sesbania sesban having the highest growth height (Gawel 1: 1.91 cm and 1.95 cm; Gawel 2: 1.95 cm and 1.97 cm) and Pennisetum pedicellatum the best percentage cover (Gawel 1: 53% and 58.33%; Gawel 2: 40.67% and 56.67%). Soil changed from sandy and strongly acid to clay-loam and slightly acid at Gawel 1, and from sandy and strongly acid to clay-loam and alkaline at Gawel 2. Soil water content and soil nutrient had increased within the ReviTec site compared to the outside with the application of compost-biochar-mycorrhiza treatment as the most promising over the two years of monitoring. Such results suggest that ReviTec approach can be used in sustainable restoration of soil hardé.

1. Introduction

Soil is a vital and indispensable resource on which development, independence, food security, economic growth and sustainability of any nation depends [1]. Thus, sustainable land use and protection of soils play a key role in food, climate, and human security [2]. Fertile soils are a non-renewable resource by human time spans as their formation and renewal could take hundreds, if not thousands of years [3]. For this reason, the human management of soil resources will have wide-ranging consequences on human security for generations to come [4]. Despite this, land degradation has become a global problem occurring in most terrestrial biomes and agro-ecologies in both low income and highly industrialized countries [4]. Globally, it is estimated that about one fifth of Earth’s land area (more than 2 billion hectares) is degraded, including more than half of all agricultural land [5], affecting more than a billion people all over the world [6]. Africa is the most affected, with about 46% of degraded areas and at least 485 million (65%) people affected [7]. Sub-Sahara Africa, especially the Sahel area is experiencing a constantly growing environmental degradation characterized by more than 65 percent of agricultural land degraded [8]. In Cameroon, about 25% of the surface area belongs to arid land and is undergoing soil deterioration. This degraded land with sol hardé is dispersed throughout the Far North region of Cameroon [9,10,11] and affect the livelihoods and well-being of the poorest households [12]. Sol hardé borrowed from the Fulfulde language, which commonly designates any land that is not very suitable for cultivation [13] is characterized by a massive and compact sandy clay surface, covered with a thick film of beating. The need to prevent further land degradation and to rehabilitate degraded lands is especially important now because the demand for accessible productive lands is increasing with an increase in the human population and consequent increased food consumption [14].
Despite the urgent need for preventing and reversing land degradation, the problem has yet to be appropriately addressed [15]. Various remediation technologies are being used for restoration of natural resources but most of them have additional impacts and are not ecologically safe [14]. Even policy actions for sustainable land management remain inconsistent and often ineffective [16]. Such technologies and policy frameworks to combat land degradation need to be supported by evidence-based and action-oriented research [17]. The past studies on land degradation had played a useful role in highlighting land degradation as a globally critical issue. However, most of them tended to focus only on simpler relationships, such as soil erosion and its impact on crop yield, while ignoring the broader values of land ecosystem services, various off-site and indirect costs in their analytical frameworks [18]. Therefore, ambitious reforestation programs aimed at restoring the degraded ecosystem in Sudano–Sahelian savannah through reforestation activities; sensitization were initiated by the Cameroon Government [19] and NGOs (“Green-Sahel” operation in 2008) to revitalize these degraded lands and convert it step by step into more productive lands. The losses from land degradation include not only environmental degradation cost measured directly on-site (e.g., soil loss and nutrient depletion), but also the cost of indirect and off-site environmental impacts (e.g., siltation of water bodies, water pollution, and biodiversity declines) [20].
To help efficiently combatting soil degradation and desertification, the soil and vegetation environmentalists of KeKo—Kesel, Koehler and Associates Biologists and the Centre for Environmental Research and Sustainable Technology (UFT) at the University of Bremen developed an ecological approach of revitalization technology called ReviTec [21]. This technology is based on experience from long-term ecological research [22]. It aims at rehabilitating essential ecosystem services of soil to allow for adapted forestry, pastures and agriculture. This eco-technology is a widely applicable tool for the initiation and acceleration of ecological succession with a mosaic-type exposure of a special substrate mixture which may be filled in biodegradable bags for erosion control [23]. The substrate consists of soil (e.g., excavation materials) and composts enhanced with locally available amendments to improve water holding capacity and nutrient status. Bio-activation with site-specific soil biota is important, including mycorrhiza fungi. Purposive sowing and planting of target and nurse plants complete the activation. The ReviTec bags can be flexibly exposed to the topography and modularly arranged in structures, such as small islands, bunds, demi-lune (half-moons), etc. These micro-topographies provide safe sites for natural colonization and function as collectors for sediment, water, and biota, and subsequently disperse these to the surrounding [24]. The concept covers three levels of scale with diverse functions. The basic model is a bag made of degradable fabric, filled with substrate (30 L) specifically amended with abiotic and biotic elements (bio-activation) to initiated and accelerated ecological succession [24]. The bags protected the substrate and promoted initial erosion control [25]. In Cameroon, three teaching, research and demonstration sites have been implemented since 2012 for the rehabilitation of soil hardé at Maroua (Salak, Boula-Mokong and Gawel) in the Far North.
Several rehabilitation trials of this type of soil have been undertaken through government actions as well as NGOs. But these have increased their limits because they are less suitable with unsatisfactory results. ReviTec technology, which combines both traditional (Zai, bund, planting hole, etc.) and scientific methods, has, on the other hand produced very satisfactory results in time and space.
The objective of this work was to identify and analyze of main mechanisms underlining the impact of the ReviTec approach in the success of vegetation (grass, herbs). We hypothesized that ReviTec structures soften soil hardé, provide “safe sites” and are favorable for the development of soils organisms. Measuring dynamic soil properties, such as soil organic carbon, soil structure, nitrogen, and water-holding capacity can be used both to compare the efficacy of different introduced organisms (vascular plants-grasses, effective mycorrhiza and soil amendments with the ReviTec substrates: Biochar, compost, matrix) in different sites.

2. Materials and Methods

2.1. Study Area and Treatments

The study areas were located in the Far North Region of Cameroon. It extends globally between 10°23′05″ and 10°42′00″ North and between 14°03′27″ and 14°21′00″ East [26]. Specifically, the study was carried out on the highly degraded lands (soil hardé) in the two experimental ReviTec sites Gawel1 (GW1: 10°40′536″ N, 14°10′256″ E, 475 m asl) and Gawel2 (GW2: 10°39′076″ N, 14°09′121″ E, 492 m asl), of Gawel locality (department of Diamare) in the Far North-Cameroon (Figure 1) located in the semi-arid dry land region and belonging to the Sudano–Sahelian agroecological zone. This zone is characterized by a mean annual rainfall between 500 and 900 mm [27]. Specifically, Gawel has an annual rainfall of 841 mm with a mean annual temperature of 27.7 °C (Figure 2). The two sites having respectively 5 ha and 27 ha.
For monitoring of vegetation (only herbaceous because almost all trees planted on structures died by suffocation) and soil parameters, six BioSoilPlots (BSP) were used (3 for both sites). This tool (BSP) enables monitoring of ReviTec activities over numerous years. A BSP consists of three circles with different radius and different measurements made in it: Inner circle (3 m radius, 30 m2), middle circle (11 m radius, 400 m2) and large circle (25 m radius, 2000 m2). BSP is centered to a ReviTec structure (midpoint of half-mount, bund or island); center points of the BSP have to be marked with a durable label (stick of steel, hit into soil, with label of number weld on) and estimate GPS coordinates of this midpoint; BSP have to be distributed more or less regularly over the site, but they should represent the relevant vegetation of the site and should include as many tree species as possible; the plots should not overlap; BSP, in summary, cover 10% of the whole site (Figure 3).
The ReviTec site of Gawel was installed to combat degradation with ReviTec structures (Figure 3) and specific treatment. The applied treatment includes loamy sand plus compost (made from aero anaerobic decomposition of cow dung and plant material) mixed with additive elements such as mycorrhiza and biochar (provided by GIZ project SFID at Mbang), all filled in the bags. All bags were amended with Brachiaria and Pennisetum seed. For the six monitored BSP, a total of 614 bags were applied to build ReviTec structures: Islands (64), Bund (310), Demi-lunes (240); only the latter two were analyzed (islands were not representative; there were only two island structures at GW1). To build a structure, we needed four bags for Island, ten bags for Bund and five bags for Demi-lunes. These structures have advantages of the water harvesting and runoff directing for the growth and survival of the vegetation.
The monitored vegetation includes Brachiaria brizantha, Pennisetum pedicellatum (seed were introduced) Sesbania sesban and Boreria chaetocepha (established spontaneously with time). Our design consists of compost, biochar and mycorrhiza (cpbcmy) treatment applied on structures and two controls (ctrl 1: out of ReviTec fence without vegetation (outside the ReviTec site) and ctrl 2: planting hole (out of structure) inside the ReviTec without bags and any substrate) (Table 1).

2.2. Sampling

The data collection was organized in two repetitions per year, one in the dry season and the other in the rainy season. The first collection was carried out in 2018, in January, in the middle of the dry season, and in July, in the beginning of the rainy season, while the second was carried out in 2019 during the same months as those of the first monitoring.
At each site (GW1 and GW2), grass and herbs species distributed on structures within three plots, known as BioSoilPlot (BSP), each representing a replication (Figure 4), were observed at each monitored period (Figure 5).
Eight (08) structures randomly selected (Bund and Demi-lune) in plots were assessed for data collection. A total of 48 structures were selected and investigated randomly (Table 2).

2.3. Assessment of Grass Growth

Parameters evaluated were height, percentage cover of the four grasses of each BioSoilPlot. Growth height in cm was measured with a decameter. Percentage cover of each species was estimated with direct observation. These parameters allow one to calculate the growth volume as follows:
Growth volume [dm3/m2] = percentage cover × mean growth height [cm]/10 [29].
Growth volume is an indicator for the overgrown 3D space as an easy to assess roughness parameter.

2.4. Assessment of Soil Characteristics

2.4.1. Soil Sampling

Soil samples were collected within the BioSoilPlot (in one hand in the bags and in another hand outside of structures) and outside of the ReviTec site (near the fence). As our soils are hard, a ‘V’ shape cut up to 15 cm depth was made. Soil of the pit was removed from the surface up to a 15 cm depth from both sides using a hand auger. This scraped soil was collected in a plastic bowl. This sample was known as the ‘primary’ sample. Such primary samples should be approximately the same weight. After collecting at least 30–35 primary samples per treatment, we mixed all the samples in a plastic bowl thoroughly and drew about ½ to 1 kg composite sample by a quartering method. Samples in the bowl were labelled and divided into approximately 4 equal parts. Two opposite portions of samples were discarded, while the remaining 2 portions were again thoroughly mixed and again divided in to 4 equal parts and 2 opposite parts again discarded. This procedure continued until ½ to 1 kg of the sample remained in the bowl. This was known as the composite sample, which was a true representative of the area. The airtight containers of polythene bags 6 × 9″ made of film about 0.13 mm thick, which was sealed by twisting or tying the neck or by means of rubber bands or adhesive tape, which were used to contain soil samples. These samples were dried, broken and sieved (2 mm) before laboratory analysis. These prepared soil samples were used for the following analyses.

2.4.2. Soil Texture

The relative mass of sand, silt and clay in the soil sample (thus, the texture) was determined by the method proposed by David, Wilson and Card [30]. Soil was spread and air-dried on a newspaper. Gravel, stones, trash and roots were removed and aggregates were crushed. Soil was then filled in a tall slender jar (like a quart jar) ¼ full. Water was added until the jar was ¾ full and a teaspoon of powdered, non-foaming dishwasher detergent was added. The jar was sealed with a tight-fitting lid, shaken manually for 10 to 15 min to break the soil aggregates, and then left undisturbed. Soil particles settled by gravity according to size. After 1 min, the depth of the sand fraction was marked on the jar, after 2 h the depth of silt, and after 2–3 days, when the water was clear, the depth of the clay fraction, was marked. The depth of the three fractions was measured in mm and respective percentages were calculated in relation to total depth. These values were used to determine the soil texture class with the United States Department of Agriculture (USDA) soil texture triangle.

2.4.3. Soil Water Content

We determined soil water content gravimetrically [31]. Eight grams of composite sub sample of soil was taken to the lab for accurate weighing with weigh boats. After weighing fresh mass, the soil was dried in an oven for over twenty-four hours at 105 °C and reweighed repeatedly until the mass ceased to change.
Water content (g): WC (g) = FM − DM
Percent water content (% DM): WC (%) = 100 × WC (g)/DM
FM = fresh mass (g); DM = dry mass (g).

2.4.4. Soil Chemical Factors

Soil Organic Carbon (SOC)

SOC content was determined using the Walkley–Black wet oxidation method with K2Cr2O7 [32]. 10 mL of 1N K2Cr2O7 and 20 mL conc. H2SO4 (containing Ag2SO4) were added to 1g dry mass of soil and then thoroughly mixed. The reaction was allowed to proceed for 30 min. The reaction mixture was diluted with 200 mL water and 10 mL of NaF solution and 2 mL of diphenylamine were added and then filtered. The solution was titrated with standard FAS [Fe (NH4)2 (SO2)2] to a brilliant green color. The blank without soil was run simultaneously.
SOC   ( % ) = 10 blank   ( blank − Reading ) × 0.003 × 100 DM
SOC = soil organic carbon, DM = dry mass of soil (105 °C).

Soil pH

Soil pH was measured potentiometrically with a calomel electrode in a mixture of soil:water at a ratio of 1:2.5 m/m [33].

Total Nitrogen (N)

Total nitrogen concentration was determined using the Kjeldahl digestion method [34]. Steam distillation with NaOH after Kjeldahl digestion of 1g of soil with H2SO4 and K2SO4-catalyst mixture. Ammonia liberated by steam distillation was collected in boric acid-indicator solution and determined by titration with 0.02N sulphuric acid. Simultaneously; blank sample (without soil) was run.

Phosphorus (P)

The Olsen method of extraction and the ascorbic acid method of analysis were used to estimate extractable soil phosphorus [35]. 2.5 g grams of soil (DM) were extracted with 50 mL of 0.5M NaHCO3. The extract was filtered and a 5 mL aliquot was taken to develop the color by the ascorbic acid method. Once developed, the color was read on a spectronic 20 at 880 nm.

Potassium (K)

Potassium in all soils was extracted using the ammonium acetate procedure [35]. Five grams of soil were extracted with 25 mL of 1N NH4OAc (Ammoniumacetate) for five minutes. The extracts were filtered through Whatman No. 1 filter paper and measured with a flame photometer (FP 8400, A. KRUSS Optronic, Hamburg, Germany) after calibration.

2.5. Statistical Analysis

Data were analyzed separately for growth volume, height, soil water content, organic carbon, organic matter content, total nitrogen, extractable phosphorous and potassium. All data concerning herbaceous species were log transformed in order to normalize them.
For all above mentioned data except growth volume, where Kruskal–Wallis test + pairwise U-test was applied, Test of distribution and then analysis of variance (ANOVA) was conducted using the XLStat version 2016 with the following model of analysis: Yijk = u + Si + Yj + eijk. where: Yijk is the dependent variable (e.g., carbon), u is the overall mean, Si is the effect of treatment or species, Yj is the effect of year and eijk is the random error.
Statistical differences between means were assessed using the Tukey range test.

3. Results and Discussion

3.1. The Growth Volume of Grass Species

Between the two monitoring periods 2018/2019 at GW1, growth volume significantly decreased between years for B. brizantha (p = 0.018) or increased for P. pedicellatum (p < 0.0001) and S. sesban (p < 0.0001). On the opposite, no significant difference was observed in the growth volume of B. chaetocepha (p = 0.12) between years 2018 and 2019. During the first monitoring in January, all grass species were dried (growth volume = 0) which is why this month was not represented in the table; with the time, they started to regrow. Growth volume varied from 0.00 dm3/m2 in January for all species, at 3.41 dm3/m2 in July 2018 and 3.50 dm3/m2 in July 2019 for P. pedicellatum, 2.90 dm3/m2 in July 2018 and 3.06 dm3/m2 in July 2019 for S. sesban and 2.51 dm3/m2 in July 2018 and 2.71 dm3/m2 in July 2019 for B. chaetocepha. Contrary to those, B. brizantha showed an important decrease in growth volume, with a significant variation from 3.32 dm3/m2 in July 2018 to 1.68 dm3/m2 in July 2019. This could justify the reduction of the growth volume of B. brizantha from years 2018 to 2019.
There was a significant difference in growth volume between all the different species during the same month of monitoring with (p < 0.0001) in July 2018 and (p = 0.002) in July 2019.
At the GW2 ReviTec site, growth volume of P. pedicellatum, S. sesban and B. chaetocepha increased with time, but B. chaetocepha did not exist in this site in July 2018, while B. brizantha considerably decreased in growth volume. In January, all species were dried (no growth volume of fresh mass) as in GW1; however, in July all grass species were fresh and colonized the structures. Growth volume varied from 0.00 dm3/m2 in January for all species, at 3.47 dm3/m2 in July 2018 and 3.62 dm3/m2 in July 2019 for P. pedicellatum, 2.78 dm3/m2 in July 2018 and 3.02 dm3/m2 in July 2019 for S. sesban, 0.00 dm3/m2 in July 2018 and 2.35 dm3/m2 in July 2019 for B. chaetocepha and 3.25 dm3/m2 in July 2018 to 2.74 dm3/m2 in July 2019 for B. brizantha. The p-value of all these species was very significant (p < 0.0001) when compared to their variation in growth volume between different months of monitoring and even between the same months of monitoring.
Our finding supposed that, despite this high growth volume at the beginning of the survey, B. brizantha seemed to have the ability to grow very fast, but with low adaptability to drought. This decrease of B. brizantha seemed to show that its disappearance with time could be explained by the fact that it was an introduced species, used to initiate and accelerate ecological succession. After ecosystem services were achieved, it seems that native species started to recolonize the different sites. This very fast colonization could be due to the short rainy season that characterizes Sahelian zones. Herbaceous species are mainly annual plants reported to survive drought by modifying their life cycle [36]. It is why, in these sites, growth volume of each species recorded for our study significantly varied with time (Table 3). P. pedicellatum and S. sesban were the most colonized species. Similar results were observed by Barbier et al. [37] in the context of increase in yield, who reported that the dominant crops are millet and sorghum due to building stone bounds in the fields to capture runoff and reduce erosion during the short rainy season in the Sahel, thus indicating the effectiveness of ReviTec to accelerate ecological succession.

3.2. Effect of Structures on Growth Height of Herbaceous Species in Both Sites

3.2.1. Development of Growth Height of Herbaceous Species

Table 4 summarizes data on difference in growth height between Bu and DL at GW1 and GW2 during the survey. It is indicated in Table 4 that growth height of all species was strongly influenced by structures at the GW1 site, with better growth on Bu than on DL during the different monitoring periods, except B. brizantha in July 2018, for which no significant different was perceived (p = 0.856). However, at GW2 site, growth height did not seem to be influenced by structures for almost all the species except S. sesban and B. brizantha that were strongly influenced by structures in July 2018 than in July 2019, although no significant difference was perceived for B. brizantha in July 2019. S. sesban and B. brizantha developed better on Bu than DL. At GW1 or GW2, Bu seemed to have been suitable for herbaceous growth, even if the differences were sometimes not significant. Similar result was observed by Ponce-Rodríguez et al. [38] who highlighted the importance of the effect of stone bunds on the growth of herbaceous vegetation. According to Klik et al. [39], the areas near the stone bunds offer better conditions for the development of the vegetation due to the retention of solids and the accumulation of mulch (organic matter, litter, etc.) which is dragged towards the stone bunds. In many cases the genetic aspect of these differences was known for many years as in the case of certain mutants [40]. As the soil water content was weak, it may impact on the plant growth according to the theory that says that plant growth is related to the tenacity with which water is held by the soil [41].

3.2.2. Development of Growth Height and Cover of Herbaceous

Figure 6a,b summarizes the variation in growth height according to percentage cover on Bu and DL at the GW1 and GW2 sites during the survey. Figure 6 reveals that growth height varied depending on the site, structure and species. Almost all the herbaceous species showed a decrease in growth height during the whole monitoring periods, except for B. chaetocepha, for which growth height had increased in both sites on Bu and DL. The best growth height was observed with S. sesban and P. pedicellatum in both sites on Bu and DL. Either at Gw1 or GW2 sites, percentage cover increased for all the herbaceous species on different structures. P. pedicellatum showed the best proportion of growth cover. It seems to be the dominant and most adapted species on Bu and DL in both sites.
There was a substantial and stable difference between species in the patterns of development strategies. The reliability of these differences from season to season and species to species indicates that they result from different inherited strategies of plant growth [42].

3.3. Influence of ReviTec Treatment on Soil Texture and pH

Table 5 indicates that soil texture and pH were strongly influenced by ReviTec treatment (cpbcmy) at both sites compared to ctrl 1 (p < 0.0001). At GW1 or GW2 ReviTec site, soil texture outside ReviTec site was sandy and their pH were acidic, as described by Seiny-Boukar [36]. It remained unchanged during the survey. The soil of Gawel was naturally degraded and characterized by a very thin layer of humeferous surface horizon which covers a fairly compact soil layer (2–20 cm to 30 cm) impermeable to water, which inhibits the growth of roots [9], is acidic (5 < pH < 6) and is deprived of exchangeable bases (CEC = 5–10 meq/100 g) [26]. Thus, without any activity, it will remain unchanged, confirming why we observed the stability of soil texture in the control area (ctrl 1) either at GW1 or GW2. This could be due to the coarse soil texture that hinders soil aggregation. Duong, Penfold and Marschner [43] found that, in sandy soils with less than 13% clay, such improvements were not possible.
Within the ReviTec sites, there were variations of these parameters with time. Few differences in texture were observed on cpbcmy treatment compared to control (ctrl 2), but the highest variation of soil texture was observed on cpbcmy treatment. Soil pH on these two plots was alkaline at GW1 and GW2. Substrate filled in ReviTec bags in addition with the activity of soil organisms attracted by the earlier vegetation established on structures contributed to the modification of soil texture and pH, thus improving soil quality and CEC. Substrates used in ReviTec such as compost, mycorrhizae and biochar might have influenced the soil particles by binding them together, as was demonstrated by Duong, Penfold and Marschner [43] who reported that organic amendments improve aggregate stability directly by binding of clay and indirectly by increasing microbial activity and the production of binding agents. One of the main strategies of the ReviTec approach is to improve biodiversity by attracting beneficial organisms such as ants and termites. These organisms are known to be the ecosystem engineers as they ensured greater mineralization of clay and silt that permitted high biogenic structures of soil [44].

3.4. Influence of ReviTec Treatment on Soil Moisture Content

Figure 7 illustrates the influence of ReviTec treatment on soil moisture content at GW1 and GW2 ReviTec sites. It can be seen from this figure that soil moisture was very high in July. This might be due the downward movement of water at the beginning of the rainy season. There was a pronounced difference in soil water content between treatment and controls of both sites. Soil moisture inside the ReviTec site was higher than outside during all the different monitoring periods in both sites. This difference could be due to the sandy soil texture of ctrl 1. It is known that this class of soil is characterized by low water holding capacity [45]. Furthermore, the plots containing cpbcmy treatment had more water than ctrl 2; however, both had a positive effect on water content. The higher value of water content on the plot with cpbcmy treatment could be explained by the fact that soil texture clearly changed with cpbcmy addition. This change in texture could be explained by the effect of the migration of particles trapped by the structures attributable to hydrological processes such as heavy rains, infiltration, and preferential flow [46]. Usually, in the Sahel, precipitation is accompanied by strong north-easterly winds [47], which diverts raindrops from their vertical trajectory [48], so that the windward sides of microdunes receive more rainwater per unit area and are more subject to splash. Splashes preferentially transfer soil particles downhill, which prevents crust development and maintains good water infiltrability [46]. The addition of clay to sandy soils has been reported to increase water and nutrient holding capacity for sandy soil [49,50,51] due to the high binding capacity of clay and therefore could also reduce nutrient leaching from compost.
Soil texture and soil organic matter (SOM) seem to be the key components that determine soil water holding capacity. This result disagreed with that of other authors who found significant effects of composts on several physical properties of coarse-textured soils (bulk density, porosity, infiltration rates, saturated hydraulic conductivity), but no effects on soil water retention [52,53]. Surface area is a very important soil characteristic, as it influences all of the essential functions of fertility, including water, air, nutrient cycling and microbial activity. The limited capacity of sandy soil to store water and plant nutrients is partly related to the relatively small surface area of its soil particles [54]. Coarse sands were said to have a very low specific surface of about 0.01 m2g–1, and fine sands about 0.1 m2 g–1 [54].

3.5. Influence of ReviTec Treatment on SOC and N

Evaluation of the ReviTec treatment on soil C and soil N data from cpbcmy compared to ctrl 1 and ctrl 2 in Table 6 revealed that one of the major soil fertility constraints of sub-Saharan Africa is low inherent nutrient reserve as previously reported [55]. For instance, soil nutrient inside the ReviTec site was higher than outside during all the different monitoring periods at both sites. As expected, this difference could be attributed to the sandy soil texture of ctrl 1 characterized by low water holding capacity [45] and where organic matter decomposition is constrained by unfavorable conditions for microbial activity [56,57,58]. However, plots with cpbcmy treatment had more nutrients than ctrl 2; however, both had a positive effect on water content compared to ctrl 1. In these plots, the positive effects of organic amendments on aboveground phytomass have been attributed to increases in soil microbial activity and nutrient availability [59,60,61]. However, results could also be influenced by higher water availability due to increased SOM. Then, the effects of organic amendments on plant biomass would depend on the balance between nutrient (especially nitrogen and carbon) and water supply.
Composts were reported to have major effects not only on soil physical, but also on soil chemical property [62,63]. As expected, compost treatment significantly increased SOC content compared to controls. Several studies have indicated that compost and biochar amendment increase SOC and N content [64,65]. However, total N content was higher in cpbcmy treatment compared to controls. This increase of total N may be due to the sorption potential of biochar that reduced N mineralization and leaching [66]. Our finding is in accordance with Laird et al. [67] who found that biochar amendments significantly increased total N value in soil or the ability of mycorrhiza to mobilize nutrients, including N in the soil [68]. The ratio C/N is generally favorable for mineralization processes supporting the development of belowground biomass and of the subsequent food web.
The persistence of SOC is related to the content of reactive mineral particles such as clay and silt that contribute to SOM stabilization, physical protection from decomposers and soil structure formation [69,70]. In sandy soils, these processes are much less effective, and the persistence of added SOC was reported to be more related to the degradability of the organic matter itself [53,57,71]. This depends on the composition of the original materials used for composting, i.e., the amount and proportion of recalcitrant C [72], and whether the final product was screened, as unscreened composts rich in slowly decomposable C were often recommended to enhance infiltration into compacted soil and reduce evaporation of soil water [73,74].

3.6. Influence of ReviTec Treatment on Soil Extractable P and Exchangeable K

Table 7 illustrates the influence of ReviTec treatment on soil extractable P and exchangeable K at GW1 and GW2 ReviTec sites and indicated that all these elements were higher in July than in January (Table 7). This might be due the downward movement of water at the beginning of the rainy season. Soil-extractable P and exchangeable K increased significantly inside the ReviTec and clearly changed with Cpbcmy addition, which still had visible residual organic materials on the surface after four years of application. Duong et al. [42] pointed out that organic amendments improve aggregate stability directly by binding of clay and indirectly by increasing microbial activity and the production of binding agents. However, they found that in sandy soils with less than 13% clay, such improvements were not possible. The influence of biochar on microbial populations in soils could not be neglected. It should be noted that soil microbial biomass commonly increases with increasing clay content, as reported by several authors [75,76,77], and this response is generally attributed to the increased surface area [76]. Surface area is a very important soil characteristic, as it influences all of the essential functions for fertility, including water, air, nutrient cycling and microbial activity. The higher surface areas of finer-textured soils can result in increased total water content and improved physical protection from grazers.

4. Conclusions

The ReviTec approach, which combines both traditional (Zai, bund, planting hole, etc.) and scientific methods, has produced very satisfactory results concerning the rehabilitation of soil hardé. ReviTec, as it is embedded in an ecosystem approach, can be adapted as soft eco-technology to the specific needs of a degraded or degradation-prone area. At Gawel sites, soil was considered as hardé or degraded vertisols, almost bare and uninhabited by soil organisms before the implementation of ReviTec. At the end of each survey in July, all the spaces either at GW1 and GW2 sites were covered by herbs, but with some bare spaces still observed. The results show considerable differences in the performance of soil parameters. Treatment within the ReviTec context significantly affected the physical and chemical soil properties, such as pH, texture, water content, available P, available K, total nitrogen content and carbon content. Referring to outside (ctrl 1), soil changed from sandy and strongly acidic to clay-loam and slightly acid at GW1, and from sandy and strongly acidic to clay-loam and alkaline at GW2. Substrate filled in ReviTec bags influenced the soil particles by binding them together and improved aggregate stability directly by the binding of clay and indirectly by increasing microbial activity and the production of binding agents. Soil water content and soil nutrient (N, P) content increased inside the two ReviTec sites compared to outside (ctrl 1). Maximum values were obtained with the cpbcmy amendment. ReviTec structures revealed their capacity to improve soil quality. Thus, the ReviTec approach can be used for sustainable restoration of soil hardé. With these results, Cameroon, with the support of national and international organizations, can rely on this ecotechnology to restore their degraded land to be in step with sustainable development.

Author Contributions

Conceptualization, P.B.T.; Formal analysis, P.B.T. and R.K.; Funding acquisition, H.K.; Investigation, P.B.T.; Methodology, R.K.; Project administration, H.K. and R.K.; Supervision, A.N., H.K. and R.K.; Validation, A.N. and H.K.; Visualization, A.N.; Writing—original draft, P.B.T.; Writing—review & editing, P.B.T., A.N., H.K. and R.K. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data available on request due to restrictions e.g., privacy or ethical. The data presented in this study are available on request from the corresponding author. The data are not publicly available due to the non-existence of a link at the moment.

Acknowledgments

Special thanks go to GIZ for their support and the facilities offered during my several trips to the ReviTec site of Gawel. GIZ was very helpful and cooperative during the many phases of the study, including the work for the trenches and pits for the soil characterization study. We acknowledge DAAD (German Academic Exchange Service) for their commitment to maintain the partnership between the University of Ngaoundere (Cameroon). Many thanks go to the University of Bremen (Germany), particularly the SUUB (State and University Library Bremen) for financial support of this publication. The authors are thankful to Juliane Filser and Thomas Buse for their excellent collaborations.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Lal, R.; Bouma, J.; Brevik, E.; Dawson, L.; Field, D.J.; Glaser, B.; Hatano, R.; Hartemink, A.E.; Kosaki, T.; Lascelles, B.; et al. Soils and sustainable development goals of the United Nations: An International Union of Soil Sciences perspective. Geoderma Reg. 2021, 25, e00398. [Google Scholar] [CrossRef]
  2. Montanarella, L.; Panagos, P. The relevance of sustainable soil management within the European Green Deal. Land Use Policy 2020, 100, 104950. [Google Scholar] [CrossRef]
  3. Dror, I.; Yaron, B.; Berkowitz, B. Microchemical contaminants as forming agents of anthropogenic soils. Ambio 2017, 46, 109–120. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  4. Nkonya, E.; Mirzabaev, A.; von Braun, J. Economics of Land Degradation and Improvement: An Introduction and Overview. In Economics of Land Degradation and Improvement—A Global Assessment for Sustainable Development; Nkonya, E., Mirzabaev, A., von Braun, J., Eds.; Springer: Cham, Switzerland, 2016; pp. 1–14. [Google Scholar] [CrossRef] [Green Version]
  5. UNCCD. Concept Note High-Level Dialogue on Desertification, Land Degradation and Drought 20 May 2021; United Nations Headquarters: New York, NY, USA, 2021; p. 5. [Google Scholar]
  6. IPCC. Special Report on Climate Change, Desertification, Land Degradation, Sustainable Land Management, Food Security, and Greenhouse Gas Fluxes in Terrestrial Ecosystems; IPCC: Geneva, Switzerland, 2019; p. 906, in press. [Google Scholar]
  7. AGNES. Land Degradation and Climate Change in Africa, March, 2020; Policy Brief No. 2; AGNES: Nairobi, Kenya, 2020; p. 8. [Google Scholar]
  8. UNEP. Pan-African Agenda on Ecosystem Restoration for Increased Resilience; UNEP: Nairobi, Kenya, 2018; p. 38. [Google Scholar]
  9. Gavaud, M. Harde Soil of Nord-Cameroon (halomorph soils, leached soils, planosoils, hydromorph soils). Setting up of references. In Bull. Liais. thème B No 2; ORSTOM: Paris, France, 1971; pp. 55–88. [Google Scholar]
  10. Brabant, P.; Gavaud, M. Soils and earth resources of Northern-Cameroon (North and Far-North Provinces). In Map and Explanatory Note No 103; ORSTOM: Paris, France, 1985; p. 369. [Google Scholar]
  11. Peltier, R. The Hardé Lands: Characterization and Rehabilitation in the Lake Tchad Basin; CIRAD-Forest: Montpellier, France, 1993; p. 125. [Google Scholar]
  12. Nachtergaele, F.; Petri, M.; Biancalani, R.; Van Lynden, G.; Van Velthuizen, H. Global Land Degradation Information System (GLADIS). Beta Version. An Information Database for Land Degradation Assessment at Global Level. Land Degradation Assessment in Drylands Technical Report, No. 17; FAO: Rome, Italy, 2010; p. 14. [Google Scholar]
  13. Vaille, J. Essais de mise en valeur des sols « hardés » du Nord-Cameroun. Agron. Trop. 1970, 25, 472–490. [Google Scholar]
  14. Ahmad, Z.; Imran, M.; Qadeer, S.; Hussain, S.; Kausar, R.; Dawson, L.; Khalid, A. Biosurfactants for Sustainable Soil Management. Agron. Trop. 2018, 150, 81–130. [Google Scholar] [CrossRef]
  15. Lal, R.; Safriel, U.; Boer, B. Zero Net Land Degradation: A New Sustainable Development Goal for Rio+20. A Report Prepared for the Secretariat of the United Nations Convention to Combat Desertification; UNCCD: Bonn, Germany, 2012; p. 32. [Google Scholar]
  16. Nkonya, E.; Gerber, N.; Baumgartner, P.; von Braun, J.; De Pinto, A.; Graw, V.; Kato, E.; Kloos, J.; Walter, T. The Economics of Desertification, Land Degradation, and Drought Toward an Integrated Global Assessment; ZEF Discussion Papers on Development Policy 150; ZEF: Bonn, Germany, 2011; p. 184. [Google Scholar]
  17. Von Braun, J.; Gerber, N.; Mirzabaev, A.; Nkonya, E. The Economics of Land Degradation; ZEF Working Paper Series 109; ZEF: Bonn, Germany, 2013; p. 35. [Google Scholar]
  18. Nkonya, E.; von Braun, J.; Mirzabaev, A.; Le, Q.B.; Kwon, H.Y.; Kirui, O. Concepts and Methods of Global Assessment of the Economics of Land Degradation and Improvement. In Economics of Land Degradation and Improvement—A Global Assessment for Sustainable Development; Nkonya, E., Mirzabaev, A., von Braun, J., Eds.; Springer International Publishing: Bonn, Germany, 2015; pp. 15–32. [Google Scholar]
  19. MINEPDED. National Biodiversity Strategy and Action Plan—Version II; MINEPDED: Yaounde, Cameroon, 2012; p. 169. [Google Scholar]
  20. Foley, J.A.; DeFries, R.; Asner, G.P.; Barford, C.; Bonan, G.; Carpenter, S.R.; Chapin, F.S.; Coe, M.T.; Daily, G.C.; Gibbs, H.K.; et al. Global consequences of land use. Science 2005, 309, 570–574. [Google Scholar] [CrossRef] [Green Version]
  21. Koehler, H.; Warrelmann, J. Further Development of the Revitalization Technology ReviTec for Degraded Soil (Project Report RevitTal05 No. FV 172); University of Bremen: Bremen, Germany, 2007; p. 84. [Google Scholar]
  22. Koehler, H.; Melecis, V. Long-Term observations of soil mesofauna. In Long Term Ecological Research: Between Theory and Application; Muller, F., Baessler, C., Schubert, H., Klotz, S., Eds.; Springer: Heidelberg, Germany, 2010; pp. 203–220. [Google Scholar]
  23. Kesel, R.; Koehler, H.; Heyser, W.; Gödeke, T. ReviTec—A New Integrated Ecological Technology for the Renaturation of Degraded sites. Soil Ecology Interdisciplinary; Springer: Berlin, Germany, 1999; pp. 173–187. [Google Scholar]
  24. Koehler, H.; Kesel, R.; Heyser, W. Field Experiments to Accelerate Succession and to Improve Quercus Ilex Establishment with a Renaturation Technique (ReviTec), MEDECOS; Millpress: Rotterdam, Netherlands, 2004; p. 13. [Google Scholar]
  25. Koehler, H.; Heyser, W.; Kesel, R. The ecological technology ReviTec in combating degradation: Concept, first results, applications. In Restoration and Stability of Ecosystems in Arid and Semi-Arid Regions Beijing; Gao, J., Veste, M., Sun, B., Beyschlag, W., Eds.; Science Press: Beijing, China, 2006; pp. 288–303. [Google Scholar]
  26. Tsozué, D.; Haiwe, B.R.; Louleo, J.; Nghonda, J.P. Local Initiatives of Land Rehabilitation in the Sudano-Sahelian Region: Case of Hardé Soils in the Far North Region of Cameroon. Open J. Soil Sci. 2014, 4, 6–15. [Google Scholar] [CrossRef] [Green Version]
  27. Kuete, M.; Melingui, A.; Mounkam, J.; Nofiele, D. New geography of Camroun; Edicef: Vanves, France, 1993; p. 207. [Google Scholar]
  28. Ferretti, M.; Fischer, R.; Mues, V.; Granke, O.; Lorenz, M. Basic design principles for the ICP Forests Monitoring Networks. Manual Part II. In Manual on Methods and Criteria for Harmonized Sampling, Assessment, Monitoring and Analysis of the Effects of Air Pollution on Forests; UNECE ICP Forests Program Co-ordinating Centre: Hamburg, Germany, 2010; p. 22. Available online: http://www.icp-forests.org/Manual.htm (accessed on 25 August 2021).
  29. Kesel, R. ReviTec Maroua: Monitoring Report August and December 2012; KeKo-Kesel Koehler & Partner: Bremen, Germany, 2013; p. 24. [Google Scholar]
  30. David, W.; Wilson, C.; Card, A. Estimating Soil Texture Sandy, Loamy, or Clayey? Colorado State University, Cooperative Extension; Colorado State University: Boulder, Colorado, USA, 2003; p. 7. [Google Scholar]
  31. Black, C.A. Methods of Soil Analysis: Part I, Physical and Mineralogical Properties; American Society of Agronomy: Madison, WI, USA, 1965; pp. 1–112. [Google Scholar]
  32. Nelson, D.W.; Sommers, L.E. Total carbon, organic carbon and organic matter. In Methods of Soil Analysis. Part 2 Chemical and Microbiological Properties; Page, A.L., Miller, R.H., Keeney, D.R., Eds.; American Society of Agronomy and Soil Science Society of America: Madison, WI, USA, 1982; pp. 539–579. [Google Scholar]
  33. Okalebo, J.R.; Gathua, K.W.; Woomer, P.L. Laboratory Methods of Soil and Plant Analysis, 2nd ed.; SACRED-Africa Press: Nairobi, Kenya, 2002; p. 128. [Google Scholar]
  34. Bremner, J.M.; Mulvaney, C.S. Total Nitrogen Methods of Soil Analysis, Part 2, Chemical and Microbiological Properties; American Society of Agronomy and Soil Science Society of America: Madison, WI, USA, 1982; pp. 1119–1123. [Google Scholar]
  35. Soltanpour, P.N.; Schwab, A.P. A new soil test for simultaneous extraction of macro- and micro-nutrients in alkaline soils. Commun. Soil Sci. Plant Anal. 1977, 8, 195–207. [Google Scholar] [CrossRef]
  36. Seiny-Boukar, L. Water Regime and Soil Degradation in North Cameroon. Ph.D. Thesis, University of Yaounde, Yaounde, Cameroon, 1990; p. 225. [Google Scholar]
  37. Barbier, B.; Yacouba, H.; Karambiri, H.; Zoromé, M.; Somé, B. Human Vulnerability to Climate Variability in the Sahel: Farmers’ Adaptation Strategies in Northern Burkina Faso. Environ. Manag. 2009, 43, 790–803. [Google Scholar] [CrossRef] [PubMed]
  38. del Carmen Ponce-Rodríguez, M.; Prieto-Ruíz, J.Á.; Carrete-Carreón, F.O.; Pérez-López, M.E.; de Jesús Muñoz-Ramos, J.; Reyes-Estrada, O.; Ramírez-Garduño, H. Influence of Stone Bunds on Vegetation and Soil in an Area Reforested with Pinus engelmannii Carr. in the Forests of Durango, Mexico. Sustainability 2019, 11, 5033. [Google Scholar] [CrossRef] [Green Version]
  39. Klik, A.; Schürz, C.; Strohmeier, S.; Demelash Melaku, N.; Ziadat, F.; Schwen, A.; Zucca, C. Impact of stone bunds on temporal and spatial variability of soil physical properties: A field study from northern Ethiopia. Land Degrad. Dev. 2019, 29, 585–595. [Google Scholar] [CrossRef] [Green Version]
  40. Zobel, R.W. Genetic control of root systems. In Plant Roots: The Hidden Half; Waisel, Y., Eshel, A., Kafkafi, U., Eds.; Marcel Dekker: New York, NY, USA, 1991; pp. 25–38. [Google Scholar]
  41. Hagan, R.M. Factors Affecting Soil Moisture-Plant Growth Relations. Report of the XIVth International Horticultural Congress, the Netherlands; H. Veenman & Zonen: Wageningen, Holland, 1955; pp. 82–102. [Google Scholar]
  42. Reid, J.B.; Tan, Y.; Griffin, W.B.; Goulden, D. Root system plasticity as a factor in crop breeding for improved nutrient uptake. Agron. N. Z. 2010, 40, 51–64. [Google Scholar]
  43. Duong, T.T.T.; Penfold, C.; Marschner, P. Differential effects of composts on properties of soils with different textures. Biol. Fertil. Soils 2012, 48, 699–707. [Google Scholar] [CrossRef]
  44. Echezona, B.C.; Igwe, C.A.; Attama, L.A. Properties of Arboreal Ant and Ground-Termite Nests in relation to Their Nesting Sites and Location in a Tropical-Derived Savanna. Psyche J. Entomol. 2012, 2012, 235840. [Google Scholar] [CrossRef]
  45. Zotarelli, L.; Scholberg, J.M.; Dukes, M.D.; Muñoz-Carpena, R. Monitoring of Nitrate Leaching in Sandy Soils. J. Environ. Qual. 2007, 36, 953–962. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  46. Ribolzi, O.; Hermida, M.; Karambiri, H.; Delhoume, J.; Thiombiano, L. Effects of aeolian processes on water infiltration in sandy Sahelian rangeland in Burkina Faso. CATENA 2006, 67, 145–154. [Google Scholar] [CrossRef]
  47. Claude, J.; Grouzis, M.; Milleville, P. A Sahelian space. La Mare d’Oursi, Burkina Faso; ORSTOM: Montpellier, France, 1991; p. 241. [Google Scholar]
  48. Visser, S.M.; Sterk, G.; Karssenberg, D. Modelling water erosion in the Sahel: Application of a physically based soil erosion model in a gentle sloping environment. Earth Surf. Process. Landf. 2005, 30, 1547–1566. [Google Scholar] [CrossRef] [Green Version]
  49. Harper, R.J.; Gilkes, R.J. Soil attributes related to water repellency and the utility of soil survey for predicting its occurrence. Aust. J. Soil Res. 1994, 32, 1109–1124. [Google Scholar] [CrossRef]
  50. Reuter, G. Improvement of sandy soils by clay-substrate application. Appl. Clay Sci. 1994, 9, 107–120. [Google Scholar] [CrossRef]
  51. Ismail, S.M.; Ozawa, K. Improvement of crop yield, soil moisture distribution and water use efficiency in sandy soils by clay application. Appl. Clay Sci. 2007, 37, 81–89. [Google Scholar] [CrossRef] [Green Version]
  52. Leroy, B.L.M.; Herath, M.S.K.; De Neve, S.; Gabriels, D.; Bommelé, L.; Reheul, D.; Moens, M. Effect of Vegetable, Fruit And Garden (VFG) Waste Compost on Soil Physical Properties. Compos. Sci. Util. 2008, 16, 43–51. [Google Scholar] [CrossRef]
  53. Arthur, E.; Cornelis, W.M.; Vermang, J.; De Rocker, E. Amending a loamy sand with three compost types: Impact on soil quality. Soil Use Manag. 2010, 27, 116–123. [Google Scholar] [CrossRef]
  54. Troeh, F.R.; Thompson, L.M. Soils and Soil Fertility, 6th ed.; Blackwell Publishing: Iowa, US, USA, 2005; p. 498. [Google Scholar]
  55. Jones, M.I.; Wild, A. Soils of West African Savanna. The Maintenance and Improvement of Their Fertility. Commonwealth Bureau of the Soils Technical Communication of the Harpenden. No. 55; Commonwealth Agricultural Bureau (CAB): Farnham Royal, UK, 1975; p. 246. [Google Scholar]
  56. Feller, C.; Bernhard-Reversat, F.; Garcia, J.L.; Pantier, J.J.; Roussos, S.; Vanvliet-Lanoe, B. Study of the organic matter of different size fractions of a tropical sandy soil. Effect of an organic amendment (compost). ORSTOM. Ser. Pedol. 1983, 20, 223–238. [Google Scholar]
  57. Weber, J.; Karczewska, A.; Drozd, J.; Licznar, M.; Licznar, S.; Jamroz, E.; Kocowicz, A. Agricultural and ecological aspects of a sandy soil as affected by the application of municipal solid waste composts. Soil Biol. Biochem. 2007, 39, 1294–1302. [Google Scholar] [CrossRef]
  58. Aranyos, J.T.; Tomócsik, A.; Makádi, M.; Mészáros, J.; Blaskó, L. Changes in physical properties of sandy soil after long-term compost treatment. Int. Agrophys. 2016, 30, 269–274. [Google Scholar] [CrossRef] [Green Version]
  59. Walter, I.; Martınez, F.; Cuevas, G. Biosolid amendment of a calcareous, degraded soil in a semi-arid environment. Span. J. Agric. Res. 2006, 4, 47–54. [Google Scholar] [CrossRef] [Green Version]
  60. Bastida, F.; Kandeler, E.; Hernández, T.; García, C. Long-Term Effect of Municipal Solid Waste Amendment on Microbial Abundance and Humus-associated Enzyme Activities Under Semiarid Conditions. Microb. Ecol. 2007, 55, 651–661. [Google Scholar] [CrossRef]
  61. Kowaljow, E.; Mazzarino, M.J.; Satti, P.; Jiménez-Rodríguez, C.D. Organic and inorganic fertilizer effects on a degraded Patagonian rangeland. Plant Soil 2010, 332, 135–145. [Google Scholar] [CrossRef]
  62. Celik, I.; Ortas, I.; Kilic, S. Effects of compost, mycorrhiza, manure and fertilizer on some physical properties of a Chromoxerert soil. Soil Tillage Res. 2004, 78, 59–67. [Google Scholar] [CrossRef]
  63. Sawar, G.; Schmeisky, H.; Hussain, N.; Muhammed, S.; Ibrahim, M.; Safdar, E. Improvement of soil physical and chemical properties with compost application in rice-wheat cropping system. Pak. J. Bot. 2008, 40, 275–282. [Google Scholar]
  64. Valarini, P.J.; Curaqueo, G.; Seguel, A.; Manzano, K.; Rubio, R.; Cornejo, P.; Borie, F. Effect of Compost Application on Some Properties of a Volcanic Soil from Central South Chile. Chil. J. Agric. Res. 2009, 69, 416–425. [Google Scholar] [CrossRef] [Green Version]
  65. Saldaña y Hernández, M.I.; Gómez-Álvarez, R.; Rivera-Cruz, M.d.C.; Álvarez-Solís, J.D.; Pat-Fernández, J.M.; Ortiz-García, C.F. The influence of organic fertilizers on the chemical properties of soil and the production of Alpinia purpurata. Cienc. Investig. Agrar. 2014, 41, 215–224. [Google Scholar] [CrossRef] [Green Version]
  66. Karhu, K.; Kalu, S.; Seppänen, A.; Kitzler, B.; Virtanen, E. Potential of biochar soil amendments to reduce N leaching in boreal field conditions estimated using the resin bag method. Agric. Ecosyst. Environ. 2021, 316, 107452. [Google Scholar] [CrossRef]
  67. Laird, D.A.; Fleming, P.; Davis, D.D.; Horton, R.; Wang, B.; Karlen, D.L. Impact of biochar amendments on the quality of a typical Midwestern agricultural soil. Geoderma 2010, 158, 443–449. [Google Scholar] [CrossRef] [Green Version]
  68. Ngakou, A.; Nwaga, D.; Nebane, C.L.N.; Ntonifor, N.; Parh, I.A. Arbuscular-mycorrhizal fungi, rhizobia and Metarhizium enhance P, N, Mg, K and Ca accumulation in fields grown cowper. J. Plant Sci. 2007, 2, 518–529. [Google Scholar] [CrossRef] [Green Version]
  69. Wortmann, C.S.; Shapiro, C.A. The effects of manure application on soil aggregation. Nutr. Cycl. Agroecosyst. 2007, 80, 173–180. [Google Scholar] [CrossRef]
  70. Ryals, R.; Kaiser, M.; Torn, M.S.; Berhe, A.A.; Silver, W.L. Impacts of organic matter amendments on carbon and nitrogen dynamics in grassland soils. Soil Biol. Biochem. 2013, 68, 52–61. [Google Scholar] [CrossRef]
  71. Castán, E.; Satti, P.; González-Polo, M.; Iglesias, M.C.; Mazzarino, M.J. Managing the value of composts as organic amendments and fertilizers in sandy soils. Agric. Ecosyst. Environ. 2016, 224, 29–38. [Google Scholar] [CrossRef]
  72. Gabrielle, B.; Da-Silveira, J.; Houot, S.; Francou, C. Simulating Urban Waste Compost Effects on Carbon and Nitrogen Dynamics Using a Biochemical Index. J. Environ. Qual. 2004, 33, 2333–2342. [Google Scholar] [CrossRef] [PubMed]
  73. Rynk, R.; Van der Kamp, M.; Willson, G.B.; Singley, M.E.; Richard, T.L.; Kolega, J.J.; Gouin, F.R.; Laliberty, L.; Kay, D., Jr.; Murphy, D.W.; et al. On-Farm Composting Handbook. Northeast Regional Agricultural Engineering Service (NRAES), Cooperative Extension Service, Ithaca; NRAES: Ithaca, NY, USA, 1992; p. 204. [Google Scholar]
  74. McCoy, S.; Cogburn, B. Composting manure for value-added products. In BioCycle Ed.; The JG Press Inc.: Emmaus, PE, USA, 2001; pp. 71–72. [Google Scholar]
  75. Amato, M.; Ladd, J. Decomposition of 14C-labelled glucose and legume material in soils: Properties influencing the accumulation of organic residue C and microbial biomass C. Soil Biol. Biochem. 1992, 24, 455–464. [Google Scholar] [CrossRef]
  76. Juma, N.G. Interrelationships between soil structure/texture, soil biota/soil organic matter and crop production. Geoderma 1993, 57, 3–30. [Google Scholar] [CrossRef]
  77. Müller, T.; Höper, H. Soil organic matter turnover as a function of the soil clay content: Consequences for model applications. Soil Biol. Biochem. 2004, 36, 877–888. [Google Scholar] [CrossRef]
Sustainability 14 00324 g001 550
Figure 1. Map of Far-North Cameroon with the location of Gawel.
Figure 1. Map of Far-North Cameroon with the location of Gawel.
Sustainability 14 00324 g001
Sustainability 14 00324 g002 550
Figure 2. Gawel climate graph.
Figure 2. Gawel climate graph.
Sustainability 14 00324 g002
Sustainability 14 00324 g003 550
Figure 3. Position of the Gawel 1 and Gawel 2 sites and of the BioSoilPlots (BSP) in the sites in detail. Source: Google Earth, Image © 2021, CN/Airbus.
Figure 3. Position of the Gawel 1 and Gawel 2 sites and of the BioSoilPlots (BSP) in the sites in detail. Source: Google Earth, Image © 2021, CN/Airbus.
Sustainability 14 00324 g003
Sustainability 14 00324 g004 550
Figure 4. BioSoilPlot design (after Basic design principles for the ICP forests monitoring networks, [28]).
Figure 4. BioSoilPlot design (after Basic design principles for the ICP forests monitoring networks, [28]).
Sustainability 14 00324 g004
Sustainability 14 00324 g005 550
Figure 5. Plan of sampling on structures. The square shapes represent the bags filled with substrate on which the vegetation evolves. Red dots illustrate sampling positions in microplots marked by cut-outs on structures.
Figure 5. Plan of sampling on structures. The square shapes represent the bags filled with substrate on which the vegetation evolves. Red dots illustrate sampling positions in microplots marked by cut-outs on structures.
Sustainability 14 00324 g005
Sustainability 14 00324 g006 550
Figure 6. Variation in growth height and percentage cover of herbaceous on the different structures during the two monitoring periods July 2018/19. GW: Gawel; Bu: Bund; DL: Demi-Lune. The error lines represent standard deviation. Growth height is represented by the bar chart and percentage cover, by the curve.
Figure 6. Variation in growth height and percentage cover of herbaceous on the different structures during the two monitoring periods July 2018/19. GW: Gawel; Bu: Bund; DL: Demi-Lune. The error lines represent standard deviation. Growth height is represented by the bar chart and percentage cover, by the curve.
Sustainability 14 00324 g006
Sustainability 14 00324 g007 550
Figure 7. Influence of ReviTec treatment on soil moisture content (mean ± Std) at GW1 and GW2 ReviTec sites. GW: Gawel; ctrl 1: control out of fence; ctrl 2: control within fence; cp: compost; bc: biochar; my: mycorrhiza. Letters a, b and c represent difference in composition of means between treatments during the same month of monitoring. The error lines represent Standard deviation.
Figure 7. Influence of ReviTec treatment on soil moisture content (mean ± Std) at GW1 and GW2 ReviTec sites. GW: Gawel; ctrl 1: control out of fence; ctrl 2: control within fence; cp: compost; bc: biochar; my: mycorrhiza. Letters a, b and c represent difference in composition of means between treatments during the same month of monitoring. The error lines represent Standard deviation.
Sustainability 14 00324 g007
Table
Table 1. Treatments used within the context of ReviTec.
Table 1. Treatments used within the context of ReviTec.
Treatments CodesSeedBagSubstrate (%)
Sandy LoamCompost (cp)Biochar (bc)Mycorrhiza (my)
control 1 ctrl 1##
control 2 planting holectrl 2##
Compost + Biochar + Mycorrhizacpbcmy##702010inoc
ctrl 1 = control out of fence, ctrl 2 = control within fence, cp = compost, bc = biochar, my = mycorrhiza, Inoc = inoculum.
Table
Table 2. Sum of selected structure for monitoring in the whole of BSP of different site.
Table 2. Sum of selected structure for monitoring in the whole of BSP of different site.
BioSoilPlot1BioSoilPlot2BioSoilPlot3Total
BuDLBuDLBuDLBuDL
GW1installed66311641521
monitored4435531212
GW2installed71169371627
monitored4453351212
Bu: Bund DL: Demi-lune GW: Gawel.
Table
Table 3. Increases in growth volume (dm3/m2) of herbaceous species per monitoring period at GW1 and GW2.
Table 3. Increases in growth volume (dm3/m2) of herbaceous species per monitoring period at GW1 and GW2.
GW1GW2
Species/PeriodsJuly 2018July 2019p-ValueJuly 2018July 2019p-Value
Brachiaria brizantha3.32 a a
(0.10)		1.68 b c
(1.58)		0.018 **3.25 a b
(0.04)		2.74 b c
(0.12)		<0.0001 ****
Pennisetum pedicellatum3.41 b a
(0.02)		3.50 a b
(0.01)		<0.0001 ****3.47 b a
(0.05)		3.62 a a
(0.02)		<0.0001 ****
Sesbania sesban2.90 b b
(0.07)		3.06 a b
(0.02)		<0.0001 ****2.78 b c
(0.10)		3.02 a b
(0.05)		<0.0001 ****
Boreria chaetocepha2.51 a c
(0.22)		2.71 a bc
(0.23)		0.120.00 b d
(0.00)		2.35 a d
(0.04)		<0.0001 ****
p-value<0.0001 ****0.002 *** <0.0001 ****<0.0001 ****
GW: Gawel. Letters represent change in composition of means between species during the same month (red color) and between periods (black color) of monitoring. Number in bracket represent standard deviation. Significance levels are indicated by **** p < 0.0001. *** p < 0.005. ** p < 0.05.
Table
Table 4. Comparison of growth height (cm) of herbaceous species between different structures in both sites.
Table 4. Comparison of growth height (cm) of herbaceous species between different structures in both sites.
Monitoring PeriodSpeciesGW1GW2
BUDLp-ValueBUDLp-Value
July 2018Brachiaria brizantha1.75 a (0.04)1.70 a (0.02)0.8561.77 a (0.06)1.62 b (0.05)0.005 **
Pennisetum pedicellatum1.89 a (0.05)1.71 b (0.05)0.0008 ***1.90 a (0.05)1.86 a (0.06)0.922
Sesbaniasesban1.91 a (0.06)1.76 b (0.05)0.006 **1.99 a (0.04)1.81 b (0.08)<0.0001 ****
Boreria chaetocepha1.78 a (0.06)1.55 b (0.04)<0.0001 ****0 b (0)0 b (0)1.000
July 2019Brachiaria brizantha1.76 a (0.07)0 b (0)<0.0001 ****1.63 b (0.01)1.58 b (0.07)0.952
Pennisetum pedicellatum1.91 a (0.04)1.72 b (0.07)0.006 **1.95 a (0.01)1.92 a (0.06)0.994
Sesbaniasesban1.95 a (0.04)1.78 b (0.09)0.01 **1.97 a (0.01)1.82 b (0.06)0.015 **
Boreriachaetocepha1.72 a (0.05)1.55 b (0.05)0.01 **1.64 a (0.08)1.63 a (0.08)1.000
GW: Gawel; Bu: Bund; DL: Demi-Lune. Letters represent change in composition of means growth height of species between different structures during the same month of monitoring. Number in bracket represent standard deviation. Significance levels are indicated by **** p < 0.0001. *** p < 0.001. ** p < 0.05.
Table
Table 5. Variation of soil texture and soil pH under the influence of ReviTec treatment at GW1 and GW2 sites.
Table 5. Variation of soil texture and soil pH under the influence of ReviTec treatment at GW1 and GW2 sites.
GW1GW2
Period MonthJanuaryJulyJanuaryJuly
Treatmentctrl 1ctrl 2cpbcmypctrl 1ctrl 2cpbcmypctrl 1ctrl 2cpbcmypctrl 1ctrl 2cpbcmyp
2018% Clay3.15 b (0.55)1.96 b (0.15)39.56 a (1.65)<0.0001 ****14.63 c (0.85)35.41 b (1.55)40.31 a (0.47)<0.0001 ****1.84 b (0.31)25.75 a (2.18)21.63 a (2.65)<0.0001 ****6.63 c (0.78)15.44 b (1.56)34.33 a (1.66)<0.0001 ****
% Silt5.42 b (0.68)25.17 a (2.01)1.96 c (0.15)<0.0001 ****1.94 b (0.36)1.31 b (0.20)16.07 a (0.80)<0.0001 ****8.52 a (0.61)4.20 b (0.40)3.13 b (0.40)<0.0001 ****1.24 c (0.36)11.23 b (1.80)42.14 a (3.61)<0.0001 ****
% Sand91.43 a (0.12)72.87 b (1.42)58.48 c (1.49)<0.0001 ****83.43 a (0.76)63.28 b (1.45)43.62 c (0.76)<0.0001 ****89.64 a (2.43)70.05 b (7.21)75.24 b (2.65)0.005 **92.13 a (0.46)73.33 b (0.44)23.53 c (2.14)<0.0001 ****
TextureSandLoamy sandSandy loam SandSandy loamClay SandSandy loamSandy loam SandSandy loamClay loam
pH5.71 b (0.97)6.87 ab (0.35)7.38 a (0.44)0.049 **5.46 b (0.31)7.17 a (0.26)7.66 a (0.23)0.001 ***5.64 b (0.92)7.28 a (0.36)7.23 a (0.38)0.026 **6.46 a (0.92)7.18 a (0.32)7.50 a (0.20)0.153
2019% Clay6.03 c (0.62)34.36 a (0.86)21.56 b (0.65)<0.0001 ****5.60 b (1.11)36.54 a (1.62)34.36 a (0.87)<0.0001 ****7.17 c (0.61)34.42 a (3.61)21.42 b (1.91)<0.0001 ****9.55 b (0.63)38.72 a (0.81)39.37 a (1.65)<0.0001 ****
% Silt6.54 b (0.60)4.92 c (0.23)15.21 a (0.40)< 0.0001 ****9.13 c (0.45)35.53 a (0.57)33.44 b (0.35)<0.0001 ****7.72 b (0.47)4.92 b (1.40)15.24 a (2.48)<0.0001 ****10.62 b (0.67)31.21 a (1.76)33.37 a (3.26)<0.0001 ****
% Sand87.43 a (1.44)60.72 b (1.00)63.23 b (0.51)<0.0001 ****85.27 a (0.63)27.93 c (0.88)32.20 b (0.66)<0.0001 ****85.11 a (2.36)60.66 b (1.87)63.34 b (1.57)<0.0001 ****79.83 a (0.10)30.07 b (0.93)27.26 b (1.87)<0.0001 ****
TextureSandSandy loamSandy clay loam SandClay loamClay loam SandSandy loamSandy clay loam SandClay loamClay loam
pH6.41 b (0.21)7.28 a (0.40)7.17 a (0.26)0.022 **6.08 b (0.45)7.28 a (0.14)7.87 a (0.12)0.001 ***5.40 b (0.92)7.24 ab (0.87)7.47 a (0.47)0.033 **6.70 b (0.80)7.48 ab (0.47)8.21 a (0.37)0.051
GW: Gawel; ctrl 1: control out of fence; ctrl 2: control within fence; cp: compost; bc: biochar; my: mycorrhiza; p: p-value. Letters represent change in composition of means of each soil particle and pH between treatments during the same month of monitoring. Number in bracket represent standard deviation. Significance levels are indicated by **** p < 0.0001, *** p < 0.005, ** p < 0.05.
Table
Table 6. Soil organic carbon (SOC), total nitrogen (N) and C/N ratio recorded at GW1 and GW2 ReviTec sites.
Table 6. Soil organic carbon (SOC), total nitrogen (N) and C/N ratio recorded at GW1 and GW2 ReviTec sites.
GW1GW2
2018201920182019
TreatmentsMonthsSOC (%)N (%)C/NSOC (%)N (%)C/NSOC (%)N (%)C/NSOC (%)N (%)C/N
ctrl 1Jan1.50 c
(0.02)		0.47 a (0.07)3.26 b (0.51)1.71 c
(0.01)		0.57 b (0.00)2.99 a (0.03)1.34 c
(0.00)		0.47 b (0.00)2.83 b (0.02)2.28 c (0.01)0.57 c (0.00)3.98 a (0.04)
ctrl 2Jan2.28 b
(0.01)		0.57 a (0.00)3.98 b (0.02)2.60 b
(0.01)		0.62 ab (0.08)4.20 a (0.52)2.47 b
(0.01)		0.66 ab (0.01) 3.75 ab (0.12)2.52 b (0.08)0.63 b (0.02)3.99 a (0.26)
cpbcmyJan3.03 a
(0.00)		0.56 a (0.01)5.43 a (0.11)3.42 a
(0.01)		0.84 a (0.04)4.09 a (0.20)3.20 a
(0.00)		0.72 a (0.08)4.50 a (0.60)2.91 a (0.00)0.76 a (0.01)3.84 a (0.05)
R2 1.0000.7510.9481.0000.9080.8501.0000.8760.8830.9840.9860.306
F 5460.2784.53427.21614,644.17714.8688.50334,545.40610.60611.27889.560102.3010.662
p <0.0001 ****0.1240.012 **<0.0001 ****0.028 **0.058<0.0001 ****0.044 **0.040 **0.002 ***0.002 ***0.578
ctrl 1Jul2.60 c
(0.01)		0.57 a (0.02)4.95 a (1.92)2.30 c
(0.00)		0.61 b (0.05)4.97 a (0.41)1.83 c
(0.01)		0.55 a (0.08)3.40 a (0.51)2.74 b (0.06)0.52 b (0.07)5.30 a (0.86)
ctrl 2Jul2.90 b
(0.01)		0.68 a (0.01)4.30 a (0.06)3.02 b
(0.00)		0.89 a (0.03)3.41 b (0.12)2.86 b
(0.10)		0.72 a (0.08)4.01 a (0.40)2.96 a (0.00)0.74 ab (0.06)4.01 a (0.35)
cpbcmyJul3.57 a
(0.01)		0.71 a (0.00)5.01 a (0.02)3.52 a
(0.01)		0.94 a (0.06)3.74 b (0.22)3.68 a
(0.06)		0.84 a (0.06)4.41 a (0.36)3.10 a (0.00)0.81 a (0.03)3.84 a (0.15)
R2 1.0000.3250.1461.0000.9520.9200.9960.8190.6550.9700.8930.741
F 9201.4180.7220.2573755.98029.65117.301405.9346.8022.85348.25612.5844.293
p <0.0001 ****0.5550.789<0.0001 ****0.0110.023 **<0.0001 ****0.0770.2020.005 **0.035 **0.132
GW: Gawel; ctrl 1: control out of fence; ctrl 2: control within fence; cp: compost; bc: biochar; my: mycorrhiza; C: Carbon, N: total nitrogen; Jan: January; Jul: July; p: p-value. Letters represent change in composition of means of each soil nutrient between treatments during the same month of monitoring. Number in bracket represent standard deviation. Significance levels are indicated by **** p < 0.0001, *** p < 0.005, ** p < 0.05.
Table
Table 7. Soil extractable P and exchangeable K recorded at GW1 and GW2 ReviTec sites.
Table 7. Soil extractable P and exchangeable K recorded at GW1 and GW2 ReviTec sites.
GW1GW2
2018201920182019
TreatmentsMonthsP (%)K (%)P (%)K (%)P (%)K (%)P (%)K (%)
ctrl 1Jan2.44 c (0.05)20.87 c (0.75)2.70 c (0.18)28.00 c (1.00)2.37 b (0.39)20.07 c (0.06)3.04 c (0.01)28.67 b (0.58)
ctrl 2Jan5.06 b (0.02)28.67 b (0.57)5.89 b (0.05)38.10 b (0.10)4.18 b (0.23)26.77 b (0.49)5.47 b (0.65)28.00 b (0.10)
cpbcmyJan7.58 a (0.06)39.10 a (0.10)9.24 a (0.05)43.10 a (0.10)7.43 a (0.60)37.73 a (0.55)8.31 a (0.29)38.17 a (0.15)
R2 1.0000.9960.9990.9940.9790.9980.9820.996
F 5,237.716821.6981,647.060522.08869.1971,301.64281.996793.864
p-value <0.0001 ****<0.0001 ****<0.0001 ****<0.0001 ****0.003 ***<0.0001 ****0.002 ***<0.0001 ****
ctrl 1Jul2.53 c (0.17)21.2 c (0.20)3.52 c (0.06)35.03 c (0.50)2.80 c (0.13)27.1 c (0.10)3.13 b (0.00)28.67 c (0.58)
ctrl 2Jul5.46 b (0.65)44.1 b (0.10)7.26 b (0.70)59.10 b (0.10)5.28 b (0.29)28.1 b (0.10)6.68 a (0.47)32.10 b (0.10)
cpbcmyJul8.32 a (0.05)56.10 a (0.10)9.36 a (0.00)60.50 a (0.45)7.89 a (0.29)45.00 a (0.20)8.41 a (0.54)46.10 a (0.10)
R2 0.9861.0000.9861.0000.9931.0000.9830.999
F 109.03847,160.500104.2218,259.284211.62215,175.50084.5692,172.349
p-value 0.002 ***<0.0001 ****0.002 ***<0.0001 ****0.001 ***<0.0001 ****0.002 ***<0.0001 ****
GW: Gawel; ctrl 1: control out of fence; ctrl 2: control within fence; cp: compost; bc: biochar; my: mycorrhiza; p: soil extractable P, K: soil exchangeable K; Jan: January; Jul: July. Letters represent change in composition of means of each soil nutrient between treatments during the same month of monitoring. Number in bracket represent standard deviation. Significance levels are indicated by **** p-value < 0.0001, *** p-value < 0.005.
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Tchida, P.B.; Ngakou, A.; Kesel, R.; Koehler, H. Changes in the Physico-Chemical Properties of Degraded Soils in Response to the ReviTec Approach Applied at Gawel (Far-North Cameroon). Sustainability 2022, 14, 324. https://doi.org/10.3390/su14010324

AMA Style

Tchida PB, Ngakou A, Kesel R, Koehler H. Changes in the Physico-Chemical Properties of Degraded Soils in Response to the ReviTec Approach Applied at Gawel (Far-North Cameroon). Sustainability. 2022; 14(1):324. https://doi.org/10.3390/su14010324

Chicago/Turabian Style

Tchida, Pascal Blaise, Albert Ngakou, Raimund Kesel, and Hartmut Koehler. 2022. "Changes in the Physico-Chemical Properties of Degraded Soils in Response to the ReviTec Approach Applied at Gawel (Far-North Cameroon)" Sustainability 14, no. 1: 324. https://doi.org/10.3390/su14010324

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