Effect of physical soil and water conservation measures on physico-chemical properties of soil

Table of content

Contents

List of tables

Abbreviation

1. Introduction

2. The states of Soil and Water Conservation in Ethiopia
2.1. Soil Conservation
2.2. Physical Soil Conservation

3. Importance of soil and water conservation for sustainable agriculture

4. Impacts of SWC Practices on soil physical properties
4.1. Bulk density
4.2. The soil texture
4.2.1. Sand content
4.2.2. Silt content
4.2.3. Clay content

5. Impacts of SWC Practices on soil chemical properties
5.1. PH
5.2. Soil organic carbon (SOC)
5.3. Total Nitrogen(TN)
5.4. Available Phosphorus (Av-P)
5.5. Cation exchange capacity (CEC)

6. Conclusion

7. Reference

List of tables

Table 1-Details of studies on the impacts of SWC practices on soil physico-chemical properties

Table 2-Selected Soil physico-chemical properties as influenced by conservation practices

Table 3- soil chemical properties in conserved and non-conserved plots

Abbreviation

MoA- Ministry of aricultur

OC- Organic carbon

SLMP- Sustainable land management program

SOM- Soil organic matter

SOC- Soil organic carbon

SWC- Soil and water conservation

TN- total Nitrogen

1. Introduction

Soil degradation is deterioration of the physical, chemical and biological or economic properties of soil (Maitima and Olson, 2001). It has a negative impact on agricultural economy and the natural environment (Taddese, 2001, (Keno and Suryabhagavan, 2014). Human activity, such as conversion of forests to agricultural land, increased cultivation of marginal land, overgrazing, and subsistence agriculture practiced on marginal lands with steep gradients; accelerate soil erosion (Lal, R., 1996). Increasing population pressure has lead people to use marginal lands for cultivation and grazing and severely overexploit the natural resource base of the region (Hurni, 1993; Shiferaw and Holden, 1998). The exploitation of these natural resources is inextricably linked to securing food and livelihoods (Dubale, 2001; Adimassu et al., 2012). This has resulted in accelerated soil erosion, deforestation, water resource depletion and environmental degradation (Desta, 2000; Berry, 2003; Mitiku et al., 2006; Nyssen et al., 2008; Change, 2014).

Land degradation and its related decline in the productivity potential of agricultural land are challenging the economic and social well-being of the current and future generations on earth (Haregeweyn et al. 2012). Soil erosion is the main cause of land degradation and a leading factor contributing to poor agricultural development in developing countries (Gemechu 2016). Currently, soil resources are the main sources of livelihoods for most people of the world, such human exploitation being the foremost factor for soil degradation (Molla and Sisheber, 2017). The sorting action of erosion removes large proportions of the clay and humus from soil, leaving behind the less productive coarse sand, gravel, and in some case even stones, impairing the quality of the remaining topsoil (Troeh F., 1980). The removal of this organic matter affects soil properties including texture, structure, nutrient availability and biological activity and makes soil more susceptible to further erosion as its aggregates becomes less stable thus, negatively affecting crop production (Alemayehu, F. and Dubale, P. ,2006)

In Ethiopia, measurements from experimental plots and micro-watersheds showed the annual soil loss from croplands is about 42 t· ha–1·year–1 (Wagayehu et al,2003).As a consequence, the productive capacity of Ethiopia’s highland soils is being reduced at an annual rate of 2% - 3%, which certainly contributes to a higher vulnerability to famine (Wagayehu et al,2003) . The slope steepness, long cultivation history with outdated technology, and overgrazing make soil erosion more severe in Ethiopia (Nyssen et al., 2004). It has been identified as a major threat to the national economy (Hurni, 1993) and among the main challenges influencing the sustainability of agriculture (Molla and Sisheber, 2017). As a result, two-thirds of the population of Ethiopia has been affected by soil erosion mainly associated with the conversion of forest to agricultural land (Hurni et al., 2015).

To solve this problem, the first initiative of soil and water conservation (SWC) investment began during the outbreak of the 1973/74 droughtin Ethiopia(Berhe ,1996).The main intent of the initiatives was to minimize erosion, restore soil fertility, rehabilitate degraded land, and increase agricultural productivity (Mekuria et al.,2007). Since the 1980s, various national SWC efforts have been undertaken with the financial support of international donors and mass mobilization of rural communities (Holden et al. 2001).The largest SWC investment made in the country was during the Derg Regime in which more than 1billion US dollars per year were invested during 1974–1991 (Rahmato 1994). Since the 1990s, the implementation of SWC measures has been an integral part of agricultural extension packages (Bewket and Sterk 2002). Since the overthrow of the Derg Regime in 1991, investments in SWC in Ethiopia have continued. For example, more than 500million US dollar has been invested in the Productive Safety Net Programmed since 2005 in which the majority of the money was allocated to SWC activities (Gilligan et al., 2009; Andersson et al. 2011). Moreover, huge financial resources have been invested in Sustainable Land Management Program (SLMP) since 2008 with the support of World Bank and Global Environmental Facility (Nedassa et al., 2011) and MERET (Managing Environmental Resources to Enable Transitions to sustainable livelihoods) project since 2003 with the financial support of WFP (Zeleke et al., 2014).

The effectiveness of SWC measures undertaken in Ethiopia was evaluated by several authors (Haregeweyn et al. 2016; Nyssen et al. 2010). According to (Dagnew et al., 2015), these evaluation reports showed that there is no consent on the effectiveness of SWC interventions among them. Some argue that SWC contributes for reduction in runoff and sediment loss (Mekuriaw, 2017) and increased soil moisture conservation (Haregeweyn et al., 2015; Nyssen et al. 2010). On the other side, it is reported that SWC structures were not effective in reducing soil erosion (Bewket and Sterk, 2002) and had not resulted in decreasing sediment concentrations (Temesgen et al. 2012). For example, construction of SWC practices such as soil and stone bunds reduced crop yield up to 7% for the first few years in Ethiopia (Adimassu et al. 2014; Kassie et al. 2011; Kato et al. 2011; Shiferaw and Holden, 1999). On the contrary, stone and soil bunds increased crop yield up to 10% in the Tigray region of Ethiopia (Nyssen et al. 2007; Vancampenhout et al. 2006; Gebremedhin et al. 1999). This shows that the results regarding the economic viability of SWC practices are inconsistent and site-specific.

In the case of on soil property, reports show that most of SWC measureshave important implications for improving soil fertility (Belayneh et al. 2019). Tesfaye and Fanuel, 2019) also reported that SWC practices have positive effect in improving soil fertilities and crop yield in Southern Ethiopia.In other site , K.Wolka et al. 2011) reported thatMost soil parameters were not significantly different in cropland with level soil bund and Stone Bund compared to non-terraced .This indicates that there is a gap in the evaluation of the impacts of SWC interventions.

Although many studies confirmed the positive impacts of SWC practices on soil physicochemical properties and crop yields, farmers frequently destruct SWCPs constructed on their fields, claiming that the practices didn’t show a positive impact/effect other than occupying their farmlands. Such claims need investigation and measured data to design alternative land management strategies.

Therefore, the main objective of this review is to discuss the effect of physical soil and water conservation practices on physicochemical properties and fertility status of soil

2. The states of Soil and Water Conservation in Ethiopia

2.1.Soil and water Conservation structures

Soil and water conservation structures include all mechanical or structural measures that control the velocity of surface runoff and thus minimize soil erosion and retain water where it is needed( Bancy M. Mati). They usually consist of engineering works involving physical structures, made of earth, stones, masonry, brushwood or other material for the construction of earthworks such as terraces, check dams, and water diversions, which reduce the effects of slope length and angle. SWC structures can be designed either to conserve water or to safely discharge it away. They supplement agronomic or vegetative measures but do not substitute for them. Suitability of SWC structure depends on Climate and the need to retain or discharge the runoff, Farm sizes and Soil characteristics

The prevention of erosion on cultivated land and other areas depends essentially on the reduction of soil detachment and runoff on the maintenance of adequate vegetation ground cover (Fitsum S., 2002). Soil conservation involves the various methods used to reduce soil erosion to prevent depletion of soil nutrients and soil moisture and to enrich the nutrients status of the soil. The conservation techniques include terracing and other.

2.2.Physical Soil Conservation

A physical soil conservation practice is applicable of soil management using knowledge or art with the goal protection of soil resource form exploitation. In addition, among those different applications, different structure applied in different farmlands .However, these conservation applications depend on climate, soil type, vegetation cover and level of economy.

3. Importance of soil and water conservation for sustainable agriculture

Effective soil and water conservation the major steps for sustainable agriculture. Sustainable agriculture can be practices by reducing negative measures and technology (Fitsum S. ,2002).To bring sustainability is on the basis of soil and water conservation, natural resource management, land management, integrated pest management using new technology, economic viability and food security on household level.

SWC practices in highland areas can foster the production of various kinds of ecosystem services that have both upstream and downstream benefits. With consciences with the farmer if proper implementation of techniques that maintain or restore the capacity of soil to retain water with the inorganic nutrients and organic matter increases.

Many studies in Ethiopia confirmed the positive impacts of soil and water conservation practices (SWCPs) on soil physicochemical properties and crop yields. For instance, soil conservation practices tested in Simada district, northwest Ethiopia, significantly improved the soil physicochemical properties (Mihrete, G.2014), Similarly, significantly lower mean bulk density was found in fields treated with SWCPs than the untreated fields in Adaa Berga district, western Ethiopia(Abay,C., 2016). Other studies conducted in Ethiopia and other countries also verified the positive impacts of SWCPs on soil physic-chemical properties and crop yields.

There are there types of soil properties, which are the physical properties (texture, structure, density, porosity, color, moisture content, water holding capacity etc) ,chemical properties (nutrient content, PH, CEC, electrical conductivity, redox potential etc.) and Biological properties (macro and microorganisms).

4. Impacts of SWC Practices on soil physical properties

4.1. Bulk density (BD)

Previous researches showed that SWC structures affect the bulk density of soil. The BD Soil treated with SWC structures is minimal compared with adjacent non-treated soil. S. Hishe et al(2017) reported that the highest mean bulk density in Middle Silluh Vally (Tigray) was recorded in non-terraced farm land (1.65 g/cm[3]) followed by terraced farm land (1.6 g/cm[3]). The same result was found by Tesfaye and Fanuel(2019) in Southern Ethiopia. According to their result, Soil bulk density (BD) was affected by soil conservation practices. It ranges from 0.96g/cm[3] (physical SWC for 5years) to 1.10g/cm[3] (non-conserved crop land) .K. Wolka et al. (2011) also reported that the effect of SWC on the mean soil bulk density was found to be minimal and slightly lower values were observed in conserved plots. Similar results were reported in different part of Ethiopia by (Yiferu et al 2018 , Gebiresilassie etal. 2013; Dulo etal. 2017; Solomon etal. 2017, Demelash and Stahr 2010,) . This could be due to the subsequent effects of reduced soil loss and crop residue through erosion, presence of higher organic matter resulted from conservation measures and decay of plant residues. A relatively higher bulk density in non-conserved plots could be related with washing out of fine organic matter rich soils by erosion and thereby exposed slightly heavier soil particulates.

4.2. The soil texture

The soil texture of the soil was assessed based on proportion of three mineral particles, sand, silt and clay.

4.2.1. Sand content

In Studies reviewed in this paper showed that the sand texture was relatively highest mean value in the non-conserved areas than conserved areas. On contrary, the lowest sand content was observed in conserved areas. S. Hishe et al (2017) reported that the sand content of non-terraced land was the highest mean (70%) and the terraced land was the lowest mean (62%).

4.2.2. Silt content

Since SWC structures reduce loss of soil particle, it increases the silt content of the soil. For example research conducted Tigray region provide evidence of silt content of the soil was highest in conserved land than non-conserved lands (S. Hishe et al 2017) that the silt content of the soil of terraced farm land was 13.5 % and non-terraced farm land silt content was 9.5%. The same result reported in Southern Ethiopia, thatthe silt fractions showed significant difference (P < 0.05) in croplands under terrace when compared with adjacent-non terraced croplands (K. Wolka et al. 2011)

4.2.3. Clay content

Similar to silt content, the clay content of the soil also affected by SWC structures. In Tigray , The clay content of terraced farm land was 26.5% and clay content of non-terraced farm land was 20.5% (S. Hishe et al,2017).The same result was recorded by K. Wolka et al. (2011) , The clay fractions showed significant difference (P < 0.05) in croplands with level soil bund when compared with adjacent-non-terraced croplands. Belayneh et al, 2019 also reported that clay content experiencing a mean value of 67.8% and 60.5% in conserved and non-conserved soil respectively in Northern Ethiopia.

5. Impacts of SWC Practices on soil chemical properties

5.1. PH

Soil pH affects solubility and availability of nutrients in the soil (Mc. Cauley et al, 2003). The exchange reactions between soil solution and the soil particles surfaces are the main regulators of soil pH (Coleman et al, 1989).Soil and water conservation practices affect PH value of soil. For example, M.Guadie et al. (2019) reported that Soil pH showed a statistically significant difference (p≤0.05) between the treated and untreated fields in Northern Ethiopia. Belyneh et al (2019) also reported that Soil pH showed slightly higher mean values in conserved plots. The analysis of variance result show that soil pH was not statistically significantly affected by conservation practices .Similar results were reported by Challa et al. (2016) and Husen et al. (2017) in the central highland of Ethiopia. This might be due to the effect of soluble bases and organic matter removal through sheet erosion from the control fields due to the absence of SWCPs, and due to the low base saturation percentage and low sediment organic matter (SOM) content and high pH value in the sediment accumulation zone behind the SWCPs of the treated fields. Relatively higher soil acidity in non-conserved plots may be related with high rainfall, associated with leaching and removal of important soil nutrients. High amount of rain water leaches soluble bases and consequently contributes to soil acidity.

5.2. Soil organic carbon (SOC)

The accumulation of SOC is one of the main soil forming processes and is determined by physical, chemical, biological and anthropogenic factors with complex interaction (Gaiser & Stahr, 2013). Previous studies in Ethiopia reported that the SOC content of the soil is affected by SWC measures. SOC showed a statistically significant difference (p < 0.05) between the treated and untreated fields in Northern Ethiopia (M.Guadie et al 2019).

In Southern Ethiopia, Gola watershed it is reported that relatively high value of organic carbon content in treated land than non-treated land. Both of the mean values of organic carbon 1.18 for treated and 1.10 for untreated farm fields are found were not significant ( H.Gankiso 2017). S.Hishe et al. also reported that a small difference in SOC concentration was found between terraced and non-terraced land. The SOC has a direct relationship with the vegetation cover and conservation measures application and inversely related with intensive human and livestock interference. Landscapes with different management had a significant effect on SOC. The same result was recorded in Southern Ethiopia (Wolaita Zone) that SWC practices influenced soil organic carbon (OC) of farmlands positively. The mean value of soil OC range between 1.34 and 1.74% in which integrated SWC established for 5years had the highest value and the minimum was obtained on non-conserved land (Tesfaye and Fanuel, 2019). Overall, it was noted that the longer the age of SWC practices and its integration with biological measures, the positive is its impact on soil OC of cultivated lands. This might show that SWC practices have a positive role in improving soil OC. As a result, supporting terracing with vegetation could result in high SOC and SOM due to high biomass return, which contributes to symbiotic fixation and soil erosion reduction.

5.3. Total Nitrogen (TN)

Total Nitrogen (TN) is the sum of all form of Nitrogen (ammonia, organic and reduced Nitrogen) and Nitrate-Nitrite in soil. The content of total nitrogen of the soil affected by SWC practices. S.Hishe et al, (2017) reported that the TN content had statistically significant difference at p<0.05 between terraced and non- terraced hillside in Northern Ethiopia. In finding of North Western Ethiopia, TN showed a statistically significant difference (p ≤ 0.05) between the treated and non-treated fields. The treated fields showed higher TN values than the untreated fields, which could be associated with the implementation of SWCPs that maintain soil fertility by decreasing the removal of SOC and TN through soil erosion. This finding is in line with Ademe et al., 2017 and Mulugeta et al., 2010, who found that higher TN content was recorded in treated fields compared with untreated fields in southern Ethiopia and northwest Ethiopia, respectively. In contrary H. Gankiso (2017) reported that the average total nitrogen content for both treated and untreated farm fields is rated low that it’s not shows a significant difference. This low value of total nitrogen could be due to the fact that the area is moist kola and this may cause leaching of nitrogen in the soil. The other reason might be related to management problems in improving the nitrogen content by growing leguminous plants that fix nitrogen from the air through the nodules of their roots.

5.4. Available Phosphorus (Av-P)

Available Phosphorus (Av-P) showed a statistically significant difference between the treated and non-treated fields in North western Ethiopia (M.Guadie et al,2019) . Low Av-P from non-treated fields was due to continuous cultivation without SWCPs, extractive crops biomass harvest, and soil erosion, as indicated by the findings of Dejene.T (2017) and Ademe et al (2017) in eastern and southern Ethiopia, respectively

The average available phosphorus high values of treated farm fields and low untreated farm fields with mean value 19.77and 18.11 are recorded in both management fields in Gola water shed, southern Ethiopia. This indicates not significant differences (H. Gankiso, (2017). In contrary Belyneh et al (2019 ) reported that the available phosphorous content of the soil between conserved and non-conserved plots did not have consistent pattern with conservation measures in Gumara watershed ,Northern Ethiopia. The application of Diammonium phosphate (DAP) may be the reason for its indistinguishable availability in the soil.

5.5. Cation exchange capacity (CEC)

The cation exchange is important in soils, as it measures the basic nutrient holding capacity (Bell 1993). Same study conducted by Bridge and Probert (1993) have noted that soils with low CEC(less than 10%) are poor at holding cationic nutrient. The CEC is a measure of the soil particles ability to exchange cations with freely mobile cations added to the soil matrix. The findings of Challa et al. (2016), Mengistu et al. (2016), and Selassie et al. (2015) reported SWC structures affect CEC of the soil. The conserved soil had significantly higher CEC than non-conserved soil. In Gumara watershed, Northwestern Ethiopia, Conservation measures caused a relatively higher CEC in conserved soils than in non-conserved but the difference did not show statistical significance. Sinore et al. (2018) reported a significantly higher CEC and exchangeable bases in a soil treated with susbania and elephant grasses than in controlled soil in Lemo District, Southern Ethiopia. Supporting terracing with such plants/ grasses strengthens the bund, generates high biomass, and increases OM and better control of erosion, consequently increases CEC in the soil. In Lole watershed, North Western Ethiopia, CEC showed a statistically significant difference (p ≤ 0.05) between the treated and untreated fields. Soils in the treated fields showed significantly higher CEC than the untreated fields (M.Guadie et al 2019). In southern Ethiopia Gola micro watershed, the mean value of treated watershed 41.03 and untreated farm fields are 41.01 and the result reveal that CEC ranges from 34.7 to 49. 84 for treated and from 38.84 to 42.57 for untreated. It was not significant differences among treated and untreated fields. The value of CEC slightly increased in all slope classes. However, it was slightly decreased in untreated fields (H. Gankiso 2017). It is necessary to note that the higher levels of the CEC are mostly related to the higher level of organic carbon in the soil. These higher CEC, are the more cations it can retain.

Table 1 Details of studies on the impacts of SWC practices on soil physical and chemical properties. Positive impact (+), negative impact (−) and not studied (NS)

Abbildung in dieser Leseprobe nicht enthalten

Table 2 Selected Soil physico-chemical properties as influenced by conservation practices in cultivated lands of Bashe micro-watershed,2018

Abbildung in dieser Leseprobe nicht enthalten

CV coefficient of variation, NC Non-conserved, PSWC-2 Physical SWC-2 year,ISWC-2 Integrated SWC-2 year,PSWC-5 Physical SWC-5 year,ISWC-5Integrated SWC-5 year,C.loam clay loam

Source - Tesfaye and Fanuel (2019)

In the above table (table 1) integrated SWC for 5 years reduced the soil bulk density; and increased soil pH (5.87 to 6.60), organic carbon (1.34 to 1.74%) and available phosphorous (8.06 to 25.23 mg kg−1) compared to non-conserved land. It showed that SWC practices have positive impacts on soil properties of cultivated lands; however, they have more pronounced effect when physical SWC practices are integrated with biological SWC practices and at a longer establishment

Table 3- The mean and their significant variations (one-way ANOVA) of soil chemical properties in conserved and non-conserved plots

Abbildung in dieser Leseprobe nicht enthalten

Av. P available phosphorous, CEC cation exchange capacity, CL conserved land, NCL non-conserved land, ns not significant at p<0.05, Ppvalue, SOC soil organic carbon, SOM soil organic matter; **,* significantly different at p<0.01 and p<0.05 respectively (two-tailed); TN total nitrogen

Source - Belayneh et al. (2019)

Soil and water conservation practices have resulted in a statistically significantly higher mean values of total nitrogen, exchangeable Na+ and Mg2+ at p<0.01, and of soil organic carbon and organic matter at p<0.05 in the watershed(Table 2). The clay content, soil reaction, cation exchange capacity, and exchangeable K+ showed non-significant, but higher mean values in conserved plots. Furthermore, the effects of conservation practices on soil properties were found more effective in cultivated land uses as compared to that of grazing land uses. This is because conservation treatments had significant effects on organic carbon, total nitrogen, exchangeable Na+ and Mg2+ in cultivated land uses but only on exchangeable Na+ in grazing land uses. The interaction effect of treatments and land uses did not reach a statistically significant result for any of the soil properties considered in this study.

6. Conclusion

Soil erosion is the deterioration of soil by the physical movement of soil particles from a given site. It is a natural process, which is usually accelerated by human action. It becomes a problem when human activity causes it to occur much faster than under normal conditions. SWC practices are the best option to sustainable agriculture, crop productivity and to increasing soil fertility. Terraces/bunds were important for many years especially during cropping season conserve the soil from runoff. SWC measures like terraces and bunds reduce soil erosion if they are correctly constructed and maintained, and if they are compatible with local environmental conditions. Conservation measures have important implications for improving soil fertility in many part of Ethiopia.

Constructing physical structure alone does not restore the soil fertility to the level that the crop is demanding. To pronounce their effect physical SWC practices should integrate with biological SWC practices and for a longer establishment. Therefore, proper guidance and follow-up, use of agro-forestry and grass strips, and maintenance are required for the watershed’s sustainability and good soil conditions. Supporting SWC structures with grasses and trees is very important for strengthening their effectiveness in improving soil fertility and decrease soil erosion in the watershed. Hence, integral use of both physical and biological SWC options and agronomic interventions would have paramount importance in improving soil quality.

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