Effect of Soil and Water Conservation for Soil Fertility Improvement

Table of Contents

1. INTRODUCTION

2. LITERATURE REVIEW
2.1 Effect of SWC measures on soil physical properties
2.1.1 Soil texture
2.1.2 Bulk density (BD)
2.1.3 Infiltration rate (conductivity)
2.2 Effect of SWC measures on soil chemical properties
2.2.1 Soil organic matter (SOM)
2.2.2 Total nitrogen (N)
2.2.3 Soil pH
2.2.4. Cation exchange capacity (CEC)
2.3 Effects of soil and water conservation on soil erosion reducing and crop production
2.3.1 Common SWC techniques used for soil erosion control
2.4 Effects of soil and water conservation on soil fertility improvement

REFERENCES

1. INTRODUCTION

The population of the world is dependent on land resource for food and other necessities. More than 97% of the total food for the world’s population is derived from land, the remaining being from the aquatic system. About 16% of the world’s agricultural land is affected by soil degradation (UNEP, 2002). Globally, out of 22% of the land suitable for sustaining agricultural productivity, around 5 to 7 Mha are being lost annually due to land degradation, consequently, threatening food security of the world. Soil and water resources conservation and management is important for the welfare of the people (Lal, 2001).

In Africa, the problem of soil erosion is estimated to cause damage of $26 billion annually to productive soils (Lal, 2001). This, according to Angima et al., (2003), leads to 5 million grams per hectare of productive top soil being lost to lakes and oceans each year. These processes of degradation contribute to the worsening poverty and further marginalization of rural people in sub-Saharan Africa. If farmers' resource base cannot be secured and rendered more productive, the decline in rural standards of living will accelerate. Soil and water conservation must therefore be central to strategies of agricultural and rural development in sub-Saharan Africa. On farm conservation must be linked to enhanced strategies for communal property resource management. Such links will ensure optimum returns from land resources and promote a holistic approach to sustainable environmental conservation and resource management.

In Ethiopia more than 85% of the population live in rural areas and derive their livelihoods from agricultural activities. Therefore, soil and water conservation in Ethiopia is not only related to improvement and conservation of the environment but also it is a key factor for sustainable development of the agriculture sector and the economy of the country at large (Teklu, 2005; Gete, 2000).SWC measures are benefiting by reducing soil erosion and changing the soil properties for agricultural productivity. Hence, it is worthwhile to investigate the effects of SWC measures on key soil properties to evaluate the benefit of treating lands with bio-physical SWC measures. Physical SWC structures should be integrated with enclosure to enhance rehabilitation of degraded watersheds/landscapes. Integration of biological SWC measures that improve soil fertility are essential on the cultivated land of the watershed.

Soil and water conservation techniques applied in cultivated land increased runoff conservation efficiency by 32% to 51%, depending on the site. At the moist subtropical site in a highland region, soil and water conservation increased soil moisture enough to potentially cause waterlogging, which was absent at the low-rainfall sites. Soil bunds combined with Vetiveria zizanioides grass in cultivated land and short trenches in grassland conserved the most runoff (51% and 55%, respectively). Runoff responses showed high spatial variation within and between land use types, causing high variation in soil and water conservation efficiency. Our results highlight the need to understand the role of the agro-ecological environment in the success of soil and water conservation measures to control runoff and hydrological dynamics. This understanding will support policy development to promote the adoption of suitable techniques that can be tested at other locations with similar soil, climatic, and topographic conditions (Sulutan et al.,2018a).

2. LITERATURE REVIEW

2.1 Effect of SWC measures on soil physical properties

The physical properties of soils determine their adaptability to cultivation and the level of biological activity that can be supported by the soil. Soil physical properties also largely determine the soil's water and air supplying capacity to plants. Many soil physical properties change with changes in land use system and its management (Tugizimana J., 2015).

2.1.1 Soil texture

Soil texture: The textural classes of top soils treated with According to Mulugeta and Karl (2010) assessment of integrated soil and water conservation practice on key soil properties shown that by using different soft wares textural classes of top soils treated with SWC measures and that of the untreated lands have differences which were confirmed through statistical analysis of the soil laboratory data. The analysis revealed a significant variation of top soil texture in percent sand, silt and clay content due to effect of SWC measures (Table 1). Soils of the non-conserved land had the highest percent clay and silt compared to the soils of the conserved one. The textural classes also have a significant variation. The majority of the sample profiles of the conserved land have a top texture of clay loam and for the untreated is clay. Herweg and Ludi (1999) pointed out that complete removal of topsoil at the loss zone causes the subsoil-dominated by clay material to move down slope and deposited on top of the fertile accumulation. They also indicated that tillage and water erosion causes colluvium to be deposited in the lower part of fields while soil profiles are truncated in the upper part. Desta et al. (2005) confirmed by their study that annual mass of soil displaced down slope from the truncated area by tillage erosion for 202 study plots was estimated to 39 - 50 kg yr -1. Age of the bund had a significant impact on the impact on the lowering of percent clay fraction as it lowers slope gradient and reduced soil erosion and soil organic matter increased with relative soil depth change.

In general bunds play a great role in reducing the incorporation of clay-dominated soil from the subsoil to the surface soil, which resulted from removal of topsoil and exposure of the subsoil by erosion. Highest clay content in the non-conserved watershed was due to the exposure of soil by tillage to soil erosion by water ultimately exposes the subsoil, which is naturally high in clay content.

Table1. Effect of SWC measures on soil texture.

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According to Kagambèga et. al., (2017) Effects of Soil and Water Conservation Techniques on Soil Properties under Degraded Lands shown that Variations in soil texture under the treatments plots in the different sites in table 2 the soils under HM were considerably higher in clay and fine silt, and slightly higher in coarse silt than the soils under the others treatments. Accordingly, the sand content was the lowest in the soils under HM treatment and the highest under the control. Although the differences were not significant, clay content and coarse silt were the highest in HM and ST treatments followed by zaï treatment and the lowest in control; Fine silt and sand content (fine or coarse).

Table2. Means (N = 5) and standard deviation (SD) of soil texture under the different treatments in the rehabilitated sites (Gampèla and Baporé) in 2010.

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Soil texture affects the infiltration and retention of water, soil aeration, absorption of nutrients, microbial activities, tillage and irrigation practices (Foth, 1990; Gupta, 2004).

2.1.2 Bulk density (BD)

The one way analysis of variance revealed the presence of significant difference in mean value of bulk density for the samples analyzed in this study. The non-conserved micro-watershed was found to exhibit significantly the highest mean value of bulk density than the micro-watershed treated with SWC measures. This could be attributed to the presence of significantly higher organic matter as a result of conservation measures. In this study, the relatively lower bulk densities of 0.92 and 0.93 g cm-3 were recorded on soils taken from the conserved grassland and cultivated lands with slopes of 6 and 12%, respectively. This implies that more roots of plants, higher organic matter and sediment are accumulated in this zone of the micro-watershed. As the land slope decreases runoff speed also decreases, sediments and organic matter started to settle ( Mulugeta and Karl , 2010).

Root abundance, crop stand, crop production and crop residues are better in lower slopes of the micro-watersheds compared to its upper slopes as soil depth upslope is shallow which limits plant growth due to shallow soil depth even with similar conservation measures (Table 2). The topsoil bulk densities of the sampled soils are in line with the ranges described by Rai (1998); Landon (1984) that is, between 0.92 to 1.17 g cm-3.

According to Mulugeta and Karl (2010) assessment of integrated soil and water conservation practice on key soil properties shown that the significant effect of SWC measures on bulk density was observed in the lower slope of the micro-watersheds where bulk density is higher in the non-conserved land than the conserved micro-watershed. The reason for this could be higher accumulation of soil sediments that were eroded from upslope. The upslope part of the two micro-watersheds has almost similar top soil bulk densities.

Table 3. The effect of SWC measures on soil bulk density.

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2.1.3 Infiltration rate (conductivity)

Infiltration rate is the soil capacity for letting water to percolate in a given period of time. The measurement is usually done in centimetres per hour. Soils with a SWC measures have a better soil infiltration rates compared to the non-conserved one. Inrelative terms soils with biological SWC measures have a better infiltration rate than a physical SWC measure due to the roots penetration effect and addition of soil organic matter from plant bodies through decomposition. Infiltration tests conducted confirmed that soil physical structures stabilized with vegetative measures had the highest mean value of infiltration rate compared to the other conservation measures. The non-conserved micro-watershed had lowest mean value of infiltration rate ( Mulugeta and Karl , 2010).

The soil organic matter content and percent clay soil separates seemed to play a role for the variation of infiltration rates. Organic matter was positively correlated with the infiltration rate while clay percentage was negatively correlated. Landon (1984) indicated that physical SWC structures enriched with vegetative measures had better infiltration rate than lands conserved with only physical structures.

2.2 Effect of SWC measures on soil chemical properties

Soil chemical properties are the most important among the factors that determine the nutrient supplying power of the soil to the plants and microbes. The chemical reactions that occur in the soil affect processes leading to soil development and soil fertility build up. Minerals inherited from the soil parent materials over time release chemical elements that undergo various changes and transformations within the soil (Lilienfein et al., 2000).

2.2.1 Soil organic matter (SOM)

Soil organic matter differences between the conserved and non-conserved micro-watersheds were statistically significant (p ≤ 0.05). The variations in mean value of organic carbon (Corg) can be attributed to the effect of SWC measures implemented. Moreover, the age of bunds stabilized with vegetative measure have a better effect in soil organic matter accumulation. This finding agrees with the findings of Million (2003) who studied the effects of indigenous soil and stone bunds on soil productivity. The study revealed that soil organic matter content of three terraced sites with original slopes of 15, 25 and 35% were higher compared with the corresponding non-terraced sites of similar slopes. Similar conditions were also observed for slope range of 15 to 25% which had 2.3% soil organic matter for the conserved land while 0.85% for the non-conserved ones ( Mulugeta and Karl , 2010).

Chemicals properties of soil total organic carbon (Ctotal) content was significantly higher in HM treatment than that of the others treatments; despite the no significant difference between ST, Zaï and control, the values were the highest in SS followed by Zaï. However in Baporé, Ctotal was significantly higher in HM, SS and Zaï treatments than control. In the two sites, total nitrogen (Ntotal) followed the same trend as the Ctotal variation in relation to treatments. Furthermore, Calcium (Ca), Magnesium (Mg) and pH (H2O) had the same trend as well as available potassium (K) although the differences were not always significant. But the C/N relation did not follow the trend. Available plant phosphorus (P) amount was the highest under Zaï treatment in the two sites (Kagambèga et. al., 2017).

According to a study made by Bot and Benites (2005), soil organic matter accumulation is often favoured at foot or lower slopes of hills of non-conserved lands for two reasons: 1) they are wetter than mid and upper slopes, 2) organic matter would be transported to the lowest point of the landscape with runoff and soil erosion. The soil organic matter content has a positive correlation with the fine soil particle content of the soil that is, with the soil textural classes. Soil texture appears to have an important impact on the amount, distribution and chemical properties of soil organic matter (SOM) components. The agricultural significance of soil organic matter in tropical soils is greater than that of any other property with the exception of soil moisture. Its functions are to improve soil structure, and thereby root penetration and erosion resistance; to augment cation exchange capacity; and to act as a store of nutrients, slowly converted to forms available plants ( Mulugeta and Karl , 2010).

2.2.2 Total nitrogen (N)

The analysis made using statistical methods revealed that the mean total nitrogen difference due to the impact of SWC measures was significant at p ≤ 0.05. Table 4 presents the mean value of sampled top soil total nitrogen content. However, physical SWC measures stabilized with nitrogen fixing plants have indicated that the total nitrogen (N) is much higher compared with other biological measures. The non-conserved land had the smallest mean value of total nitrogen (N). Million (2003) also found that the mean total nitrogen content of the terraced site with the original slope of 15, 25 and 35% were higher by 26, 34 and 14%, respectively, compared to the average total nitrogen contents of their corresponding non-terraced sloping lands. Moreover Mulugeta and Karl (2010) assessment of integrated soil and water conservation practice on key soil properties made a linear regression analysis to see correlation of nitrogen with soil organic matter has shown that there is a strong positive relation between them at (p ≤ 0.01 and = 0.89) ( Mulugeta and Karl , 2010).

Table 4. Effect of SWC measures on total nitrogen (N) within 25 cm of soil depth.

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2.2.3 Soil pH

Soil reaction has a direct influence on chemical and biological soil properties and parameters. Low productive soils and sites were associated with low pHs and corresponding low levels of exchangeable bases and organic matter. Soil pH in a soil can be attributed to the type of parent material, extent of soil erosion or the leaching of bases as a result of climatic factors. Soil pH is an indispensable means for characterizing soil from the standpoints of nutrient availability and soil physical conditions like structure, permeability, workability etc. It is also indicative of the status on microbial environment/ community and its net effect on the mineralization of organic residues like humus and/or immobilization of available nutrients and also provides the most rational basis for managing soils for selective agricultural land uses such as crop production, pasture cultivation, forestry, etc.

According to Mulugeta and Karl (2010) assessment of integrated soil and water conservation practice on key soil properties shown that soil pH is also associated with soil fertility status. Soils with high organic matter content have a higher soil pH which favours better exchange of bases and increase availability of nutrients that are needed for the growth of plants in a given soil and ecology. The mean value of pH for the sampled soils in this study shows minor difference between the conserved and non-conserved micro-watersheds .

Table 5. Effect of SWC measures on soil pH.

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2.2.4. Cation exchange capacity (CEC)

The cation exchange capacity (CEC) is a measure of the number of adsorption sites per unit weight of soil at a particular pH. CEC is affected quite dramatically by pH changes. Soils with high in organic matter or 2:1 type clays have a high CEC. In contrast, soils dominated by kaolinite and hydrous oxide clays generally have a low CEC. In many weathered tropical soils the maintenance of organic matter is critical in order to maintain the CEC at a satisfactory level.

According to Mulugeta and Karl (2010) assessment of integrated soil and water conservation practice on key soil properties by using A linear regression analysis confirmed the presence of significant positive relationship between CEC and percent phosphorous (P) in the studied micro-watersheds were found to be significantly different between the conserved and non-conserved (Table 6).

Table 6. Effect of SWC measures on available phosphorous (P).

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It is evident that the total available phosphorus is much higher in the conserved one. Organic sources of phosphorous are important in these areas for amending the agricultural land for a better land productivity ( Mulugeta and Karl , 2010).

According to Han et. al., (2018) Effects of Soil and Water Conservation Practices on Runoff, Sediment and Nutrient Losses by using a linear regression analysis runoff and sediment are the carriers of nutrients. Soil and water conservation practices exert influences on nutrient loss by retaining runoff and reducing erosion. TN and TP losses under different soil and water conservation practices are shown in Figure 5. According to t-test result, the impact of rainfall on TN (p values for bare land 20 m, bare land 10 m, agricultural land 10 m, narrow terraces 10 m, fish-scale pits 20 m and shrub 30% 10 m are 0.015, 0.011, 0.042, 0.037, 0.039 and 0.034, respectively, all of which are less than 0.05) and TP (p values for bare land 20 m, bare land 10 m, agricultural land 10 m, narrow terraces 10 m, fish-scale pits 20 m and Shrub 30% 10 m are 0.014, 0.013, 0.047, 0.038, 0.042 and 0.039, respectively, all of which are less than 0.05) was significant .

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2.3 Effects of soil and water conservation on soil erosion reducing and crop production

Existing literature and information shows that soil and water conservation practices such as terraces, mulching, cover crops, tree planting along contours can considerably reduce soil loss due to water erosion if they are well planned, correctly constructed and properly maintained (Taddese, 2001; Mekonen and Tesfahunegn, 2010). If not maintained, they can provoke land degradation. However, according to GebremariamYaebiyo Dimtsu*, Mulubrehan Kifle, Girmay Darcha,( 2018). Rsearch result shown that its representativeness with respect to intensive SWC practices such as stone bunds, hillside and bench terraces, trenches, gabion check dams and exclosure with enrichment of plantations have been carried out. SWC interventions have been started before 15 years ago in this watershed Tigray, Ethiopia; but they have not been evaluated scientifically; hence, old SWC measures have been evaluated in this study.

Investments in SWC practices enhance crop production, food security and household income (Adgo et al., 2013). Studies show that despite the availability of many best SWC practices in watershed management, they are highly localized, and are not being expanded to other areas, while land degradation due to soil erosion and deforestation are still the main problems in Ethiopia. Other studies such as Tesfaye et al. (2013) and Teshome et al. (2014) revealed that the adoption rates of SWC technologies vary considerably with in the country. This is because investments by farmers in SWC are influenced by ecological, economic and social impacts of the SWC technologies. Despite the massive mobilization of resources for SWC measures, only a few studies have been done to evaluate the effectiveness of integrated watershed management on rehabilitation of degraded watershe. Accordin to GebremariamYaebiyo Dimtsu*, Mulubrehan Kifle, Girmay Darcha,( 2018). research result stated that the estimated sediment deposition of each SWC structure indicated that the highest values (126 and 123.9 t/ha/yr) were recorded on the lower uncultivated land and upper cultivated land positions of the watershed, respectively (Figure1)

Likewise, the lowest sediment deposition (75.9 t/ha/yr) was recorded on the lower landscape position of the watershed (Figure 1). There was overflow of sediments along the old SWC structures. Farmers in the lower part of the watershed used cut-off drains to reduce the over run-off and sediments on their cultivated land; and the upper beneficiaries increased the height of the structures on their farmland when they filled with sediments. Up to 1.1 m deep soil accumulated along SWC structures.

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Figure 1. Sediment deposition behind SWC structures

2.3.1 Common SWC techniques used for soil erosion control

The most common soil and water conservation practices used by farmers were agroforestry (45%), followed by contour bund (29%), bench terracing (11%). Strip grass, ditches and fallow, were used less frequently than the other practices accounting respectively 7%, 4% and 1% on table 8, Joas Tugizimana,(2011).

Table 8 Common practices for soil erosion control

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2.4 Effects of soil and water conservation on soil fertility improvement

Accoring to Hongli Mu & Suhua Fu & Baoyuan Liu & Bofu Yu &Aijuan, (2018). Wang research study shown that soil and water conservation (SWC) measures can be adopted to conserve soil and water and improvesoil fertility. in the Beijing mountain area on soil fertility. Six runoff plots, including a fish pit (fallow) (FPF). Fish pit (Platycladus orientalis L. Franco) (FPP), narrow terrace (fallow) (NTF), narrow terrace (Juglans regia L.) (NTJ), tree pan (Juglans regia L.) (TPJ), and fallow land (FL), were established to analyze the differences in soil fertility in the Beijing mountain area. Soil samples were collected in 2005 and 2015 from the six runoff plots. Soil particle size; soil total nitrogen (TN), total phosphorous (TP), total potassium (TK), alkali-hydrolysable nitrogen (Ah-N), available P (Av-P), and available K (Av-K); and soil organic matter (SOM) were measured. The soil integrated fertility index (IFI) was calculated. The results showed that the soil nutrient content and IFI significantly decreased from 2005 to 2015 in the FL plot and significantly increased in the five runoff plots with SWC measures. Compared to the other runoff plots with SWC measures, the FPP plot more significantly improved the soil nutrient content and IFI. The TN, AhN, Av-K, SOM, and IFI in the FPP plots increased by 98%, 113%, 61%, 69 and 47%, respectively, from 2005 to 2015. The IFI for the FPP, NTJ, and TPJ exceeded the average IFI of the farmland soil in the study region.

The results indicated that the combination of engineering practices and vegetative measures effectively improved soil fertility. A t test was used to compare the soil fertility parameters of the 5 SWC measures in 2005 and 2015, and theprincipal component analysis was conducted in SPSS 20.0

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Score of parameter to soil fertility of SWCs in 2015

Figure 2 The score of parameter to soil fertility of soil and water conservation measures (SWCs) in 2005 and 2015 (FL - fallow; FPF - fish pit (fallow); FPP - fish pit (Platycladus orientalis L.Franco); NTF - narrow terrace (fallow); NTJ - narrow terrace (Juglans regia L.); TPJ - tree pan (Juglans regia L.))

Table 9 The soil nutrient content of the six runoff plots between 2005 and 2015 was significantly different based on the test (P < 0.05). Dawe et al. (2003) and Remit et al.

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Table 10 Content of soil nutrient parameters in different soil and water conservation measures

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