The Cradles of Adoption: Perspectives from Conservation Agriculture in Ethiopia

Abstract

Several technologies have been provided to farmers to increase production under the rainfed systems of Ethiopia. However, much attention has been focused on drought emergency relief and associated interventions. Conservation agriculture (CA), among others, has been recently encouraged as part of the sustainable intensification technology in the Ethiopian smallholder farming systems. However, CA research in Ethiopia has traditionally stayed for a long time on a station-based research approach over a controlled environment followed by demonstration plots conducted, in most cases, for a short period. Considering large natural agro-hydro-ecological diversifications and the socio-economic conditions of smallholder farmers, it is possible to envisage that various versions of CA may be adopted based on different climate and topographic settings. Hence it entails various forms of adoption research depending on the biophysical and socio-economic conditions. Therefore, adopting CA technology is not as simple as adopting the technology or its components, as adoption is not only based on benefits but is also a process of inculcating CA into the human and social elements (culture, gender, social, and beliefs), and integrating CA within the farming systems (e.g., crop type, rotations, and agronomic management), and production systems (e.g., irrigated, rainfed, and livestock). In this regard, a review of CA technology usage provides an important perspective to explore the findings and the functionality of current CA research systems regarding the nature of its development, promotion, and dissemination in Ethiopia. This manuscript explores how CA is viewed by local farmers and associated researchers using the results from station to farmer-designed on-farm studies in the Ethiopian highlands, including irrigated and rain-fed production systems. This review paper will be crucially important for researchers and policymakers to develop conservation agriculture as one strategic issue for future sustainable irrigation and natural resource conservation.

1. Introduction

Several technologies have been provided to increase production under the rainfed systems of Ethiopia, although much attention has been focused on drought emergency relief [1]. Over the past four decades, new technologies have been introduced in the agriculture sector, such as the use of improved crop varieties [2], the extension of drip irrigation [3,4,5,6], the adoption of conservation agriculture practices [7], the use of alternative energy sources [8,9,10], and the use of biochemical fertilizers and pesticides [11]. However, there has been limited adoption of such technologies over various climate and socioeconomic settings of the highlands of Ethiopia, and the adoption rate of these technologies by farmers is still very low. This low adoption rate has been due to several constraining factors, which include technical, political, legal, cultural, and socio-economic factors [12].

Conservation agriculture (CA), among other practices, has been encouraged as part of the sustainable intensification technology in the Ethiopian smallholder farming systems [13,14,15]. By definition, CA has been defined by three linked principles, which include continuous minimum soil disturbance, permanent organic soil cover, and diversification of crop species grown in sequences [15]. However, CA practice and research in Ethiopia have traditionally stayed for a long time on a station-based approach in an over-controlled environment followed by demonstration plots in farmers’ fields. Over the past sixty decades, there has been a theoretical movement away from such centralized research systems to a system on a more participatory basis where researchers and farmers under on-farm experiments develop new practices. On-farm experimentation shortens the overall time for the farmer to understand the processes, constraints, and impacts [16]. However, there might be limited interaction with researchers or farmers when developing and proving various agricultural technologies in the country in various environmental settings [17] and input levels.

Ethiopia is a diverse country where the climate and agro-ecological settings extend from extreme lowlands (<200 m above mean sea level, asl) to highlands (4620 m asl) with cool climates, and in between a great diversification of natural resources, habitats, biodiversity, and climates exist. Similarly, the mode of farming activities, the type of crop and livestock production systems, the ways to cope with different climate extremes, and the use of types of farming implements or technologies significantly varies and depends on various biophysical, and socio-economic conditions [18]. From such diversification, it is possible to state that a single version of CA technology might not be sufficient for all local situations in the country, and hence it entails various forms of CA depending on site-specific conditions. Because the adoption encompasses all processes of increasing benefits, the adoption of CA technology is not as simple as using the technology itself. The CA adoption process includes the process of inculcating CA into human elements (e.g., culture, gender, social, and beliefs) [12], integrating CA with the local farming systems (e.g., crops, crop rotations, and agronomic management practices) [18], and associating CA with different modes of production systems (irrigated, rainfed, and livestock) [6]. These items must be considered while evaluating the technology under the farmers’ field conditions.

Globally, CA has been used in principle as well as on a contextual basis [19]. The formulated principles of CA have been stated as a production system based on the three interrelated elements defined earlier. Soil cover can include either live cover crops [20,21], terminated cover crops [22], mulches of crop residues [23], or transported mulches [24]. This shows that CA with only the cover component may have various versions contextually, and may also vary when used for particular objectives, such as protection against erosion [25], increasing soil moisture in dry regions, enriching the soil with organic matter [24], and preventing the growth and regrowth of weeds [26]. Diversified cropping sequences or patterns are composed of at least two or three species including one legume [27,28], however, more species diversity might be needed [29,30]. Similarly, the crop rotation component of CA has various versions that may be developed from variations in local climate conditions. However, contrasting results have been reported on the impacts of different conservation practices globally, particularly between the no-till system and the other forms of conservation tillage (CT) [31,32]. Contrariwise, CT uses one component of CA (residue retention) but substantially disturbs the soil [33,34], hence the findings on CT cannot be directly compared with the findings on CA.

Zero tillage or CT practices still depend on tillage as the structure-forming element in the soil and can be used as transition steps towards full CA. In general, the success of the CA system depends on the interactive synergies among and between the biological, physical (mechanical), and chemical properties and processes over and in the soil to enhance the benefits in the production system. The implementation of CA with mostly undisturbed soils, diverse rotations, and cover crop mixes, particularly in continuous irrigated and rainfed systems, would be the most “natural” system of farming practices in the Ethiopian highlands [16,33]. Irrigated CA maintains a conducive habitat for soil microorganisms throughout the year by providing cover mulch, little soil disturbance, and more soil moisture. Globally, CA practice was extensively used to address the productivity and sustainability issues of large commercial farms in developed nations, and efforts to adapt it to smallholder farms have been extended to developing nations [35].

While the principles and conceptual framework of CA are clear and acceptable worldwide, why are disappointing results reported on the realization of CA [19], particularly for smallholder farms? In particular cases, there is still debate around the feasibility and relevance of CA for African smallholder agricultural systems, including in Ethiopia [36]. Eventually, the aggregated set of practices that combine to form true CA have not been clearly understood and context-specific research in space and time [37] has not been promoted and acknowledged nationwide. Despite the complex behavior of CA in Ethiopia and contradicting literature on its benefits and limited adoption by farmers, CA continues to be a strongly promoted approach to a resilience (e.g., drought shock absorbance) mechanism [25]. Ultimately, the national focus would be on the adoption of CA on overextended local research works in a participatory manner and accumulate scientific evidence on the various beneficial uses of CA. The national strategy of CA may be encouraged by FAO and international research centers, such as the International Crops Research for the Semi-arid Tropics (ICRISAT), and the International Council for Research in Agroforestry (ICRAF) [38].

In this regard, the current review of CA technology provides an interesting case study to explore the findings and the functionality of current CA research systems concerning the nature of its development, promotion, and dissemination in Ethiopia. This paper explores how CA is viewed by CA researchers using the results from on-farm experimental research sites, or station-based researches in the Ethiopian highlands with evidences from global experiences. We explore the context of CA promotion, the farmers’ interest and perceptions yet to be addressed, and political contexts for the wider promotion of CA in the nation. A focused review was conducted on various scales of input availabilities for CA (land, water, nutrients, and energy) that can influence the functionality of CA in national research systems.

2. Challenges and Opportunities of CA in Ethiopia

Agriculture remains crucial for the livelihoods of most rural communities in Ethiopia, amidst the emerging threat of climate change and climate variability. Agriculture, the main base for food security, supports about 80% of the rural population [39]. However, the alarming rise in population to about 121 million, followed by alternating drought and flood remains the country’s major constraint for food production. For instance, the population doubling time decreased from 60 years to about 25 years and is likely to further decrease in the future [40,41]. A marked increase in both the intensity and frequency of droughts has recently become apparent, and in the past 15 years, the country has been hit by climate-change-induced disasters more than 10 times [42]. The prevailing low adaptive capacity of the poorest people will also contribute to the vulnerability of the country to climate change and variability.

In response to feeding the ever-increasing population, the Ethiopian government has promoted the intensification and diversification of agricultural production systems. By definition, intensification is increasing agricultural productivity per unit area. In Ethiopia, fertilizer has been applied in increasing order as a means of attaining intensification and the per capita consumption of DAP (diammonium phosphate; N-P-K, 18-46-0) and urea (N-P-K; 46-0-0) fertilizers are increasing alarmingly from year to year [43]. In addition, farmers’ synthetic fertilizer consumption rate has increased by about seven-fold since the 1960s while the rising price of fertilizers has hindered farmers from intensifying food production [43]. The government of Ethiopia must promote intensification, not with more fertilizer but with a sustainable intensification approach—the adoption of CA based on the nation’s ecological diversification. The crop diversification (in time and space) component of CA would make efficient use of the inputs, increase resilience, and may be adopted by farmers as a production approach under current and future changing climatic conditions.

As a strategy, altering the length of the growing period [44] and varying planting and harvesting dates [39] are key components in the management of crop intensification and diversification practices used to increase agricultural production. In line with this, most farmers living in different parts of Ethiopia have several local adaptation measures where contextual integration or combination with CA may be essential. Growing different improved crop varieties that survive in different seasonal climatic conditions or soil conditions [45] and growing early maturing crop varieties that are tolerant to temperature or water stresses [46] will be key components of CA. Such systems serve as an important form of insurance against rainfall fluctuations, and may also be used with deficit irrigation systems [39]. This supports the idea that growing different crop species and crop varieties on the same plot or different plots reduces the risk of crop failure. In addition, certain crop species may be beneficial to each other, one for the other as a cover or as a nutrient source, and minimize the incidence and intensity of pests, disease, and weeds, and this, in turn, gives minimum assured returns in CA for livelihood security. In general, crop diversification practices have been traditionally common in Ethiopia since ancient times and also includes livestock in wider cases [47].

Ethiopia has a high level of continued soil erosion seriously threatening peoples’ livelihoods, especially in the drought-prone parts of the country. In this case, the use of various layers of continuous and diverse crop cover, defined as one component of CA, can control soil erosion [25]. Hence, CA is vital to ensure the resilience of crop production systems from soil erosion due to nutrient losses, from increased precipitation events, from extended intervals between rainfall events by increasing soil water infiltration and residual soil moisture, thereby increasing yield and the biomass of crops. For example, Figure 1 shows how Vetch forage (Vicia vilosa) was intercropped with maize (Zea mays) at the stage of tassels with some residual soil moisture and crop residues left for the next crop period. When such practices are repeated for a number of years, CA can assist to restore soil health by capturing soil carbon and enabling reduced oxidation of organic matter in the soil [32].

In combination with CA, improving the use of irrigation technology is perceived as an effective means to stabilize yields in rainfed systems [48,49], particularly in countries such as Ethiopia where about 85% of the rainfall occurs during about 25% of the time in the year [50]. Irrigation can improve agricultural productivity by supplementing water during dry spells [51] and by deterring crop losses due to drought [52]. Moreover, efficient use of water by using drip irrigation-based CA would increase the efficiency of water use thereby increasing the number of hectares of production in dry periods (Figure 2). Other benefits of using (organic) mulch include the regulation of soil temperature [53] and the reduction of pests and diseases during dry periods [54].

The landholding size per farmer in Ethiopia is currently declining, and associated with this, the average number of oxen per farmer has decreased, and renting oxen for such a small land size is not rewarding. As an option, the use of herbicides before crop planting to reduce tillage frequency is not attractive due to the rising costs of imported chemicals (herbicides). However, Ethiopia’s agroecological diversification encourages the growth of various bowls of cereal or vegetables, and the use of several tillage systems including hoe tillage that would be pertinent to the cultivation of vegetables under the small land tenure size of Ethiopian farmers. The overall traditional systems of production should be properly integrated and contextualized in the various forms of CA practices and the scientific community should work with the local community in the process of refining and innovating such technology for site-specific climate-smart management.

3. Yield Returns and CA Implementation

Experimental CA studies in continuous wet and dry monsoon phases showed a higher and more stable crop yield of irrigated vegetables in the Ethiopian highlands. Although short-term yield effects are variable for cereal crops in other parts of the world [55], the benefits are important because they determine to a large extent the attractiveness of CA to farmers [55]. The negative effects on certain crops at a particular location, usually in the initial years, may discourage the adoption of CA by farmers [19]. However, the variability in short-term crop yield responses to CA is commonly affected by several factors which include, among others, the crop type, soil characteristics, mode of farming, adaption methods or approaches, climate settings, and human factors.

For instance, one beneficial effect of CA is improved rainwater use efficiency through enhanced infiltration and reduced evaporation losses. In this case, when moisture is a limiting factor, crop yields may be improved [55]. However, under more humid conditions and on poorly drained soils, the equivalent effect can cause waterlogging resulting in yield reduction of the same crop; the farmer may choose a moisture-tolerant crop (e.g., rice) and improve the yield return. For example, CA practices were widely adopted in the commercial farming sector in Zimbabwe and equal or improved maize (Zea mays) yields were obtained compared to conventional production systems in dry years but tended to be depressed during wet seasons [56], and this finding seemed contradictory to CA practice since the study lacked some important CA elements (e.g., crop diversification). However, with such missing components, the yield result was positive or equal [57,58].

In addition, in the 4-year experiment in the Ethiopian highlands under supplementary irrigation at the initial stages (maturity during wet seasons), CA apart from numerous other advantages, improved yield and the early maturity of pepper compared with conventional tillage. In the same study, most of the initial and development stages of pepper were sufficiently supported by irrigation and fruit filling stages by rainfall, and the yield return achieved in CA treatment was higher compared with conventional practice (CP) [54]. The yield differences between the treatments were caused by soil moisture availability under CA practice due to the use of grass mulch and minimum soil disturbance, particularly at the initial development stages during the dry months. The yield of pepper was associated with the period of transplanting of pepper relative to the rainfall onset [54]. For the years where irrigation contribution was higher (46% for CA and 56% for CP), the pepper yield was significantly higher than for the years with less irrigation (35% for CA and 37% for CP). This showed that when pepper had less irrigation in its initial stages, most of its growth and fruit stages would be stressed by overwatering followed by reduced pepper fruit production. The authors concluded that transplanting pepper about 2 months before the rainy season can improve the yield since the rainy season coincides with the flowering and fruit development stages. The improved yield under CA in the dry years is largely due to the improved water use in the presence of cover mulch or crop residues, whereas in wet seasons, the absence of tillage with no residue mulch can result in the opposite effect, such as higher run-off and lower infiltration leading to lower yields [59]. The difference in crop yield in the same production period may be due to the local difference in the type of soil, the kind of tillage equipment used, the irrigation approach, the field type (closed or open system), and the level of soil moisture during plowing. Even though the short-term yield effects of CA is variable over space and time, productive benefits accumulate over time as mulching arrests soil degradation and gradually improves the soil in biological, chemical, and physical terms where yield responses tend to be positive.

4. Weed Infestation and CA

Weed control is often recognized as laborious and costly in CA in the first years, with a greater requirement for herbicides than conventional tillage [60]. Consequently, carefully designed tillage may be required in the first year of CA since more labor may be required in cleaning the land from the surface and burying tuber weeds. In addition, such tillage operations should be made in dry periods so that all roots of weeds would be turned-up, dried, and dead. This weed clearing of the land may vary in space and time where appropriate tillage or weeding equipment shall be used at different locations and time scales. Thus, in the establishment of CA practice, weed control can be difficult and costly, but with good management, the weed population would decline over time, due to the combined effects of seed bank depletion in the surface soil, as the seed is no longer incorporated by tillage and the mulch prevents weed seeds from touching the soil and germinating. Moreover, the direct effects of residue cover on weed germination or seed viability may reduce the weed population after the first year [15].

Good ground cover resulting from mulching or covering crops would create less weed pressure with CA, however, ground cover originates after the first year on the cleaned land and care must be taken that all the undergrowth, residues or mulches should be seed-free so that it will not germinate in the next cropping season. According Belay [55] the weeds were managed by using transplanting, drip irrigation, and localized fertilization which are positive activities to control weeds. In line with CA, transplanting crops increased the advantage of the early growth of the crop over the weeds and increased its competitiveness [26]. Other than vegetables, cereal crops, such as sorghum and millet, may also be transplanted and improve yield growing over weed-infested farms [60].

In principle, weed and crop species compete for light, water, and soil nutrients [61]. In this regard, the targeted application of nitrogen and phosphorus fertilizers may substantially reduce weed infestation on cereal crops [62] that would be a sound justification for vegetable yield increase in the Ethiopian highlands in dry and wet phases. Similar to fertilization, targeted irrigation using a drip system has provided an advantage to the main crop in our experimental results by allowing no water into the weed area so that the crop can grow faster and provide cover and suppress weeds [63]. Moreover, within a species, faster-growing varieties may have an advantage over slow-maturing varieties, moreover, genotypes that have a broader leaf area index (e.g., green pepper) may also have an advantage of weed suppressing [64]. When choosing the variety to plant, these criteria can be taken into consideration depending on the weed types present in the field. Based on the type of weeds present, seeding time can be adjusted to improve crop competitiveness; therefore, a good understanding of weed type, specific germination conditions, and their life cycles is important. Ethiopian farmers traditionally adjust the crop density to reduce the weed population and increase crop competitiveness by increasing the leaf area index of the crop and suppressing weed germination or growth [65,66].

A good crop rotation is a key element of a management plan to reduce weed pressure and the associated costs of weed control over time [67]. Any effort to promote CA should underline the importance of an intensive and diversified crop rotation in combination with no tilling where several rules may be used to sequence the crops in rotation [68]. Cover crop rotations can include species that provide a quick and dense groundcover to outgrow the weeds, or species that can produce large quantities of slow decomposing biomasses followed by the main crop [68]. Mulching provides soil cover when the crop is not present or as an additional cover during the planting season [24] with the main function of reducing light from reaching the soil surface and slowing the photosynthesis process thereby inhibiting weed germination [26]. Relay cropping is a method of multiple cropping where one crop is seeded into a standing second crop well before harvesting the second crop [69]. The intercropping of hairy vetch at the fruiting stage of maize shown in Figure 1 is an example of relay cropping. It was used as a nitrogen fixation technique to increase soil fertility and to produce a fodder crop using residual soil moisture without affecting the yield of the main crop (maize) [70]. In addition, the relay cropping system will also compete for nutrients, water, and sunlight with weeds, where weeds could not complete their growth and produce seeds [69]. Relay cropping may solve several conflicts, such as the inefficient use of available resources, controversies in sowing time, fertilizer application, and soil degradation [71].

In practicing a CA system, the use of weed seed-free cover mulch is important. Although there are non-living mulch materials (e.g., plastic) used in different cropping systems, this is not cost-effective for smallholder farmers and there are issues with plastic waste and disposal which results in environmental pollution. For its effective function, sufficient mulch (about 40–100% coverage) has to be applied to cover the soil surface [72]. When using crop residues, it is important to ensure that the residue is evenly distributed on the soil surface to complete the cover where the distribution of residue can be done mechanically or manually during or after harvest. However, manual distribution has a tradeoff with labor depending on the type of residue and biomass used for mulching. Farmers must assess temporal biomass and labor availability since such factors vary periodically (e.g., labor may be available in excess in dry periods when there is no irrigation). In semi-arid regions and on smallholder farms, crop residues may not be readily available, or may compete with use for animal feed or fencing material for housing. In addition, issues related to free grazing, fires, and termites limit the crop residue in the fields.

5. Farming Equipment and Labor Requirements for CA

Concerning the tillage element in Ethiopia, almost all types of tillage systems have been used in the past depending on local climatic and soil variability. Traditionally, the common tillage systems over a certain area are assumed by farmers to be the best measure of that particular climate and topographic setting. Ethiopian tillage practice using oxen drawing Maresha has been sustained for centuries since ancient times [73]. However, at the expense of more labor requirements, the oxen plowing system is currently under stress because of shrinking cultivated areas per household [74], and reduced fodder availability, due to the price rise of oxen (Figure 3a) for meat [75], and land extended degradation [76]. A shift from oxen traction to motorized traction remained stagnant due to the challenges of the rising prices of imported tractors that were higher than ox prices (Figure 3b). In contrast with moldboard or other tractor-drawn tillage tools, the Maresha plow does not turn the soil over and leaves more crop residues on the soil surface thereby providing control over soil erosion. In such cases, the Maresha tillage under normal conditions has a pro-action to CA practice. Apart from high labor efficiency, the use of tractors in the fragmented highland farms (less tractor mobility) is limited or non-existent due to the high initial and probably high operating costs [77]. The prices of Ethiopian zebu (humped cattle) ox and the Massey Ferguson Tractor in Ethiopia have increased exponentially since 1985.

On the other hand, the land holdings size per farmer in Ethiopia is declining, and associated with this, the average number of oxen per farmer has fallen to less than 0.5 ha, and about 30 to 40% of farmers in the northern highlands do not have an ox [74]. Nowadays, the cost of fodder and grazing land for keeping oxen throughout the year is also very challenging and people in some potential production areas are changing their land to eucalyptus plantations [78] and migrating to small towns. It is clear then, that families with less than one hectare of tenure land will find it very challenging to keep a pair of oxen all year or to buy a motorized tractor in-group. The use of herbicides for killing weeds before planting to reduce tillage is nowadays becoming impractical due to the rising costs of herbicide (e.g., glyphosate) treatment, which may probably be feasible for relatively rich farmers with uncompromising health hazards and groundwater pollution [79]. The reason given by farmers for the repeated tillage practices in the Ethiopian highlands is probably to increase infiltration by minimizing run-off, particularly capturing the rainfall falling in pre-sowing periods (March to May), although the effect of tillage has been contradictory to the reports of Admassu [80]. The negative effects of no-tillage may occur especially on the clay-poor, structurally weak soils of the semi-arid areas [58] since the beneficial effects of mulching on such soils may not always be sufficient to offset the negative effects, particularly during the first years.

We may then envisage that as the change from hoe tillage to animal traction in Ethiopia is generally associated with an expansion in the cultivated area, reciprocally, the decrease in farm sizes may favor a movement towards hoe tillage (minimum). When the rise in the cost of fuel and energy increases, such a tillage shift would, however, be expected to happen in the country. In association with this, shifting to hoe cultivation may lead smallholder farmers to save limited fodder resources for more productive animals, such as milking cows or fattening small remnants [81]. Hence, CA can provide a major benefit by removing the need for tillage and thus allowing a larger proportion of the land to be cropped but the integration must be directed well because no-tillage without continuous mulch or residues commonly results in increased weed pressure [82] and the associated increase in labor use. Hoe tillage is better suited to the cultivation of sorghum, maize (Zea mays), rice, and grain legumes, as these crops require less tillage than small grain crops (e.g., teff, millet, wheat, and barley). However, more labor may also be associated with such additional practices of CA.

Most farmers in Ethiopia sow and fertilize maize crops manually with on-the-spot application while a farmer opens the furrow with oxen plowing. One of the most important benefits of CA for small farmers is the reduction in labor requirements for tillage, however, if only manual weeding is practiced, then labor requirements may increase, making the CA system unattractive to farmers. Farmers’ access to labor (family or hired) critically affects their ability to adopt new technologies and increases overall production [83]. Although labor is a potential limitation in Ethiopia, farmers nowadays have turned to practices minimizing tillage and changing the cropping systems [84]. Consequently, significantly higher labor is required under conventional systems compared to the improved alternative CA system [85] due to the reduction in tillage frequencies. In the Ethiopian context, no-tillage systems under CA would reduce labor, on average by about 3–4 times [4,85]. However, there is also a concern about weeds where some studies indicated that a decline in tillage frequency in rainfed agriculture is associated with an increase in the labor requirements for weeds [86]. In addition, more labor is also associated with CA due to mulching, seeding, and land (bed) preparation. However, under sufficient CA practices, weed growth would be suppressed and less labor would be needed.

In the drip irrigation system under CA, labor for tillage, irrigation, weed, and for fertilizer application would be practically reduced [24,87]. However, the manual removal of weeds in the conventional system is very labor-intensive compared to the CA system where complete mulching hinders weed growth and regrowth on a farm [88]. While there is a reduced labor for herbicide chemical spray in the CA system [89], labor remains an important constraint in the adoption of improved irrigation practices and CA approaches in the current Ethiopian context. However, under a high density of population and a small land tenure size, labor shortages may not be a critical challenge in CA agriculture [90]. If CA is to spread in the smallholder farmers’ production system, issues of access to relevant inputs at reasonable prices need to be addressed, and an important aspect of this problem is that of equipment where without functional equipment for direct seeding of crops under CA, it remains a serious challenge to properly test and demonstrate its benefits.

6. Fragmented Land Tenure with Free Grazing and CA

Communal grazing lands all year and aftermath grazing in dry periods (after crop harvest) are the traditional sources of livestock feed in Ethiopia. Aftermath grazing is a traditional livestock feeding activity in Ethiopia where farmers leave free grazing cattle in a newly harvested cropland (Figure 4) and continue for about eight to nine dry months where cattle are left free. As a result, the traditional uncontrolled and free grazing system has caused severe land degradation. Free cattle movement at times on wet or moist soils increases trampling or compaction effects [91]. Moreover, farmers cut and carry crop stalks and straws for dry period feeding, and free cattle aftermath grazing on cultivated lands removes almost all types of the remaining crop residue during dry periods. However, with appropriate livestock policies and public interventions, livestock have the potential to speed up the cycling of nutrients back to the soil [92]. This shows that the introduction of CA in Ethiopia has tradeoffs between livestock farming in two aspects: the free grazing tradition and the complete removal of residues over the cultivated lands.

In most cases, due to the small land tenure size of Ethiopian farmers, crop productivity is lower and therefore crop residues are scarcer and competition for them is greater. In the rainfed systems of Ethiopian farmers with prolonged dry seasons (more than 8 months), the demand for residues for feed is the greatest [93]. The adoption of CA in dry environments will only advance when it can be demonstrated to farmers that leaving at least part of the residues on the soil surface provides a greater benefit to system productivity than feeding it to animals. Thus, in the irrigated areas, where production levels are high and two or more crops per year are feasible, competition for residues between the needs of CA and livestock feed is not very problematic. Moreover, farmers are currently used to restricting cattle, particularly in aftermath grazing over cultivated lands. In such practices, CA adoption may spread faster over a wide area through cattle restriction regulations where livestock farming combined with CA may strengthen the cut and carry system, and cattle feed byproducts and manure may integrate with the CA system. Perceptively, a multi-layer crop-crop or crop-forage or forage-forage intercropping or relay cropping may enhance CA cultivation and livestock systems.

More confidently, Ethiopian farmers are intuitive in practicing the fallowing of cultivated land for about 3 to 5 years to improve soil fertility and increase crop production [7,94,95]. On a contextual basis, fallowing is a traditional practice of letting the land without tillage and leaving it either for open grazing of their cattle (low land tenure size); letting the land for control grazing (high land tenure size), or sowing leguminous crops [96]. Such practices in general increase the coverage of the soil [97], reduces the carbon oxidation from tillage [98], and maintains a conducive habitat for soil microorganism regeneration [99]. Similar to the challenges of fallowing practices, a fragmented adoption of CA is also a challenge for CA intervention. All the neighboring farmers should apply the CA system so that free cattle grazing would be avoided and the transfer of weed seeds, pests, and disease from farm to farm would be minimal. While CA encourages greater biomass production, be it for cattle feed or back to the soil as residue, articulation of various local practices needs good management, knowledge, and decision-making skills.

7. Pest Management and Conservation Agriculture

Ecologically based principles to manage pests and diseases that address the growing concern about the indiscriminate use of chemical pesticides would be the concern of integrated pest management practices in conservation agriculture [89]. The concern of diversified crop rotation as one component of CA plays an important role in mitigating the pest and disease challenges in the production system. Crop rotation disrupts insect and pathogen reproduction and hence their life cycle. Plant nutrients are restored when certain plant species are included in crop rotation, requiring less chemical fertilizer and hence is a useful technique in the practice of sustainable agriculture [100]. In contrast to monocultures or double-farmed rotations, diversified crop rotations refer to multiple rotations of three or more crops [101]. Carefully selecting a crop rotation scheme has the potential not only to reduce trade-offs between crop viability and environmental impacts but also to maintain long-term soil fertility, and disrupt the weed and disease cycle process through intrinsic nutrient recycling [102]. In this regard, Ethiopia, as discussed in this section, has diversified agroecology settings where several crop types are possible to be grown depending on the available soil moisture level, soil type, and temperature levels.

8. Water Saving Roles of CA in Irrigation

Several studies revealed the immediate advantage of CA on water productivity in the Ethiopian highlands [5,57]. However, CA practices are known not only to improve soil moisture saving but also to enhance the infiltration of water to the subsoil by reducing surface runoff or evapotranspiration during irrigation events. A one-year CA experiment by [103] and a five-year experiment by [104] both in Northern Ethiopia indicated that CA reduced runoff by about 68% and 38%, respectively. Similarly, average runoff reductions of about 53% and 51% were reported, respectively, by [13] under CA compared with the conventional tillage practices. Findings in some studies in the state of Amhara showed a reduction of runoff under CA in the range of 17–62% compared to CT practices [4].

On the other hand, in the central rift valley of Ethiopia on the Melkasa experimental site, about a 21% soil moisture saving and a 15% increase in soil infiltration rate were reported by [105] from ten years of CA practice compared with CT. Similarly, after six years of CA practice, a significant improvement in soil moisture saving of around 31% was reported by [55,106] in southern Ethiopia while about 28% and 51% soil moisture savings were also reported by Assefa and Belay, respectively [4,54], from three years of CA practice in the northwestern part of the nation. Yimam [107] reported soil moisture savings of 4 to 10% under CA compared to conventional tillage practices.

Runoff and soil loss were significantly reduced by practicing CA and more soil organic carbon were obtained in a CA experiment in northern Ethiopia [104]. The effectiveness of any soil and water conservation measure depends primarily on the cover factor followed by the practice factor, which is related to tillage systems. Hence the fact that CA practices have a positive impact on reducing soil erosion would be unquestionable since CA strictly follows sufficient soil cover and minimum soil disturbance [25,29].

9. Environmental Sustainability: CA against Soil Erosion and Pollution

Agricultural activities exacerbate the removal of soil and nutrients by either runoff or percolation [108] and primarily affect plant growth. Concurrently, the soil and nutrient components of surface runoff and percolation may also deteriorate the water quality of wells, reservoirs, and lakes [109]. Hence, there is a need for a paradigm shift to improve smallholder agriculture systems that promote sustainable intensification, which encourages an increase in crop productivity with minimum inputs and protects the environment at the same time [110].

Conservation agriculture is suitable for the maintenance of environmental services. Many of the environmental services, such as soil organic matter stability, reduced erosion (the prominent challenge in Ethiopia), and enhanced carbon sequestration contribute to the mitigation of climate change. Fuel use and tractor hours are reduced by up to 75% in conservation agriculture [89] with tremendous declines in greenhouse gas emissions. Other environmental benefits include the reduced siltation of most of the reservoirs in the country, eutrophication of most water bodies (e.g., Lake Tana, Lake Abaya), and pesticide contamination of most wells, rivers, and dam reservoirs (e.g., Gefersa, Angereb, and Aba Samuel dams) in Ethiopia [109].

In this regard, the CA system is valuable to mitigate the environmental effects of droughts by ensuring some biological production, surface cover, and erosion control even under severe conditions, due to the greatly improved soil aggregation, biodiversity, and organic matter status, and subsequently improved water infiltration and water storage in the soil.

10. Soil Organic Matter, Soil Quality, and Soil Fertility under CA

Studies indicated that no-tillage combined with residue mulching can lead to the accumulation of soil organic matter under continuous irrigated and rainfed phases of production [24,111]. Although it is often difficult to quantify effects, it appears that soil organic matter is improved mainly due to increased biomass production in the CA systems rather than no-tillage [111]. While a promising increase in organic matter content was reported under CA in clay dominant soils in sub-humid Ethiopian highlands [5,24], conversion to no-tillage has resulted in small annual increases in soil organic matter under dry land conditions on the sandy soils of West Africa [112]. It implies that increased inputs of organic matter, for example, manure and organic mulch practices were predicted to result in large increases in soil OM (Figure 5).

Chivenge [113] demonstrated that reduced tillage is likely to have a strong positive effect on soil OM in finer-textured soils due to the lack of physical and structural protection of OM in sandy soils (Figure 5a), in which the OM contents depend strongly on the amounts of crop residue added regularly to the soil. Thus the effects of no-tillage is likely to be larger on heavier-textured soils that have a larger equilibrium content of soil OM for a given input [114]. Although reduced soil erosion under CA is likely to play a role in the long term [115], the evidence supports the conclusion that the OM content of any given soil is determined largely by the amounts of OM returned to the soil, independent of whether it is incorporated or used as a cover mulch.

In general, fields that receive large inputs of organic matter in the form of crop residues, manure, or compost (fields that are close to the homestead), are generally rich in OM, while fields that receive no or little organic matter (the outfields far away from the homestead) have small soil OM contents [116,117]. Connected with this, the rate of decline of OM is greater with conventional tillage compared with the no-tillage treatment [118]. However, such data must be interpreted with caution, since the lack of soil mixing under CA may lead to increased stratification with the accumulation of OM in the topsoil. In addition, there is also organic matter from the roots, if the residue was grown in the field and not brought to the field as mulch.

Although stratification of OM may lead to improved soil surface properties, and enhanced infiltration, it may lead to an overestimation of the benefits of CA in increasing overall soil OM contents. In general, after 4 years of irrigated CA experiments, the soils from CA plots did not disperse immediately after immersion into pure water compared to the soils of conventional tillage [24] probably due to the accumulation of organic matter and bondage of soil particles together [119,120,121,122] by organic glue or carbon content (Figure 6).

In Bako’s experimental study, a significant improvement in soil nutrients, such as total nitrogen (17%), soil organic carbon (7%), available phosphorous (8%), and soil pH (2%) were reported by [123]. In southern Ethiopia on the Derashe experimental site, the increments so far reported were 9% (Potassium), 22% (calcium), 10% (cation exchange capacity), 11% (soil organic carbon), 4% (soil pH), and 11% (soil organic matter) by Lejissa [124] from short-term CA practice (two years).

Similarly, Liben [55] reported a 33% increase in soil organic carbon from six years of CA experiments at the Melkasa experimental site. In northern Ethiopia, in the May Zeg-Zeg areas the increment reported was low, around 2%, from six years of CA practice. Assefa [5] reported around a 6% increment in carbon and around a 4 to 5% increment in nitrogen from Robit Bata and Dengeshita, respectively. An exceptional report by Oicha [103] reported a short-term (one year) significant increase (6%) of soil organic matter in North Ethiopia around the Gumselasa area. In general, CA is proven to be an alternative way to improve soil fertility and soil quality in the Ethiopian highlands.

11. The Socio-Economic, Farmers’ Perception, and Political Aspects of CA Adoption in Ethiopia

A study on the socioeconomic potential for CA adoption was conducted by Tesfaye [125] and indicated that Ethiopia had the lowest potential (9%) next to Kenya (20%), and Malawi had the highest potential (46%). The main biophysical factor for low CA adoption was the high population and cattle density in Ethiopia. In fact, there is multitude of factors (age, gender, labor, education, belief, and taboo, etc.) in Ethiopia influencing farmers’ decisions to adopt agriculture practices, such as CA, which may also depend on plot and household characteristics for adoption decisions. Specifically, the significant positive impacts of access to information indicates that public policies aimed at improving access to information will help to promote the adoption of sustainable agriculture practices [126].

Sociocultural research, education, and promotion are the most critical ways to enable the adoption of CA, all of which work on changing the mindset of activators to CA adoption. Farmers generally undergo this change in a relatively faster way when they experience or are exposed to the real benefits of CA while researchers or extension agents may obtain evidence to see the benefits of CA through better access to research findings and information networks. However, the most challenging exercise for CA involves a complete change in the farming system. As such, it is almost impossible for research and extension systems to develop appropriate “packages” that fit the needs of all farmers and farmer groups in that the adaptation of the principles to local conditions requires large levels of farmer participation. According to Bazezew et al. [14] adopter farmers have more age, better educational status, less fertile soil, own a greater size of land, have a minimum distance between the residence and plot, and have cultivated their land. Adopters are also known to participate in local or village administration and take social responsibility or better-accessed extension services in the form of field visits, demonstrations, and farm training, etc. Tsegaye [127], from two districts in Ethiopia, found that those farmers who had adopted all three components of CA had higher yields than non-adopters and that yields increased by the number of components of CA adopted. Similarly, the adoption of the three CA components substantially increased labor productivity (yield per unit of labor), implying that most labor is saved from the full adoption of all the CA components.

Global experience indicates that CA is more knowledge-intensive than input-intensive, in that success depends more on what the farmer does (management) than on the level of inputs he applies [128]. This is one of the reasons for the far slower adoption of CA in the smallholder sector than on large farms in Ethiopia. Whereas large farmers are often well connected to knowledge and information systems, this is generally not the case in small-farm communities. Therefore, information sharing within the community is often the primary source of new knowledge, and thus knowledge tends to be far more based on traditional concepts and practices. On the other hand, farmers in smallholder communities in Ethiopia generally have less clear land tenure than commercial farmers. Unless farmers have clear ownership of the land, they are unlikely to adopt CA. In general, the more risk-averse a farmer is, the less willing he is to change the traditional practices to new technologies, such as CA [128]. Given that the adoption of CA technology is a necessary step toward increasing food production, it is essential to reduce the level of risk aversion through better education, outside contact, and other appropriate measures.

12. Conclusions

Global experience indicates that conservation agriculture is an alternative and sustainable solution to control a multitude of problems, such as soil erosion, water shortage, soil moisture stresses, soil degradation, and environmental pollution. Most developing countries, including Ethiopia, have currently initiated adopting conservation agriculture as a climate-smart agricultural technology, although there are various implementation challenges. The tradeoffs for implementing CA and the livestock industry in the Ethiopian context would be solved only if the implementation is supported with research and by improving the knowledge base of the system, which takes time and there are several pieces of evidence promoting the two practices together. Other critical issues in implementing CA include weed infestation, the availability of farming equipment, labor requirements, land tenure and fragmentation, and an outbreak of pests. Conversely, CA is an environmentally friendly practice that enhances beekeeping since chemical usage is limited. In addition, the country’s diversified agro-ecological settings followed by the capital-intensive production approach are the most important pushing factors leading to sustainable irrigation when integrating with conservation agriculture. However, changing the socio-economic and political environment through better research, education, and promotion would be a vital role for CA promoters in the country. It shows that the adoption of CA always comes after emergent and iterative processes where sustainable technological change may emerge over time or may start anew. This always demands the need for research at different locations in the country to reach a comprehensive conclusion on the expansion of CA. In this regard, the synthesized information about CA in this review article may, therefore, be used by policymakers to help to transform rainfed dependent agriculture to more sustainably intensified irrigated agriculture.