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Random-effects model with explanatory covariates Results of the random-effects model developed to determine the influence of explanatory covariates on the CA to CT yield ratio.
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Conservation agriculture (CA) has become a dominant paradigm in scientific and policy thinking about the sustainable intensification of food production in sub-Saharan Africa. Yet claims that CA leads to increasing crop yields in African smallholder farming systems remain controversial. Through a meta-analysis of 933 observations from 16 different c...
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... For example, a meta-study of no-till trials worldwide found no significant increase in SOC storage implying that there is no carbon removal from the atmosphere under no-till systems (Don & Jantz, 2013). Other metaanalyses conducted such as by Pittelkow et al. (2015) and Corbeels et al. (2020) have produced mixed results that cast doubts on the positive carbon storage potential reported in reviews and meta-analysis mentioned earlier. However, in these two metaanalyses, the authors admit that the data used covered a mixture of no-till systems which were not always based on the three principles of CA. ...
... In the case of the Pittelkow et al. (2015) study, data from conservation tillage studies were also used which meant that some of the data that was included was not from no-till systems. The study by Corbeels et al. (2020) did indicate that when the data was from CA systems, climate benefits were present. In addition, the meta-analysis conducted by Don and Jantz (2013) suggests that there is a risk that no-till systems cause N 2 O emissions, making the carbon footprint of no-till cropping systems significantly worse than that of tillage-based cropping systems. ...
Proponents of Conservation Agriculture (CA) believe that by not tilling the soil, climate-friendly agriculture is achieved by reducing greenhouse gas emissions from agriculture and by storing atmospheric carbon in the soil. However, some scientists question climate benefits of CA. Literature shows that carbon storage through soil organic carbon (SOC) accumulation of up to 1 t ha–1 y–1 is possible without increasing nitrous oxide (N2O) emissions under a CA system. Opposing studies were flawed by analysing not complete CA systems and leaving out some of the principles. It is shown that each tillage operation releases up to 300 kg carbon dioxide equivalents (CO2e) per hectare, and each of the average annual 10 t ha–1 of eroded topsoil can emit additional 300 kg CO2e ha–1. A case study in Germany confirms these findings that with full application of CA the carbon footprint of agricultural food production can be significantly decreased, helping to mitigate climate change. It is concluded that net soil carbon storage is possible if all the principles of CA are consistently implemented. It is also concluded that together with other complementary production measures, CA has the potential to make agriculture carbon neutral.
... Moreover, the time required to reach yield stability varies from farmer to farmer, and it is primarily attributed to farmers' initial lack of CA knowledge and skills to manage challenges associated with weed control, residues, pests, and diseases Corbeels et al. 2020;Mwila et al. 2021). ...
Conservation agriculture (CA) has the potential to improve agriculture’s resilience to climate change, reduce environmental degradation, and improve food security in sub-Saharan Africa (SSA). However, despite this potential, adoption rates of CA have remained relatively low in SSA, as CA is faced with major challenges. Due to low mechanization rates, the high labour requirements of CA constitute an important obstacle to the adoption of CA. The low adoption of CA in SSA has sparked national and international debates about the suitability of CA for African farming systems and about the strategies that have been used to promote it. The rise of medium-scale farmers across SSA, who use tractors and implements, offers a new perspective for CA. These farmers do not only cultivate increasingly large land areas, but also provide machinery services, share knowledge, and act as role models to small-scale farmers. However, it remains unclear whether mechanized medium-scale farmers, who typically cultivate between five and a hundred hectares of farmland, can play a key role in the upscaling of CA in SSA. Previous studies have focused on socio-economic and psychological factors in studying farmers’ decisions to adopt various CA practices. Yet, the interests of medium-scale farmers regarding mechanized Conservation Agriculture (MCA) have remained largely unexplored. Further, even though mechanization may incentivize CA adoption in SSA, little research has focused on the performance of MCA using four-wheel tractors. Against this backdrop, this research sought to investigate the extent and how sustainable agricultural mechanization can unlock the potential of CA, focusing on medium-scale farmers and using Zambia as a case study country. The study had three objectives, which are addressed in three different chapters: 1) to analyze the perceptions and intentions of medium-scale farmers with regard to MCA in Zambia; 2) to analyze the discourses about CA expressed by Zambian farmers and various key stakeholders; and 3) to investigate the short-term agronomic and economic differences between mechanized conventional tillage and MCA. To achieve these objectives, a mixed-method research approach was used, involving qualitative and quantitative methods. The introduction of the thesis presents the study rationale, discusses CA status in SSA and Zambia, and examines the literature on the increase of medium-scale farmers in Zambia as an important opportunity for MCA adoption. To address the first objective, the second chapter employs Taylor and Todd’s socio-psychological framework of the Decomposed Theory of Planned Behavior to examine the intentions of medium-scale farmers towards MCA. Three constructs are considered: normative issues, attitudes and perceived control behaviour. The chapter is based on responses from a survey that was conducted with 119 medium-scale farmers from selected districts in Zambia. The data were analyzed using descriptive statistics and Spearman’s rank correlation coefficient. This chapter reveals that medium-scale farmers have very strong intentions to apply mechanization on their farms, which is linked to strong subjective norms, attitudes and perceived control. The favourable attitude towards MCA is based on its perceived usefulness, easiness and compatibility with their current practices. Further, perceived resources and efficacy also influence farmers’ intentions to adopt MCA. Other important factors in determining farmers’ intentions to use MCA include social and media influence, technical training and extension services, as well as farmers’ background characteristics. To address the second objective, presented in Chapter 3, a discourse analytical research approach was applied to examine actors’ viewpoints on CA. The chapter is based on in-depth interviews, interviews with key informants, focus group discussions and a review of selected local media reports. Based on the analysis, six CA narratives were identified in the Zambian context, which can be labelled as follows: (1) Yield stability of CA is attainable within a few years; (2) CA is the farming choice of the future; (3) Opinion leaders and key stakeholders are pushing the new CA frontiers; (4) CA is Africa’s ancient way of farming; (5) The Youths is getting inducted to apply CA; and (6) The number of CA adopters is higher than reported. The chapter reveals that despite the numerous discourses in favour and against CA that are reported in the literature, there are unreported context-specific CA discourses that are inherent to the study sites in Zambia. The fourth chapter, which addresses the third objective, presents a large-scale on-farm experiment to explore whether there are short-term agronomic and socio-economic differences between mechanized conventional tillage and MCA. This question is relevant because short-term differences can have a stronger influence on the adoption of CA than effects that only become manifest in the long run. The experiment was conducted using a randomised complete block design trial to compare three treatments: (1) disc harrowing (DH) plus residue burning, which represents the widely used conventional practice; (2) ripping tillage (RT); and (3) direct seeding (DS) plus soil cover. The experiment focused on maize and soyabean and covered two years, of which the first was more “dry” and the second more “wet”. All operations were performed using a 60hp four-wheel tractor. The analysis shows that, as compared to conventional DH, DS leads for both crops to time and fuel-saving. This effect is also observed, though to a lower extent, in RT. The cost of production was for both crops highest for DH and lowest for DS, whereas RT fell in-between. MCA treatments led to relatively higher grain yields in the dry season for both crops. However, in the wet season, DH and RT resulted in significantly higher maize yields than DS. The analyses also show that DS resulted in higher profitability for soyabean in both seasons, while the profitability of maize was higher for DS in the dry season and higher for DH in the wet season. MCA treatments led to higher returns per unit of investment and higher returns to labour compared to DH. Overall, the chapter demonstrates that, even in the short term, MCA has multiple agronomic and economic benefits. Considering the findings regarding the three objectives together, the study indicates that deciphering the discourses and perceptions of key actors about MCA improves the chances of identifying nuanced policies and interventions that may accelerate MCA uptake by medium-scale farmers. The findings of the mechanized experiment show that the agronomic and economic gains of MCA can even be achieved even if adopters hire all tractor operations. However, to harness the synergies between CA, mechanization, and the rise of medium-scale farmers for increased agricultural productivity and sustainability in SSA, more research on the enabling environment for MCA and appropriate policies is still needed.
... Crop responses to CA in SSA have been meta-analyzed (Corbeels et al. , 2020Rusinamhodzi et al., 2011). The effects of long term tillage and residue retention on crop yield can be determined by meta-analysis of long term studies on soil texture, crop rotation, nitrogen input, climate, herbicide use, and soil disturbance levels. ...
... The effects of long term tillage and residue retention on crop yield can be determined by meta-analysis of long term studies on soil texture, crop rotation, nitrogen input, climate, herbicide use, and soil disturbance levels. In a meta-analysis of 933 observations from 16 SSA countries, Corbeels et al. (2020) found that CA yields are only slightly higher than CT yields. Mulching and crop rotations/intercropping increase maize yields. ...
... Maize yield rises 8.4% when CA principles are implemented simultaneously. A meta-analysis by Corbeels et al. (2020) revealed that CA outperformed CT on all soil types below seasonal rainfall of 800 mm but only on coarse-textured soils under 800e1200 mm in SSA. The negative effects of CA on mediumtextured soils were significantly lower than on medium-and fine-textured soils, probably due to the higher risk of waterlogging on these soil types. ...
Common farming practices in sub-Saharan Africa (SSA) such as intensive and repeated tillage, complete crop residue removal, and biomass burning create risks of soil degradation. To reduce these risks, conservation agriculture (CA) uses minimal soil disturbance, crop residue retention, and crop rotation in order to reduce soil erosion, improve soil quality and crop production, and facilitate climate change mitigation and adaptation. Nevertheless, CA adoption in SSA is extremely low. This paper aims to review current practices, challenges, and constraints to the adoption of CA in SSA. Our analyses show that CA is practiced in only about 1.25% of the total cultivated area in SSA, despite two decades of efforts to promote CA adoption among smallholder farmers. Specific difficulties in CA adoption by smallholder farmers in SSA may be attributed to i) lack of locally adaptable CA systems, particularly those integrating the needs of livestock production; ii) lack of adequate crop residues for surface mulch; iii) inconsistent and low crop yields; iv) lack of smallholder CA equipment for direct sowing; v) limited availability, high cost, and inadequate knowledge associated with the use of appropriate fertilizer and herbicides; and vi) lack of CA knowledge and training. Other problems relate to the management of specific soil orders, e.g., CA implementation on steeply sloping land and poorly drained soils such as Vertisols. CA adoption by smallholder farmers is also obstructed by socio-economic factors due to smallholder farmers’ focus on short term yield increases and their lack of access to markets, loans, and education. To facilitate wider adoption by smallholder farmers in SSA, CA approaches should be downscaled to fit the existing tillage tools and the specific agroecological and socio-economic farm settings.
... Productivity Yield 14 (Pittelkow et al., 2015a(Pittelkow et al., , 2015bRusinamhodzi, 2015;Cooper et al., 2016;Marcillo and Miguez, 2017;Knapp and van der Heijden, 2018;Hallama et al., 2019;Shackelford, Kelsey, and Dicks, 2019;Toler et al., 2019;Corbeels et al., 2020;Jat et al., 2020;Sun et al., 2020;Reich, Paul, and Snapp, 2021;Adil et al., 2022) Stability of the production 2 (Knapp and van der Heijden, 2018;Reich, Paul, and Snapp, 2021) Pest pressure 3 (Osipitan et al., 2019;Shackelford, Kelsey, and Dicks, 2019;Toler et al., 2019) Water use efficiency 3 (Jat et al., 2020;Kumara, Kandpal, and Pal, 2020;Adil et al., 2022) Economic sustainability ...
Conservation agriculture (CA) is an approach to farming that is defined by three principles: (1) minimal soil disturbance (no-till), (2) crop diversity in time and space, and (3) soil coverage by crop residues and/or cover crops. These principles provide a roadmap to protect and improve soil. However, the narrow criteria for defining CA may fail to account for tradeoffs between soil health and other ecosystem services. A literature review of meta-analyses dealing with CA and an online survey in France were conducted to explore the implementation and performances of CA. Research on CA systems has focused on crop productivity and soil quality whereas research on other dimensions of cropping system sustainability are lacking. The effects of CA on other aspects of sustainability such as biodiversity and profitability are less prevalent in the literature. The online survey results show that 63% of respondents thought that CA helps reduce pesticide use, 91% that CA improves water use efficiency, and 77% that CA helps to store carbon and achieve the objectives of the 4 per 1000 international initiative. Given the prevalence and widespread support for CA, we advocate for moving CA from its current definition based on the means toward a definition that includes performance-based metrics that address different ecosystem services. CA has potential to help address challenges associated with climate change, biodiversity loss, and water pollution, but opportunities may be missed without developing performance targets that go beyond soil conservation.
... There have been many studies on the effects of CA on crop productivity and its benefits with respect to soil health (Corbeels et al., 2020b;Kimaro et al., 2016;Mhlanga et al., 2022b;Swanepoel et al., 2018;Thierfelder et al., 2015Thierfelder et al., , 2017Thierfelder and Mhlanga, 2022). Other studies, however, have fuelled the debate on CA practicality and adoption in sub-Saharan Africa (SSA) (Giller et al., 2009(Giller et al., , 2015Kassam et al., 2019). ...
Conservation agriculture (CA), combining reduced or no tillage, permanent soil cover, and improved rotations, is often promoted as a climate-smart practice. However, our understanding of the impact of CA and its respective three principles on top- and subsoil organic carbon stocks in the low-input cropping systems of sub-Saharan Africa is rather limited. This study was conducted at two long-term experimental sites established in Zimbabwe in 2013. The soil types were abruptic Lixisols at Domboshava Training Centre (DTC) and xanthic Ferralsol at the University of Zimbabwe farm (UZF). The following six treatments, which were replicated four times, were investigated: conventional tillage (CT), conventional tillage with rotation (CTR), no tillage (NT), no tillage with mulch (NTM), no tillage with rotation (NTR), and no tillage with mulch and rotation (NTMR). Maize (Zea mays L.) was the main crop, and treatments with rotation included cowpea (Vigna unguiculata L. Walp.). The soil organic carbon (SOC) concentration and soil bulk density were determined for samples taken from depths of 0–5, 5–10, 10–15, 15–20, 20–30, 30–40, 40–50, 50–75 and 75–100 cm. Cumulative organic inputs to the soil were also estimated for all treatments. SOC stocks at equivalent soil mass were significantly (p<0.05) higher in the NTM, NTR and NTMR treatments compared with the NT and CT treatments in the top 5 cm and top 10 cm layers at UZF, while SOC stocks were only significantly higher in the NTM and NTMR treatments compared with the NT and CT treatments in the top 5 cm at DTC. NT alone had a slightly negative impact on the top SOC stocks. Cumulative SOC stocks were not significantly different between treatments when considering the whole 100 cm soil profile. Our results show the overarching role of crop residue mulching in CA cropping systems with respect to enhancing SOC stocks but also that this effect is limited to the topsoil. The highest cumulative organic carbon inputs to the soil were observed in NTM treatments at the two sites, and this could probably explain the positive effect on SOC stocks. Moreover, our results show that the combination of at least two CA principles including mulch is required to increase SOC stocks in these low-nitrogen-input cropping systems.
... Therefore, they tend to focus on strategies to maintain or increase crop yields in the short term at the expense of consideration of long-term land health [78]. Thus, these millennial farmers will strive to maintain crop yields, even though their methods do not follow existing conservation principles [79,80]. Potato farming in this research area is the primary source of income for millennial farmers, so they maintain cultivation methods to provide maximum yields. ...
Land degradation in mountainside areas is a serious threat that requires conservation actions, and the role of millennial farmers in this issue is crucial for future agricultural land sustainability. The perception of degraded land condition (LC) and the risk of farming due to ongoing agricultural land degradation (RISK) are suspected to be able to drive the intention to make conservation efforts. Based on the norm activation model, this study aims to analyze the influence of millennial farmers’ perceptions on the condition of degraded agricultural land and the risk of land degradation on their intention to perform conservation-based potato farming (CBPF). This study involved 169 millennial potato farmers on the western slope of Mount Slamet, Central Java, Indonesia. Data were collected using a cross-sectional survey from January to March 2022. The hypothesis was tested using structural equation modeling. The results showed that more than 90% of respondents stated that agricultural land had been degraded. The risk and personal norms (PN) have a significant effect on the intention of CPBF (β = 0.144, β = 0.505; p-value <0.01), respectively. Unexpectedly, LC did not directly affect the intention to practice CPBF (β = 0.076, p-value = 0.159). This study provides insight into understanding the behavioral intentions of agricultural land conservation, especially millennial farmers’ perceptions of land degradation in their farming areas. To encourage the millennial farmers’ agricultural land conservation intentions, it should be started by increasing the awareness of farmers’ PN since they only pay little attention to degraded LC.
... Some academic researchers have argued that the benefits of CA have been overstated or that CA proponents have presented biased evidence regarding the superior performance of CA compared to conventional-tillage agriculture (e.g., Giller et al., 2009;Sumberg and Thompson, 2012;Pittelkow et al., 2014;Powlson et al., 2014;Corbeels et al., 2020). These reports have included mixed or undifferentiated data sets in their analyses, conflating varying lengths of time that the CA systems under study have been operating or not taking account of the differing complexities of dissimilar cropping systems. ...
... Giller et al. (2015) metaanalysis also challenges the claims that CA increases crop yields but concurrently reports comparatively higher stability of crop yields in dry climates. Corbeels et al. (2020) claim that the crop yield benefits that can be expected from CA are relatively small and report that average yields under CA are only slightly higher than those of conventional tillage systems in their African sub-Saharan meta-analysis. Den Putte et al.'s (2010) European meta-analysis concludes that in spite of (limited) negative effects on yields, CA is a viable option for European agriculture from the viewpoint of agricultural productivity, as long as interaction with soil type, crop type and climate are accounted for. ...
... Knapp and van der Heijden (2018) assess the temporal stability of NT + CC yields and conclude that it does not differ significantly from that of CT. Alternately, there is convergence regarding CA producing the best yield in arid soils (Corbeels et al. , 2020De Vita et al. 2007;Giller et al. 2021;Pittelkow et al. 2015). ...
... Regarding economic profitability, it is generally accepted that both NT and CA represent lower costs for the farm (Corbeels et al. 2020;Laxmi et al. 2007;Pittelkow et al. 2015a). However, inconsistencies do emerge from the literature when the optimal size of the farm for a profitable implementation of CA is inspected. ...
The rationale of this study originates from the primary sector’s multiple roles in the global warming issue. Agriculture is reported among the main causes of anthropogenic global warming. At the same time, it is profoundly impacted by climate change and concurrently holds potential as a solution through the sequestration of soil organic carbon (SOC) facilitated by Conservation Agriculture (CA). However, the findings in the literature are controversial on the SOC sequestration capacity and the profitability of CA implementation. Considering the new and old objectives of the sector, this paper tackles the assessment of the actual capabilities of CA to be a viable strategy to pursue the social good of climate change mitigation and concurrently be profitable for farmers. The economic profitability and environmental performance of CA are assessed analysing data from a field experiment in Northern Italy (European temperate area) and identifying the best management practice by means of a data envelopment analysis.
... However, both the implementation and the adoption of CA are challenging due to the limitations of CA. Conservation agriculture is knowledge-intensive for the farmers, can interfere with livestock feeding and crop residue sales, has location-specific crop yields benefits, and takes time to increase crop yields (Corbeels et al., 2020;Giller et al., 2009). Thus, the expansion and the adoption of CA require evidence of its adaptation to site-specific conditions ( Palm et al., 2014); making this study unique for smallholder, subsistence, rainfed farming in Maniema Province in the DRC. ...
Abstract
Conservation agriculture, a sustainable farming practice combining no or minimum soil disturbance, crop diversification, and soil cover, can benefit humans and the biophysical environment. However, less than half of Sub-Saharan African countries implement conservation agriculture, and the majority of smallholder farmers are using unsustainable practices. Research and field trials on conservation agriculture adaptation to soil and agroecological conditions are vital for increasing adoption of conservation agriculture in Sub-Saharan Africa. The objectives of this study were to (i) evaluate the change in soil chemical properties and soil biology from implementation of conservation agriculture, (ii) assess cowpea (Vigna unguiculata L. Walp.) yield and variability under conservation agriculture compared to the conventional farming practice, and (iii) evaluate differences in soil chemical properties, soil biology, and crop yields under conservation agriculture in savannah and forest ecosystems compared to conventional agriculture in smallholder farming in the province of Maniema in the Democratic Republic of the Congo. Soils under conservation agriculture had 6.5 times more (p < 0.001) earthworms, 23% and 10% greater (p < 0.05) concentrations of soil phosphorus and potassium, respectively, and 100% greater (p < 0.001) cowpea yield than soils under conventional agriculture. Measured across all sites, conservation agriculture and conventional cowpea yields had coefficients of variation of 25% and 16%, respectively. This study showed for the first time that conservation agriculture implementation contributes to soil health and food security associated with smallholder farming in the Democratic Republic of the Congo.
Keywords: Conservation agriculture; Democratic Republic of the Congo; Soil health; Soil biology; Smallholder farming; Ecosystem
... The effects of CSA are all not positive. For example, Corbeels et al. (2020) found that CA only confers small yield gains over conventional agriculture in 16 SSA countries and conclude that 'CA may not be the technology for African smallholder farmers to overcome low productivity and food insecurity in the short-term'. The missing link from the foregoing is an assessment of the extent to which CSA practices mediate vulnerability and resilience to climate shocks using multi-year household data as such data allow for better measurements of outcomes during and after shocks. ...
Climate and weather shocks pose risks to livelihoods in Southern Africa. We assess the extent to which smallholders are exposed to climate shocks in Zambia and how behavioural choices influence the negative effects of these shocks on vulnerability and resilience. We use household data from the nationally representative Rural Agricultural Livelihoods Survey and employ an instrumental variable probit regression model to control for the endogeneity of key choice variables. There are four main findings. First, droughts are the most prevalent climate shock faced by rural smallholder farmers in Zambia, but the extent of exposure differs spatially, with the Southern and Western Provinces being the hardest hit. Nationally, 76% of all smallholder farmers are vulnerable and only 24% are resilient, with female households most vulnerable. Second, increased climate shocks correlate with both increased vulnerability and reduced resilience, with short-and long-term deviations in seasonal rainfall worsening vulnerability and resilience. Third, higher asset endowments and education are correlated with reduced vulnerability and increased resilience. And last, climate-smart agricultural practices significantly improve household resilience. These findings imply a need to support scaling of climate-smart agricultural technologies and to invest in risk mitigation strategies such as weather-indexed insurance and targeted social cash transfers. ARTICLE HISTORY
