Climate Smart Agriculture in smallholder farming systems in the central rift valley of Ethiopia : potentials for improving productivity, climate change adaptation and mitigation
Climate Smart Agriculture (CSA) is an approach that aims at achieving sustainable food production and security through providing flexible but socially acceptable cultivation methods. For this, CSA seeks to sustainably increase yields, to build resilience to climate variability and change, and to red...
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| description | Climate Smart Agriculture (CSA) is an approach that aims at achieving sustainable food production and security through providing flexible but socially acceptable cultivation methods. For this, CSA seeks to sustainably increase yields, to build resilience to climate variability and change, and to reduce net greenhouse gas (GHG) emissions. Practices commonly subsumed under CSA are, among others, conservation agriculture (CA), agroforestry, inclusion of legumes, use of drought tolerant crop varieties and stress adapted livestock breeds, crop diversification and integrated soil fertility management. The success of implementing CSA practices is context specific and has to be adapted to fit local conditions. Hence, CSA has to be studied under specific regional settings. In my PhD thesis, I set up two conservation tillage plot experiments (Paper I) in the Ethiopian rift valley on soils with contrasting management histories, a high input field at the University farm of Hawassa and a low input field run by smallholders in Lokabaya. The experiments tested increasing levels of maize intensification under zero and conventional tillage, using split plot design, with tillage practices assigned to main plots and intensification levels to sub plots. Maize yields and selected soil properties were studied throughout two seasons. Seed priming with or without compost addition had no effect on maize yields at neither location, whereas mineral fertilizer addition increased yields, particularly when combined with mulching of maize residues at the drier Lokabaya site. However, mulching at a rate of 3 ton ha-1 did not significantly affect yields compared to mineral fertilizer addition alone, despite an increasing trend at Lokabaya. The effect of tillage practice was mixed, with zero tillage showing better (Lokabaya farm 1 in 2015 and Hawassa in 2016) or comparable (Lokabaya both farms 2016, farm 2 in 2015) yields with conventional tillage, with the exception of significantly lower yields at the humid Hawassa site with zero tillage during the dry 2015 season. In general, zero tillage did not lead to a consistent yield penalty at any of the sites (except at Hawassa in the dry 2015 season), suggesting that smallholder farmers in the area could achieve reasonable yields without having to till, thereby saving significant amounts of labor and money. Being a short-term experiment over just two growing seasons, there was no significant effect on soil properties like SOC, TN, bulk density |
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| fullrecord | <record><control><sourceid>cristin_3HK</sourceid><recordid>TN_cdi_cristin_nora_11250_3154518</recordid><sourceformat>XML</sourceformat><sourcesystem>PC</sourcesystem><sourcerecordid>11250_3154518</sourcerecordid><originalsourceid>FETCH-cristin_nora_11250_31545183</originalsourceid><addsrcrecordid>eNqNjktqw0AQRLXJIji5Q2VvgxVHELILxsb7eC-aUY_UMB_R0xLoWLlh5OADeFUU9XjUc_V7DBLJGD-R1PDdq7gp2KQMSSiRQhhy6FjhSaOkHmUpxrHcZhsYjpMpBah4w7zivCB7nGyQPArhC2O2lREKBT4rJI6a55tpzW5yJrPYsoW7H3EDpZ5BHY1GJjmBUocoJv1_fame_Ori13tuqrfz6Xq87JxKMUltykptXb83-_ZQNx9N_Xl4hPkD_zpb7w</addsrcrecordid><sourcetype>Open Access Repository</sourcetype><iscdi>true</iscdi><recordtype>dissertation</recordtype></control><display><type>dissertation</type><title>Climate Smart Agriculture in smallholder farming systems in the central rift valley of Ethiopia : potentials for improving productivity, climate change adaptation and mitigation</title><source>NORA - Norwegian Open Research Archives</source><creator>Raji, Shimelis Gizachew</creator><creatorcontrib>Raji, Shimelis Gizachew ; Aune, Jens ; Sogn, Trine ; Børresen, Trond ; Doersch, Peter</creatorcontrib><description>Climate Smart Agriculture (CSA) is an approach that aims at achieving sustainable food production and security through providing flexible but socially acceptable cultivation methods. For this, CSA seeks to sustainably increase yields, to build resilience to climate variability and change, and to reduce net greenhouse gas (GHG) emissions. Practices commonly subsumed under CSA are, among others, conservation agriculture (CA), agroforestry, inclusion of legumes, use of drought tolerant crop varieties and stress adapted livestock breeds, crop diversification and integrated soil fertility management. The success of implementing CSA practices is context specific and has to be adapted to fit local conditions. Hence, CSA has to be studied under specific regional settings. In my PhD thesis, I set up two conservation tillage plot experiments (Paper I) in the Ethiopian rift valley on soils with contrasting management histories, a high input field at the University farm of Hawassa and a low input field run by smallholders in Lokabaya. The experiments tested increasing levels of maize intensification under zero and conventional tillage, using split plot design, with tillage practices assigned to main plots and intensification levels to sub plots. Maize yields and selected soil properties were studied throughout two seasons. Seed priming with or without compost addition had no effect on maize yields at neither location, whereas mineral fertilizer addition increased yields, particularly when combined with mulching of maize residues at the drier Lokabaya site. However, mulching at a rate of 3 ton ha-1 did not significantly affect yields compared to mineral fertilizer addition alone, despite an increasing trend at Lokabaya. The effect of tillage practice was mixed, with zero tillage showing better (Lokabaya farm 1 in 2015 and Hawassa in 2016) or comparable (Lokabaya both farms 2016, farm 2 in 2015) yields with conventional tillage, with the exception of significantly lower yields at the humid Hawassa site with zero tillage during the dry 2015 season. In general, zero tillage did not lead to a consistent yield penalty at any of the sites (except at Hawassa in the dry 2015 season), suggesting that smallholder farmers in the area could achieve reasonable yields without having to till, thereby saving significant amounts of labor and money. Being a short-term experiment over just two growing seasons, there was no significant effect on soil properties like SOC, TN, bulk density and moisture content.
The rift valley region is characterized by a mixed farming system, which faces severe feed shortage for livestock. As a result, there is little if any crop residue retention on the farm level. Together with the very low fertilizer use in the region, this has caused gradual nutrient depletion and soil degradation. Intercropping cereals with forage legumes could remedy this to some degree by contributing good quality fodder for livestock. Together with the retention of N-rich legume residues, this could improve soil quality over time. An experiment was set up (Paper II) using two forage legumes, lablab (Lablab purpureus) and crotalaria (Crotalaria juncea) as intercrop to maize. To explore how intercrops would compete with maize, the intercrops were sown either three or six weeks after sowing maize. Maize yields and land equivalent ratios (LER) were evaluated. The experiment also included plots with forage legumes grown as sole crops in 2015, followed by monocrop maize in 2016 to assess the residual effect of a legume-maize rotation. To account for potential N carryover from legumes grown in the previous year, fertilization rates were reduced by half in 2016 in both maize following sole forage legumes and maize-forage legume intercropping,. LER values up to 1.78 and 1.48 for Hawassa and Lokabaya, respectively, were found for combined lablab and crotalaria intercropped three weeks after maize. This suggests that by integrating these forage legumes into maize, smallholder farmers could benefit by achieving reasonable maize yields, harvesting additional biomass for livestock fodder, improving soil quality over time, and reduce the pressure on crop residues, particularly in dry years. In the 2016 season, with mineral fertilization reduced by 50%, there was no significant maize grain yield loss in any of the treatments involving legumes compared with fully fertilized maize monocrop, despite reduced biomass yields of the forage legumes due to early shading by maize. This suggests that smallholders could achieve reasonable maize yields with reduced fertilization levels while reducing mineral N input, thus contributing to CSA goals. However, the study also showed that rainfall variability has a large impact on legume growth, so that the overall effects of legume intercropping are difficult to predict.
Grain legumes are vital sources of cheap protein and cash for smallholder farmers, but their yields are low due to numerous climatic and biophysical constraints. To address these constraints, two field experiments with each two varieties of Haricot bean (Phaseolus vulgaris) and mung bean (Vigna radiata) were set up at Hawassa and Lokabaya to test artificial inoculation with commercially available rhizobia (2015 and 2016) and P addition with and without inoculation (in 2016 only) (Paper III). Symbiotic performance (i.e. biological N fixation) was estimated by the 15N natural abundance method. Inoculation did not significantly affect symbiotic performance or yields irrespective of location or growing season. By contrast, addition of 20 kg P ha-1 together with inoculation resulted in 50% increase of biologically fixed N by both grain legumes at the low-input Lokabaya site but not at the Hawassa site in 2016. Overall, haricot bean fixed 71 to 99 kg ha-1 N at the more fertile Hawassa site but only 17 to 36 kg ha-1 N at the less fertile Lokabaya site. This means that while rhizobial inoculation and P addition may increase the amount of N derived from the atmosphere to >50%, N yields remained small at Lokabaya, suggesting that in order to close the yield gap commonly experienced by smallholder farmers in the rift valley, long term integrated nutrient management would be needed. The yield difference between the sites was smaller for mung bean and the response to P addition more positive at the low-input Lokabaya site, suggesting that mung bean could be a suitable grain legume for smallholders with marginal soils.
As highlighted in Paper II, inclusion of legumes could be an important component of CSA by improving overall productivity and yield stability as well as soil fertility in the long run. However, using legumes to intensify maize production also entails increased risk of nutrient losses to water and atmosphere, including emission of the strong climate gas nitrous oxide (N2O). Intensified maize production could also reduce the soil’s ability to take up and oxidize atmospheric methane. N2O emissions and CH4 uptake were therefore measured throughout two cropping seasons in selected treatments of the maize-legume intercropping experiment at Hawassa (Paper IV). In the first season (2015), representing a drought year, cumulative N2O emissions were largest in lablab intercropped 3 weeks after sowing maize, with all other treatments being equal or lower than the fertilized maize monocrop. After reducing mineral N input to intercropped systems by 50 % in the second season, N2O emissions were comparable with the fully fertilized maize monocrop. Maize yield-scaled N2O emissions in the first season increased linearly with aboveground legume N-yield (p = 0.01), but not in the second season (p = 0.31), when early rains resulted in less legume biomass because of shading by maize. Growing season N2O-N emission factors varied from 0.02 to 0.25 and 0.11 to 0.20 % of the estimated total N input in 2015 and 2016, respectively. Growing season CH4 uptake ranged from 1.0 to 1.5 kg CH4-C ha−1 with no significant differences between treatments or years, but setting off the N2O-associated global warming potential by up to 69 %. These results suggest that leguminous intercrops entail some risk for increased N2O emissions when developing high aboveground biomasses in dry years. In return legume N can replace some of the fertilizer N without compromising maize yields in the following year, thus supporting CSA goals while intensifying crop production in the region.</description><language>eng</language><publisher>Norwegian University of Life Sciences, Ås</publisher><ispartof>PhD Thesis, 2019</ispartof><rights>info:eu-repo/semantics/openAccess</rights><oa>free_for_read</oa><woscitedreferencessubscribed>false</woscitedreferencessubscribed></display><links><openurl>$$Topenurl_article</openurl><openurlfulltext>$$Topenurlfull_article</openurlfulltext><thumbnail>$$Tsyndetics_thumb_exl</thumbnail><link.rule.ids>230,311,776,881,4038,26544</link.rule.ids><linktorsrc>$$Uhttp://hdl.handle.net/11250/3154518$$EView_record_in_NORA$$FView_record_in_$$GNORA$$Hfree_for_read</linktorsrc></links><search><creatorcontrib>Raji, Shimelis Gizachew</creatorcontrib><title>Climate Smart Agriculture in smallholder farming systems in the central rift valley of Ethiopia : potentials for improving productivity, climate change adaptation and mitigation</title><title>PhD Thesis</title><description>Climate Smart Agriculture (CSA) is an approach that aims at achieving sustainable food production and security through providing flexible but socially acceptable cultivation methods. For this, CSA seeks to sustainably increase yields, to build resilience to climate variability and change, and to reduce net greenhouse gas (GHG) emissions. Practices commonly subsumed under CSA are, among others, conservation agriculture (CA), agroforestry, inclusion of legumes, use of drought tolerant crop varieties and stress adapted livestock breeds, crop diversification and integrated soil fertility management. The success of implementing CSA practices is context specific and has to be adapted to fit local conditions. Hence, CSA has to be studied under specific regional settings. In my PhD thesis, I set up two conservation tillage plot experiments (Paper I) in the Ethiopian rift valley on soils with contrasting management histories, a high input field at the University farm of Hawassa and a low input field run by smallholders in Lokabaya. The experiments tested increasing levels of maize intensification under zero and conventional tillage, using split plot design, with tillage practices assigned to main plots and intensification levels to sub plots. Maize yields and selected soil properties were studied throughout two seasons. Seed priming with or without compost addition had no effect on maize yields at neither location, whereas mineral fertilizer addition increased yields, particularly when combined with mulching of maize residues at the drier Lokabaya site. However, mulching at a rate of 3 ton ha-1 did not significantly affect yields compared to mineral fertilizer addition alone, despite an increasing trend at Lokabaya. The effect of tillage practice was mixed, with zero tillage showing better (Lokabaya farm 1 in 2015 and Hawassa in 2016) or comparable (Lokabaya both farms 2016, farm 2 in 2015) yields with conventional tillage, with the exception of significantly lower yields at the humid Hawassa site with zero tillage during the dry 2015 season. In general, zero tillage did not lead to a consistent yield penalty at any of the sites (except at Hawassa in the dry 2015 season), suggesting that smallholder farmers in the area could achieve reasonable yields without having to till, thereby saving significant amounts of labor and money. Being a short-term experiment over just two growing seasons, there was no significant effect on soil properties like SOC, TN, bulk density and moisture content.
The rift valley region is characterized by a mixed farming system, which faces severe feed shortage for livestock. As a result, there is little if any crop residue retention on the farm level. Together with the very low fertilizer use in the region, this has caused gradual nutrient depletion and soil degradation. Intercropping cereals with forage legumes could remedy this to some degree by contributing good quality fodder for livestock. Together with the retention of N-rich legume residues, this could improve soil quality over time. An experiment was set up (Paper II) using two forage legumes, lablab (Lablab purpureus) and crotalaria (Crotalaria juncea) as intercrop to maize. To explore how intercrops would compete with maize, the intercrops were sown either three or six weeks after sowing maize. Maize yields and land equivalent ratios (LER) were evaluated. The experiment also included plots with forage legumes grown as sole crops in 2015, followed by monocrop maize in 2016 to assess the residual effect of a legume-maize rotation. To account for potential N carryover from legumes grown in the previous year, fertilization rates were reduced by half in 2016 in both maize following sole forage legumes and maize-forage legume intercropping,. LER values up to 1.78 and 1.48 for Hawassa and Lokabaya, respectively, were found for combined lablab and crotalaria intercropped three weeks after maize. This suggests that by integrating these forage legumes into maize, smallholder farmers could benefit by achieving reasonable maize yields, harvesting additional biomass for livestock fodder, improving soil quality over time, and reduce the pressure on crop residues, particularly in dry years. In the 2016 season, with mineral fertilization reduced by 50%, there was no significant maize grain yield loss in any of the treatments involving legumes compared with fully fertilized maize monocrop, despite reduced biomass yields of the forage legumes due to early shading by maize. This suggests that smallholders could achieve reasonable maize yields with reduced fertilization levels while reducing mineral N input, thus contributing to CSA goals. However, the study also showed that rainfall variability has a large impact on legume growth, so that the overall effects of legume intercropping are difficult to predict.
Grain legumes are vital sources of cheap protein and cash for smallholder farmers, but their yields are low due to numerous climatic and biophysical constraints. To address these constraints, two field experiments with each two varieties of Haricot bean (Phaseolus vulgaris) and mung bean (Vigna radiata) were set up at Hawassa and Lokabaya to test artificial inoculation with commercially available rhizobia (2015 and 2016) and P addition with and without inoculation (in 2016 only) (Paper III). Symbiotic performance (i.e. biological N fixation) was estimated by the 15N natural abundance method. Inoculation did not significantly affect symbiotic performance or yields irrespective of location or growing season. By contrast, addition of 20 kg P ha-1 together with inoculation resulted in 50% increase of biologically fixed N by both grain legumes at the low-input Lokabaya site but not at the Hawassa site in 2016. Overall, haricot bean fixed 71 to 99 kg ha-1 N at the more fertile Hawassa site but only 17 to 36 kg ha-1 N at the less fertile Lokabaya site. This means that while rhizobial inoculation and P addition may increase the amount of N derived from the atmosphere to >50%, N yields remained small at Lokabaya, suggesting that in order to close the yield gap commonly experienced by smallholder farmers in the rift valley, long term integrated nutrient management would be needed. The yield difference between the sites was smaller for mung bean and the response to P addition more positive at the low-input Lokabaya site, suggesting that mung bean could be a suitable grain legume for smallholders with marginal soils.
As highlighted in Paper II, inclusion of legumes could be an important component of CSA by improving overall productivity and yield stability as well as soil fertility in the long run. However, using legumes to intensify maize production also entails increased risk of nutrient losses to water and atmosphere, including emission of the strong climate gas nitrous oxide (N2O). Intensified maize production could also reduce the soil’s ability to take up and oxidize atmospheric methane. N2O emissions and CH4 uptake were therefore measured throughout two cropping seasons in selected treatments of the maize-legume intercropping experiment at Hawassa (Paper IV). In the first season (2015), representing a drought year, cumulative N2O emissions were largest in lablab intercropped 3 weeks after sowing maize, with all other treatments being equal or lower than the fertilized maize monocrop. After reducing mineral N input to intercropped systems by 50 % in the second season, N2O emissions were comparable with the fully fertilized maize monocrop. Maize yield-scaled N2O emissions in the first season increased linearly with aboveground legume N-yield (p = 0.01), but not in the second season (p = 0.31), when early rains resulted in less legume biomass because of shading by maize. Growing season N2O-N emission factors varied from 0.02 to 0.25 and 0.11 to 0.20 % of the estimated total N input in 2015 and 2016, respectively. Growing season CH4 uptake ranged from 1.0 to 1.5 kg CH4-C ha−1 with no significant differences between treatments or years, but setting off the N2O-associated global warming potential by up to 69 %. These results suggest that leguminous intercrops entail some risk for increased N2O emissions when developing high aboveground biomasses in dry years. In return legume N can replace some of the fertilizer N without compromising maize yields in the following year, thus supporting CSA goals while intensifying crop production in the region.</description><fulltext>true</fulltext><rsrctype>dissertation</rsrctype><creationdate>2019</creationdate><recordtype>dissertation</recordtype><sourceid>3HK</sourceid><recordid>eNqNjktqw0AQRLXJIji5Q2VvgxVHELILxsb7eC-aUY_UMB_R0xLoWLlh5OADeFUU9XjUc_V7DBLJGD-R1PDdq7gp2KQMSSiRQhhy6FjhSaOkHmUpxrHcZhsYjpMpBah4w7zivCB7nGyQPArhC2O2lREKBT4rJI6a55tpzW5yJrPYsoW7H3EDpZ5BHY1GJjmBUocoJv1_fame_Ori13tuqrfz6Xq87JxKMUltykptXb83-_ZQNx9N_Xl4hPkD_zpb7w</recordid><startdate>2019</startdate><enddate>2019</enddate><creator>Raji, Shimelis Gizachew</creator><general>Norwegian University of Life Sciences, Ås</general><scope>3HK</scope></search><sort><creationdate>2019</creationdate><title>Climate Smart Agriculture in smallholder farming systems in the central rift valley of Ethiopia : potentials for improving productivity, climate change adaptation and mitigation</title><author>Raji, Shimelis Gizachew</author></sort><facets><frbrtype>5</frbrtype><frbrgroupid>cdi_FETCH-cristin_nora_11250_31545183</frbrgroupid><rsrctype>dissertations</rsrctype><prefilter>dissertations</prefilter><language>eng</language><creationdate>2019</creationdate><toplevel>online_resources</toplevel><creatorcontrib>Raji, Shimelis Gizachew</creatorcontrib><collection>NORA - Norwegian Open Research Archives</collection></facets><delivery><delcategory>Remote Search Resource</delcategory><fulltext>fulltext_linktorsrc</fulltext></delivery><addata><au>Raji, Shimelis Gizachew</au><format>dissertation</format><genre>dissertation</genre><ristype>THES</ristype><Advisor>Aune, Jens</Advisor><Advisor>Sogn, Trine</Advisor><Advisor>Børresen, Trond</Advisor><Advisor>Doersch, Peter</Advisor><atitle>Climate Smart Agriculture in smallholder farming systems in the central rift valley of Ethiopia : potentials for improving productivity, climate change adaptation and mitigation</atitle><btitle>PhD Thesis</btitle><date>2019</date><risdate>2019</risdate><abstract>Climate Smart Agriculture (CSA) is an approach that aims at achieving sustainable food production and security through providing flexible but socially acceptable cultivation methods. For this, CSA seeks to sustainably increase yields, to build resilience to climate variability and change, and to reduce net greenhouse gas (GHG) emissions. Practices commonly subsumed under CSA are, among others, conservation agriculture (CA), agroforestry, inclusion of legumes, use of drought tolerant crop varieties and stress adapted livestock breeds, crop diversification and integrated soil fertility management. The success of implementing CSA practices is context specific and has to be adapted to fit local conditions. Hence, CSA has to be studied under specific regional settings. In my PhD thesis, I set up two conservation tillage plot experiments (Paper I) in the Ethiopian rift valley on soils with contrasting management histories, a high input field at the University farm of Hawassa and a low input field run by smallholders in Lokabaya. The experiments tested increasing levels of maize intensification under zero and conventional tillage, using split plot design, with tillage practices assigned to main plots and intensification levels to sub plots. Maize yields and selected soil properties were studied throughout two seasons. Seed priming with or without compost addition had no effect on maize yields at neither location, whereas mineral fertilizer addition increased yields, particularly when combined with mulching of maize residues at the drier Lokabaya site. However, mulching at a rate of 3 ton ha-1 did not significantly affect yields compared to mineral fertilizer addition alone, despite an increasing trend at Lokabaya. The effect of tillage practice was mixed, with zero tillage showing better (Lokabaya farm 1 in 2015 and Hawassa in 2016) or comparable (Lokabaya both farms 2016, farm 2 in 2015) yields with conventional tillage, with the exception of significantly lower yields at the humid Hawassa site with zero tillage during the dry 2015 season. In general, zero tillage did not lead to a consistent yield penalty at any of the sites (except at Hawassa in the dry 2015 season), suggesting that smallholder farmers in the area could achieve reasonable yields without having to till, thereby saving significant amounts of labor and money. Being a short-term experiment over just two growing seasons, there was no significant effect on soil properties like SOC, TN, bulk density and moisture content.
The rift valley region is characterized by a mixed farming system, which faces severe feed shortage for livestock. As a result, there is little if any crop residue retention on the farm level. Together with the very low fertilizer use in the region, this has caused gradual nutrient depletion and soil degradation. Intercropping cereals with forage legumes could remedy this to some degree by contributing good quality fodder for livestock. Together with the retention of N-rich legume residues, this could improve soil quality over time. An experiment was set up (Paper II) using two forage legumes, lablab (Lablab purpureus) and crotalaria (Crotalaria juncea) as intercrop to maize. To explore how intercrops would compete with maize, the intercrops were sown either three or six weeks after sowing maize. Maize yields and land equivalent ratios (LER) were evaluated. The experiment also included plots with forage legumes grown as sole crops in 2015, followed by monocrop maize in 2016 to assess the residual effect of a legume-maize rotation. To account for potential N carryover from legumes grown in the previous year, fertilization rates were reduced by half in 2016 in both maize following sole forage legumes and maize-forage legume intercropping,. LER values up to 1.78 and 1.48 for Hawassa and Lokabaya, respectively, were found for combined lablab and crotalaria intercropped three weeks after maize. This suggests that by integrating these forage legumes into maize, smallholder farmers could benefit by achieving reasonable maize yields, harvesting additional biomass for livestock fodder, improving soil quality over time, and reduce the pressure on crop residues, particularly in dry years. In the 2016 season, with mineral fertilization reduced by 50%, there was no significant maize grain yield loss in any of the treatments involving legumes compared with fully fertilized maize monocrop, despite reduced biomass yields of the forage legumes due to early shading by maize. This suggests that smallholders could achieve reasonable maize yields with reduced fertilization levels while reducing mineral N input, thus contributing to CSA goals. However, the study also showed that rainfall variability has a large impact on legume growth, so that the overall effects of legume intercropping are difficult to predict.
Grain legumes are vital sources of cheap protein and cash for smallholder farmers, but their yields are low due to numerous climatic and biophysical constraints. To address these constraints, two field experiments with each two varieties of Haricot bean (Phaseolus vulgaris) and mung bean (Vigna radiata) were set up at Hawassa and Lokabaya to test artificial inoculation with commercially available rhizobia (2015 and 2016) and P addition with and without inoculation (in 2016 only) (Paper III). Symbiotic performance (i.e. biological N fixation) was estimated by the 15N natural abundance method. Inoculation did not significantly affect symbiotic performance or yields irrespective of location or growing season. By contrast, addition of 20 kg P ha-1 together with inoculation resulted in 50% increase of biologically fixed N by both grain legumes at the low-input Lokabaya site but not at the Hawassa site in 2016. Overall, haricot bean fixed 71 to 99 kg ha-1 N at the more fertile Hawassa site but only 17 to 36 kg ha-1 N at the less fertile Lokabaya site. This means that while rhizobial inoculation and P addition may increase the amount of N derived from the atmosphere to >50%, N yields remained small at Lokabaya, suggesting that in order to close the yield gap commonly experienced by smallholder farmers in the rift valley, long term integrated nutrient management would be needed. The yield difference between the sites was smaller for mung bean and the response to P addition more positive at the low-input Lokabaya site, suggesting that mung bean could be a suitable grain legume for smallholders with marginal soils.
As highlighted in Paper II, inclusion of legumes could be an important component of CSA by improving overall productivity and yield stability as well as soil fertility in the long run. However, using legumes to intensify maize production also entails increased risk of nutrient losses to water and atmosphere, including emission of the strong climate gas nitrous oxide (N2O). Intensified maize production could also reduce the soil’s ability to take up and oxidize atmospheric methane. N2O emissions and CH4 uptake were therefore measured throughout two cropping seasons in selected treatments of the maize-legume intercropping experiment at Hawassa (Paper IV). In the first season (2015), representing a drought year, cumulative N2O emissions were largest in lablab intercropped 3 weeks after sowing maize, with all other treatments being equal or lower than the fertilized maize monocrop. After reducing mineral N input to intercropped systems by 50 % in the second season, N2O emissions were comparable with the fully fertilized maize monocrop. Maize yield-scaled N2O emissions in the first season increased linearly with aboveground legume N-yield (p = 0.01), but not in the second season (p = 0.31), when early rains resulted in less legume biomass because of shading by maize. Growing season N2O-N emission factors varied from 0.02 to 0.25 and 0.11 to 0.20 % of the estimated total N input in 2015 and 2016, respectively. Growing season CH4 uptake ranged from 1.0 to 1.5 kg CH4-C ha−1 with no significant differences between treatments or years, but setting off the N2O-associated global warming potential by up to 69 %. These results suggest that leguminous intercrops entail some risk for increased N2O emissions when developing high aboveground biomasses in dry years. In return legume N can replace some of the fertilizer N without compromising maize yields in the following year, thus supporting CSA goals while intensifying crop production in the region.</abstract><pub>Norwegian University of Life Sciences, Ås</pub><oa>free_for_read</oa></addata></record> |
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| title | Climate Smart Agriculture in smallholder farming systems in the central rift valley of Ethiopia : potentials for improving productivity, climate change adaptation and mitigation |
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