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C R Black - One of the best experts on this subject based on the ideXlab platform.
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water use in a Grevillea robusta maize overstorey agroforestry system in semi arid kenya
Forest Ecology and Management, 2003Co-Authors: J E Lott, A A H Khan, C R BlackAbstract:Abstract Novel approaches involving a combination of sap flow measurements of transpiration and allometric estimates of biomass production were used to determine seasonal water use by trees and crops in agroforestry systems. The results were used to test the hypothesis that agroforestry may improve productivity by capturing a greater proportion of annual rainfall than annual crops. Grevillea robusta A. Cunn., which is reputed to have a deep rooting habit, was grown in semi-arid Kenya either as sole stands or in combination with maize (Zea mays L.). Water use by individual trees and maize plants was determined using constant temperature heat balance gauges and scaled to provide stand-level estimates of transpiration based on linear relationships (r2>0.70) between sap flow and leaf area across a range of tree ages and environmental conditions. Maximum stand-level transpiration rates for Grevillea ranged from 2.6 to 4.0 mm per day, consistent with previous studies in similar environments. Biomass production by Grevillea was closely correlated with stand-level transpiration (r2>0.69–0.74), suggesting that non-destructive estimates of biomass increments can be used to provide reliable estimates of seasonal transpiration. Cumulative water use by Grevillea over the 4.5-year observation period was comparable in the sole tree and agroforestry treatments, reaching a maximum utilisation of annual rainfall of 64–68% 3–4 years after planting. Approximately 25% of the water transpired by the trees was used during the dry season, indicating that they were able to utilise off-season rainfall, comprising 16% of the total annual rainfall, and residual water remaining in the soil profile after the cropping period. During the 1995 long rains, when 221 mm of rain was received, transpiration by sole maize was
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Water use in a Grevillea robusta–maize overstorey agroforestry system in semi-arid Kenya
Forest Ecology and Management, 2003Co-Authors: J E Lott, A A H Khan, C R BlackAbstract:Abstract Novel approaches involving a combination of sap flow measurements of transpiration and allometric estimates of biomass production were used to determine seasonal water use by trees and crops in agroforestry systems. The results were used to test the hypothesis that agroforestry may improve productivity by capturing a greater proportion of annual rainfall than annual crops. Grevillea robusta A. Cunn., which is reputed to have a deep rooting habit, was grown in semi-arid Kenya either as sole stands or in combination with maize (Zea mays L.). Water use by individual trees and maize plants was determined using constant temperature heat balance gauges and scaled to provide stand-level estimates of transpiration based on linear relationships (r2>0.70) between sap flow and leaf area across a range of tree ages and environmental conditions. Maximum stand-level transpiration rates for Grevillea ranged from 2.6 to 4.0 mm per day, consistent with previous studies in similar environments. Biomass production by Grevillea was closely correlated with stand-level transpiration (r2>0.69–0.74), suggesting that non-destructive estimates of biomass increments can be used to provide reliable estimates of seasonal transpiration. Cumulative water use by Grevillea over the 4.5-year observation period was comparable in the sole tree and agroforestry treatments, reaching a maximum utilisation of annual rainfall of 64–68% 3–4 years after planting. Approximately 25% of the water transpired by the trees was used during the dry season, indicating that they were able to utilise off-season rainfall, comprising 16% of the total annual rainfall, and residual water remaining in the soil profile after the cropping period. During the 1995 long rains, when 221 mm of rain was received, transpiration by sole maize was
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long term productivity of a Grevillea robusta based overstorey agroforestry system in semi arid kenya i tree growth
Forest Ecology and Management, 2000Co-Authors: J E Lott, S B Howard, C R BlackAbstract:Abstract The work reported here formed part of a multidisciplinary project to examine the changing tree/crop interactions, expressed in terms of resource capture, tree and crop growth and system performance, that occur as the trees in semi-arid agroforestry systems establish and mature. Grevillea robusta (A. Cunn.; Grevillea) trees were grown in a dispersed planting arrangement, either as sole stands or in combination with cowpea (Vigna unguiculata L.) or maize (Zea mays L.). Allometric approaches were used to monitor leaf area and leaf, branch and trunk biomass over a 4.5-year period. Seasonal and annual growth increments and the corresponding mean daily growth rates were calculated; crop growth, development and yield were also determined over nine growing seasons. Tree height, leaf area and trunk and branch biomass were reduced in the agroforestry treatment (CTd) during the first 600 days after planting as a result of competition with the associated crops. Tree height subsequently increased more rapidly in the agroforestry treatment (CTd) and regained parity with the sole Grevillea treatment (Td) by ca. 820 days after planting. However, although seasonal and annual biomass increments were comparable in both treatments once the trees became the dominant component of the system, above-ground biomass in CTd Grevillea never recovered fully to Td values during the observation period; trunk volume and biomass were consistently lower in CTd than in Td Grevillea, reducing their economic value. Tree growth continued throughout the dry season, sometimes at rates similar to or greater than observed during the cropping seasons, indicating that the trees were able to utilise residual soil moisture or deep reserves within the profile. This finding is discussed in relation to recent interpretations of niche separation in savanna vegetation. The factors responsible for the observed reductions in tree growth in the agroforestry system are examined; effects on crop yields and system performance are considered in Part II.
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long term productivity of a Grevillea robusta based overstorey agroforestry system in semi arid kenya ii crop growth and system performance
Forest Ecology and Management, 2000Co-Authors: J E Lott, S B Howard, C R BlackAbstract:Maize and cowpea were grown as sole stands or in agroforestry systems containing Grevillea trees (Grevillea robusta A. Cunn.). Crop and system performance were examined over a 4.5-year-period (nine growing seasons) commencing in October 1991; failure of the rains caused the loss of one cropping season. A rotation of cowpea (Vigna unguiculata L. Walp.) and maize (Zea mays L.) was grown during the first five seasons after planting the trees, while maize was grown continuously during the final four seasons. Sole maize was also grown under spectrally neutral shade netting which reduced incident radiation by 25, 50 or 75% to establish the relative importance of shade and below-ground competition for water and nutrients in determining the performance of understorey crops. The above-ground biomass and grain yield of understorey crops were not significantly affected by the presence of Grevillea during the first four seasons, but were greatly reduced in subsequent seasons as the trees became increasingly dominant; maize yields reached 50% of the sole crop values only once during the final four seasons, when rainfall was unusually high. The hypothesis that competition for water was the primary limiting factor for understorey crops was supported by the observation that above-ground biomass and grain yield were greater in the shade net treatments than in agroforestry maize, demonstrating that shade was not solely responsible for the substantial yield losses in the latter treatment. Performance ratios (ratio of values for the agroforestry system relative to sole stands) for total above-ground and trunk biomass in Grevillea were initially low, reflecting the impact of competition with associated crops during tree establishment, but increased to unity within 2.5 years. Performance ratios for the understorey crops exhibited the reverse trend, initially being close to unity but approaching zero for three of the final four seasons. Performance ratios were never close to unity for both trees and crops during the same season, indicating that there was always competition for available resources irrespective of crop species or tree size. The implications for agroforestry system design and future research are discussed. # 2000 Elsevier Science B.V. All rights reserved.
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Allometric estimation of above-ground biomass and leaf area in managed Grevillea robusta agroforestry systems
Agroforestry Systems, 2000Co-Authors: J E Lott, S B Howard, C R BlackAbstract:Non-destructive methods for determining the biomass and leaf area of individual trees throughout their growing cycle are an essential tool in agroforestry research, but must be capable of providing reliable estimates despite the influence that management strategies such as pruning may have on tree form. In the present study, allometric methods involving measurements of the diameter of all branches provided reliable estimates of canopy leaf area and biomass for Grevillea trees ( Grevillea robusta A. Cunn.; Proteaceae) grown as poles, but proved unsuitable for routine measurements because of their time-consuming nature. An alternative, less laborious method based on measurements of trunk cross-sectional area immediately below the first branch of the canopy provided satisfactory allometric estimates of leaf area and canopy biomass. Trunk biomass was determined from measurements of tree height and diameter at breast height using established methodology based on the assumption that trunk volume may be calculated using a quadratic paraboloid model; biomass was determined as the product of trunk volume and the specific gravity of the wood. The theoretical basis, development and validation of allometric methods for estimating tree growth are discussed and their wider applicability to other agroforestry systems is assessed.
J E Lott - One of the best experts on this subject based on the ideXlab platform.
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water use in a Grevillea robusta maize overstorey agroforestry system in semi arid kenya
Forest Ecology and Management, 2003Co-Authors: J E Lott, A A H Khan, C R BlackAbstract:Abstract Novel approaches involving a combination of sap flow measurements of transpiration and allometric estimates of biomass production were used to determine seasonal water use by trees and crops in agroforestry systems. The results were used to test the hypothesis that agroforestry may improve productivity by capturing a greater proportion of annual rainfall than annual crops. Grevillea robusta A. Cunn., which is reputed to have a deep rooting habit, was grown in semi-arid Kenya either as sole stands or in combination with maize (Zea mays L.). Water use by individual trees and maize plants was determined using constant temperature heat balance gauges and scaled to provide stand-level estimates of transpiration based on linear relationships (r2>0.70) between sap flow and leaf area across a range of tree ages and environmental conditions. Maximum stand-level transpiration rates for Grevillea ranged from 2.6 to 4.0 mm per day, consistent with previous studies in similar environments. Biomass production by Grevillea was closely correlated with stand-level transpiration (r2>0.69–0.74), suggesting that non-destructive estimates of biomass increments can be used to provide reliable estimates of seasonal transpiration. Cumulative water use by Grevillea over the 4.5-year observation period was comparable in the sole tree and agroforestry treatments, reaching a maximum utilisation of annual rainfall of 64–68% 3–4 years after planting. Approximately 25% of the water transpired by the trees was used during the dry season, indicating that they were able to utilise off-season rainfall, comprising 16% of the total annual rainfall, and residual water remaining in the soil profile after the cropping period. During the 1995 long rains, when 221 mm of rain was received, transpiration by sole maize was
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Water use in a Grevillea robusta–maize overstorey agroforestry system in semi-arid Kenya
Forest Ecology and Management, 2003Co-Authors: J E Lott, A A H Khan, C R BlackAbstract:Abstract Novel approaches involving a combination of sap flow measurements of transpiration and allometric estimates of biomass production were used to determine seasonal water use by trees and crops in agroforestry systems. The results were used to test the hypothesis that agroforestry may improve productivity by capturing a greater proportion of annual rainfall than annual crops. Grevillea robusta A. Cunn., which is reputed to have a deep rooting habit, was grown in semi-arid Kenya either as sole stands or in combination with maize (Zea mays L.). Water use by individual trees and maize plants was determined using constant temperature heat balance gauges and scaled to provide stand-level estimates of transpiration based on linear relationships (r2>0.70) between sap flow and leaf area across a range of tree ages and environmental conditions. Maximum stand-level transpiration rates for Grevillea ranged from 2.6 to 4.0 mm per day, consistent with previous studies in similar environments. Biomass production by Grevillea was closely correlated with stand-level transpiration (r2>0.69–0.74), suggesting that non-destructive estimates of biomass increments can be used to provide reliable estimates of seasonal transpiration. Cumulative water use by Grevillea over the 4.5-year observation period was comparable in the sole tree and agroforestry treatments, reaching a maximum utilisation of annual rainfall of 64–68% 3–4 years after planting. Approximately 25% of the water transpired by the trees was used during the dry season, indicating that they were able to utilise off-season rainfall, comprising 16% of the total annual rainfall, and residual water remaining in the soil profile after the cropping period. During the 1995 long rains, when 221 mm of rain was received, transpiration by sole maize was
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long term productivity of a Grevillea robusta based overstorey agroforestry system in semi arid kenya i tree growth
Forest Ecology and Management, 2000Co-Authors: J E Lott, S B Howard, C R BlackAbstract:Abstract The work reported here formed part of a multidisciplinary project to examine the changing tree/crop interactions, expressed in terms of resource capture, tree and crop growth and system performance, that occur as the trees in semi-arid agroforestry systems establish and mature. Grevillea robusta (A. Cunn.; Grevillea) trees were grown in a dispersed planting arrangement, either as sole stands or in combination with cowpea (Vigna unguiculata L.) or maize (Zea mays L.). Allometric approaches were used to monitor leaf area and leaf, branch and trunk biomass over a 4.5-year period. Seasonal and annual growth increments and the corresponding mean daily growth rates were calculated; crop growth, development and yield were also determined over nine growing seasons. Tree height, leaf area and trunk and branch biomass were reduced in the agroforestry treatment (CTd) during the first 600 days after planting as a result of competition with the associated crops. Tree height subsequently increased more rapidly in the agroforestry treatment (CTd) and regained parity with the sole Grevillea treatment (Td) by ca. 820 days after planting. However, although seasonal and annual biomass increments were comparable in both treatments once the trees became the dominant component of the system, above-ground biomass in CTd Grevillea never recovered fully to Td values during the observation period; trunk volume and biomass were consistently lower in CTd than in Td Grevillea, reducing their economic value. Tree growth continued throughout the dry season, sometimes at rates similar to or greater than observed during the cropping seasons, indicating that the trees were able to utilise residual soil moisture or deep reserves within the profile. This finding is discussed in relation to recent interpretations of niche separation in savanna vegetation. The factors responsible for the observed reductions in tree growth in the agroforestry system are examined; effects on crop yields and system performance are considered in Part II.
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long term productivity of a Grevillea robusta based overstorey agroforestry system in semi arid kenya ii crop growth and system performance
Forest Ecology and Management, 2000Co-Authors: J E Lott, S B Howard, C R BlackAbstract:Maize and cowpea were grown as sole stands or in agroforestry systems containing Grevillea trees (Grevillea robusta A. Cunn.). Crop and system performance were examined over a 4.5-year-period (nine growing seasons) commencing in October 1991; failure of the rains caused the loss of one cropping season. A rotation of cowpea (Vigna unguiculata L. Walp.) and maize (Zea mays L.) was grown during the first five seasons after planting the trees, while maize was grown continuously during the final four seasons. Sole maize was also grown under spectrally neutral shade netting which reduced incident radiation by 25, 50 or 75% to establish the relative importance of shade and below-ground competition for water and nutrients in determining the performance of understorey crops. The above-ground biomass and grain yield of understorey crops were not significantly affected by the presence of Grevillea during the first four seasons, but were greatly reduced in subsequent seasons as the trees became increasingly dominant; maize yields reached 50% of the sole crop values only once during the final four seasons, when rainfall was unusually high. The hypothesis that competition for water was the primary limiting factor for understorey crops was supported by the observation that above-ground biomass and grain yield were greater in the shade net treatments than in agroforestry maize, demonstrating that shade was not solely responsible for the substantial yield losses in the latter treatment. Performance ratios (ratio of values for the agroforestry system relative to sole stands) for total above-ground and trunk biomass in Grevillea were initially low, reflecting the impact of competition with associated crops during tree establishment, but increased to unity within 2.5 years. Performance ratios for the understorey crops exhibited the reverse trend, initially being close to unity but approaching zero for three of the final four seasons. Performance ratios were never close to unity for both trees and crops during the same season, indicating that there was always competition for available resources irrespective of crop species or tree size. The implications for agroforestry system design and future research are discussed. # 2000 Elsevier Science B.V. All rights reserved.
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Allometric estimation of above-ground biomass and leaf area in managed Grevillea robusta agroforestry systems
Agroforestry Systems, 2000Co-Authors: J E Lott, S B Howard, C R BlackAbstract:Non-destructive methods for determining the biomass and leaf area of individual trees throughout their growing cycle are an essential tool in agroforestry research, but must be capable of providing reliable estimates despite the influence that management strategies such as pruning may have on tree form. In the present study, allometric methods involving measurements of the diameter of all branches provided reliable estimates of canopy leaf area and biomass for Grevillea trees ( Grevillea robusta A. Cunn.; Proteaceae) grown as poles, but proved unsuitable for routine measurements because of their time-consuming nature. An alternative, less laborious method based on measurements of trunk cross-sectional area immediately below the first branch of the canopy provided satisfactory allometric estimates of leaf area and canopy biomass. Trunk biomass was determined from measurements of tree height and diameter at breast height using established methodology based on the assumption that trunk volume may be calculated using a quadratic paraboloid model; biomass was determined as the product of trunk volume and the specific gravity of the wood. The theoretical basis, development and validation of allometric methods for estimating tree growth are discussed and their wider applicability to other agroforestry systems is assessed.
S B Howard - One of the best experts on this subject based on the ideXlab platform.
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long term productivity of a Grevillea robusta based overstorey agroforestry system in semi arid kenya i tree growth
Forest Ecology and Management, 2000Co-Authors: J E Lott, S B Howard, C R BlackAbstract:Abstract The work reported here formed part of a multidisciplinary project to examine the changing tree/crop interactions, expressed in terms of resource capture, tree and crop growth and system performance, that occur as the trees in semi-arid agroforestry systems establish and mature. Grevillea robusta (A. Cunn.; Grevillea) trees were grown in a dispersed planting arrangement, either as sole stands or in combination with cowpea (Vigna unguiculata L.) or maize (Zea mays L.). Allometric approaches were used to monitor leaf area and leaf, branch and trunk biomass over a 4.5-year period. Seasonal and annual growth increments and the corresponding mean daily growth rates were calculated; crop growth, development and yield were also determined over nine growing seasons. Tree height, leaf area and trunk and branch biomass were reduced in the agroforestry treatment (CTd) during the first 600 days after planting as a result of competition with the associated crops. Tree height subsequently increased more rapidly in the agroforestry treatment (CTd) and regained parity with the sole Grevillea treatment (Td) by ca. 820 days after planting. However, although seasonal and annual biomass increments were comparable in both treatments once the trees became the dominant component of the system, above-ground biomass in CTd Grevillea never recovered fully to Td values during the observation period; trunk volume and biomass were consistently lower in CTd than in Td Grevillea, reducing their economic value. Tree growth continued throughout the dry season, sometimes at rates similar to or greater than observed during the cropping seasons, indicating that the trees were able to utilise residual soil moisture or deep reserves within the profile. This finding is discussed in relation to recent interpretations of niche separation in savanna vegetation. The factors responsible for the observed reductions in tree growth in the agroforestry system are examined; effects on crop yields and system performance are considered in Part II.
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long term productivity of a Grevillea robusta based overstorey agroforestry system in semi arid kenya ii crop growth and system performance
Forest Ecology and Management, 2000Co-Authors: J E Lott, S B Howard, C R BlackAbstract:Maize and cowpea were grown as sole stands or in agroforestry systems containing Grevillea trees (Grevillea robusta A. Cunn.). Crop and system performance were examined over a 4.5-year-period (nine growing seasons) commencing in October 1991; failure of the rains caused the loss of one cropping season. A rotation of cowpea (Vigna unguiculata L. Walp.) and maize (Zea mays L.) was grown during the first five seasons after planting the trees, while maize was grown continuously during the final four seasons. Sole maize was also grown under spectrally neutral shade netting which reduced incident radiation by 25, 50 or 75% to establish the relative importance of shade and below-ground competition for water and nutrients in determining the performance of understorey crops. The above-ground biomass and grain yield of understorey crops were not significantly affected by the presence of Grevillea during the first four seasons, but were greatly reduced in subsequent seasons as the trees became increasingly dominant; maize yields reached 50% of the sole crop values only once during the final four seasons, when rainfall was unusually high. The hypothesis that competition for water was the primary limiting factor for understorey crops was supported by the observation that above-ground biomass and grain yield were greater in the shade net treatments than in agroforestry maize, demonstrating that shade was not solely responsible for the substantial yield losses in the latter treatment. Performance ratios (ratio of values for the agroforestry system relative to sole stands) for total above-ground and trunk biomass in Grevillea were initially low, reflecting the impact of competition with associated crops during tree establishment, but increased to unity within 2.5 years. Performance ratios for the understorey crops exhibited the reverse trend, initially being close to unity but approaching zero for three of the final four seasons. Performance ratios were never close to unity for both trees and crops during the same season, indicating that there was always competition for available resources irrespective of crop species or tree size. The implications for agroforestry system design and future research are discussed. # 2000 Elsevier Science B.V. All rights reserved.
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Allometric estimation of above-ground biomass and leaf area in managed Grevillea robusta agroforestry systems
Agroforestry Systems, 2000Co-Authors: J E Lott, S B Howard, C R BlackAbstract:Non-destructive methods for determining the biomass and leaf area of individual trees throughout their growing cycle are an essential tool in agroforestry research, but must be capable of providing reliable estimates despite the influence that management strategies such as pruning may have on tree form. In the present study, allometric methods involving measurements of the diameter of all branches provided reliable estimates of canopy leaf area and biomass for Grevillea trees ( Grevillea robusta A. Cunn.; Proteaceae) grown as poles, but proved unsuitable for routine measurements because of their time-consuming nature. An alternative, less laborious method based on measurements of trunk cross-sectional area immediately below the first branch of the canopy provided satisfactory allometric estimates of leaf area and canopy biomass. Trunk biomass was determined from measurements of tree height and diameter at breast height using established methodology based on the assumption that trunk volume may be calculated using a quadratic paraboloid model; biomass was determined as the product of trunk volume and the specific gravity of the wood. The theoretical basis, development and validation of allometric methods for estimating tree growth are discussed and their wider applicability to other agroforestry systems is assessed.
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productivity microclimate and water use in Grevillea robusta based agroforestry systems on hillslopes in semi arid kenya
Agriculture Ecosystems & Environment, 2000Co-Authors: C R Black, J E Lott, S B Howard, A A H Khan, J S Wallace, N A Jackson, D M SmithAbstract:This paper describes a multi-disciplinary project to examine the changing interactions between trees and crops as the trees in semi-arid agroforestry systems establish and mature; the project is one of the most detailed and highly instrumented long-term studies of tree and crop growth, system performance, resource capture, hydrology and microclimate ever carried out within an agroforestry context. Its primary objective was to compile a comprehensive experimental database to improve the mechanistic understanding of tree/crop interactions and support the development and validation of process-based simulation models describing resource capture and tree and crop growth in semi-arid agroforestry systems. Grevillea robustaA. Cunn. (Grevillea) trees were grown as mono-cultures or in mixtures with cowpea (Vigna unguiculata L.) or maize (Zea mays L.) over a 68-month period. Allometric approaches were used to determine seasonal and annual growth increments for leaf area and leaf, branch and trunk biomass in Grevillea. Crop performance was examined during each growing season, while the spatial distribution of tree and crop roots was established during the latter stages of the experiment using coring and mini-rhizotron approaches. Detailed hydrological studies examined effects on the soil water balance and its components (precipitation, interception, runoff and soil moisture status); equivalent measurements of spatial and temporal variation in microclimatic conditions allowed the mechanistic basis for beneficial and detrimental effects on understorey crops and the influence of proximity to trees on crop performance to be examined. Transpiration by Grevillea and water movement through lateral and tap roots were measured using sap flow methodology, and light interception by the tree and crop canopies was routinely determined. This multi-disciplinary study has provided a detailed understanding of the changing patterns of resource capture by trees and crops as agroforestry systems mature. This paper provides an overview of the underlying rationale, experimental design and core measurements, outlines key results and conclusions, and draws the attention of readers to further papers providing more detailed consideration of specific aspects of the study. © 2000 Elsevier Science B.V. All rights reserved.
A A H Khan - One of the best experts on this subject based on the ideXlab platform.
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water use in a Grevillea robusta maize overstorey agroforestry system in semi arid kenya
Forest Ecology and Management, 2003Co-Authors: J E Lott, A A H Khan, C R BlackAbstract:Abstract Novel approaches involving a combination of sap flow measurements of transpiration and allometric estimates of biomass production were used to determine seasonal water use by trees and crops in agroforestry systems. The results were used to test the hypothesis that agroforestry may improve productivity by capturing a greater proportion of annual rainfall than annual crops. Grevillea robusta A. Cunn., which is reputed to have a deep rooting habit, was grown in semi-arid Kenya either as sole stands or in combination with maize (Zea mays L.). Water use by individual trees and maize plants was determined using constant temperature heat balance gauges and scaled to provide stand-level estimates of transpiration based on linear relationships (r2>0.70) between sap flow and leaf area across a range of tree ages and environmental conditions. Maximum stand-level transpiration rates for Grevillea ranged from 2.6 to 4.0 mm per day, consistent with previous studies in similar environments. Biomass production by Grevillea was closely correlated with stand-level transpiration (r2>0.69–0.74), suggesting that non-destructive estimates of biomass increments can be used to provide reliable estimates of seasonal transpiration. Cumulative water use by Grevillea over the 4.5-year observation period was comparable in the sole tree and agroforestry treatments, reaching a maximum utilisation of annual rainfall of 64–68% 3–4 years after planting. Approximately 25% of the water transpired by the trees was used during the dry season, indicating that they were able to utilise off-season rainfall, comprising 16% of the total annual rainfall, and residual water remaining in the soil profile after the cropping period. During the 1995 long rains, when 221 mm of rain was received, transpiration by sole maize was
-
Water use in a Grevillea robusta–maize overstorey agroforestry system in semi-arid Kenya
Forest Ecology and Management, 2003Co-Authors: J E Lott, A A H Khan, C R BlackAbstract:Abstract Novel approaches involving a combination of sap flow measurements of transpiration and allometric estimates of biomass production were used to determine seasonal water use by trees and crops in agroforestry systems. The results were used to test the hypothesis that agroforestry may improve productivity by capturing a greater proportion of annual rainfall than annual crops. Grevillea robusta A. Cunn., which is reputed to have a deep rooting habit, was grown in semi-arid Kenya either as sole stands or in combination with maize (Zea mays L.). Water use by individual trees and maize plants was determined using constant temperature heat balance gauges and scaled to provide stand-level estimates of transpiration based on linear relationships (r2>0.70) between sap flow and leaf area across a range of tree ages and environmental conditions. Maximum stand-level transpiration rates for Grevillea ranged from 2.6 to 4.0 mm per day, consistent with previous studies in similar environments. Biomass production by Grevillea was closely correlated with stand-level transpiration (r2>0.69–0.74), suggesting that non-destructive estimates of biomass increments can be used to provide reliable estimates of seasonal transpiration. Cumulative water use by Grevillea over the 4.5-year observation period was comparable in the sole tree and agroforestry treatments, reaching a maximum utilisation of annual rainfall of 64–68% 3–4 years after planting. Approximately 25% of the water transpired by the trees was used during the dry season, indicating that they were able to utilise off-season rainfall, comprising 16% of the total annual rainfall, and residual water remaining in the soil profile after the cropping period. During the 1995 long rains, when 221 mm of rain was received, transpiration by sole maize was
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productivity microclimate and water use in Grevillea robusta based agroforestry systems on hillslopes in semi arid kenya
Agriculture Ecosystems & Environment, 2000Co-Authors: C R Black, J E Lott, S B Howard, A A H Khan, J S Wallace, N A Jackson, D M SmithAbstract:This paper describes a multi-disciplinary project to examine the changing interactions between trees and crops as the trees in semi-arid agroforestry systems establish and mature; the project is one of the most detailed and highly instrumented long-term studies of tree and crop growth, system performance, resource capture, hydrology and microclimate ever carried out within an agroforestry context. Its primary objective was to compile a comprehensive experimental database to improve the mechanistic understanding of tree/crop interactions and support the development and validation of process-based simulation models describing resource capture and tree and crop growth in semi-arid agroforestry systems. Grevillea robustaA. Cunn. (Grevillea) trees were grown as mono-cultures or in mixtures with cowpea (Vigna unguiculata L.) or maize (Zea mays L.) over a 68-month period. Allometric approaches were used to determine seasonal and annual growth increments for leaf area and leaf, branch and trunk biomass in Grevillea. Crop performance was examined during each growing season, while the spatial distribution of tree and crop roots was established during the latter stages of the experiment using coring and mini-rhizotron approaches. Detailed hydrological studies examined effects on the soil water balance and its components (precipitation, interception, runoff and soil moisture status); equivalent measurements of spatial and temporal variation in microclimatic conditions allowed the mechanistic basis for beneficial and detrimental effects on understorey crops and the influence of proximity to trees on crop performance to be examined. Transpiration by Grevillea and water movement through lateral and tap roots were measured using sap flow methodology, and light interception by the tree and crop canopies was routinely determined. This multi-disciplinary study has provided a detailed understanding of the changing patterns of resource capture by trees and crops as agroforestry systems mature. This paper provides an overview of the underlying rationale, experimental design and core measurements, outlines key results and conclusions, and draws the attention of readers to further papers providing more detailed consideration of specific aspects of the study. © 2000 Elsevier Science B.V. All rights reserved.
D M Smith - One of the best experts on this subject based on the ideXlab platform.
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productivity microclimate and water use in Grevillea robusta based agroforestry systems on hillslopes in semi arid kenya
Agriculture Ecosystems & Environment, 2000Co-Authors: C R Black, J E Lott, S B Howard, A A H Khan, J S Wallace, N A Jackson, D M SmithAbstract:This paper describes a multi-disciplinary project to examine the changing interactions between trees and crops as the trees in semi-arid agroforestry systems establish and mature; the project is one of the most detailed and highly instrumented long-term studies of tree and crop growth, system performance, resource capture, hydrology and microclimate ever carried out within an agroforestry context. Its primary objective was to compile a comprehensive experimental database to improve the mechanistic understanding of tree/crop interactions and support the development and validation of process-based simulation models describing resource capture and tree and crop growth in semi-arid agroforestry systems. Grevillea robustaA. Cunn. (Grevillea) trees were grown as mono-cultures or in mixtures with cowpea (Vigna unguiculata L.) or maize (Zea mays L.) over a 68-month period. Allometric approaches were used to determine seasonal and annual growth increments for leaf area and leaf, branch and trunk biomass in Grevillea. Crop performance was examined during each growing season, while the spatial distribution of tree and crop roots was established during the latter stages of the experiment using coring and mini-rhizotron approaches. Detailed hydrological studies examined effects on the soil water balance and its components (precipitation, interception, runoff and soil moisture status); equivalent measurements of spatial and temporal variation in microclimatic conditions allowed the mechanistic basis for beneficial and detrimental effects on understorey crops and the influence of proximity to trees on crop performance to be examined. Transpiration by Grevillea and water movement through lateral and tap roots were measured using sap flow methodology, and light interception by the tree and crop canopies was routinely determined. This multi-disciplinary study has provided a detailed understanding of the changing patterns of resource capture by trees and crops as agroforestry systems mature. This paper provides an overview of the underlying rationale, experimental design and core measurements, outlines key results and conclusions, and draws the attention of readers to further papers providing more detailed consideration of specific aspects of the study. © 2000 Elsevier Science B.V. All rights reserved.
