Current Opinion in Environmental Sustainability, Feb 1, 2014
The perception that agroforestry systems have higher potential to sequester carbon than comparabl... more The perception that agroforestry systems have higher potential to sequester carbon than comparable single-species crop systems or pasture systems is based on solid scientific foundation. However, the estimates of carbon stock of agroforestry systems in Africa-reported to range from 1.0 to 18.0 Mg C ha À1 in aboveground biomass and up to 200 Mg C ha À1 in soils, and their C sequestration potential from 0.4 to 3.5 Mg C ha À1 yr À1-are based on generalizations and vague or faulty assumptions and therefore are of poor scientific value. Although agroforestry initiatives are promising pathways for climate-change mitigation, rigorous scientific procedures of carbon sequestration estimations are needed for realizing their full potential.
The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution author... more The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations.
The use of general descriptive names, registered names, trademarks, service marks, etc. in this p... more The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. While the advice and information in this book are believed to be true and accurate at the date of publication, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein.
Agricultural lands are often used for constructing stormwater treatand E horizons of the soil pro... more Agricultural lands are often used for constructing stormwater treatand E horizons of the soil profile are sandy and have ment areas (STAs) to abate nutrient loading to adjacent aquatic low P sorption capacities, whereas Bh and Bw horizons systems. Flooding agricultural lands to create STAs could stimulate have greater P sorption capacities (Mansell et al., 1991) a significant release of phosphorus (P) from soil to the water column. To assess the suitability of agricultural lands, specifically those im-due to greater Al-and Fe-oxide contents (Nair et al., pacted by animal operations, for the construction of STAs, soils from 1998). Although a constructed wetland can be a costdifferent components of the New Palm-Newcomer dairies (Nubbin effective method for removing soluble P from runoff Slough Basin, Okeechobee, Florida, USA) were collected by horizon waters, the ambient storage of P in soils, as well as other and their P retention and release capacities estimated. In general, P physico-chemical characteristics of the soils (e.g., pH, released from A-horizon soil under flooded (anaerobic) conditions Ca, Mg, Fe, and Al contents) are critical for selecting was greater than under drained (aerobic) conditions due to redox an STA construction site. Studies of P sorption characeffect on iron (Fe) and consequent P releases. However, the P released teristics and release potential of soils of any proposed from Bh-horizon soil was greater under aerobic conditions than under site should indicate whether the STAs would effectively anaerobic conditions, possibly due to excessive aluminum (Al) content sequester P. The objectives of this study were to (i) in the horizon. Double acid-extractable calcium (Ca), magnesium determine the P sorption capacity of soils collected from (Mg), Al, and P explained 87% of the variability in P release under different horizons and (ii) estimate the P releasing poaerobic conditions, and 80% of that under anaerobic conditions. The tential of the soils to the water column. P release maxima indicated a high solubility of P in A-horizon soil from both active and abandoned dairies (13 and 8% of the total P, respectively), suggesting that these soils could function as potential MATERIALS AND METHODS sources of P to the overlying water column when used in STA construction. Preestablishment of vegetative communities or chemical amend-Site Description ment, however, could ameliorate high P flux from soil to the water Construction of the Nubbin Slough STA is proposed as a column. part of the Lake Okeechobee Water Retention/Phosphorus Removal Critical Restoration Project. The project is designed to increase regional water storage north of Lake Okeechobee L and areas used for animal operations are known to by on-site wetland restoration and water retention, and to accumulate P in soils. Both surface and subsurface reduce P in surface runoff. The site is located in Newcommer discharges from these areas have been detrimental for and New Palm dairies, which are 2.1 km north of Lake Okeeprotecting and restoring adjacent water bodies. Conchobee and 10.5 km southeast of the town of Okeechobee. The site occupies an area of approximately 4.49 km 2 (Fig. 1). structed wetlands and retention reservoirs are consid-The site has an abandoned-intensive component, referring to ered low-cost alternatives for treating wastewater from land that had previously been under dairy production for 34 various sources, including agricultural runoff. A signifiyr, but had been used for pastures or forage production for cant portion of the water-column P can be removed by the last 8 yr. The site also has an active-intensive component, biological (Newbold et al., 1983; Greenway and Woolreferring to areas with active dairies for the last 20 yr, and a ley, 1999; Reddy et al., 1999) and chemical processes native component, referring to nonimpacted or forested areas. both in natural and constructed wetlands (Diaz et al., The abandoned-intensive, active-intensive, and native com-1994; Pant et al., 2001). In many watersheds, land areas ponents occupy 13, 18, and 7% of the total land area of the previously used for agricultural operations are being proposed STA, respectively, while the forage-pasture, grazing converted to wetlands. Flooding these areas can stimufield, and spray field components account for 31, 15, and 16% late the dissolution of stored P and increase the P conof the total, respectively. The adjacent land use of the proposed STA site includes intensive agriculture, wetland and centrations in the water column (Pant and Reddy, 2000).
Current Opinion in Environmental Sustainability, Feb 1, 2014
The perception that agroforestry systems have higher potential to sequester carbon than comparabl... more The perception that agroforestry systems have higher potential to sequester carbon than comparable single-species crop systems or pasture systems is based on solid scientific foundation. However, the estimates of carbon stock of agroforestry systems in Africa-reported to range from 1.0 to 18.0 Mg C ha À1 in aboveground biomass and up to 200 Mg C ha À1 in soils, and their C sequestration potential from 0.4 to 3.5 Mg C ha À1 yr À1-are based on generalizations and vague or faulty assumptions and therefore are of poor scientific value. Although agroforestry initiatives are promising pathways for climate-change mitigation, rigorous scientific procedures of carbon sequestration estimations are needed for realizing their full potential.
The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution author... more The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations.
The use of general descriptive names, registered names, trademarks, service marks, etc. in this p... more The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. While the advice and information in this book are believed to be true and accurate at the date of publication, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein.
Agricultural lands are often used for constructing stormwater treatand E horizons of the soil pro... more Agricultural lands are often used for constructing stormwater treatand E horizons of the soil profile are sandy and have ment areas (STAs) to abate nutrient loading to adjacent aquatic low P sorption capacities, whereas Bh and Bw horizons systems. Flooding agricultural lands to create STAs could stimulate have greater P sorption capacities (Mansell et al., 1991) a significant release of phosphorus (P) from soil to the water column. To assess the suitability of agricultural lands, specifically those im-due to greater Al-and Fe-oxide contents (Nair et al., pacted by animal operations, for the construction of STAs, soils from 1998). Although a constructed wetland can be a costdifferent components of the New Palm-Newcomer dairies (Nubbin effective method for removing soluble P from runoff Slough Basin, Okeechobee, Florida, USA) were collected by horizon waters, the ambient storage of P in soils, as well as other and their P retention and release capacities estimated. In general, P physico-chemical characteristics of the soils (e.g., pH, released from A-horizon soil under flooded (anaerobic) conditions Ca, Mg, Fe, and Al contents) are critical for selecting was greater than under drained (aerobic) conditions due to redox an STA construction site. Studies of P sorption characeffect on iron (Fe) and consequent P releases. However, the P released teristics and release potential of soils of any proposed from Bh-horizon soil was greater under aerobic conditions than under site should indicate whether the STAs would effectively anaerobic conditions, possibly due to excessive aluminum (Al) content sequester P. The objectives of this study were to (i) in the horizon. Double acid-extractable calcium (Ca), magnesium determine the P sorption capacity of soils collected from (Mg), Al, and P explained 87% of the variability in P release under different horizons and (ii) estimate the P releasing poaerobic conditions, and 80% of that under anaerobic conditions. The tential of the soils to the water column. P release maxima indicated a high solubility of P in A-horizon soil from both active and abandoned dairies (13 and 8% of the total P, respectively), suggesting that these soils could function as potential MATERIALS AND METHODS sources of P to the overlying water column when used in STA construction. Preestablishment of vegetative communities or chemical amend-Site Description ment, however, could ameliorate high P flux from soil to the water Construction of the Nubbin Slough STA is proposed as a column. part of the Lake Okeechobee Water Retention/Phosphorus Removal Critical Restoration Project. The project is designed to increase regional water storage north of Lake Okeechobee L and areas used for animal operations are known to by on-site wetland restoration and water retention, and to accumulate P in soils. Both surface and subsurface reduce P in surface runoff. The site is located in Newcommer discharges from these areas have been detrimental for and New Palm dairies, which are 2.1 km north of Lake Okeeprotecting and restoring adjacent water bodies. Conchobee and 10.5 km southeast of the town of Okeechobee. The site occupies an area of approximately 4.49 km 2 (Fig. 1). structed wetlands and retention reservoirs are consid-The site has an abandoned-intensive component, referring to ered low-cost alternatives for treating wastewater from land that had previously been under dairy production for 34 various sources, including agricultural runoff. A signifiyr, but had been used for pastures or forage production for cant portion of the water-column P can be removed by the last 8 yr. The site also has an active-intensive component, biological (Newbold et al., 1983; Greenway and Woolreferring to areas with active dairies for the last 20 yr, and a ley, 1999; Reddy et al., 1999) and chemical processes native component, referring to nonimpacted or forested areas. both in natural and constructed wetlands (Diaz et al., The abandoned-intensive, active-intensive, and native com-1994; Pant et al., 2001). In many watersheds, land areas ponents occupy 13, 18, and 7% of the total land area of the previously used for agricultural operations are being proposed STA, respectively, while the forage-pasture, grazing converted to wetlands. Flooding these areas can stimufield, and spray field components account for 31, 15, and 16% late the dissolution of stored P and increase the P conof the total, respectively. The adjacent land use of the proposed STA site includes intensive agriculture, wetland and centrations in the water column (Pant and Reddy, 2000).
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