T E M P E R A T E R E G I O N S T R O P I C A L R E G I O N S Nair, 2007
Agroforestry Practices in North America Alley cropping Trees planted in single or grouped rows with crops in the wide alleys between the tree rows Producing specialty crops for medicinal, ornamental, or culinary uses in forested areas Forest farming Strips of perennial vegetation (tree/shrub/grass) planted between croplands/pastures and streams, lakes, wetlands, ponds, etc. Riparian buffer strips Combining trees with forage (pasture or hay) and livestock production Silvopasture Row trees around farms and fields, managed as part of crop or livestock operation to protect crops, animals, and soil from wind hazards Windbreaks
SPECIAL SUBMISSIONS: AGROFORESTRY SYSTEMS AND ENVIRONMENTAL QUALITY Journal of Environmental Quality Volume 40 (3), May – June 2011, pages 784–866.
Environmental Quality is becoming a serious issue… EDITORIAL : Published: May 4, 2011 (in print on May 5, 2011) Washing Away the Fields of Iowa To an untrained eye, the fields of Iowa have a reassuring solidity. You cannot tell that the state has lost half its topsoil in the past century. According to a new report from the Environmental Working Group, Iowa’s soil is washing away at rates far higher than anyone realized. … This pace of erosion … has been exacerbated by a fundamental bias in federal farm policy and supports. In the dozen years before 2009, Iowa received nearly $17 billion in subsidies that fostered high-intensity farming and less than $3 billion to support conservation. … there is an intense push to create greater yield on more acreage and less incentive than ever to practice sound soil conservation. This is all the more tragic because the techniques for conserving soil are well understood. It requires planting buffer zones between fields and rivers and contour strips on sloping fieldsand planting regimes that keep crop cover on the soil by rotating between 3 and 4 crops, not just soybeans and corn. It also requires comprehensive conservation regulations and enforcement and, above all, facing the fact that erosion is not nature or bad farmers at work. It is the legacy of bad agricultural policy.
Mechanisms of Soil Productivity Improvement in Agroforestry Major tree-mediated processes that determine the extent and rate of soil improvement in AFS: Nutrient cycling related to tree biomass Biological N2 fixation by (NFTs) Nutrient uptake from deeper soil layers. Other tree-mediated benefits:
Improved soil physical conditions and higher soil microbiological activities
Biodiversity Maintaining variation in genetic composition and a variety of species. For the purposes of conserving diversity through agroforestry systems, both genetic diversity and species diversity are important
Agroforestry and Biodiversity Compared to agri. systems, AF systems have:
Higher number of various life forms (birds, mammals, anthropods, insects, …)
Improved plant species richness and diversity including endangered plant species (IUCN Red List)
Enhanced land connectivity (animal and insect corridors)
Better aquatic diversity in streams and waterways following better water-quality
BIODIVERSITY Ecological Diversity of Tropical Homegardens 35 Mean # of plant species/garden (less than 1.0 ha in size) 3.0 Mean species density (no. of species /100m2) 5.92 Mean Margalef Index (Species richness) 1.27 Mean Shannon-Wiener Index (Evenness and abundance) Mohan et al., 2007.
Habitat Protection for Vertebrates under Agroforestry Systems
Agroforestry and Biodiversity Mixed-species AF can help maintain a higher level of biodiversity in various ways: Intensification of AFS leading to reduced exploitation of protected areas, Increasing biodiversity in working landscapes through the expansion of AFS into traditional farmlands, and Increasing the species diversity of trees in farming systems. Better aquatic diversity in streams and waterways following better water-quality
Nutrient-leaching rates from soils under AFS can be lower than those from treeless systems.
The “safety-net” effect: The deeper and more extensive tree roots will take up more nutrients from the soil compared to crops with shallower root systems.
The reduction of nutrient loading leads to water-quality enhancement in heavily fertilized agricultural landscapes.
Water Quality Enhancement
Water soluble P (WSP) concentrations by depth in silvopasture and treeless pasture sites on Spodosols in two counties (Alachua and Suwannee) in Florida, USA. Michel et al., 2007.
Degraded cropland Riparian buffers for reclamation of degraded croplands … the same site, 15 years later Source: A. M. Gordon and N. Thevathasan, Univ of Guelph, ON, Canada.
Multiple Species Riparian Vegetative Buffer Strips (VBS) An effective approach to reducing NPSP (non-point source pollution). Possible mechanisms: enhanced infiltration of runoff and sediment trapping. Tall fescue (Festucaarundinacea), the most effective species in the claypan region near Columbia, MO. VBS reduced sediment, total N, and total P losses by 32, 42, and 46%, resp., compared to control during 2004 to2008 (Udawatta et al., 2011).
Riparian Buffer: Bear Creek National Restoration Watershed (ISU)
Carbon Sequestration The process of capture and secure storage of C from the atmosphere It entails the transfer of atmospheric C, especially CO2,and its secure storage in long-lived pools. (UNFCCC = UN Framework Convention on Climate Change)
Average Global Temperature and Atmospheric Carbon Dioxide Concentrations, 1880-2007
Mitigation (of) & Adaptation (to) Climate Change Mitigation Avoiding emissions and sequestering GHGs: [Technological change and substitution that reduce emissions] Adaptation Reducing the vulnerability of natural systems against actual or expected climate change effects.
Climate Change Mitigation Goal: Reduce net emissions and enhance sink capacity Avoiding or Reducing the Emissions
Increasing input-use efficiency
(Soil and water conservation) 2. Sequestering CO2 in Terrestrial Biosphere
Soil C sequestration
(Aggregation, physical protection, recalcitrant C)
Climate Change Adaptation Goal: Develop strategies to reduce the negative impacts 1. Enhancing Soil Resilience
C Sequestration in Land-Use Systems Aboveground (Vegetation) Belowground (Soils) AFS are believed to have a higher potential to sequester C because of their perceived ability for greater capture and utilization of growth resources (light, nutrients, and water) than in single-species crop- or pasture systems. Estimates of C stored in AFS (Mg C ha-1): Aboveground: 0.29 to 15.21 yr-1 Belowground: 30 to 300, up to 1-m depth.
Carbon Sequestration in Soils Carbon sequestration in soils as a climate-change-mitigation strategy is based on the assumption that the movement (flux) of C from air to soil can be increased while the release of C from the soil back to the atmosphere is decreased. The soil C pool, to 1 m depth, consists of:
Soil organic C (SOC) estimated at 1550 Pg
(1 petagram = 1015 g = 1 billion ton), and
Soil inorganic C about 750 Pg.
The total soil C pool (2300 Pg) is 3X the atmos. pool
Schematic presentation of the general land-use continuum in most forested tropical countries, with changes in both types and amount of tree cover in landscapes. Schematic presentation of the general land-use continuum in most forested tropical countries, with changes in both types and amount of tree cover in landscapes. General land-use continuum in forested tropical countries with changes in types and extent of tree cover. (Source: Consortium Research Program, 2011.)
2 1 3 Homegardens Kerala, India Silvopasture Florida, USA Dehesa, Northern Spain 2 1 1 4 3 6 4 5 6 Shaded cacao Bahia, Brazil Parklands Ségou, Mali Silvopasture MG, Brazil Univ. Florida, Cent for Subtropical Agroforestry: Carbon Sequestration Studies, 2005 -
Locations of CSTAF (Univ of FL) Soil Carbon Sequestration Studies
General Objectives Quantify SOC accumulation and sequestration in different types of agroforestry systems in a variety of ecological and geographical conditions. Determine C storage in different soil fractions up to at least 1 m depth Quantify, wherever possible, C contribution by C3 and C4 plants (~ trees and herbaceous plants) using natural C isotopic differences between the two groups.
Changes in soil C stock under different AF vs. non-AF systems (Nair et al., 2010).
Tree-based systems, compared to treeless under similar conditions, store more C in deeper soil.
High tree density -> high SOC content, esp. in the upper 50 cm soil and <53 µm soil fraction.
SOC stock under longer term AF systems with high tree-density (e.g., homegardens, shaded perennials) comparable to that of natural forests.
In sparse tree-density AFS, soil stores more C near than away from the tree.
C3 plants (trees) contribute to more C in the silt- + clay-sized (<53 µm) fractions than C4 plants in deeper soil profile.
Traditional systems with large C stock seem to have limited potential for sequestering additional C.
Some Recent Publications Book: Kumar BM, and Nair PKR 2011C Seq in AF Systems. Springer, Netherlands Journal Articles: Nair PKR. 2011.J EnvQual40: 784–790. Howlett D, Mosquera-Losada M-R, Nair P KR, Nair, VD. 2011.J EnvQual40:825-832. Tonucci RG, Nair PKR, Nair VD, Garcia R 2011.J EnvQual40: 833–841. Nair PKR, Nair VD, Kumar BM, Showalter JM 2010. Adv Agron108: 237–307. Haile SG, Nair VD, Nair PKR. 2010. Global Change Biology 16: 427–438. Gama-Rodrigues EF, Nair PKR, Nair VD, et al. 2010. Environ Manage 45: 274–283. Saha SK, Nair PKR, Nair VD, Kumar BM. 2010. Plant and Soil328: 433–446. Nair PKR, Kumar BM, Nair VD. 2009. J Soil Sci. Pl Nutrition172: 10–23. Nair PKR, Nair VD, Kumar BM, Haile SG. 2009. Environ Sci Policy 12: 1099–1111. Saha SK, Nair PKR, Nair VD, Kumar, B. M. 2009.AgroforSyst76: 53–65. Haile SG, Nair PKR, Nair VD. 2008.J EnvQual 37: 1789–1797. Takimoto A, Nair PKR, Nair VD. 2008. Agri EcosystEnv 125:159–166. Takimoto A, Nair PKR, Alavalapati JRR. 2008. Mitig Adapt Strat13: 745–761. Takimoto A, Nair VD, Nair PKR. 2008.AgroforSyst 76: 11–25. Some Recent Publications Haile, S.G., Nair, P. K. R., and Nair, V. D. 2008. Carbon storage of soil-size fractions in Florida silvopastoral syst. J. Environ. Qual.37: 1789 – 1797. Haile, S. G., Nair, V. D., and Nair, P. K. R. Contribution of trees to soil carbon sequestration in silvopasture. Global Change Biology(in press). Howlett, D. S. 2009. Environ amelioration potential of silvopastoral AF syst in Spain: Soil C sequestr and phosphorus retention. Ph D Diss., U of Fla. Nair, P. K. R., Kumar, B. M., and Nair, V. D. 2009. Agroforestry as a strategy for carbon sequestration. J. Soil Sci. Pl Nutrition172: 10–23. Nair, P. K. R., Nair, V. D., Kumar, B. M., and Haile, S. G. Soil C sequestr in trop. AF syst: A feasibility appraisal. Environ Science and Policy(in press). Saha, S. K., Nair, P. K. R., Nair, V. D., and Kumar, B. M. Soil C storage and plant diversity of homegardens in Kerala, India Agrofor Syst76: 53– 65. Saha, S. K., Nair, P. K. R., Nair, V. D., and Kumar, B. M. Carbon storage in soil size-fractions … tree-based systems. Plant and Soil (in press). Takimoto, A., Nair, P. K. R., and Nair, V. D. 2008. Carbon stock and seq potential of … AF systems in W Afr Sahel. Agri. Ecosys. Env. 125: 159 – 166. Takimoto, A., Nair, P. K. R., and Alavalapati, J. R. R. 2008. Socioecon of C seq … W. Afr Sahel. Mitig Adapt of Strateg Global Change13: 745–761. Takimoto, A., Nair, V. D., and Nair, P. K. R. 2008. Soil C seq potential of AF practices in the West African Sahel. Agrofor Syst 76: 11–25.
Soil BD, extrapolation of site specific values
Bulk Density of Soils Bulk Density is the mass of a unit volume of soil; i.e., weight of the solid particles in a standard volume of field soil Weight of soil BD = Volume of soil If weight is 1.33 Mg and volume is 1 m3, “Average” BD = 1.33 Mg m-3 Consider two soils, BD 1.0 and 1.2; same C content (%): The latter will store 20% more C than the former per unit volume.
AF: The Way Forward The debate on the role of AF is focused on econ. and accounting, not enough on science. A practice cannot bypass the principles. Available sci. data on AF are not rigorous. Precise measurements are difficult: expenses, sampling problems, dynamic nature of systems. Powerful analytical/predictive tools not applied. The “why”s and “how”s of observed behavior… Chronosequence studies, rate processes, … Meeting the criteria of research quality:
Peer-reviewed publications in high-impact journals.