• Authors:
    • Lawrence, D.
    • Tully, K. L.
    • Scanlon, T. M.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 161
  • Year: 2012
  • Summary: The mitigation of nutrient leaching losses is an important ecosystem service, and is easily affected by small-scale management decisions. This study was conducted on eight coffee agroforests in Costa Rica, in order to identify particular mechanisms preventing nutrient leaching losses. First, we examined how nitrogen (N) and phosphorus (P) leaching losses differed between coffee agroforests amended with mineral or organic fertilizers. Monthly N and P concentrations were measured in soil water using tension lysimeters (at 15 and 100 cm) between October 2008 and September 2009, and a water balance model was developed to estimate annual nutrient leaching losses from these agroforests. Second, we examined the effects of human interventions (fertilizer type and quantity), biology (shade trees), and chemistry (soil properties) on nutrient leaching losses. Despite differences in the quantity and form of fertilizer inputs, N and P losses at 100 cm did not differ significantly between organically and conventionally managed agroforests (119 kg N ha -1 yr -1 and 1.5 kg P ha -1 yr -1, respectively). Rather, N losses declined linearly with increasing shade tree biomass, which is determined by farmers. Phosphorus losses, on the other hand, declined with increasing soil iron pools, which are independent of management decisions.
  • Authors:
    • Haeger, A.
  • Source: Agroforestry Systems
  • Volume: 86
  • Issue: 2
  • Year: 2012
  • Summary: Agroforestry systems can mitigate greenhouse gas (GHG) emissions, conserve biodiversity and generate income. Whereas the provision of ecosystem services by agroforestry is well documented, the functional relationships between species composition, diversity and carbon (C)-storage remain uncertain. This study aimed to analyze the effects of management (conventional vs. organic), woody plant diversity and plant composition on aboveground and belowground C-storage in coffee agroforestry systems. It was expected that organic farms would store more C, and that an increase in plant diversity would enhance C-storage due to complementarity effects. Additionally, it was expected that steep slopes decrease C-storage as a result of topsoil erosion. Woody plants were identified on 1 ha plots within 14 coffee farms (7 conventional and 7 organic). C-stocks in trees, coffee plants and roots were estimated from allometric equations. C-stocks in litter and topsoil (0-25 cm) were estimated by sampling. On average, farms stored 93 +/- A 29 Mg C ha(-1). Soil organic carbon accounted for 69 % of total C. Total C-stocks were 43 % higher on organic farms than on conventional farms (P < 0.05). Conventional and organic farms differed in vegetation structure, but not in species diversity. It was found that the combined effect of farm type, species richness, species composition and slope explained 83 % of the variation in total C-storage across all farms (P < 0.001). Coffee agroforestry in general and organic farms in particular may contribute to GHG mitigation and biodiversity conservation in a synergistic manner which has implications for the effective allocation of resources for conservation and climate change mitigation strategies in the agricultural sector.
  • Authors:
    • Harmand, J.
    • Henault, C.
    • Skiba, U.
    • Blanchart, E.
    • Hergoualc'h, K.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 148
  • Year: 2012
  • Summary: Agroforestry represents an opportunity to reduce CO2 concentrations in the atmosphere by increasing carbon (C) stocks in agricultural lands. Agroforestry practices may also promote mineral N fertilization and the use of N-2-fixing legumes that favor the emission of non-CO2 greenhouse gases (GHG) (N2O and CH4). The present study evaluates the net GHG balance in two adjacent coffee plantations, both highly fertilized (250 kg N ha(-1) year(-1)): a monoculture (CM) and a culture shaded by the N-2-fixing legume tree species Inga densiflora (CIn). C stocks, soil N2O emissions and CH4 uptakes were measured during the first cycle of both plantations. During a 3-year period (6-9 years after the establishment of the systems), soil C in the upper 10 cm remained constant in the CIn plantation (+0.09 +/- 0.58 Mg C ha(-1) year(-1)) and decreased slightly but not significantly in the CM plantation (-0.43 +/- 0.53 Mg C ha(-1) year(-1)). Above-ground carbon stocks in the coffee monoculture and the agroforestry system amounted to 9.8 +/- 0.4 and 25.2 +/- 0.6 Mg C ha(-1), respectively, at 7 years after establishment. C storage rate in the phytomass was more than twice as large in the CIn compared to the CM system (4.6 +/- 0.1 and 2.0 +/- 0.1 Mg C ha(-1) year(-1), respectively). Annual soil N2O emissions were 1.3 times larger in the CIn than in the CM plantation (5.8 +/- 0.5 and 4.3 +/- 0.3 kg N-N2O ha(-1) year(-1), respectively). The net GHG balance at the soil scale calculated from the changes in soil C stocks and N2O emissions, expressed in CO2 equivalent, was negative in both coffee plantations indicating that the soil was a net source of GHG. Nevertheless this balance was in favor of the agroforestry system. The net GHG balance at the plantation scale, which includes additionally C storage in the phytomass, was positive and about 4 times larger in the CIn (14.59 +/- 2.20 Mg CO2 eq ha(-1) year(-1)) than in the CM plantation (3.83 +/- 1.98 Mg CO2 eq ha(-1) year(-1)). Thus converting the coffee monoculture to the coffee agroforestry plantation shaded by the N-2-fixing tree species I. densiflora would increase net atmospheric GHG removals by 10.76 +/- 2.96 Mg CO2 eq ha(-1) year(-1) during the first cycle of 8-9 years. (c) 2011 Elsevier B.V. All rights reserved.
  • Authors:
    • Yang, H.
    • Walters, D. T.
    • Dobermann, A.
    • Cassman, K. G.
  • Source: Annual Review of Environment and Resources
  • Volume: 28
  • Issue: 1
  • Year: 2003
  • Summary: Agriculture is a resource-intensive enterprise. The manner in which food production systems utilize resources has a large influence on environmental quality. To evaluate prospects for conserving natural resources while meeting increased demand for cereals, we interpret recent trends and future trajectories in crop yields, land and nitrogen fertilizer use, carbon sequestration, and greenhouse gas emissions to identify key issues and challenges. Based on this assessment, we conclude that avoiding expansion of cultivation into natural ecosystems, increased nitrogen use efficiency, and improved soil quality are pivotal components of a sustainable agriculture that meets human needs and protects natural resources. To achieve this outcome will depend on raising the yield potential and closing existing yield gaps of the major cereal crops to avoid yield stagnation in some of the world's most productive systems. Recent trends suggest, however, that increasing crop yield potential is a formidable scientific challenge that has proven to be an elusive goal.