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Sustainable intensification of agriculture: Balancing food and environmental objectives

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Land clearing and increased use of agrochemicals make agriculture one of the largest drivers of global climate change. The doubling of cereal production during the past 50 years has reduced hunger and malnutrition worldwide, but much of this increase was attained by the use of new crop varieties and greater inputs of fertilizer, water, and pesticides. Over the next 50 years, the global population may reach 9 billion, and require a further doubling of food production. Increasing agricultural production while maintaining environmental quality is one of humanity's grand challenges. I present two case studies from the tropics (Latin America and East Africa) where sustainable agricultural strategies can optimize tradeoffs between intensifying crop production and environmental impacts. In Costa Rica, I investigated the balance between nitrogen losses, carbon storage, and yields in shade coffee farms. I found that (1) agroforests capture a similar proportion of added nitrogen regardless of whether it comes from a mineral or organic source, and (2) nitrogen losses decrease significantly with increasing tree biomass with minimal consequences for yield. In sub-Saharan Africa, a region poised to increase fertilizer application 6-fold in the coming years, I investigated the tradeoffs between maize yields and nitrogen losses in response to increasing fertilizer levels. I found that the current “one-size-fits-all” approach to fertilizer management will have considerable environmental and human health consequences and recommendations must be tailored to a region’s climate and soil type.

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Sustainable intensification of agriculture: Balancing food and environmental objectives

  1. 1. Sustainable intensification of agriculture: Balancing food and environmental objectives Kate Tully, PhD Earth Institute at Columbia University
  2. 2. Feeding 9 billion people sustainably • Population likely to be at 9 billion by 2050 • Increase food production • Must balance food production and environmental objectives 2
  3. 3. Consequences of nutrient loss MODIS 2009 • Eutrophication • Hypoxia • Groundwater contamination • Human health effects 3
  4. 4. How do we maximize productivity and minimize nutrient loss... 4
  5. 5. Tropical Agriculture • Majority of population growth set to occur • Intensifying and expanding • Rain-fed • Small-holder systems • Operating at the “margin” • Effect of management? 5
  6. 6. 6 Map: Liu et al. 2010- PNAS Costa Rica Intensified No N stress East Africa Intensifying N scarcity China : 588 Midwest: 155 SSA: 7 N Input data: Vitousek et al. 2009 – Science kg N ha-1 yr-1
  7. 7. Coffee agroforest - Costa Rica • Wet tropics • High fertilizer use – (40-300 kg N) • High yields • Landscape matrix - intensified 7 Rationale: Landscape-level consequences • Groundwater contamination
  8. 8. 8
  9. 9. 9
  10. 10. 10
  11. 11. 11
  12. 12. How do we maximize productivity and minimize nutrient loss... ...if we change nutrient source? ...if we change tree management? 12
  13. 13. Turrialba Colorado San Juan Norte San Juan Sur 4 conventional AF 4 organic AF 1 monoculture 13
  14. 14. Farm Inputs 14
  15. 15. Nutrient content 15 • Coffee leaves and beans • Shade tree leaves • Forest floor • Top and subsoil
  16. 16. Tully et al. 2012 – Agr Ecosys Environ 16 Partial nutrient balances 96 38300 OAFMONO CAF FERTILIZERNitrogen (kg/ha) Arrow indicates flux (kg/ha/yr)
  17. 17. 17 96 38300 OAF 4530 kg/ha 2580 kg/ha 1100 kg/ha MONO CAF FERTILIZER 71% 71%33% Nitrogen (kg/ha) Arrow indicates flux (kg/ha/yr)
  18. 18. 18 96 38300 OAF 4530 kg/ha “loss” = leaching, gaseous, SOM 2580 kg/ha 1100 kg/ha MONO CAF FERTILIZER 71% 71%33% 29% loss67% loss 29% loss Nitrogen (kg/ha) Arrow indicates flux (kg/ha/yr)
  19. 19. Soil solution chemistry • Gravity lysimeters • Porous cup lysimeters – Use suction to collect water from soil matrix – 15 and 100 cm • Three mgmt types 19
  20. 20. Nitrate-N similar in agroforests Tully et al. 2013- Agroforest Syst 20
  21. 21. Water balance • D = Drainage • P = Precipitation • I = Interception • ET = Evapotranspiration (Hamon 1963) – Root fraction at 15cm • OF = Hortonian overland flow (Ksat) – Rainfall > Infiltration rate D=P– I –ET – OF 21
  22. 22. Nloss(kg/ha/y) Ploss(kg/ha/y) N losses similar in agroforests Tully et al. 2012- Agr Ecosyst Environ 22 ~1.5 ~120
  23. 23. Tree-crop-soil system 23 Tully et al. 2012- Biogeochemistry
  24. 24. 24
  25. 25. What about productivity? 25
  26. 26. How do we maximize productivity and minimize nutrient loss... 26 ...if we change nutrient source? ...if we change tree management?
  27. 27. More trees, less loss Tully et al. 2012- Agr Ecosyst Environ 27 Nloss
  28. 28. Nitrogen stored in trees 28Tully unpublished
  29. 29. Carbon stored in trees 29Tully unpublished
  30. 30. Yield doesn’t decline with tree density 30
  31. 31. Balancing yields and losses 31 • More trees = less N loss • More trees ≠ less coffee • More N = more coffee • Monoculture • High yields, high loss • Conventional AF • Good yields, same loss
  32. 32. 32 Liu et al. 2010 - PNAS Costa Rica Intensified No N stress East Africa Intensifying N scarcity
  33. 33. Subsistence maize - East Africa 33 • Sub-humid tropics • Low nutrient inputs < 7 kg N/ha/yr • Low yields < 1 ton maize/ha/yr • Intensifying landscapes Rationale: Unknown consequences
  34. 34. I. AFRICAN GREEN REVOLUTION Yield stagnation in Africa 34 Hazell and Wood 2008- PNAS
  35. 35. Initial goal of African Green Revolution 35 <7 kg N/ha 50 kg N/ha
  36. 36. 36 Soil gas and water fluxes from sub-Saharan Africa – terra incognita
  37. 37. Yala, Kenya 37 Tumbi, Tanzania 85% sand 928 mm 1 rainy season 35% clay 1816 mm 2 rainy seasons
  38. 38. Sand vs. Clay 38 Sand Particles Clay Particles
  39. 39. How do we maximize productivity and minimize nutrient loss... ...if we increase fertilization rates? ...in different soil types? 39
  40. 40. 6 fertilizer treatments • 0, 50, 75, 100, 150, and 200 kg N/ha applied by hand • Replicated in 4 blocks of 6 plots each Fertilizer application split between two events • 1/3 at planting (DAP) • 2/3 at topdressing (urea) Experimental Design
  41. 41. Organic treatment 41 N-fixer: Gliricidia sepium 75 kg N/ha/yr
  42. 42. Nitrogen in soil solution • Porous cup lysimeter • Three depths: – Kenya 15, 120, 200 cm – Tanzania 50, 120, 200 cm • Daily collections following rainfall events • Collected at regular intervals throughout growing season 42
  43. 43. Nitrate analysis using ISEs 43
  44. 44. Field method validation 44 n = 160 Tully and Weil (in press) - Comm Soil Sci Plant Anal
  45. 45. 45 “Birch Effect” Nitrate at 15 cm in Kenyan Clay
  46. 46. 46 Nitrate at 50 cm in Tanzanian Sand
  47. 47. Build solute transport model Soil moisture content 0.5 0.25 0.0 47 Fluxes at 200 cm
  48. 48. Fertilizer-NO3 responses differ in sands and clays 48 Threshold behavior? clay sand
  49. 49. Soil properties • Large potential for NO3 storage clay subsoil • Anion exchange capacity • Could become saturated? 49 M. Almaraz- unpublished data
  50. 50. Nitrogen in gas 50 Static chambers N2O Chemiluminescent analyzer NO “Nox Box”
  51. 51. Kenya Fertilizer-N2O responses differ in sands and clays Threshold behavior? Hickman unpublished data 5 4 3 2 1 0 MeanN2Oflux(gN/ha/day) Fertilizer N (kg/ha) 0 50 100 150 Tanzania2012 N2Oflux(gN/ha/day) 100 75 50 25 0 Fertilizer N (kg/ha) 0 50 100 150 200200 2012 51 Hickman et al. (in review) Ecol Letters Post-topdressing
  52. 52. What about productivity? 52
  53. 53. Maize yields plateau 53
  54. 54. Nitrate-N exceed MCL at 50 kg N 54
  55. 55. Apply organics in Tanzania 55 Treatment (kg N ha-1) Maize yield (tons/ha) N leaching (kg/ha/seas on) N2O+NO (kg/ha/seas on) Loss Factor (g N lost/ kg maize) 0 1.1 57.3 2.7 52.2 50 2.9 74.2 4.7 26.8 75 2.8 80.0 4.5 30.5 200 2.5 119.7 5.1 49.7 Legume (75) 2.7 13.0 3.8 6.6
  56. 56. Soil organic matter(s)! 56 FAO 1999
  57. 57. Balancing yields and losses 57 • Kenya • 75 kg N with low N losses and high yields • Long term? • Tanzania • High N losses at low fertilizer levels • Add organics to reduce N losses
  58. 58. Balancing yields and losses 58 • Coffee farms • Conventional agroforests show potential for high yields and low losses • Subsistence maize • Soil type matters! • Clays – okay in short term • Sands – need organics
  59. 59. Research Directions 59
  60. 60. Primary Research Themes 60 • Effects of agricultural intensification on ecosystem services • nutrient cycling • water quality • Does heterogeneity promote resilience? • species composition  field • management practices  farm • organization  landscape
  61. 61. Sub-Saharan Africa 61
  62. 62. Kenya Tanzania Consequences of increased fertilizer 62 Diverse landscapes in SSA
  63. 63. Role of trees 63
  64. 64. Co-benefits: More C, More N 64 Treatment (kg N ha-1) Maize yield (tons/ha) N leaching (kg/ha/seas on) N2O+NO (kg/ha/seas on) Loss Factor (g N lost/ kg maize) 0 1.1 57.3 2.7 52.2 50 2.9 74.2 4.7 26.8 75 2.8 80.0 4.5 30.5 200 2.5 119.7 5.1 49.7 Legume (75) 2.7 13.0 3.8 6.6 • Hungry for C? • What kinds of C?
  65. 65. Broader collaborations • Growing population – Healthy people, healthy soils • Economic development – Inherent limitations – Latent potentials 65
  66. 66. Local Research 66
  67. 67. Agro-ecosystem Services 67
  68. 68. Agriculture is the largest source of N pollution in the Chesapeake Bay 68 68,000 Mg
  69. 69. Adaptive management 69
  70. 70. Tradeoffs: Less N, More C 70 Modified from Gold et al. (2001)
  71. 71. Nitrate in Watersheds 71 Surface water Groundwater USGS 2012
  72. 72. Modeling and scaling 72 field farm landscape
  73. 73. Modeling and scaling 73 species management organization
  74. 74. Acknowledgements University of Virginia Jefferson Scholars Foundation Bankard Fund for Public Economy Raven Society The Earth Institute at Columbia University National Science Foundation Gates Foundation The Marine Biological Laboratory 74
  75. 75. 75 Questions? ¿Preguntas? Maswali?
  76. 76. Extra Slides 76
  77. 77. Nitrogen from fertilizer and manure 77
  78. 78. 78
  79. 79. Role of soil type 79 • Understand drivers • Improve management
  80. 80. Education and Collaboration • Field courses • Graduate research – Soil C and N loss – Soil mineralogy – Isotopes – On-farm studies – Hydrologic models • Graduate programs – Moi University (KE) – Sokoine University (TZ) • Local partners – Technical schools – Capacity building 80
  81. 81. Education and Collaboration • Intro Courses – Intro to Horticulture – Intro to Crop Production • Upper Level Courses – Applied Ecosystem Biogeochemistry – Global Food Systems • Graduate research – Soil retention– AEC – Cover crops • Soil organic N • Soil organic C – Modeling applications – Remote sensing – Integrated monitoring systems – Decision-support tools 81
  82. 82. Tanzania: NO3-N exceeds MCL at 200 cm 82 Nitrate at 200 cm in Tanzanian Sand
  83. 83. FAO Food Balance Sheet 83 20 40 60 80 100 120 140 1000 2000 3000 4000 Protein/day(grams) Calories/day Per Capita Nutrient Availability (shaded areas below minima) 10.3% 2.9%16.6% 70.3% Source: Barrett & Maxwell (2005), data: FAO food balance sheets
  84. 84. Nutrient Balance in Kenya 84 Treatment (kg N ha-1) Maize yield (tons/ha) N leaching (kg/ha/seas on) N2O+NO (kg/ha/seas on) Loss Factor (g N lost/ kg maize) 0 6.4 0.26 0.32 0.09 50 7.6 0.23 0.38 0.08 75 8.7 0.23 0.39 0.07 200 8.8 0.75 0.88 0.19
  85. 85. Nitrate at 200 cm in Kenyan Clay 85 Nitrate at 200 cm in Kenyan Clay
  86. 86. Where is the N going? 86 Pre-fertilization 200 kg N Applied
  87. 87. Human health effects of elevated nitrate concentrations in drinking water • “Blue baby syndrome” • Affect adults with hereditary blood disorders • Negatively affect thyroid functioning • Spontaneous abortion • Carcinogenic outcomes 87
  88. 88. 1995-97 2002-04 © IFDC Pan-African soil nutrient depletion kg nutrient/ha 88
  89. 89. 89
  90. 90. Emission Factors (%N lost as N oxide) Treatment (kg N ha-1) 2012 (KE) 2013 (Tz) 50 0.075 0.030 75 0.034 0.026 100 0.044 0.069 150 0.061 0.050 200 0.070 0.085 Gliricidia (75) 0.039 50 0.19 6.42 75 0.23 6.16 100 0.72 4.74 150 1.21 2.71 200 0.93 1.53 Gliricidia (75) 1.23 N2O NO Less than IPCC default of 1% Hickman unpublished 90
  91. 91. 91
  92. 92. Fertilization and Loss 92
  93. 93. 93
  94. 94. 94
  95. 95. 95
  96. 96. 96

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