The future of the Lowland Belizean Savannas?. Using cluster analysis to explore multivariate spatial patterns in savanna soils PETER FURLEY & SARAH BEADLE UK Belize association 15 th November 2014
Outline World savannas Neotropical and Belizean savannas Data Sources Aims Methodology Nature of lowland savanna soils Soil variability Implications for agriculture
World savannas
Neotropical and Belizean savannas
Upland Belizean savannas generally occur over ~500m asl cooler climatic regime with orographic rainfall deeply weathered, highly leached, acidic soils mostly very infertile soils (low organic matter and nutrients) steep relief causes rapid runoff and freely drained soils distinct catena effect cyclical pattern from savanna woodland to grassland due to fire incidence
Lowland Belizean savannas closer to sea level and coastal influences marked seasonality with wetting and drying soils are acidic with low nutrient reserves relatively flat and poorly drained with younger parent materials soils are mostly coarse textured at the surface but with fine fractions washed to depressions and the subsurface where they may impede drainage
Current land use of lowland savannas CATTLE RANCHING FRUITS SMALLHOLDER FARMING SHRIMP FARMING GRAVEL EXTRACTION TIMBER LOGGING
Data Sources Overseas Development Agency (ODA) Darwin Project Biogeographical Monographs Programme for Belize
Aims 1. To establish the nature and distribution of soil resources in the lowland savannas 2. To use this knowledge to assist discussion of alternative management strategies
Methodology Select variables Normalize variables 1. Collate data 2. Pre-process data 3. Cluster Analysis Weight variables Remove Outliers Soil Data Data for clustering Hierarchical Clustering k-means Clustering 4. Interpretation Cluster Memberships Cluster Validation Site Characteristics Data Interpretation Management Strategies
Nature of the savanna soils Surface 1. ph 2. Clay 3. Total Nitrogen 4. Available Phosphorus Subsurface 5. Total Exchangeable Bases 6. Organic Matter
Nature of the savanna soils Property Mean value Comment Surface ph 5.45 84% are strongly or moderately acidic (i.e. 6) Subsurface ph 5.69 77% are strongly or moderately acidic (i.e. 6)
Nature of the savanna soils Property Mean value Comment Surface clay 13.18% 16% classed as a type of clay soil Subsurface clay 34.93% 67% classed as a type of clay soil, with 35% pure clay soils SANDY PROFILE CLAY RICH PROFILE RESULT OF HIGH CLAY
Surface Nature of the savanna soils Property Mean Comment Total Nitrogen 0.12% 80% fall in low range ( 0.2%) Available Phosphorus 2.29ppm Only 14% above the critical level of 4ppm Total Exchangeable Bases 3.40cmol/kg (= Ca + Mg + Na + K) 65% in low range ( 2cmol/kg) Organic Matter 6.14% 85% fall in very low low range, with 56% in very low range
Soil variability Surface clay % Subsurface TEB cmol/kg Surface Clay Subsurface Total Exchangeable Bases
Groupings 1 2 3 4 5 High Clay % Low ph both horizons, high N, high OM, low P & TEB High ph both horizons, high OM, P, N & TEB High surface ph, low subsurface ph, low surface properties 5 2 1 Low Clay % High subsurface OM, low subsurface ph, low available P Low subsurface OM, high subsurface ph, high available P 3 4
Low clay groups Group 3 4 Average Main Drainage Conditions Main parent Surface material Average Clay Percentages Good Good Good Coastal Deposits Riverine Deposits Coastal Deposits Subsurface 34.93 Surface ph 5.48 4.88 5.45 Subsurface 23.63pH 5.64 6.02 5.69 Total Nitrogen (%) 0.07 0.11 0.12 13.18 Available 1.68 6.00 2.29 Phosphorus 6.48 (ppm) 4 2 Total Exchangeable 1.67 3.47 3.40 Bases GROUP (cmol/kg) 3 GROUP 4 AVERAGE Organic Matter (%) 4.51 4.59 6.14
High clay groups Surface Average Clay Percentages Subsurface 55.53 52.2 45.5 34.93 28.7 17.89 13.57 13.18 GROUP 1 GROUP 2 GROUP 5 AVERAGE
High clay groups A: Eocene (60mya) Miocence (5mya) C: Quaternary (2.5mya-present) Coastline moves gradually Eastwards Sands and gravels from Fluvial deposits Rio Bravo Booth s River Sand and silt from fluvial outwash on flood plains Calcareous sands and muds Fault Block Fault Blocks B: Pliocene (5-2.5mya) D: Current Soil Conditions Lower energy deposition of clays in lagoonal conditions 3 & 4 1 2 1 2 3 & 4 Cretaceous Limestones (KT) Early Tertiary Limestones (Et) Key Late Tertiary clays (Lt) Quaternary alluvium, river terrace etc. (Q)
High clay groups Group 2 Average Main Drainage Conditions Poor Good Average annual rainfall (mm) 1681-1845 1845-2066 Main parent material Bedrock Coastal Deposits Main vegetation type Waterlogged Dense savanna Surface ph 6.07 5.45 Available Phosphorus (ppm) Total Exchangeable Bases (cmol/kg) 4.12 2.29 17.40 3.40
Implications for agriculture
Implications for agriculture OPTION 1 No till cropping
Implications for agriculture OPTION 2 Ridge Furrow
Key Points Soils are generally infertile, BUT they are variable Lowland savannas are a valuable, often underappreciated natural resource Current physical and chemical limitations for cultivation Potential for agriculture in the future Resource value is greater than agriculture?
Subsurface Surface Property All Lowland Belizean savannas Group 2 only Upland Belizean savannas Brazilian Cerrados Clay 13.18 13.57 24.44 45.50 ph 5.45 6.07 5.23 4.8 Total N 0.12 0.26 0.4 - OM 6.14 8.79 8.8 3.25 Available P 2.29 4.12 - - TEB 3.40 17.40 29.91 2.49 Clay 34.93 45.50 38.33 48.00 ph 5.69 6.55 6.01 4.95 Total N 0.03 0.03 0.14 - OM 0.97 0.63 2.32 1.25 Available P 1.61 2.98 - - TEB 6.67 23.67 27.76 1.83
Mean S.D Min Max Subsurface Clay Mean Rank 1 55.53 10.50 33.00 70.00 1 2 45.50 18.23 28.00 73.00 3 3 23.63 13.76 0.00 42.00 4 4 2.00 2.00 0.00 5.00 5 5 52.20 14.20 27.00 65.00 2 T 34.93 21.35 0.00 73.00 Subsurface ph 1 5.59 0.64 4.30 7.03 4 2 6.55 1.26 4.90 8.00 1 3 5.64 0.93 4.20 8.40 3 4 6.02 1.01 5.10 7.70 2 5 5.42 0.72 4.36 7.20 5 T 5.69 0.90 4.20 8.40 Subsurface Total N 1 0.03 0.03 0.00 0.10 3 2 0.03 0.02 0.01 0.06 2 3 0.03 0.02 0.00 0.10 4 4 0.02 0.04 0.00 0.10 5 5 0.04 0.72 0.01 0.06 1 T 0.03 0.03 0.00 0.10 Subsurface OM 1 1.29 1.73 0.41 7.98 1 2 0.63 0.36 0.30 1.21 4 3 0.96 1.53 0.06 7.70 3 4 0.30 0.20 0.03 0.61 5 5 1.00 0.79 0.08 2.45 2 T 0.97 1.39 0.03 7.98 Mean S.D Min Max Subsurface Available P Mean Rank 1 1.71 1.72 0.00 5.40 2 2 2.98 1.82 0.00 5.00 1 3 1.48 1.48 0.00 5.70 4 4 1.58 1.19 0.00 3.30 3 5 1.08 0.88 0.00 2.00 5 T 1.61 1.52 0.00 5.70 Subsurface TEB 1 5.36 9.25 0.20 31.20 3 2 23.67 21.07 0.90 50.00 1 3 6.77 12.75 0.10 65.10 2 4 0.67 0.87 0.10 2.30 5 5 2.22 2.34 0.60 8.50 4 T 6.67 12.41 0.10 65.10 Surface Clay 1 17.89 12.13 2.00 49.00 2 2 13.57 9.94 11.00 38.00 3 3 6.48 3.83 1.00 17.00 4 4 4.00 6.03 0.00 16.00 5 5 28.70 11.04 9.00 47.00 1 T 13.18 11.72 0.00 49.00 Surface ph 1 5.62 0.54 4.80 6.51 2 2 6.07 0.67 5.30 7.10 1 3 5.48 0.59 4.30 7.10 3 4 4.88 0.55 4.00 5.70 5 5 5.01 0.29 4.46 5.30 4 T 5.45 0.61 4.00 7.10 Mean S.D Min Max Surface Total N Mean Rank 1 0.08 0.06 0.01 0.18 4 2 0.26 0.04 0.21 0.31 2 3 0.07 0.04 0.00 0.16 5 4 0.11 0.06 0.03 0.18 3 5 0.31 0.11 0.22 0.55 1 T 0.12 0.11 0.00 0.55 Surface OM 1 5.38 2.66 1.38 9.66 3 2 8.79 1.53 6.74 11.08 2 3 4.51 3.61 0.29 16.50 5 4 4.59 1.91 1.27 6.77 4 5 13.10 4.04 9.35 21.92 1 T 6.14 4.29 0.29 21.92 Surface Available P 1 2.30 1.57 0.00 5.30 3 2 4.12 2.40 0.00 6.00 2 3 1.68 1.42 0.00 4.82 4 4 6.00 2.62 2.00 8.40 1 5 1.27 0.96 0.00 2.00 5 T 2.29 2.02 0.00 8.40 Surface TEB 1 2.37 2.54 0.60 10.70 4 2 17.40 7.95 3.80 27.10 1 3 1.67 1.75 0.00 8.90 5 4 3.47 4.24 0.80 11.90 3 5 3.48 4.01 0.40 13.90 2 T 3.40 5.18 0.00 27.10