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Transcript
THE VALUE OF SOIL ORGANIC MATTER A. B. Which soil would you pick to grow plants in your garden? What is Soil Organic Matter? • Definition: “The organic fraction of soil including plant, animal, and microbial residues, fresh and at all stages of decomposition… and highly carbonized compounds such as charcoal, graphite and coal” Soil organic matter = (2 x C) + O, H, N, P, S, etc. FUNCTIONS OF SOIL ORGANIC MATTER SOIL ORGANIC MATTER AND SUSTAINABILITY • Provides soil nutrients and enhances soil nutrient availability over several growing seasons. • Improves soil physical, chemical and biological properties for plant growth. • Buffers changes in soil properties due to disturbance or variation in other environmental factors (e.g. climate). • Reduces environmental contamination and soil loss. • Possibly reduces need for external inputs and enhances internal recycling when crop residues and/or organic soil amendments are applied. RESERVOIR OF PLANT NUTRIENTS • 95% or more of total N in soil is organic N • If soil contains 0.2 % total N then: 0.2 kg N/100 kg soil * 95% * 2,000,000 kg soil/hectare plow layer = 3800 kg organic N/hectare plow layer or 3393 lb organic N/acre plow layer CARBON IN SOIL • What are the major forms of C in soil? Organic residues CO2 (60-80%) Soil Soil organisms (3-8%) Nonhumic substances (3-8%) Soil humus (15-35%) Organic residues in soil Complex humic substances (10-30%) FORMS OF SOIL ORGANIC MATTER Particulate organic matter and sand particles under magnification AGE OF SOIL ORGANIC CARBON Sample Description Grassland soil (North Dakota) Virgin soil Manured orchard Bridgeport loam, Wyoming Surface sod layer Clay fraction from virgin soil Continuous wheat plot Mollisol, Saskatchewa Surface soil B horizons Buried horizons Mean Residence Time --- years --1,175 ± 100 880 ± 74 3,280 6,690 1,815 545 to present 700 to 4,000 5,900 and 8,410 MANAGEMENT PRACTICES THAT DECREASE SOIL ORGANIC CARBON • • • Frequent tillage Burning for clearing Removal of crop residues • Inadequate fertilization • Soil erosion EFFECTS OF TILLAGE ON SOIL OM LOSS OF SOIL ORGANIC C WITH TILLAGE Sanborn Field EFFECTS OF LAND-USE ON SOIL OM IN THE TROPICS Research conducted on the Pacific island of Guam LOSS OF SOIL ORGANIC MATTER “Soil organic matter is one of our most important national resources; its unwise exploitation has been devastating; and it must be given its proper rank in any conservation policy as one of the major factors affecting the levels of crop production in the future” William A. Albrecht University of Missouri (1938) LONG-TERM SUSTAINABLE MANAGEMENT AND SOIL CARBON Lowland Taro System in Palau PRACTICES THAT INCREASE SOIL ORGANIC MATTER • Adopt conservation tillage, residue management and mulch farming • Apply organic wastes to soil • Use N and other nutrient sources more efficiently • Convert marginal and degraded lands to restorative land uses • Adopt soil conservation practices • Eliminate summer (bare) fallow and incorporate legumes and other appropriate cover crops in rotations Kimble et al., 2002 CONSERVATION TILLAGE Tillage No-Till EFFECT OF ROTATIONS ON SOIL OM SOIL C DISTRIBUTION WITH DIFFERENT LAND MANAGEMENT PRACTICES Landscape position GR TOC AF CR GR POM C AF CR --------------------------- g kg-1 soil -------------------------- DOC AF GR CR -------- mg kg-1 soil ------ Upper 19.5 24.5 19.5 3.54 6.60 3.03 106.8 123.3 80.1 Middle 22.5 23.5 22.0 5.42 5.76 4.52 105.7 147.2 75.0 Lower 25.5 24.0 18.5 7.12 7.38 3.28 133.5 124.6 72.4 LSD(0.10) ------------- 2.4 ------------ ----------- 2.68 ------------ ------------ 22.2 ------------ Greenley Agroforestry Watershed Research in Northeastern Missouri RESIDUE QUALITY AND DECOMPOSITION • Carbon to nitrogen of the residue > 25 may result in N deficiency in soil for plant growth and slow down the rate of decomposition. • Plant residues containing high proportions of lignin and tannins decompose relatively slower than other plant residues. Woody materials contain high proportions of lignin. Oak leaves contain relatively high tannin content. • The smaller the pieces of residue, the faster it will decompose. CO2 efflux (µ mol m-2 sec-1) COMPACTION AND DECOMPOSITION 60 Non--compacted Non 45 Check High litter Non--compacted Non 30 Compacted Compacted 15 0 May 11 July 20 Sampling date Compaction also decreased soil moisture and increased soil temperature EFFECTS OF GM CROPS Transgenic Crop Climate Management practices Pesticides Fertilization Tillage (Animal waste) Nutrient export Crop residues Root exudates Soil properties: Microbially-mediated nutrient transformations: Rhizosphere • Mineralization/immobilization • Oxidation/reduction • Fixation/gaseous loss • Solubilization Gene transfer • Clay type and content • pH • Soil structure • Soil organic matter DIFFICULTY IN CREATING A CARBON BALANCE??? Biosphere 2, designed to be an artificial, selfcontained, self-supporting ecosystem. All water, air and nutrients were recycled in the structure. Had problems with maintaining atmosphere fit for life partially due to role of soil organic matter. http://www.bio2.edu GLOBAL CARBON CYCLE AND C SEQUESTRATION In Gt or Gt/year 1 Gt =1 Pg = 1015g Historic net loss of 66 – 90 Gt C from soil REASONS FOR CONSERVING SOIL ORGANIC C ANY QUESTIONS?