BasicBasic BiologicalBiological FactorsFactors ofof

SoilSoil CarbonCarbon andand + + - Carbon is essential for life. Soil organic matter (SOM) contains the Plants take up inorganic nitrogen (NH4, NO3). nutrients and energy organisms and plants need. + At harvest, nitrogen may leave the farm in commodities or can be CO2 NitrogenNitrogen returned if livestock consume the crops and the manure is returned to CO2 the fields. O2 O Photosynthesis Light 2 + Precipitation adds small amounts of nitrogen to the soil. CO Through the process of + + 2 C H O N gas in the atmosphere is converted to NH by chemical and 6 12 6 photosynthesis, plants absorb CO 2 4 CO (sugar) 2 biological processes (nitrogen fixation). 2 from the atmosphere, transform Litter Crop Residues Animal it into plant carbon, and + Crop residues and green and animal manures contain organic N. Organic Soil Manure CO3, HCO3 sequester it in either above- or Horizons Reactions H2O H O 2 below-ground biomass and/or soil Microbial Activity carbon. Above-Ground Crop Carbon Dioxide Mineralization Grain Microbial Activity 6 CO2 + 12 H2O + Light C6H12O6 + 6 O2 + 6 H2O Export Leaching Losses N2 - Air

The Soil Food Web N-fixationRhizobia

Volatilization Kristina A. Goings Soil organisms are responsible for the transformation of plant material to Denitrification Dead Crop Biomass + National Soil Survey Center, NRCS, USDA, Lincoln, Nebraska humus. Plant and animal residue make up a large portion of organic matter Roots CO2, through photosynthesis, is converted to plant material. (OM) in soil. SOM or humus is the glue that helps hold soil into CarbonCarbon // NitrogenNitrogen RatioRatio aggregates. Plant cover helps stop both wind and water erosion as does + When the crop is harvested and removed from the farm, carbon is Microorganisms the aggregation effect of SOM. Fertilizer Nitrate Soil Organic Matter lost. If livestock consume the crop, the carbon may be returned to Carbon / Nitrogen (C/N) ratios are important. Plant and animal residues that the soil in the form of manure. have a C/N of 30:1 and over, have too little N to allow for rapid decomposition. Nitrification Burrowing animals, insects, and earthworms mix, help form aggregates, Nitrosomonas Therefore, the microorganisms will take ammonium and nitrate out of the soil to and add nutrients to the soil. When animals die, they decompose returning Nitrobacter + Crop residue, roots, and manure are a carbon (energy) source for fuel decomposition. This depletes the soil of nitrate and ammonium. Plants and nutrients to the soil. Insects chop up plant and animal residue which microorganisms. animal residues with low C/N ratios (20:1 and less) have sufficient N for the increases the surface area available to microorganisms for decomposition. Microorganisms microorganisms to decompose the residues without taking from the soil. Ammonia + Converting organic carbon to CO is mineralization of carbon. When Leached 2 microorganisms respire, CO is released to the atmosphere. Insects Nitrate 2 + High C/N ratio Animals Birds Short-term SOM is residue that is readily decomposed. Short-term SOM is a source of nitrogen, phosphorus, and sulfur for plants. + The conversion of organic N to inorganic N is mineralization. Short-term SOM lasts 1 to 3 years. Low C/N ratio Fungi + The opposite of mineralization is immobilization. + + Long-term SOM (humus) is the carbon form that resists Corn Legume Nitrification is the conversion of +NH4 (ammonia) to- NO3 (nitrate), decomposition and may last for greater than 1000 years. carried out by two microorganisms -- Nitrosomonas and Nitrobacter. Animals + + Ammonia can be volatilized (turned to gas) and lost to the atmosphere. Soil carbon losses are exacerbated through erosion and, to a lesser extent, may be lost through leaching of dissolved organic carbon + Decomposition is slower. + Decomposition is rapid due to higher Organic Matter: + When NO is converted to nitrous oxide, it is called denitrification. 3 (DOC). + Microorganism will deplete soil nitrogen within the plant. waste, residue, and Worms of nitrate and ammonium until + Microorganisms are satisfied with metabolites of plants, + Nitrate is mobile in soil and therefore easily leached. + The basic processes of the carbon cycle are: CO in through they die and release nitrate plant N. When microorganisms die, animals, and 2 + photosynthesis, and CO out through decomposition. and ammonium. nitrate and ammonia are released, microorganisms Erosion and runoff remove N from the agricultural field. 2 Bacteria increasing soil N. The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, and marital or family status. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA's TARGET Center at 202-720-2600 (voice and TDD). To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, Room 326W, Whitten Building, 14th and Independence Avenue, SW, Washington, DC 20250-9410 or call 202-720-5964 (voice or TDD). USDA is an equal opportunity provider and employer.