Agricultural Ecology

Information about Agricultural Ecology

Published on February 7, 2008

Author: Melissa1

Source: authorstream.com

Content

Agricultural Ecology:  Agricultural Ecology Agricultural systems…:  Agricultural systems… The success of an agricultural system depends on its soil. The success of an agricultural system depends on its food web The success of an agricultural system depends on limiting factors Soil Properties:  Soil Properties Soil is a living, viable ecosystem – “dirt” is what you get under your fingernails. Soil is classified according to its texture –the amount of sand, silt and clay in it. Sand 0.2 mm Silt 0.02 mm Clay 0.002 mm Soil properties:  Soil properties Soil with more clay in it has greater nutrient holding ability than soil with less clay in it. This is the process known as Cation Exchange Capacity (CEC). Cation Exchange Capacity:  Cation Exchange Capacity Remember the macro and micronutrients needed for living organisms? List them…a quick quiz Na, Cl, C, H, O, P, K, I, N, S, Ca, Fe, Mg Mo, B, Cl, Mn, Cu, Zn Remember that most of these nutrients follow a sedimentary nutrient cycle. Cation Exchange Capacity:  Cation Exchange Capacity Nutrients that are in a sedimentary cycle, are make accessible to plants through the soil. In the soil, most of the nutrients become available after they dissolve in water. When a chemical dissolves in water, it becomes an ion – a charged particle. Positively charged ions are called cations, negatively charged ions are called anions. Cation Exchange Capacity:  Cation Exchange Capacity Sand Silt Clay - Sand - - - - - - - Ca++ K+ Na+ Mg++ Fe+3 Plant root hair H+ More nutrient and water holding capacity:  More nutrient and water holding capacity Silt Clay Sand Organic matter What does organic matter do for the soil?:  What does organic matter do for the soil? Source of decomposable nutrients – keeps nutrient cycles running Acts like a sponge – helps hold water in the soil Also acts to hold anions in the soil What are the sources of organic matter in the soil? Other ways water is held in soil:  Other ways water is held in soil Silt Clay Sand Sand Sand Sand Note: the smaller the particle, the smaller the pore space between particles and the more water can be held. If the pore spaces are too small, then water doesn’t drain well and the soil can become ANOXIC. Soil Horizons:  Soil Horizons A horizon B horizon C horizon A horizon: where most roots are, most weathered, lots of organic matter B horizon: material leaches down from A C horizon: weathered parent material, i.e. broken down bedrock Soil: Summary of main pts.:  Soil: Summary of main pts. Soil is a complex, living ecosystem that takes millennia to build. Although some erosion is “natural”, accelerated erosion, will lose soil and nutrients. Soil texture and organic matter content are important. Soil pH is, too. More on this later. Take a look at Figure on page 308 of your text! Agricultural ecosystems: nutrient cycles:  Agricultural ecosystems: nutrient cycles The most limiting nutrient to most types of agricultural production (crops, grazing, agro-forestry) is Nitrogen. So, here’s the nitrogen cycle… Slide15:  N2 (in atmosphere) N N NO3 Haber-Bosch Process NH4 Nitrogen fixation N-fixing bacteria NH4 Plants Consumers enzymes High temp. & Pressure Nitrifying bacteria NO3 Decomposers Denitrifying bacteria N2O Limitations on Nitrogen Cycle:  Limitations on Nitrogen Cycle The enzyme for nitrogen fixation is destroyed by oxygen N-fixing bacteria can not tolerate acid pH. All of the bacteria require adequate water supplies, but not too much. How current agriculture affects N cycle:  How current agriculture affects N cycle When manures are used as fertilizer, can increase rates of N cycling. When mulches are used to manage water, can increase rates of N cycling. Plowing increases O2 content of soil, decreasing N fixation. Chemical fertilizers make soil acidic, decreasing N fixation. Accelerated erosion increases leakiness and washes away bacteria. Positive Effects Negative Effects Agricultural Food Webs:  Agricultural Food Webs Agricultural Food Webs:  Agricultural Food Webs Crop Plant Harvested Used by Humans Waste? Consumed by “pest” Consumed by predator Food Web # 1 Food Web # 2 How do we maximize #1 and minimize #2?:  How do we maximize #1 and minimize #2? Through the use of pesticides Through the use of plowing Through the use of IPM? Types of pesticides:  Types of pesticides Chlorinated Hydrocarbons – e.g. DDT, long half-life Organophosphate – e.g. Malathion, shorter half-life Carbamates – e.g. Sevin, shorter half-life Naturally-occurring pesticides – e.g. pyrethrins, short half-life, more targeted. Half-life:  Half-life Amount Time 100 50 25 12.5 6.25 0 1 2 3 4 5 So, the half-life on DDT is 30 years! How long will it take to get down to 3.125% of its original concentration? 1.625%? Biological Amplification:  Biological Amplification Pesticide Resistance & Food webs:  Pesticide Resistance & Food webs If you sprayed the plant shown here, which population will recover first? What does that mean to future food webs in your field? Key terms to know & understand:  Key terms to know & understand Contour plowing Strip cropping Mulching Monoculture Target organism

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