Lecture 5: Soil and Fertility

what is the role of livestock in agriculture?

provide manure, traction, and transport

livestock provide _______ to the soil

fertility

true or false: the main role of livestock in agriculture is to provide meat

false

what is the role of synthetic fertilizer? why is this problematic?

the primary source of fertility for wealthy countries

requires large amounts of fossil fuels

what do plants need?

sunlight, water, temperature, CO2, and other nutrients (potassium, nitrogen, phosphorous)

what does it mean for soil to be a historical variable?

soil is a product of human actions and decisions

soil fertility changes a lot

net primary productivity

the growth of all photosynthesizers (all plants)

where is net primary productivity the greatest?

near the equator- warmer and wetter

true or false: the places with the greatest net primary productivity are the same places we produce the most agriculture

false

why are the places with the highest net primary productivity, not the places we rely on with our food?

large amounts of water leach nutrients from the top layer of soil

there are different ways that ________ can limit productivity

climate

what are some of the climatic constraints on plant growth?

wetness, moisture, severe moisture, temperature (too hot/cold), severe temperature, water

insulation

energy from the sun

how does soil fertility form?

decomposition of bedrock (the parent rock) and the decomposition of litter (plants)

the smaller the organism the ______ the percent described

smaller

what do the smaller organisms do?

key in the decomposition of plant material, but they are not well described

rocks have a variety of compositions that involve different nutrients, what does this mean for the soil?

when they break down they create variety in soil

the texture of the soil is a function of the

rock type

if particles are so small, like clay, what does it mean for the soil?

there is not a lot of room between the particles, the water cannot penetrate it, which means it cannot hold or drain water easily

if it is raining on a hill slope, which particles run off? what does it mean if there is a creek at the bottom?

the smallest, and lightest particles

if there is a creek this means the particles will redistribute across the landscape- accumulation near the rive (buildup of nutrients)

weathering

the process by which rock breaks down into smaller particles, forming the foundation of soil

recycling of mineral elements

breakdown of geological bedrock by weathering/climate

the growth of plants and then their decomposition creating nutrient-rich organic matter (humus) that decomposes to become soil

water circulates/moves nutrients between layers- can move nutrients down by leaching, can also come up from the soil profile

how can the soil at the top be less fertile?

water leaches nutrients from the top making the surface soil less fertile

what processes add nutrients to the soil?

biomass growth (parent rock dissolved, atmospheric N fixed)

plant decomposition

manure

farming: organic and inorganic fertilizers

what processes remove nutrients from the soil?

drainage- leaching

denitrification

recrystallization

removal of animal waste

harvest: plants, animals

humus

dark organic matter in the soil that is formed by the decomposition of plant and animal matter

compare the soil of grasslands to tropical rainforests

soil in tropical rainforests is not fertile because there is so much rainfall that nutrients are leached from the soil (despite high biomass growth)

soil in grasslands is more fertile because grass dies and decomposes quickly, and biomass growth cycles faster, nutrients don’t leach away because there is not too much rain (in the winter they receive little rain)

what are the ways nitrogen can be fixed and made available to plants?

lightning can break bonds and release nitrogen which falls to the earth with rain

some bacteria in the soil can process and release it into the soil

symbiotic micro-organisms associated with certain plants (legumes) (don’t need to die to provide nitrogen)

soil organic matter

the portion of organic residues in soil in various stages of decay from plants and animals

soil organic carbon

carbon stored in soil organic matter

this carbon constitutes the largest terrestrial carbon pool and makes soils integral to our plant’s carbon cycle

CO2 is brought into plants through

photosynthesis

carbon sequestration

the process of capturing CO2 from the atmosphere and storing it in the soil

what can release the carbon stored in the soil?

land use changes (agriculture)

human emissions

heterotrophic respiration

autotrophic respiration

above ground vegetation (like trees) is a much smaller pool than

below ground soil carbon

what are the ways to restore soil fertility?

slash-and-burn

fallow periods

livestock manure

crop rotation

how does slash-and-burn restore soil fertility?

cut (forest/trees) and then burn, which releases the nutrients from above-ground biomass into the soil

how do fallow periods restore soil fertility?

leaving the land dormant, which builds up nutrients through natural plant growth and decomposition

how does livestock manure restore soil fertility?

livestock eat plants and then processing the nutrients in their waste

how does crop-rotation restore soil fertility?

different plants deplete different nutrients and some plants restore nutrients (like legumes and nitrogen)

mineral fertilizers (artificial fertilizers)

inorganic substances that provide nutrients (synthetic nitrogen, superphosphate, potassium) to plants

true or false: we have likely lost a lot of knowledge about crop rotation over the years

true

organic fertilizers

fertilizers that are natural produced- manure, compost, green manure

what are the benefits of organic fertilizers over mineral fertilizers?

released gradually based on plant needs

less subject to drainage

more complete and balanced chemically

support microorganisms that stimulate growth