envr 1000 - unit 6, resources & agriculture, pt 1

what is the % of agricultural land on earth?

~40%

ganges river basin

• Irrigation, nutrients provided by runoff from the
  Himalayas = high agricultural fertility
  • A major agricultural region and population center
  - >700 million inhabitants, or nearly 10% Earth’s population
  - Enormous wheat, barley, rice, livestock production

Agriculture

the practice of cultivating soil, growing crops and/or
raising animals to provide food for humans

form of resource intensification?

agriculture - a way to
increase the productivity and biocapacity of a unit of land

Subsistence agriculture

Traditional agricultural methods, using human
and animal muscle power, to produce enough good to feed oneself and
one’s family

Industrialized agriculture

Modern agricultural methods which require a
large input of capital and require less land and labor than traditional
methods

soil

A complex plant-supporting system comprised of biotic +
abiotic elements

what is soil made up of?

- Weathered rock
- Organic matter (OM)
- Gases
- Water
- Nutrients
- Small life forms (earthworms, bacteria, fungi...)

can humans and animals survive without soil?

no as terrestial plants depend on soil

how many organisms live a square meter of soil?

1 billion

what do soil organisms do?

Provide essential ecosystem services
- Ensuring soil fertility
- Breakdown of toxic materials
- Purifying water
- Decomposing plant and
animal waste and detritus
- Nutrient cycling
- Minerals are cycled from soil
to organisms and back to soil

parent material

base geological material from which soil is formed
- Mineral content and type determines starting composition of soil

organic matter (OM)

living & dead organisms & decaying plant and animal material

water

loaded with dissolved minerals and organic acids
- Important for supporting plant growth

gases

generally not like the surface air we breathe
- Rich in carbon dioxide and methane
- Lower in oxygen

Anaerobic decomposition

microorganisms break down organic material (OM) in absence of oxygen
- Takes longer to break down
- Produces little heat
- Produces biogases like methane

Aerobic decomposition

organic materials decompose in the presence of oxygen
- Faster than anaerobic decomposition

subsistence agriculture energy requirements?

large energy inputs from humans and animals

what came before industrialized agriculture?

subsistence agriculture

humus

a dark, spongy, crumbly mass of material formed by partial
decomposition

what does humus do?

• Gives soil a loose, spongy, friable structure
  - Increases water and air holding capacity,
  which is beneficial for plants and other soil
  residents

how is humus produced?

Partial decomposition of organic material (ex: compost)

how is soil formed?

• climate

• organisms

• topography

• parent material

• time

climate

heat and moisture speed up reactions, stimulate biological activity

organisms

burrowing and bioturbating organism help mix and aerate soil, add
organic matter, facilitate microbial decomposition

topography

natural topography influences how soils move, where water and
sunlight can reach, rates of erosion (e.g., steep hills vs. plains)

parent material

chemical and physical characteristics of parent material are
greatest influences on the resulting soil

time

soil formation may take decades or millennia, allowing the above factors
to change with time and produce variety of soils

weathering

break down of parent material to form soil

types of weathering

• physical (mechanical)

• chemical

• biological

Physical (mechanical) weathering

wind, rain, freeze/thaw; no chemical changes in parent material

chemical weathering

substances chemically interact with and alter parent material

biological weathering

organisms break down parent material

soil horizons

Horizontal layers into which many soils are organized, from surface to parent material

soil texture categories

• clay

• silt

• sand

• other immediate categories

loam

soil with an even mixture of clay, silt, sand

best soil texture for plant growth?

Medium-pore size silty sands
- Loamy soils with mix of pore
sizes

what does soil texture determine?

workability (relative ease of cultivation and growing crops)

what does soil texture influence

porosity and permeability: key hydrological characteristics of a soil

porosity

measure of the volume of space (called pore size) between soil particles

permeability

degree of interconnectedness of the spaces and ease of fluid movement

what does porosity and permeability determine?

how
fast water moves through soils

Larger spaces between soil particles +
more interconnected pore spaces =

faster water movement

what does porosity and permeability influence?

How water moves after large rainfalls
(percolation / runoff)
- Groundwater flow and aquifer recharge
- Permafrost freezing and thawing
- Movement of nutrients and toxic chemicals
through soil

soil fertility

the ability of soil to sustain agricultural growth by providing
nutrients, water, and air essential for plant growth and soil life

do characteristics of soil and soil profiles vary?

yes, regional differences affect soil fertility

which ecosystem has more fertile and productive soil? prairie grasslands or tropical rainforests?

prairie grasslands

why don’t tropical rainforests have more fertile and productive soil?

In rain forests, most nutrients are tied up in plant tissue
• More leaching of nutrients and minerals in rainforest

• less humus available

leaching

drain away soluble chemicals like nutrients through movement of water