Soil particle
–
–
–
–
–
–
–
–
–
K+
K+
K+
Ca2+
Ca2+
Mg2+
H+
H+
H2O + CO2
H2CO3
HCO3– +
Root hair
Cell wall
Slide 11
Organic Components
Humus builds a crumbly soil that retains water but is still porous.
It also increases the soil’s capacity to exchange cations and serves as a reservoir of mineral nutrients.
Topsoil contains bacteria, fungi, algae, other protists, insects, earthworms, nematodes, and plant roots.
These organisms help to decompose organic material and mix the soil -- detrivores.
Slide 12
In contrast with natural ecosystems, agriculture depletes the mineral content of soil, taxes water reserves, and encourages erosion.
The goal of sustainable agriculture is to use farming methods that are conservation-minded, environmentally safe, and profitable.
Slide 13
Irrigation
Irrigation is a huge drain on water resources when used for farming in arid regions.
The primary source of irrigation water is underground water reserves called aquifers.
The depleting of aquifers can result in subsidence = the settling or sinking of land.
Slide 14
Land subsidence caused by excessive removal of groundwater
Land subsidence in California
Sinkhole in Florida
Slide 15
Irrigation can lead to salinization = the concentration of salts in soil as water evaporates.
Drip irrigation requires less water and reduces salinization.
Slide 16
Fertilization
Soils can become depleted of nutrients as plants and the nutrients they contain are harvested.
Fertilization replaces mineral nutrients that have been lost from the soil.
Commercial fertilizers are enriched in nitrogen, phosphorus, and potassium.
Organic fertilizers are composed of manure, fishmeal, or compost.
Slide 17
Adjusting Soil pH
Soil pH affects cation exchange and the chemical form of minerals.
Cations are more available in slightly acidic soil, as H+ ions displace mineral cations from clay particles.
Slide 18
Controlling Erosion
Topsoil from thousands of acres of farmland is lost to water and wind erosion each year in the United States.