Soil and Plant Nutrition

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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

Soil Conservation and Sustainable Agriculture

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.