Soil Productivity and Conservation

THE GMIS

Importance of Soil

• As the key resource in crop production• It supports the physical, chemical, and

biological processes• Regulates water flow such as– Infiltration– Root-zone storage– Deep percolation– Run-off

Importance of Soil

• Acts as a buffer between inputs and environment

• Functions as “degrader” or “immobilizer” of agricultural chemicals, wastes, or other pollutants

• Soil also sequesters carbon from the atmosphere

Important Soil attributes

• Texture• Structure• Bulk density and rooting depth• Permeability and water storage capacity• Carbon content• Organic matter and biological activity• pH• Electrical conductivity

Importance of Soil

• Soil: the layer of material that covers the land – Where plants anchor and grow– Made of weathered rock, decomposing plant and

animal matter– Has spaces for air and water movement– Soils differ in organic content which effects the

ability to support plant life.

5

Layers of composition

• 3 major types of soil– Horizon A: Topsoil– Horizon B: Subsoil– Horizon C: Parent Rock– Horizon D: Bedrock

• Each layer has different characteristics depending on where it is found.

6

Grasslands

• Horizon A is deep and supports root growth; small particles of rock mixed with decaying plant and animals (Humas).

• Horizon B is the subsoil (mix of dirt and rock).

• Horizon C is mostly large pieces of rock.

• Horizon D is bedrock solid rock.

7

Forest

8

Deserts

• Horizon A: limited plant growth so little decomposition, so thin top soil or none at all.

9

Disturbing soils

• Soils change over time naturally

• Human impact: deforestation leads to increased erosion of topsoil (no roots to hold soil in place)

10

Productivity of Ecosystems

• Ecosystems have different productivities, based on light availability, soil types, precipitation, temperature, nutrients.

• Productivity: the quantity of biomass of plants produced each year on a given area (g/m2)

11

Productivity of different ecosystems:

12

Three functions of soil(from NRC)

1. Provides the physical, chemical, and biological processes for the growth of plants

2. To store, regulate, and partition water flow through the environment

3. To buffer environmental change by decomposing organic wastes, nitrates, pesticides, and other substances that could become pollutants

Soil Quality

• Defined: The capacity of soil to function or the fitness for use

• Can be maintained through use of appropriate crop production technologies and resource management systems

• Two concepts of measuring soil quality– More traditional: focuses on inherent soil properties– More recent: focuses on dynamic properties of soil

Land capability and suitability

• Two types of measurements:– Land Capability Classes (LCC’s)– Prime farmland designation

• Used to measure land capabilities for a particular purpose:– Growing crops and trees– Grazing animals– Nonagricultural uses

Prime Farmland

• Based on physical and morphological soil characteristics:– Depth of water table to the root zone– Moisture-holding capacity– Degree of salinity– Permeability – Frequency of flooding– Soil temperature– Erodibility– Soil acidity

Prime Farmland

• Factors needed to sustain high yields when treated and managed– Growing season– Moisture supply– Soil quality

• Totals 222 million acres, or 54% of US cropland excluding Alaska

Productivity

• Measures output per unit input• Often measured as crop yield per acre• Can reflect soil degradation if yields decline as

soils become degraded and more inputs are used to compensate for decline in soil quality

Erodibility

• Highly erodible lands (HEL) is a soil quality measure that is important to USDA conservation policy

• USDA uses the erodibility index (EI) to classify erosion potential

Erosion Productivity Loss

• Measure of productivity loss that converts total erosion from tons per acre per year to inches per year

• 3 factors reflected in this measure:– Erosion rates– Soil depth– Rental values of land