CHM031 | Soil Fertility and Soil Productivity

Soil fertility

The ability of soil to provide nutrients in proper quantities and in a balanced way for the growth of plants. Fertile soil should have the proper proportion of nutrients and optimum pH.

Soil productivity

The capacity of soil, in its normal environment, to support plant growth. It is affected by factors other than soil fertility, such as weeds and farming methods.

Infiltration of water

Water retention capacity of soil

Soil structure

Water draining ability of soil

Active soil life

Nutrient release capability

Content of organic matter

Parent soil characteristics

Minerals present in soil

Ground water

Soil pH

Exploitable depth of the soil

Leaching

Loss of water-soluble plant nutrients in soil
• Common with nutrients that are highly soluble such as N. These nutrients are carried to lower areas, far beyond the reach of many plant roots. Soil with many leached nutrients are infertile.

Soil capping

Occurs when soil is covered (capped) with an impervious material which prevents.
• the penetration of rainwater into soil,
• which leads to surface runoff.
• decreases moisture content and increases erosion

Soil erosion

Occurs when the top fertile soil is carried away by moving water and/or wind
• Leads to loss of topsoil and plant nutrients

Monocropping

Practice of growing one type of crop on a piece of land for long periods of time.
• Crops grown use only the nutrients they need while others remain unused → leads to exhaustion of nutrients
• Also increases the likelihood of buildup of pests and diseases, which may be passed on from residues of the former crop → leads to low yield
• Also leads to decrease in biodiversity

Accumulation of salts

Mineral salts come from decomposition of parent rock or decomposition of organic matter.
• Under normal conditions, salts are washed away by rainwater. However, in arid and semi-arid areas, rainfall is irregular and not enough to remove salts from soil
• may lead to deficiency of water in plants as water moves out of the root in the soil under the increased soil osmotic pressure

Change in pH

Inappropriate use of fertilizers may change soil pH
• Use of acidic fertilizer over long periods of time can decrease soil pH, which may affect the activity of soil microorganisms and availability of nutrients

Burning of vegetation

When vegetation is burned, organic matter is destroyed
• Affects the activities of microorganisms such as N fixation and decomposition of organic matter
• Soil is exposed to agents of erosion such as wind and water
• Accumulation of resulting ash also causes imbalance of nutrients in soil

Fertilizer

A chemical or natural substance added to soil to increase its fertility

Chemical fertilizer manufacturers

Must guarantee the analysis of all fertilizers.
• Total N expressed as percent N
• Available P expressed as percent P2O5
• Soluble K (potash) expressed as percent K2O

Nitrogen (N)

Promotes leaf growth

Phosphorus (P)

Enhances development of roots, flowers, seeds, fruits

Potassium (K)

Strong stem growth, movement of water in plants, promotion of flowering and fruiting

Secondary Macronutrients

Ca, Mg, S

Micronutrients

Cu, Fe, Mn, Mo, Zn, B

Occasionally significant

Si, Co, V

Quick release fertilizers

Made from water soluble compounds; derived from synthetic nutrients

Slow release fertilizers

Made from natural materials; release nutrients at a slower rate, based on moisture and temperature

Surface runoff

Pollutants are leached off to the bodies of water

Slow release fertilizers

Advantages
Good for well-established lawns
Encourage more uniform growth
Less likely to burn lawn and other plants
Extended release of nutrients puts less stress on plants
Less likely to leach
Do not need to be watered in
Green up lasts longer

Slow release fertilizers

Disadvantages
Nutrients not immediately available to plants
Cool soil may inhibit effectiveness
Organic fertilizers require more water
May be more expensive
Green up may take longer

Quick release fertilizers

Advantages
Nutrients immediately available to plants
Useful when plants need an immediate boost of nutrients
Soluble nitrogen is easily dissolved in H2O once applied
Stimulate quick grass-shoot growth and greening

Quick release fertilizers

Disadvantages
Rapid release into the environment may lead to nutrient leaching
Last only 2-4 weeks
Over application can burn lawns and other plants
Requires more fertilizer applications and mowing