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.

Factors affecting Soil Fertility

Infiltration of water
Soil structure
Active soil life
Content of organic matter
Minerals present in soil
Soil pH
Water retention capacity of soil
Water draining ability of soil
Nutrient release capability
Parent soil characteristics
Ground water
Exploitable depth of the soil

Leaching

loss of water-soluble plant nutrients in soil

Leaching

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.

Soil Capping

• 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

Soil Erosion

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.

Monocropping

Crops grown use only the nutrients they need while others remain unused → leads to exhaustion of nutrients

Monocropping

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 7

Monocropping

Also leads to decrease in biodiversity

Accumulation of Salts

mineral salts come from decomposition of parent rock or decomposition of organic matter.

Accumulation of Salts

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

Change in pH

inappropriate use of fertilizers may change soil pH

Change in 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

Burning of Vegetation

• 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.

Three Main Macronutrients

N

P

K

N

promotes leaf growth

P

enhances development of roots, flowers, seeds, fruits

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

SLOW RELEASE FERTILIZERS

QUICK RELEASE FERTILIZERS

Pollutants

are leached off to the bodies of water

Point-Source Contamination

can be traced to specific points of discharge from wastewater treatment plants and factories or from combined sewers.

Air Pollution

spreads across the landscape and is often overlooked as a major nonpoint source of pollution. Airborne nutrients and pesticides can be transported far from their area of origin.

Eroded Soil and Sediment

can transport considerable amounts of some nutrients, such as organic nitrogen and phosphorus, and some pesticides, such as DDT, to rivers and streams.