Soil fertility is the ability of the soil to supply the required type and amount of nutrients for optimum plant growth.
Soil productivity is the ability of the soil to produce high crop yield for longer period of time.
Factors contributing to soil fertility
Good soil depth: deep soils give plant roots a greater area for nutrient absorption.
Proper drainage: well drained soils are aerated and aeration promotes healthy root development.
Good water holding capacity: this ensures that enough water is retained in the soil for plant use.
Adequate nutrient supply: A good soil should have correct amount of plant nutrients.
Good soil structure: good soil structure ensures aeration and respiration of plant roots and soil living organisms.
Correct soil pH: different plant nutrients are available 0at specific pH values.
Good soil texture: a good soil texture encourages aeration, drainage, root penetration and ability to retain nutrients.
Good soil colour: soil colour influences soil temperature e.g. dark colour absorbs heat.
Freedom from pests and diseases: weeds compete with crops for plant nutrients and other growth factors. Pests make utilisation of nutrients by plants ineffective.
Presence of organic matter: a fertile soil should have large amounts of humus because humus improves soil structure and adds plant nutrients into the soil.
Loss of soil fertility
Leaching: this refers to the loss of nutrients from the upper to the lower layers of the soil where plant roots may not access them.
Soil erosion: the washing away of top fertile soil by running water, wind e.t.c. It ends in loss of nutrients as well.
Mono cropping: this leads to exhaustion of a particular nutrient from the soil.
Continuous cultivation of the soil: this destroys the soil structure making the soil loose and easily eroded.
Presence of weeds: These compete for growth factors with the crops.
Water logging: This encourages acidity and leaching of nutrients, and poor aeration.
Build up of pests and diseases.
Soil capping: this refers to the development of impervious layers on the soil surface as a result of use heavy machines.
Change in soil pH: this makes some nutrients and living organisms un available.
Development of hard pans: these are impervious layers below the soil surface. They form as a result of Ploughing at the same depth for a long time.
Burning of vegetation: this destroys soil living organisms, organic matter and causes evaporation of nutrients.
Accumulation of salts: these may make the soil saline and toxic and hinder absorption of water into the plant roots.
Pollution: of the environment with materials like polythene paper, plastic materials, toxic chemicals, etc.
Excessive irrigation: this leads to loss of soil particles and nutrients.
Excessive drainage: This leads to loss of soluble nutrients which are drained off with water.
Maintenance of soil fertility/ ways of improving soil fertility
- Addition of organic matter.
- Use of minimum tillage to conserve soil structure.
- Application of inorganic fertilizers.
- Mulching to conserve soil moisture.
- Weed control.
- Erosion control by afforestation, terracing e.t.c.
- Control of pests and diseases using chemicals and cultural methods
- Controlled irrigation in areas with limited water supply.
- Crop rotation with grass brakes to help the soil regain its fertility.
- Improving on drainage by planting deep rooted crops or constructing surface drains.
- Controlling pH e.g. through liming to ensure availability of nutrients and living organisms in the soil.
- Proper disposal of wastes to avoid pollution.