Soil Fertility I : Introduction - Form 1 Agriculture Note

• Introduction
• Characteristics of a Fertile Soil
• How Soil Loses Fertility
• Maintenance of Soil Fertility

Introduction

- Soil fertility is the ability of the soil to provide crops with the required nutrients in their proper proportions.

Characteristics of a Fertile Soil

• Good depth - Good soils give roots greater volume to obtain plant nutrients and provide strong anchorage.
• Good aeration - for the respiration of plant roots and use by soil organisms.
• Good water holding capacity - ensures provision of adequate water for plant growth.
• Proper drainage - ensures provision of adequate air for plant growth.
• Correct soil pH - different crops have different soil pH requirements.
• Adequate nutrients supply - it should supply the required nutrients in the correct amounts and in a form available to plants.
• Free from excessive infestation of soil borne pests and diseases.

How Soil Loses Fertility

• Leaching: vertical movement of dissolved minerals from the top to the lower horizons of the soil profile.
• Soil erosion - The removal and carrying away of the top fertile soil from one place to another.
• Monocropping - This is the practice of growing one type of crop on a piece' of a land over a long time.
• Continuous cropping - crops take away a lot of nutrients from the soil which are never returned. Growing crops continuously without giving the soil time to rest makes the soil infertile.
• Change in soil pH - changes in soil pH affect the activity of soil microorganisms as well as the availability of soil nutrients.
• Burning of vegetation - burning of vegetation cover destroys organic matter. It also exposes the soil to the agents of soil erosion.
• Accumulation of salts - soils with a lot of salts are said to be saline. State of having too much salt in the soil is referred to as soil salinity. Salts accumulation cause water deficiency in plants. It may also lead to change in soil pH.

Maintenance of Soil Fertility

Soil fertility is maintained through the following methods:

• Control of Soil Erosion ;
  • Terracing,
  • Contour cultivation,
  • Strip cropping,
  • Cut off drains
  • Planting cover crops.
    
    
• Crop Rotation ;
  • Practice of growing different crops on the same field in different seasons in an orderly sequence.
• Control of Soil pH :
  • Application of liming materials such as limestone, quicklime, magnesium carbonate and slaked lime if the soil is acidic.
  • Application of acidic fertilizers if the soil is alkaline.
  • Application of manures.
• Proper drainage;
  Done through:
  
  • Breaking hard pan.
  • Construction of water channels.
  • Growing crops on cambered bed
  • Pumping out water from the soil.
• Weed control:
  
  • Use of herbicides.
  • Slashing
  • Uprooting.
  • Mulching
  • Use of proper farming practices such as early planting, correct spacing and cover crops.
• Intercropping –
  
  • Farming practice where different crops species are grown together in the field.
• Minimum Tillage;
  
  • Use of herbicides.
  • Uprooting of weeds.
  • Slashing weeds
  • Mulching
  • Strip cultivation.
• Use of Inorganic Fertilizer ;
  • Chemical compounds manufactured to apply specific plant nutrients for example calcium ammonium nitrate (CAN).
• Use of Manure;
  
  • Well decomposed manures release nutrients into the soil and increase its water holding capacity.