Soil

Soil can be defined as the unconsolidated weathered materials found in the upper most layer of the earth surface on which plants grow. It provides support and nutrients for the plants. The three types of soil are; Sandy Soil, Clay Soil and Loamy Soil.

Sandy Soil

A soil is said to be sandy if the proportion of sand particles in a sample of the soil is high. The particles are mainly quartz (SiO2).

Properties of Sandy Soil

  1. Sandy soil is coarse, grained and gritty.
  2. It absorbs and loses water easily
  3. It is loose with large pore spaces.
  4. Percolation in sandy soil is high but capillarity is low.
  5. It does not support water logging and erosion.
  6. It supports leaching, hence it is low in plant nutrients.
  7. Sandy Soil has grey or brownish colour.

Loamy Soil

This contains a mixture of both clay and sand with some humus in roughly equal proportion. Loamy soils are the most fertile and the humus in it gives it a mellow tilth i.e. the size of the soil particles and the air spaces between the particles are the most suitable for cultivation.

Properties of Loamy Soil

  1. Loamy Soil is moist, loose with moderate sized pore space
  2. The structure breaks easily when wet and friable when dry
  3. It contains lots of organic matter (humus)
  4. It can easily be worked or cultivated
  5. It does not support erosion and water logging
  6. It is the best soil for cultivation of crops.
  7. It does not support erosion and water logging

Clay Soil

A soil is said to be clayed if the proportion of clay in a sample of the soil is very high

Properties of Clay Soil

  1. The particles are fine, powdery and smooth when dry.
  2. The particles are sticky and moody when wet.
  3. The particles are tightly bound together with little pore (air) spaces.
  4. Percolation in clay is low but capillarity is high.
  5. It does not support leaching, hence it contain plant nutrients.
  6. It is poorly aerated.
  7. It supports water-logging and erosion.

Effects of Soil on Vegetation

Soil factors play an important role in determining the vegetation of a region. Soils account for the variation in type of plants that are found in regions with similar climates. To support a rich growth of plants, soil must have the following characteristic:

  1. A rich humus content
  2. A rich mineral content
  3. A good water-holding capacity; this is determined by the amount of humus and clay in it.
  4. Good soil porosity

Soil nutrients

Soil nutrients are essential elements and compounds present in the soil that are vital for the growth and development of plants. These nutrients are necessary for various physiological processes in plants, including photosynthesis, metabolism, and the formation of proteins, enzymes, and hormones. The availability and balance of soil nutrients greatly influence plant health, crop yield, and overall ecosystem productivity.

Water-Holding Capacity of Soil

Water holding capacity of soil refers to the ability of the soil to retain water. The amount of water retained by any soil depends or the size of the particles, the humus content, aeration, temperature and presence of microbes. Clay and humus retain a higher amount of the water than sand. In clay soil, most of the water is held firmly to the surface of the soil particles (hygroscopic water) and this is not usually available to plants. In sandy soil very little amount of water is retained as most of it drains off. Loamy soil is able to retain more water within its particles. This is called capillary water and is available for plants use.

Renewal & Maintenance of Soil Fertility

Some of the ways soil fertility can be renewed and maintained are:

Manure

Manure is organic material derived from animal waste or dung, and decomposed remains of dead plants and animals. It is applied to the soil to improve its quality and boost the yield of healthy crops. Manure is a natural, cost-effective fertilizer that is rich in organic matter and humus.

The process of applying manure to the soil is called manuring. It should be done regularly to ensure the plants remain strong and healthy.

Types of Manure

Compost Manure

Compost is a mixture of organic waste or residues. Composting is the process of converting plant and animal waste into manure. It involves digging a pit on the farm where all organic waste such as animal dung, vegetables, weeds, etc., is collected. The pit is then covered with a thick layer of mud to prevent air and water from entering. The pit is left undisturbed for months, allowing microbes to decompose the waste and produce manure.

Compost manure improves the soil's ability to retain nutrients and water, as well as enhancing its structure.

Green Manure

Some crops are grown specifically to provide organic matter. Leguminous crops fix nitrogen in the soil. When cultivated or composted into the soil, they increase organic matter and make phosphorus and certain trace elements available to plants. Green manure helps reduce soil erosion and leaching, while also improving soil structure and suppressing weeds.

Farmyard Manure

Farmyard manure is the decomposed mixture of animal dung, urine, bedding material, and fodder residues. It is a by-product of farm animal waste. While low in mineral nutrients, farmyard manure is high in organic matter. It varies depending on the source and is often low in phosphorus, which may require supplementation with phosphate fertilizers.

Farmyard manure improves soil structure, enhances microbial activity, and increases the soil's nutrient and water retention capacity.

Benefits of Using Manure

  1. It is an affordable option for improving soil quality.
  2. It enhances soil fertility by adding organic matter and humus.
  3. It helps to control weed growth.
  4. It minimizes soil erosion and nutrient loss through leaching.
  5. It is environmentally friendly and does not cause pollution.
  6. It improves soil aeration by increasing soil porosity.
  7. It strengthens the structure of the soil, making it more resilient.
  8. It boosts the soil’s ability to retain water and nutrients.
  9. It promotes the exchange of gases in the soil, aiding plant growth.
  10. It enhances the texture of the soil, making it easier to work with.
  11. It encourages the activity of beneficial microorganisms in the soil.

Fertilizer

Fertilizer is a chemical substance that supplies essential nutrients such as phosphorus, potassium, and nitrogen, which are necessary to enhance soil fertility. It can be natural or synthetic and is applied to the soil or plant tissues to provide plants with the nutrients they need for growth.

In addition to providing nutrients, chemical-based fertilizers can also serve as insecticides, protecting plants from pests. Common fertilizers include NPK (nitrogen, phosphorus, potassium), potash, ammonium sulphate, and urea. NPK fertilizers boost soil nutrients by adding nitrogen, potassium, and phosphorus, while urea mainly increases nitrogen levels in the soil.

While fertilizers offer several benefits, they also have potential negative environmental impacts. Overuse can lead to soil and water pollution, as fertilizers often contain synthetic, non-biodegradable chemicals. Continuous use can make the soil more acidic, leading to soil degradation.

Although fertilizers provide quicker nutrient uptake for plants, manures are a more environmentally friendly alternative, as they do not contribute to pollution or harm the ecosystem.

Liming

Liming involves adding calcium and magnesium-rich substances to the soil, such as chalk, limestone, marl, or hydrated lime. The lime used for agricultural purposes is commonly referred to as agricultural lime.

The main purpose of applying agricultural lime is to raise the soil's pH level, making it less acidic.

Acidic soils can hinder plant growth by limiting the absorption of essential nutrients like nitrogen, phosphorus, and potassium. Some plants, such as legumes, struggle to grow in highly acidic conditions.

Crop Rotation

Crop rotation is the planned sequence of planting different crops over several years in the same growing area. It involves growing a variety of crops in the same field in a specific order across different seasons.

This practice helps to replenish certain nutrients depending on the crops planted. For instance, rotating a nitrogen-intensive crop like corn with a nitrogen-fixing crop like soybeans can help maintain a balanced level of nutrients in the soil.

Legumes are often included in crop rotation to enhance soil fertility. Crops that need high nutrient levels, such as wheat, can then be planted after legumes to take advantage of the improved soil conditions.

Advantages of Crop Rotation

  1. It mitigates the build-up of pathogens and pests that often occurs when one species is grown continuously.
  2. It improves and maintains soil fertility.
  3. It improves the soil structure.
  4. It increases crop yield.
  5. It reduces the great dependence on fertilizers.
  6. It increases water efficiency.
  7. It minimizes soil erosion.
  8. It controls the growth of weeds to a great extent.
  9. Two or three crops can be grown in a year with good harvests.

Mixed Cropping

Mixed cropping is the practice of growing two or more crops simultaneously on the same piece of land. Examples include groundnut and corn, yam and beans, wheat and gram, or sunflower and groundnut.

Considerations for Practicing Mixed Cropping

  1. The crops grown together should have different water requirements and maturation times.
  2. One crop should have deep roots, while the other should have shallow roots.
  3. The nutrient requirements of one crop should be less than those of the other.
  4. One crop should be tall, while the other should be shorter.

Leguminous Crops

Definition: Leguminous crops are plants from the Leguminosae or Fabaceae family, known for their ability to fix atmospheric nitrogen through a symbiotic relationship with nitrogen-fixing bacteria in their root nodules.

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