AGRIC/O: SOIL TEXTURE

This Unit is about soil texture as understood in Agriculture.

SOIL TEXTURE

Is the degree of fineness or coarseness of a soil which is determined by the proportions of various sized particles it has.

SOIL TEXTURAL CLASSES

Sandy Soil

  • The soil particles have a diameter varying from 2.0mm – 0.02mm. A soil is said to be sandy when it has more than 70% of sandy particles by weight. It has a course feeling, feels gritty and rough when dry or wet. The particles are loosely arranged so it is well aerated and well drained.
  • It has a low water holding capacity so doesn’t retain enough water for plant growth.
  • It has good heat transfer so sandy soils are usually warm.
  • Sandy soils are reliable to erosion and leaching. It has low capacity due to large pore spaces.
  • It is low in plant nutrients.
  • Sandy soils are usually acidic.
  • It is easy to work or cultivate so it referred to as a light soils.

SIH

The particles of silt range from 0.02 – 0.002mm in diameter.

It has a smooth and powder feeling.

High in nutrient content.

Prevents movements of water into the sub soil so that crops can not use it.

It cultivated when wet, it becomes compact and this will lead to surface capping.

Clay soil

  • Soil particles are less than 0.002mm in diameter. A soil will be said to be clay if it has more than 35% of the clay particles by weight.
  • It has high water holding capacity so it tends to get water logged.
  • It has poor aeration and poor drainage due to the narrow pore spaces between the fine particles.
  • It has high capillarity.
  • It is in plant nutrients.
  • It varies form being slightly acidic to slightly alkaline.
  • It has poor heat transfer due to the small spaces so clay soils tend to be cold.
  • It is not leacher or eroded.
  • It has a fine smooth feeling when dry but it is sticky when wet.
  • It is difficult to work or cultivate for example when cultivated wet, it gets puddle so it is called heavy soil.
  • It is difficult to work or cultivated wet, it gets puddle so it is called heavy soil.

Loam

  • Loam is a mixture of all the other 3 without about 45% sand, 40% and 15% clay. It is rich organic matter usually between 1 -4% of organic matter.
  • It moderately fine textured. It is well drained and well aerated.
  • It is rich in plant nutrients, it is easy to cultivate and is the most suitable for crop production.

N.B

There are several types of loams that differ in characteristics depending on the ratio in which the different soil separates occur for example:-

Sandy loams

Contains 50 – 80% sand, 20 – 50% silt and clay and about

0.1 – 3% organic matter. They are moderately course textured. Moderately fertile, slightly acidic, it has a moderately water holding capacity and are suitable for growing cereals and vegetables.

Silty loam

These have 20 – 30% sand, and 70 – 80% silt and clay, has 0.1 – 4% organic matter, fine textured they are fairly well drained, they are high implant nutrients, they are slightly acidic. They have a moderately high water holding capacity. They have poor drainage and aeration which have to be improved upon before the soil can be used for crop production.

Clay loams

  • It has 20 – 50% sand, 20 – 60% silt, 20 – 30% clay and 0.1 – 6% organic matter. It is fine textured.
  • It is poor aerated and poorly drained.
  • It holds high amounts of water and potential nitrogen.
  • It ranges form slightly acidic to slightly alkaline and has to be drained before it can be used for crop production.

Experiment F

An experiment to determine soil texture by feel.

Apparatus

  • Different samples of soils and water.

Procedure

  • Take a small sample of each dry soil and feel it between the tips of your fingers then you fill in the table.
  • Add a little moisture to the soil and rub it between the finger tips and the thumb and record in the table what you feel.
  • Try rolling moist soils between your hands and see if it can form a ribbon, if so describe the nature of the ribbon.

Observations

Soil sample Feeling of dry soil Feeling of moist soil Can it form a ribbon?What nature Conduction about soiltextual class
A Gritty & course Cutting feeling courseCourse and gritty It doe not form a ribbon , particles remain loose Sandy soil
B Very fine and very smooth Very sticky It does a plastic form a ribbon Clay soil
C Moderately smooth Slight sticky Forms a ribbon which breaks silt
D Fine particles Moderately sticky Forms ribbon Day loam
E Moderately course and gritty Moderately gritty but lightly stick Doesn’t form a ribbon Clay sand
F Fine course  small particles fairly smooth Gritty slightly sticky Doe form a firm ribbon loam

Influence of soil texture on crop production

  • The course textured soils have a poor water holding capacity so they can not retain enough water for crop production.
  • In fine textured soils, there is poor aeration so plant roots and soil organism will not be able to respire well. Carbon dioxide will build up to toxic levels and organic matter decomposition will not take place.
  • Medium textured oils e.g. loam encourage crop production since they have good aeration, drainage good capillarity they are easy to cultivate.
  • The course textured soils are highly reliable to leaching and erosion and this makes them poor in plant nutrients.
  • The fine textured soils have a very high water capacity which would lead to water logging and death of many crops.
  • The fine textured soils have poor heat transfer, they remain cold and this is undesirable for germination, most of the soil organisms and root development.
  • Fine textured soils becomes sticky when wet and haid when dry. This makes cultivation difficult.

Ways through which different soils can be  improved before they can be used for crop production.

Improving clay soils

  • Drainage; this involves removal of excess water to allow free aeration and heat transfer so that there will be greater micro organism activity.
  • Application of Humas or organic matter to aggregate the fine particles into large more porous crumbs this will improve on aeration and raise soil temperatures.
  • Marling with sandy soils to get inter mediate characteristics.
  • Addition of agriculture lime to aggregate particles and make the soil less sticky therefore easier to cultivate.
  • Improving sandy soils
  • Addition of organic matter to increase water holding capacities, reduce leaching, increase on nutrients and increase activities of soil organisms.
  • Marling with clay soil so as to get soil with inter mediate characteristics.
  • Regular irrigation using sprinklers to ensure that crops get enough water.
  • Application of artificial fertilizers to increase on nutrients.
  • Applications of agriculture lime to aggregate particles as well as reduce of soil acidity.

THIS VIDEO EXPLAINS MORE ABOUT SOIL TEXTURE

ASSIGNMENT : SOIL TEXTURE assignment MARKS : 10  DURATION : 1 week, 3 days

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