Year 11 Soils notes and tasks.
The soil on which we farm on is very important to the farmers
It can take millions of years to form some soil.
Soils are formed from Bedrock or P
, which
may have come from volcanic (igneous) rocks such as granite which
have been pushed up from beneath the earth, or sediments such as
limestone or rocks made from compressed volcanic ash. Or
Metamorphic rock such as schist, which is crystalised sedimentary
or igneous rocks.
Over time w
ring breaks the rock down into finer
particles…rain, frost, heat, wind, lightning all contribute to make the
parent material smaller. These small particles are often rich in
s. On these grew plants such as lichen and moss
which died and de
ed, creating a layer of organic
matter on top of the rock. This initial layer of
is called Humus. This continued to
build up over time, larger plants grew and died, animals lived,
deficated and died there, bacteria and insects too, creating layers of
rich soil. The top-soil is the richest because this is
where most of the organic matter is. Soils are one of the most
complex ecosystems in the world and are essential to life through the
recycling of nutrients, carbon, and oxygen.
A series of buried soils and volcanic ash
layers, in a roadside cutting
near Mount Tarawera.
The cl
te and t
phy also play a major role in
how soils are formed, ie soil on a slope may wash down in rain and
collect in a valley, making the valleys more fertile than slopes.
Other major factors may be glaciation, which grings away at the
parent material into a fine powder, called silt, which may then be
dispersed by the wind or washed across plains by rivers.
Soils can be divided into three types or texture.
which has large course particles, s
which is smoother
and finer and c
which has microscopic particles and
feels sticky when wet. These three types give a soil different qualities.
Ie. a clay soil holds water more so is cooler and may have less air
spaces called pores, sandy soils drain water better and have more
or larger pore spaces
Question: Describe how do you think these qualities may affect
plant growth?
When the soil is a combination of sand, silt and clay it is called a
loam. It should then be an ideal soil for growing most plants in.
As plants grow the soil literally supports them, the need it to stand
upright, it has to have good s
e to allow air around the
roots for a process called r
tion and also the soil
cannot be to hard or the roots would struggle to push through.
Water is also important as this allows the roots to absorb or ‘imbibe’
the nutrients in the soil. Soil should have
% mineral
material (rock particles)
% organic material.
% water,
% air and
Question: What are some of things that may change these
percentages and make the soil less ideal?
A farmer must know the condition his soil is in and maintain it. He
can improve poor structure or damage done by co
ng by cultivating it, improving ae
n or
drainage and soil cr
b. This is often done prior to sowing so
new seeds have a better chance. If the soil is too compacted it will not
drain well, ponding can occur and it will have less pore spaces,
particularly if it is a clay based loam which aggregates and forms
large hard
Because clays hold water and, if structure is poor-less air, this means
it may also be colder. Soil Temperature effects plant growth
because cell division increases with warmth, that is one reason why
grass gows fast in spring and slower in winter because the soil
warms up in spring and stimulates growth. This means clay soils with
a poor structure heat up slower, so grass growth takes longer.
Question: Describe what happens to grass in the 4 seasons of the
year… draw a graph that show growth rates over spring,
autumn, summer and winter and expain what factors may affect
Another factor that effects plant growth in the soil is wether the soil
acid al
is too
. This is know as the pH
levels of the soil. (pH means potential Hydrogen and refers to how
much hydrogen a plant can attract).
Research task… write a paragraph that describes some of the
factors that might turn a soil acidic or alkaline: Use link on “understanding soil acidity and pH”,
read and take notes.
If the soils are too
plants cannot obtain the
nutrients they need as the nutrients become ‘trapped’ in the soil
(cannot attract hydrogen).
Farmers can help fix the acidity to the optimum pH of around pH 6.5 7 by adding lime (CaCo2) to
help unlock the n
to make it more acidic.
ze the acidity and
in the soil. Sulphur can be added
Cultivation and sowing are the terms used to describe some of the
management practices farmers use to work-up, maintain and plant
their soil.
Copy and Paste some pictures of various methods of cultivation
ie. Ploughing, harrowing, rolling, discing, drilling, direct drilling
etc into this document with a brief description of what each one
When plants grow the use up the nutrients in the soil. Naturally some
of the nutrients would be returned to the soil as it decomposes, but
because we harvest or feed a lot of what is grown nutrients need to
be replenished some other way. This is usually in the form of
Inorganic or O
fertilizers. Nitrogen (N), phosphorus
(P), Potassium (K) and sulphur (S) are the usual elements added to
boost nutrient levels.
Organic fertilizers are usually composts or effluents. These also
help add organic matter as well and can help build good soil
structure -water retention, aeration and ‘hu
Inorganic fertilisers such as Urea, Super-phosphate, Nitrophoska etc
are brand names for various levels of N. P. K. or S.
On the side of every fert package it should contain information on
what it contains…this is called its NPKS ratio.
Research: Each element of the NPK or S helps the plants in
different ways… find out and describe how plants benefit from
Nitrogen, Phosphate or Potassium.