Cultivation

Cultivation can help a soil with a clod structure by breaking it up into smaller particles. The more you cultivate, the finer the soil becomes. When the soil structure is changed by cultivation to suit plant growth and seed germination, it is described as having tilth.
  Cultivation can help:

• bury crop residues
• kill weeds
• soil water and air movement
• drainage
• root growth and development.

Cultivation needs to be managed carefully as it can damage the soil structure. Over-cultivation can cause crop yield to decrease and production costs to increase.

Crops with small seeds need a very fine tilth like that shown in the photo.

Carrots and melons require a tilth that is crumbly and fine.

Equipment used  for cultivation

Conventional cultivation is the method that is normally carried out.

To start with the soil is turned over and weeds and unwanted plants are  turned into the soil. Ploughs and discs are used to do this. This is called primary cultivation.

The plough cuts a passage though the soil and turns in the furrow slice. Sometimes the weeds and grass are sprayed with herbicide before doing this.

Disc harrows are used to cut the ploughed soil into smaller pieces.

The disc harrows will also bring larger clods to the surface and put the finer crumbs deeper in the soil.

The next step is to make a seedbed. This is called secondary cultivation.

Cultivators and harrows are used to do this. The harrow is like a rake, and helps make a seedbed.

They have a number of tines, which are pulled through soil to produce a fine seedbed.

The harrows will help level the soil and kill any small weeds.

A roller is used to crush and roll lumps of soil that the tine harrows  bring up.
It also can be used to break surface caps and push down the surface soil.

Rotary hoes are made of a series of blades that rotate using the tractor’s power take-off. Rotary hoes produce a fine seedbed but can damage the soil structure when not used correctly.

Rotary hoes probably do the most damage to the soil structure. They can damage the soil structure very quickly by churning the soil into tiny particles. In the diagram you can see the action of the rotary hoe blades on the soil. The soil is smoothed and compacted to the depth of the blades.

Cultivation

Wet soil

When the ground is cultivated the soil particles press together and the soil can become compacted. A compacted soil has the soil pores crushed and pushed together. A compacted layer is called a pan.

Rotary hoes tend to work at the same depth and this can cause compaction.

When heavy machinery is used there can be an increased chance of a pan forming.

The blades on the rotary hoe churn the soil into very fine pieces.

A compacted soil can lead to water ponding and poor drainage. All these effects can put plants under stress. Root growth can be restricted because plants have to  grow above the compacted layer. Plants growing in these conditions will find it difficult to take up nutrients and water. This can limit crop growth and yield. Seed germination will also be patchy. Some soil types are more susceptible to compaction than others. Dense clay soils compact easily.

Wet soil can also form large clods, and smear under machinery wheels. When the soil dries out it will be difficult to work and    break up.

If the soil is very dry it can become very hard and crack. Sometimes this is called capping. When this soil is worked up it will becomes very fine and have a lack of organic matter. This soil will be at risk of wind and water erosion.

When the soil is very fine it can be  at risk of erosion. In the photo you can see the soil particles have been washed away, leaving channels.

Plant and organic material

Cultivation can affect organic  material in two ways:

• The organic material is  removed from the soil, which can leave the soil bare. The bare soil will move  easily and can be exposed to wind erosion. When plant material is turned into  the soil there is increased air in the soil. This speeds up the rate organic  matter breaks down and lowers the soil level.
• Soil  aggregates can break down when the organic matter levels are low. A fine layer  forms on the surface, which can set hard. Water and air movement in to the soil  below is slowed down. The soil is at risk of wind erosion.

Answer the following 11 questions about cultivation.

Background: A soil had been regularly cultivated with a rotary hoe for 20 years.  The diagrams show the soil before and after cultivation and the effect on the  soil and plant growth. Compare the pictures below. Use the words in the table  to compare how each of the things in the table is different.

What's next?

Go to: 7 Overcoming cultivation problems.