Soil management and fertiliser

The physical, biological and chemical properties of soils can be changed  to grow better crops.

Soil management involves changing or modifying and improving the soil's condition  and structure.

An ideal soil structure has large open pore spaces for water, air and  good levels of organic matter.

Fertiliser

When these lettuces are harvested, nutrients    are lost from the soil.

Plants use nutrients from the soil. They also    add organic matter and nutrients to the land. Every time products are sold    off a property, nutrients will be lost. Soil fertility decreases. Good    management involves returning nutrients to the soil in various ways.

Supply of nutrients

Nutrients can be replaced in a variety of ways.

Parent rock breakdown

• When rocks and minerals weather and break down they release nutrients.

Fertiliser

• Growers spread fertiliser to replace important elements lacking in the soil. Trace elements can also be replaced by using fertiliser.

Nitrogen-fixing bacteria

• Legumes, for example, lupins, peas and beans, can take nitrogen from the air and turn it into a useable form. Growers sometimes grow legumes as a green-manure crop. Legumes add nitrogen when they decompose. The plants in the photo below are peas.

Organic matter

Dead grass, plants, leaves and animals decompose and put nutrients into the soil. Animal manure and urine also will add nutrients. Ploughing in stubble or adding compost, dairy effluent, or animal manure also adds organic matter.

Soil fertility decreases when nutrients are removed or not available.

Loss of nutrients

Harvesting plants

Minerals are removed when plants are harvested and taken from the land.

Leaching

Many important nutrients can wash into the deeper layers of the soil. This is termed leaching. Plant roots are unable to reach the nutrients. Nitrogen and potassium can be lost in this way.

Unavailability

Sometimes minerals are unavailable to plants even when they are present in the soil. The minerals are in a form that can't enter the roots of the plants. In very acid soils plants are unable to take up some nutrients.

Test your understanding by answering these multiple-choice questions.

What's next?

Go to: 3 Using fertilisers.