DKO SOIL MANAGEMENT PRACTICESAS 90919

Level 1 Ag Hort Sci External Exam

4 Credits

Contents

How can we change the soil?• Irrigation?• Drainage• Crop rotation• Fertiliser or compost application• Liming• Cultivation• Effluent application

• What can we measure in the soil?

• What is the soil made of?

What is soil made of?

Have a go at answering this question. There are 5 components:

•M•A•L•O•W

INERALS

IR

IVING ORGANISMS

RGANIC MATTER

ATER

Mineral components• When rocks/ stones get broken down they create the

mineral part of the soil. These ‘bits’ are the sand, silt and clay particles.

• Clay = < 0.002 mm

• Silt = 0.002 – 0.02 mm

• Sand = > 0.02 mm

• The mix of sand silt and clay determines soil texture (More on

this latter)

Air• Contains oxygen which is necessary for plant roots and

the living soil organisms. No oxygen in the soil = no life in the soil.

• Air travels into the soil from the surface through the pores (holes) in the soil.

• Air is sucked into the soil by water as it drains downwards.

Living organisms• Soil organisms are more important

than everyone thinks…• They improve soil structure (worms

dig holes)

• And they breakdown (digest) the OM to release the nutrients to the plant.

Living organisms include:

BacteriaFungiNematodesWormsAntsCentipedesSlugs…

Micro

Macro

Organic matter• If it was once living then it is now dead .Organic matter

(OM) is dead plants and animals. It can be large particles down to very small particles.

• The very small particles of OM are called humus

Water

Essential for:• photosynthesis• Plant turgidity• Nutrient uptake

• The only way water can get into the plant is via the roots (root hairs).

Plant Nutrients• There are 16 essential plant

nutrients. 13 of these come from the soil and are absorbed as ions.

• These soil nutrients (ions) are ‘chemically held’ by the soil minerals (sand silt clay).

• As OM breaks down it eventually will be broken down into the ions and absorbed by the plant.

Macro Nutrients

N NH4

P H2PO4

K K+

Ca Ca2+

Mg Mg2+

S SO42-

Micro Nutreints

FeMnZnCuBMoCl

Plant Nutrients availability

Four factors decide how much of a nutrient is available to the plant

• How much enters the soil (from fertiliser or compost)

• How much leaves the soil (from plant uptake or leaching)

• How much the soil can hold onto (it needs a high surface area to hold the ions)

• The pH (acidity) of the soil.

Soil pH

• The correct pH …• Allows plant nutrients to be

released by the soil• Encourages living organisms

Soil pH• Different plants have different

pH preferences.• The pH of most vege gardens

should be about 6.5. This is a good pH for most vege plants.

• However if you had a crop of potatoes – the best pH would be…

Soil texture• The % of sand silt and clay

determine the soil texture

• Soil texture determines a lot of soil characteristics

• The ideal soil is a loam

• You tube and soil texture measurement

• You tube – soil texture the feel test

Soil structure• Macro/ micro pores, Porosity,• Peds

Water Holding Capacity

Cultivation• Compaction is when the soil has been compressed and

the pores squashed so that air can no longer enter the soil

Topography

Browning off on the ridges of the hills.

Irrigated grapes in the foreground

Soil Amendments• Lime – artificial fertiliser – organic fertilisers

Drainage

To improve drainage…• Lay pipe drains or open drains• Plant in raised beds• Improve soil structure• Add lime to clay soils (floculation)

Signs of poor drainage

Yellowing of plants

Mottled subsoil

Pugging of surface

Poor structure

Irrigation

Crop rotation

Revision Questions

1. Name the 5 components of soil

2. What three particles define the soil texture?

3. Place the following in order of smallest to largest

Sand clay silt

4. What 2 functions do living organisms perform in the soil?

5. In an ideal soil, what proportion of the soil is air?

Activity – The perfect soil• What percentages of each of the soil components would

be in the perfect soil?

•M•A•L•O•W

INERALS

IR

IVING ORGANISMS

RGANIC MATTER

ATER