IRRIGATION – watering

Water is essential for plant growth. It is a major factor of crop productivity.

The advantages of irrigation are:

1. It provides ample water, necessary for seed germination.

2. It helps to maintain soil stability.

3. It can produce extra yields and

4. Improvements in crop quality.

The disadvantages of irrigation are:

1. Its excessive use may leach nutrients, from the soil.

2. The problem of capping on the soil surface is particularly frequent in silty and sandy loams. This leads to reduced germination of seeds.

A rough well-aerated soil surface – good surface soil structure. Individual soil crumbs.

A capped soil surface -loss of surface structure. The compaction cuts off the oxygen supply from the air.

3. Some pests and diseases thrive in moist conditions e.g. slugs, snails, botrytis and seedling damping-off.

4. Extra costs – of water, of the handling of equipment, of the equipment.

THE WATER BALANCE

What happens to all the water we receive in the form of precipitation, and where does it go? Most of the U.K. receives an excess amount of rainfall and snow in winter and an insufficient supply (for plants) during the summer. The limited amount of water that remains on the soil surface is affected by the sun’s radiant energy, to be evaporated from the soil surface or transpired from plants. It is the imbalance of supply of natural water in summer, when most vegetable crops grow, that determines how much you need to irrigate. WATER BALANCE is the relationship between precipitation on one hand, and the loss by evaporation, transpiration and drainage on the other.

Measurement of rainfall and evaporation/transpiration is an important part of knowing how much to irrigate in dry weather. You will study soil water in greater depth in the Lesson dealing with soil composition.

IRRIGATION EQUIPMENT

There is a wide range of irrigation eguipment available, varying from static nozzles to automatic oscillating sprinklers.

The main choices for a gardener are:

1. Hand-held watering can.

2. Hose pipe long enough to reach the vegetable plot plus sprinkler/rotary rainer.

3. Lay flat polythene tubing, also seep hoses and leaky pipe systems.

1. Trickle Irrigation

Trickle irrigation is available as lay-flat tubing and seephoses, both of which enable water to be applied at ground-level near the root zone.

Advantages of trickle irrigation.

I. Slow application of water.

ii. No soil panning.

iii. Useful for.frames or propagation beds.

LAYFLAT TUBING

This consists of polythene tubing. Water emerges from holes the size of pin-pricks punched into it.

SEEPHOSE

This consists of a stitched polythene pipe. Water emerges from the stitching.

(Both types work best with soft water)

2. Overhead Irrigation

Overhead irrigation through sprinklers and oscillating spraylines is useful for large-scale vegetable cropping. Oscillation of spraylines ensures relatively slow application. Rotary sprinklers move slowly round so that a circular pattern is covered.

The disadvantages of overhead irrigation:

I. Water can be lost by evaporation off leaves and the soil surface.

ii. Can cause panning of the surface soil. SPRINKLER IRRIGATION

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Advantages

1. Quick application of water.

2. Medium droplet size with long distance of throw,

3. Rotating pattern allows water absorption.

OSCILLATING SPRAYLINE

DRAINAGE

Waterlogging of soils causes the pore-spaces to fill up with water, and encourages the re-arrangement of soil particles, bringing silts to the surface. Soil structure is destroyed, and platy structures, (horizontal layers in the soil) appear. The worst type of soils are the clays; these show typical red and grey mottling of iron and manganese oxides.

Digging ditches and constructing pipe and c1inker drains to drain away water is advantageous in any garden. The topic of drainage will be dealt with in depth in a later Lesson.

Improving .the drainage, incorporating organic matter, liming regularly and a careful choice of rotation can ensure that a good soil structure is maintained, provided cultivations are carried out at the correct time.

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