Techniques to increase plant production

AS 90451Describe physical factors of the environment and techniques

used to modify them for plant production

Contents In the previous PPT we covered •PLANT PROCESSES•ENVIRONMENTAL FACTORS•AND PLANT GROWTH•TECHNIQUES

•In This presentation we focus on TECHNIQUES including:

•Hothouse Production•CO2 enrichment,

•artificial shelter, •sprinkler irrigation, •tile drainage, •hail cannon, •wind machines,• reflective mulch, •training systems.

Hot Houses• The ultimate method of manipulating the

environment is to build a hothouse.• The primary reason for having a hot house is to

increase air temperature. • Most glasshouse grown plants generally require

high temperatures during the day, and lower temperatures during the night.

For example, young capsicum plants require optimum day and night-time temperatures of 25°C and 18–23ºC respectively.

Warmer temperatures in a hothouse increases insect activity, thus increasing pollination (fruit set).

Tomato hothouse Increased air temperature in the glasshouse increases the rate of photosynthesis,

which produces more carbohydrates and speeds up the ripening process.

Ventilation reduces the chances of plant diseases, as it increases air movement, and reduces temperature and humidity. This ensures that fungal spores do not settle on leaves.

Bit of a tradeoff – do you open the vents to decrease humidity and decrease the temp. Or keep them closed to increase temp but risk too much humidity?

CO2 Enrichment

• ‘Normal’ air contains about 380 - 390 ppm (0.3%) of CO2.

• All plants grow well at this level but as CO2 levels are raised, photosynthesis increases proportionately resulting in more sugars and carbohydrates available for plant growth.

• Any actively growing crop in a tightly clad greenhouse with little or no ventilation can readily reduce the CO2 level during the day to as low as 200 ppm. This decrease in photosynthesis decreases plant growth – so growers need to ventilate hothouses to avoid this.

• A CO2 generator increases levels fro 380 to 1000 - 1,300 ppm. Resulting in increased production

CO2 Enrichment

• CO2 EnrichmentPlate 1. Carbon dioxide generator.

Carbon dioxide generator for a large greenhouse (burns fossil fuels to generate CO2

Plates 6b. Liquid CO2 tanks.

Liquid Carbon dioxide tank supplying a greenhouse.

CO2 Enrichment

Practice Question• If a backyard gardener places a portable gas heater into her

greenhouse. Describe the effect will it have on plant production and explain how this is more effective than an electric heater.

• Hint:

Artificial ShelterCould be in the form of:•Fences, wind belts, shade cloth barriers, walls, etc.•Shelter reduces wind (air movement) and can provide extra shading. As a result: •Sunlight is reduced in the southern area of land adjacent to the shelter.•Humidity is increased on the inside of the shelter belt.•Temperature is increased on the inside of the shelter belt.•The frequency of frost is increased on the inside of the shelter belt.

Artificial Shelter• There are no roots associated with artificial shelter, so vines close to the

shelter have no competition for nutrients, water and some light. Therefore there is minimal drop-off in yields from these rows, unlike the drop in yields associated with natural shelter. The incidence of bird damage is reduced, due to there being no nesting or resting sites for birds.

Natural Shelter Belts• Natural = plants.• Porosity of shelter should be about 50%.• Shelter should be a continuous length, with no gaps. • Are slow to develop • Have a maintenance cost (need to be pruned each year at

around $100/hr)

Benefits of shelter

Fruit damage• Strong winds result in fruit such as apples “banging” each

other, resulting in bruising and therefore a lowering of quality.• Strong winds may cause fruit such as kiwifruit, that are grown

on a support system, to come in contact with wires or wood, causing marking and bruising, thereby reducing crop quality.

Benefits of shelter

Pollination• Insects such as bees require

calm conditions for flight between hives and target fruit crops. Shelter maintains these conditions, allowing bees to move from flower to flower, and in doing so, pollinate crops, resulting in optimum fruit set and the potential for high yield.

Sprinkler irrigation• We already know of the importance of

water in photosynthesis, nutrient uptake and fruit development.

• Sprinkler irrigation (any irrigation) simply gives more control over the timing and amount of water delivery.

• Advantages in relation to fruit production are particularly important as increased fruit size can be achieved.

Tile Drainage• Tile Drainage (any drainage system)

primary function is to get rid of excess soil water and therefore increase oxygen availability to the roots.

• Drainage will therefore increase respiration and nutrient uptake.

• Nutrient uptake will increase because it requires energy for nutrient uptake (increased respiration ) and because there will be more root growth and hence increased access to soil nutrients.

Hail Cannons• Hail canons are used to shatter ice

particles inside hail clouds.• They use repeated sonic booms to

achieve this.

YouTube- How a hail cannon works

• Hail is only a problem in fruit production when the fruit is on the vine and there is a cold spell. Ie at the end of the growing season going into autumn.

Wind machines• Wind machines are used to provide frost

protection for orchards and vineyards. When an inversion layer forms above the plants, the temperature may be up to 5°C warmer 10 to 16 metres above the plants. Under these conditions, colder air becomes trapped below the inversion layer increasing the risk of frost damage at ground level. Wind machines can move warmer air from the inversion layer downward to prevent or minimise frost damage caused by colder air.

Frost damage• Frost damage happens

early in the growing season shortly after budbreak. If the developing flowers area damaged it can greatly reduce or even completely destroy the entire years crop before it has started.

Reflective mulch

• Exactly what it sounds like – a much layer that:• Suppresses weeds• Retains soil moisture• And reflects the light back up towards the plant.• And repel some insect pests (the shiney light scares them

away)

• Therefore it increases water availability, nutrient availability, and light availability.

Training systems• Training systems are designed to shape the

tree/ vine to achieve one or more of:• Improved aeration around branches• Reduce competition for light between trees• Improve the ability of a tree to harvest light• Support branches/ vines laden with heavy

fruit• Improve workability of the plant in relation

to spraying and harvesting.

Fruit development• All fruit requires the

following process.

• Flower bud set• Flower burst• Pollination• Fertilisation• Fruit development• Fruit ripening

Fruit developmentProcess Environmental factors to consider

Bud set Some flower buds require a chill factor to set the bud (eg apples)

Bud burst (blossom) Usually occurs in spring – prone to frost damage

Pollination Usually requires insect activity = warm air temp!

Fertilisation Pollen grain grows pollen tube – respiration = warm air temp and healthy flower needed.

Fruit development Most fruit is sugar and water – lots of sugar + lots of sunlight + plenty of water availability

Fruit Ripening Requires heat! And often direct light!

Heat units• Crop growth and development is often described in terms of

time, e.g., it takes 60 frost free days for barley to mature • However, a consideration of temperature is also important

because temperature determines the rate of growth. The time/temperature relationship that governs plant growth and development is measured in heat units. or growing-degree days.

• Heat units are calculated by adding the minimum and maximum daily temperatures together and dividing by two

• For example, a day with minimum and maximum temperatures of 10 and 20°C respectively, would generate 15 heat units [(20 + 10) / 2 = 15].

Effect of Light and Water on Plant Production

Kiwifruit Data ExerciseKiwifruit Data

Canopy Crop Load Fruit / m2 Fruit weight (g)

lighterlow crop load 26 113

high crop load 36 107

denserlow crop load 35 91

high crop load 48 84

Overall, canopy density had a greater effect on fruit weight than crop load.

Exercise 1 Graph the above data to show the relationship between canopy density and crop loading

Exercise 2 Explain the effect of canopy density on fruit size.

Exercise 3 Explain the effect of crop load on fruit size.

Exercise 4 Justify the manipulation in terms of quantity and quality of kiwifruit.

Pests and Diseases• Pests and diseases can influence the crop that can be

grown in a certain region, ie apples aren’t grown in the Waikato and grapes are no longer commercially grown in West Auckland due to dampness of the climates (botrytis).

• New growth of all plants are very susceptible to pests and diseases.• Pests chew the tender tasty tips of plants restricting

the development of the plants and their ability to carry out plant processes.

• Fungi such as mildew destroy apical buds.• Pests chew the plants providing an entry point for

diseases which restricts the ability of the plant to grow at an optimum rate.

Crop quality and quantity are affected by physical factors in a glasshouse.This photo is of an orchid glasshouse that is being used modify physical factors.

• List the environmental factors that could be altered with a glasshouse.

2009 exam Q1• Many commercial glasshouse growers increase

the carbon dioxide levels in glasshouses in order to increase crop yields. Artificially raising carbon dioxide levels is called enrichment.

Explain how increasing carbon dioxide levels increases crop yield.In your explanation:• describe, by giving figures, the carbon dioxide levels before and after enrichment• explain how plant growth is improved, leading to increased crop yield.

Q Achievement Achievement with Merit Achievement with

Excellence

ONE

(a)

A1

or

M1

Describes how the carbon dioxide levels change before and after grower intervention.

Example:

The computer increases the levels of carbon dioxide from 330 ppm to over 800 ppm.

Explains how plant growth is improved, leading to increased crop yield.

Example:

By increasing the volume of carbon dioxide, the rate of photosynthesis is increased, which increases growth. This leads to higher and earlier yields, and ensures better fruit setting, etc.